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ASME Conference Presenter Attendance Policy and Archival Proceedings

2016;():V008T00A001. doi:10.1115/IMECE2016-NS8.
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This online compilation of papers from the ASME 2016 International Mechanical Engineering Congress and Exposition (IMECE2016) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Applications of Computational Heat Transfer

2016;():V008T10A001. doi:10.1115/IMECE2016-65148.

Flow past square cylinders has attracted a great deal of attention because of its practical significance in engineering e.g., High rise buildings, monuments and towers. Similarly, bridge pillars, and legs of offshore platforms are continuously subjected to the load produced by maritime or fluvial streams. The presence of separated flows, reattachment, formation the vortices, un steadiness of flow, mass and momentum transfer across shear layer makes the flow field quite complex. Many research work was carried out for a single square cylinder and flow past two square cylinders, but with corner medications in square cylinder of different size arranged in tandem was not taken up. This has motivated to take up the flow past two different sized square cylinders i.e., smaller in upstream and larger in downstream which is numerically simulated by using Fluent software. Reynolds number of 100 and 200 is considered for the investigation. The flow is assumed to be two dimensional, unsteady and incompressible. The computational methodology is carried out once the problem is defined, the first step in solving the problem is to construct a geometry then proper assignment of boundaries are set. After setting the boundary types, the geometry is discretized into small control volumes. Once the surface mesh is completed by using Gambit software, the mesh along with boundary conditions are exported to fluent, which is CFD solver usually run in background mode. The run would continue until the required convergence criterion is reached or till the maximum number of iterations is completed. Results indicate, in case of chamfered and rounded corners in square cylinders of different size, there is decrease in the wake width and thereby the lift and drag coefficient values. The lift coefficients in Square cylinders of different size with corner modifications decreases but Strouhal number increases when compared with a single square cylinder without corner modifications. Frequency of vortex shedding decreases with the introduction of second cylinder either in the upstream or downstream of the first cylinder. As the centre distance between two square cylinders i.e., PPR (pitch to perimeter ratio) with and without corner modifications is increased to 6, the flow velocity almost approaches to flow past a single square cylinder with and without modifications for same condition. When the size of the upstream square cylinder with and without modifications is smaller than that of the downstream square cylinder, the size of the eddies is always smaller in between the cylinders compared to the downstream of the second cylinder. The flow velocity in between the cylinders with and without corner modifications are less compared to the downstream of the second cylinder. Pressure on the downstream side of the cylinder is smaller than that on the upstream side of the cylinder for with and without corner modifications. Also, the front portion of the cylinder is experiencing highest pressure compared to the second cylinder for all the three cases i.e., PPR = 2, 4 and 6. Pressure at the upper side, bottom side and back side of square cylinder with and without corner modifications is of negative pressure, it is because of vortices generated at that surfaces. The downstream cylinder is found to experience higher lift compared to the upstream cylinder. The results are presented in the form of while the downstream cylinder is found to experience higher drag compared to the streamlines, flow velocity, pressure distribution, drag coefficient, lift coefficient and strouhal number.

Commentary by Dr. Valentin Fuster
2016;():V008T10A002. doi:10.1115/IMECE2016-65255.

Colorless Distributed Combustion (CDC) has shown significant improvements in terms of high combustion efficiency, ultra-low pollutants emission, low combustion noise, uniform thermal field, and enhanced stability. Colorless distributed combustion is fostered through reduced oxygen concentration and high temperature oxidizer to result in distributed reaction over a larger volume of the combustor and uniform thermal field. In this paper, the interaction between fluid mechanics (velocity field, characterized through particle image velocimetry) and the reaction region (identified through hydroxyl planar laser induced fluorescence) is investigated with focus on swirl assisted distributed combustion. Nitrogen/Carbon Dioxide mixture was added to the normal air upstream of the burner to simulate the hot reactive gases. Comparing the PIV data for reacting conditions with OH-PLIF revealed significant difference between normal swirl and CDC flames. In swirl flame, the flame was located around the shear layer of the entry jet (with both the inner and outer recirculation zones) where the velocity fluctuations and OH-PLIF fluctuations coincided. Flame transitioning to CDC pushed the reaction zone further downstream to locate at a position of lower velocity than what was found for swirl flames. In addition, the reaction zone occupied a much larger volume with lower signal intensity to exhibit distributed reaction. Experiments performed at same flow rates and velocities but with no reduction in oxygen concentration confirmed that the change in reaction behavior is attributed to the lower oxygen concentration rather than the increased flowrates due to dilution.

Commentary by Dr. Valentin Fuster
2016;():V008T10A003. doi:10.1115/IMECE2016-65806.

Cold gas dynamics spraying (CGDS) is a process employing aerodynamics particle acceleration and high-speed impact dynamics surface-coating technology. The main advantages of CGDS include : (1) A low level of residual stresses; (2) CGDS can collect and reuse the undeposited particle more efficient than thermal spray processes; (3) Coatings can be deposited on materials that are temperature-sensitive; (4) Thick coatings can be produced to allow for free-standing structures or for rapid prototyping; (5) CGDS is safer because it is operated in low temperatures and low noise levels (6) Easy implementation due to its simplicity of technical design; (7). CGDS could produce high thermal and electrical conductivity of coatings.

In the CGDS process, a high-pressure gas stream (generally 20–30 atm) carries metal particles (usually 1–50 μm in diameter) through a DeLaval type nozzle to reach a supersonic velocity before impact on the substrate. Typically, the impact velocities in the CGDS process range from 300 to 1200 m/s. When the particle exceeds the minimum deposition speed, adiabatic shear instabilities occur. This minimum deposition speed is also called critical velocity. In this paper, single particle impact simulations were performed to investigate the critical velocities of different particle sizes on the bonding process. This paper presents a three-dimensional numerical analysis of the particle critical velocity on the bonding efficiency in Cold Gas Dynamic Spray (CGDS) process by using ABAQUS/CAE 6.9-EF1. The particle impact temperature in CGDS is one of the most important factors that can determine the properties of the bonding strength to the substrate. In the CGDS process, bonding occurs when the impact velocity of particles exceed a critical velocity, which can reach minimum interface temperature of 60% of melting temperature in °C. The critical velocity depends not only on the particle size, but also the particle material. Therefore, critical velocity should have a strong effect on the coating quality. In the present numerical analysis, impact velocities were increased in steps of 100 m/s from the lowest simulated impact velocity of 300 m/s. This study illustrates the substrate deformations and the transient impact temperature distribution between particle(s) and substrate. In this paper, an explicit numerical scheme was used to investigate the critical velocity of different sizes of particle during the bonding process. Finally, the computed results are compared with the experimental data. Copper particles (Cu) and Aluminum substrate (Al) were chosen as the materials of simulation.

Commentary by Dr. Valentin Fuster
2016;():V008T10A004. doi:10.1115/IMECE2016-66210.

Finite Element Analysis (FEA) and the Laplace Transform-Based Fundamental Collocation Method (FCM) are used to solve the heat diffusion equation in two-dimensional regions having arbitrary shapes and subjected to arbitrary initial and mixed type boundary conditions. In the FEA method, the time derivative is replaced with a finite difference approximation. The resulting time dependent global equations are solved incrementally starting with the initial conditions. The FCM approach is applied in the Laplace transform domain to obtain temperatures in the s-domain, T(x,y,s). An inversion technique is used to retrieve the time domain solution, T(x,y,t). To compare applicability and accuracy of these methods, both techniques are applied to transient heat flow problems for which exact solutions are known.

Commentary by Dr. Valentin Fuster
2016;():V008T10A005. doi:10.1115/IMECE2016-66227.

It is a recognized hard task for the traditional thermal design of compact heat exchangers to obtain the optimal geometric parameters efficiently and effectively, owing to its complex trial-and-error process. In response to this issue, a simplified conjugate-gradient method (SCGM) combined with a sequential unconstrained minimization technique (SUMT) as a favorable optimization technique is incorporated with the traditional thermal design in this study, and then the key geometric parameters of fin-and-tube heat exchangers (FTHEs) are investigated and optimized successfully. In this method, the minimum total weight of FTHEs as the final objective is discussed, involving two geometric parameters, diameter of tube and height of shape as search variables. Aiming to minimize the objective function, SCGM is introduced to the SUMT to update the search variables continually with the fixed search steps and the search directions. Meanwhile, with the known geometric parameters from the SUMT, the log-mean temperature difference method (LMTD) is applied to determine the heat transfer area under the combined structure sizes for a given heat duty. Additionally, optimization results for three different heat duty is discussed in this work. The results show that it is effective to obtain the optimal sets of geometric parameters of FTHEs by the present method, and there are some guidance values for the thermal designs of compact heat exchangers.

Commentary by Dr. Valentin Fuster
2016;():V008T10A006. doi:10.1115/IMECE2016-66379.

In this paper, the thermal properties of graphite under external pressure were systematically investigated based on first-principles calculations and Boltzmann transport equation (BTE). This method is relatively simple and general to any other crystals. It was found that a compressive pressure can significantly increase the interaction between the layers in graphite and increase the phonon group velocity, the phonon mean free paths, thus the cross-plane thermal conductivity decreases. The effects of pressure on the in-plane thermal conductivity are much weaker than those on the cross-plane value. Our results indicate that the thermal properties of graphite can be strongly modulated by pressure engineering. Moreover we extracted the phonon dispersion and phonon lifetime of graphite under or without external pressure. And changes in the density of states and the cumulative thermal conductivity under 12GPa pressure are analyzed by comparing with no pressure. Our investigation here provides a physical insight into the modulation and heat transfer mechanism of graphite theoretically, which can help the design of graphite-like materials in experiment and practical application.

Commentary by Dr. Valentin Fuster
2016;():V008T10A007. doi:10.1115/IMECE2016-66870.

The increased computational and storage demand has increased the heat dissipation of servers in data centers. The flow inside the data center is highly dynamic due to various parameters such as server workload, server fan speed, tile porosity, Computer Room Air Conditioning (CRAC) air flowrates, CRAC supply & return air temperatures and data center cold & hot aisle arrangements. Data center facility level transient CFD analysis was reported in recent literature which needs weeks to accomplish the computation. Hence, such facility level simulations are difficult to achieve with good accuracy. The main contributions of this paper are transient experiments, transient CFD model & transient effects on thermal and flow field due to variation in server load of server rack inside the raised floor plenum data center.

In the current study we have developed a transient CFD model of three racks in a raised floor plenum data center room with cold and hot aisle containment based on experiments. The middle 42U (1U = 4.45 cm) rack houses four server simulators each having height of 10U. The flow tiles supply the cold air as inlet with average velocity of 1.53 m/s at 17°C. All the rack servers were modelled with 75% porosity and estimated thermal mass Each server simulator was assigned a total heat dissipation of 2500 W, with a total heat load of 10 kW per rack. The effect on rack inlet and outlet air temperatures were monitored by providing server heat loads as step & ramp inputs to the middle simulator rack. The results show that the rack level transient effects are significant and cannot be ignored.

Commentary by Dr. Valentin Fuster
2016;():V008T10A008. doi:10.1115/IMECE2016-67625.

This study focuses on developing computational models for hybrid or liquid cooled data centers that may reutilize waste heat. A data center with 17 fully populated racks with IBM LS20 blade servers, which consumes 408 kW at the maximum load, is considered. The hybrid cooling system uses a liquid to remove the heat produced by high power components, while the remaining low power components are cooled by air. The paper presents three hybrid cooling scenarios. For the first two cases, air is cooled by direct expansion (DX) cooling system with air-side economizer. Unlike the cooling air, two different approaches for cooling water are investigated: air-cooled chiller and ground water through liquid-to-liquid heat exchanger. Waste heat re-use for pre-heating building water in co-located facilities is also investigated for the second scenario. In addition to the hybrid cooling models, a fully liquid cooling system is modeled as the third scenario for comparison with hybrid cooling systems. By linking the computational models, power usage effectiveness (PUE) for all scenarios can be calculated for selected geographical locations and data center parameters. The paper also presents detailed analyses of the cooling components considered and comparisons of the PUE results.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Condensation Heat Transfer

2016;():V008T10A009. doi:10.1115/IMECE2016-67417.

Shell-and-tube vacuum condensers are present in many industrial applications such as chemical manufacturing, distillation, and power production [1–3]. They are often used because operating a condenser under vacuum pressures can increase the efficiency of energy conversion, which increases the overall plant efficiency and saves money. Typical operating pressures in the petrochemical industry span a wide range of values, from one atmosphere (101.3 kPa) down to a medium vacuum (1 kPa). The current shellside condensation methods used to predict heat transfer coefficients are based on data collected near or above atmospheric pressure, and the available literature on shellside vacuum condensation generally lacks experimental data. The accuracy of these methods in vacuum conditions well below atmospheric pressure has yet to be validated.

Recently, HTRI designed and constructed the Low Pressure Condensation Unit (LPCU) with a rectangular shellside test condenser. To date, heat transfer data have been collected in the LPCU for shellside condensation of a pure hydrocarbon and of a hydrocarbon with noncondensable gas at vacuum pressures ranging from 2.8 to 45 kPa (21 to 338 Torr). Traditional condensation literature methods underpredict the overall heat transfer coefficient by 20.8% ± 20.4% for the pure condensing fluid; whereas they overpredict heat transfer by 36.8% ± 40.0% with the addition of the noncondensable gas.

Over or under predicting the overall heat transfer coefficient in the presence of noncondensable gases leads to inefficient condenser designs and the inability to achieve desired process conditions. With the addition of the noncondensable gas, the measured heat exchanger duty was significantly reduced compared to the pure fluid, even at inlet mole fractions below 5%. In one case, a noncondensable inlet mole fraction of 0.63% was estimated to reduce the duty by approximately 10%.

Analysis of the acquired high-speed videos shows that the film thickness changes significantly from the top row to the bottom. The videos also display condensate drainage patterns and droplet interactions. The ripples and splashing of the condensate observed in the videos indicates that the Nusselt idealized model is not appropriate for analysis of a real condenser. This article presents the collected heat transfer data and high-speed images of shellside vacuum condensation flow patterns.

Topics: Condensation , Vacuum
Commentary by Dr. Valentin Fuster
2016;():V008T10A010. doi:10.1115/IMECE2016-67459.

The numerous studies on condensation flow patterns and heat transfer were focused on the horizontal inside single tube. A number of heat and mass transfer correlations are used for design of shellside condensers based on tubeside condensation flow regimes. Due to a complex geometry and measurement difficulty in a tube bundle, there are few publications reported on shellside condensation flow regime and heat transfer characteristics. To investigate the condensation flow patterns and heat and mass transfer mechanism at the different flow regimes, a horizontal shellside condenser was tested from a multipurpose condensation rig recently. The horizontal test bundle is made of 36 tubes with the staggered tube layout. The tube OD is 19 mm and the tube length is 1.0 m using stainless steel. Four visualization windows were placed on the front and back sides on the shell for photographing condensation flow patterns. Steam and steam/air mixture were used as the test fluids. The condensation flow patterns, condensate film thickness and droplets distribution were recorded using a high-speed digital camera at a wide range of condensation process conditions. The experimental data show that the condensation flow regime changes from the shear-controlled flow to gravity-controlled flow depending on the vapor and condensate loads, bundle location and the concentration of the non-condensable gas. These experimental data provide a fundamental approach for developing the heat and mass transfer correlateons at different shellside condensation patterns. This paper presents the experimental result on shellside condensation patterns associated with heat transfer characteristics.

Commentary by Dr. Valentin Fuster
2016;():V008T10A011. doi:10.1115/IMECE2016-67906.

In this study Transport Membrane Condenser (TMC), a new waste heat and water recovery technology based on a nanoporous ceramic membrane vapor separation mechanism has been studied for waste heat and water recovery in power plant application. TMC is able to extract condensate pure water from the flue gas in the presence of other non-condensable gases (i.e. CO2, O2 and N2). The effects of mass flow rate of flue gas and water vapor content of flow on the heat transfer and condensation rate of a TMC shell and tube heat exchanger have been studied numerically. A single phase multi-component model is used to assess the capability of single stage TMC heat exchangers in terms of waste heat and water recovery at various inlet conditions. Numerical simulation has been performed using ANSYS-FLUENT software and the condensation rate model has been implemented applying User Define Function.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Evaporation Heat Transfer

2016;():V008T10A012. doi:10.1115/IMECE2016-65656.

An innovative concept of full separation multi effect distillation (FSMED) desalination system has been proposed in the present study. A full separation tank (FST) is integrated to a conventional multi effect distillation (MED) water treatment system to enhance the water productivity and thermal efficiency. The concentrated brine from the MED is atomized into tiny droplets and fully evaporated in the FST due to the effective convective heat transfer between water droplets and hot air-steam flow. A simplified non-equilibrium vaporization model is developed to describe the movement and evaporation behavior of a single water droplet in FST. Simulations are conducted to investigate the effect of the radiation heat transfer and droplet gravity on the droplet evaporation and movement behavior. The relationship of the water droplet size and falling distance with the hot air-steam temperature, and initial injection/spray parameters is investigated and presented. Results from the study provide important guidance to the design of such a water treatment system.

Commentary by Dr. Valentin Fuster
2016;():V008T10A013. doi:10.1115/IMECE2016-66148.

The dynamic behavior of impinging water droplets is studied in the context of varying surface morphologies on smooth and microstructured superhydrophilic surfaces. The goal of this study is to evaluate the capability of contact angle wall adhesion models to accurately produce spreading phenomena seen on a variety of surface types. We analyze macroscale droplet behavior, specifically spreading extent and impinging regime, in situations of varying microscale wetting character and surface morphology. Axisymmetric, volume of fluid (VOF) simulations with static contact angle wall adhesion are conducted in ANSYS Fluent. Simulations are performed on water for low Weber numbers (We<20) on surfaces with features of length scale 5–10μm. Advanced microstructured surfaces consisting of unique wetting characteristics and lengths on each face are also tested. Results show that while the contact angle wall adhesion model shows fair agreement for conventional surfaces, the model underestimates spreading by over 60% for surfaces exhibiting estimated contact angles below approximately 0.5°. Microstructured surfaces adapt the wetting behavior of smooth surfaces with higher effective contact angles based on contact line pinning on morphology features. The propensity of the model to produce Wenzel and Cassie-Baxter states is linked to the spreading radius, introducing an interdependency of microscale wetting and macroscale spreading behavior. Conclusions describing the impact of results on evaporative cooling are also discussed.

Topics: Drops , Modeling
Commentary by Dr. Valentin Fuster
2016;():V008T10A014. doi:10.1115/IMECE2016-66964.

The objective of the current work is to present a new correlation for predicting heat transfer coefficients (HTCs) for flow boiling in horizontal microfin tubes. Correlations to predict HTCs have been proposed by numerous authors such as Yu et al., Thome et al., Cavallini et al., Yun et al., Chamra and Mago, Wu et al., and other researchers. The correlations proposed are semi-empirical due to the difficulties associated with modeling the physics of flow boiling in microfin tubes. The above correlations are based on smooth tube flow boiling correlations which are modified to capture the effect of the inner grooves in the microfin tubes on the boiling process. In a previous work, it has been demonstrated that no single correlation can reasonably predict the flow boiling HTCs over a wide range of operating conditions and tube geometric parameters (Merchant and Mehendale). A new model has been proposed and validated using an experimental database of 1576 points from published literature. For the full dataset, the new correlation has X30% of 67.3%, compared to Cavallini et al. and Wu et al. with X30% of 44.2% and 40.6% respectively. The performance of the new model for tube diameters less than and greater than 5 mm has also been discussed for halogenated refrigerants and CO2.

Commentary by Dr. Valentin Fuster
2016;():V008T10A015. doi:10.1115/IMECE2016-66975.

For falling film evaporation, the most important considerations from a thermal design standpoint are the onset of film dryout and the local heat transfer coefficients in partially and fully wet conditions. Previous methods developed for the prediction of (i) pool boiling heat transfer coefficient (HTCs), (ii) the onset of dryout, and (iii) falling film heat transfer coefficient consist of empirical, tube-specific constants which are quite difficult, if not impossible, to determine, and hence have limited utility. New methods to predict these parameters have been developed in the present study, which eliminate the special constants by incorporating dimensionless parameters that capture the effect of refrigerant properties and macro-level tube-geometry. The predictions of the new model have been found to be better than or comparable to those of the best available existing models.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Fundamentals of Boiling/Condensation Including Nano-Scale Effects

2016;():V008T10A016. doi:10.1115/IMECE2016-65866.

Boiling influences many industrial processes like quenching, desalination and steam generation. Boiling heat transfer at high temperatures is limited by the formation of a vapor layer between the solid and fluid. Low thermal conductivity of this vapor layer inhibits heat transfer. Electrowetting (EW) fields can breakdown this vapor layer to promote wetting, and this concept works for many quenching media including water and organic solvents. This work studies the suppression of this vapor layer and measures the resulting heat transfer enhancement during quenching of metals. We image the fluid-surface interactions and boiling patterns in the presence of an electrical voltage. EW fields replace film boiling with periodic wetting-rewetting cycles and thus fundamentally change the heat transfer mode. The increased wettability substantially reduces the cool down time. The cooling rate can by increased by as much as 3X. The results show that electric fields can dynamically tune the classical quenching curve. This study opens up new avenues to control the metallurgy of metals via electrical control of the cooling rate.

Commentary by Dr. Valentin Fuster
2016;():V008T10A017. doi:10.1115/IMECE2016-66666.

The increasing demand of heat dissipation in power plants has pushed the limits of current two-phase thermal technologies such as heat pipes and vapor chambers. One of the most obvious areas for thermal improvement is centered on the high heat flux condensers including improved evaporators, thermal interfaces, etc, with low cost materials and surface treatment. Dropwise condensation has shown the ability to increase condensation heat transfer coefficient by an order of magnitude over conventional filmwise condensation. Current dropwise condensation research is focused on Cu and other special metals, the cost of which limits its application in the scale of commercial power plants. Presented here is a general use of self-assembled monolayer coatings to promote dropwise condensation on low-cost steel-based surfaces. Together with inhibitors in the working fluid, the surface of condenser is protected by hydrophobic coating, and the condensation heat transfer is promoted on carbon steel surfaces.

Commentary by Dr. Valentin Fuster
2016;():V008T10A018. doi:10.1115/IMECE2016-67294.

The effect of wettability on boiling heat transfer (BHT) coefficient and critical heat flux (CHF) in pool boiling of water on hydrophilic surfaces having different contact angles was investigated. Hot alkali solutions were utilized to promote cupric and cuprous oxide growth which exhibited micro and nanoscale structures on copper surfaces, with thicknesses on the order of a couple of micrometers. These structure and surface energy variations result in different levels of wettability and roughness while maintaining the effusivity of the bare copper surface. The study showed that the BHT coefficient has an inverse relationship to wettability; the BHT coefficient decreases as wettability increases. Furthermore, it was shown that this dependency between BHT coefficient and wettability is more significant than the relationship between BHT coefficient and surface roughness. The CHF was also found to increase with increases in wettability and roughness. For the most hydrophilic surface tested in this study, CHF values were recorded near the 2,000 kW/m2 mark. This value is compared with maximum values reported in literature for water on non-structured flat surfaces without area enhancements. Based on these results it is postulated that there exists a true hydrodynamic CHF limit for pool boiling with water on flat surfaces, very near 2,000 kW/m2, independent of heater material, representing an 80% increase in the limit suggested by Zuber [1].

Commentary by Dr. Valentin Fuster
2016;():V008T10A019. doi:10.1115/IMECE2016-68183.

The effect of surface roughness on the pool boiling heat transfer of water was investigated on superhydrophilic aluminum surfaces. The formation of nanoscale protrusions on the aluminum surface was confirmed after immersing it in boiling water, which modified surface wettability to form a superhydrophilic surface. The effect of surface roughness was examined at different average roughness (Ra) values ranging from 0.11–2.93 μm. The boiling heat transfer coefficients increased with an increase in roughness owing to the increased number of cavities. However, the superhydrophilic aluminum surfaces exhibited degradation of the heat transfer coefficients when compared with copper surfaces owing to the flooding of promising cavities. The superhydrophilic aluminum surfaces exhibited a higher critical heat flux (CHF) than the copper surfaces. The CHF was 1,650 kW/m2 for Ra = 0.11 μm, and it increased to 2,150 kW/m2 for Ra = 0.35 μm. Surface roughness is considered to affect CHF as it improves the capillary wicking on the superhydrophilic surface. However, further increase in surface roughness above 0.35 μm did not augment the CHF, even at Ra = 2.93 μm. This upper limit of the CHF appears to result from the hydrodynamic limit on the superhydrophilic surface, because the roughest surface with Ra = 2.93 μm still showed a faster liquid spreading speed.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Fundamentals of Multiscale Modeling and Simulations of Heat Transfer

2016;():V008T10A020. doi:10.1115/IMECE2016-65459.

Phonon transport within nanoporous bulk materials or thin films is of importance to applications in thermoelectrics, gas sensors, and thermal insulation materials. Considering classical phonon size effects, the lattice thermal conductivity KL can be predicted assuming diffusive pore-edge scattering of phonons and bulk phonon mean free paths. In the kinetic relationship, kL can be computed by modifying the phonon mean free paths with the characteristic length ΛPore of the porous structure. Despite some efforts using the Monte Carlo ray tracing method to extract ΛPore, the resulting KL often diverges from that predicted by phonon Monte Carlo simulations. In this work, the effective ΛPore is extracted by directly comparing the predictions by the kinetic relationship and phonon Monte Carlo simulations. The investigation covers a wide range of period sizes and volumetric porosities. In practice, these ΛPore values can be used for thermal analysis of general nanoporous materials.

Commentary by Dr. Valentin Fuster
2016;():V008T10A021. doi:10.1115/IMECE2016-67448.

A heat pipe has been known as a thermal superconductor utilizing a liquid-vapor phase change, and it has drawn significant attentions for advanced thermal management systems. However, a challenge is the size limitation, i.e., the heat pipe cannot be smaller than the evaporator/condenser wick structures, typically an order of micron, and a new operating mechanism is required to meet the needs for the nanoscale thermal management systems. In this study, we design the nanoscale heat pipe employing the gas-filled nanostructure, while transferring heat via ballistic fluid-particle motions with a possible returning working fluid via surface diffusions along the nanostructure. The enhanced heat flux for the nano heat pipe is demonstrated using the nonequilibrium molecular dynamics simulations (NEMDS) for the argon gas confined by the 20 nm-long Pt nanogap with a post wall with the temperature difference between the hot and cold surfaces of 20 K. The predicted results show that the maximum heat flux through the gas-filled nanostructure (heat pipe) nearly doubles that of the nanogap without the post wall at 100 < T < 140 K. The optimal operating conditions/material selections are discussed. The results for the nanogap agree with those obtained from the kinetic theory, and provide insights into the design of advanced thermal management systems.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Fundamentals of Phonon and Electron Transport and Coupling

2016;():V008T10A022. doi:10.1115/IMECE2016-67377.

Pump-probe thermoreflectance is a well-known non-contact optical measurement technique for thermal property analysis of thin film materials on a semi-infinite substrate. Two laser lines are commonly used, one of which is used to heat the structure (the pump) and the other is used to measure the change in reflectivity (the probe) to infer thermal properties of the material/structure. This work extends the technique to freestanding cantilever beams. The pump beam applies a constant flux to the free end of the cantilever thereby inducing a thermal gradient along its length which is measured by the probe beam. Measurement of the thermal gradient allows for determination of the thermal conductivity of the material. Convective and radiative heat losses are minimized by performing the experiment at high vacuum and removing the substrate underneath the beam. We demonstrate the technique by measuring the thermal conductivity for four Si cantilever beams that are 1.29 μm thick. The average thermal conductivity for the beams was measured to be 96.9 ± 1.76 Wm−1K−1.

Commentary by Dr. Valentin Fuster
2016;():V008T10A023. doi:10.1115/IMECE2016-68083.

The Green-Kubo method in the framework of equilibrium molecular dynamics (EMD) simulations is an effective method that has been widely used to calculate thermal conductivities of materials. The previous studies focused on the thermal conductivity values or the average values from repetitive simulations. Little research has been done to investigate the uncertainties of the thermal conductivities from EMD simulations. In this paper, we use solid argon as the material system to study the factors influencing the uncertainties of the predicted thermal conductivities. We find that the uncertainties decrease with the total simulation time as (ttotal)−α and increase with correlation time as (tcorre)β, where 0.48 < α, β < 0.52. We also find that the uncertainties decrease with increasing temperature, but the simulation domain size has a negligible effect. We propose some guidelines for selecting appropriate simulation parameters (e.g., the correlation time and total simulation time) to achieve a desired level of uncertainty. This work is potentially useful for future studies on calculating the thermal conductivities of materials using EMD simulations.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Fundamentals of Radiative Transport

2016;():V008T10A024. doi:10.1115/IMECE2016-65036.

Intense investigations have been focused on radiative heat transfer in oxygen-enhanced inverse diffusion flames since it plays a significant role not only in fundamental combustion research, but also in terrestrial and spacecraft fire safety study. To investigate the characteristics of the radiative heat transfer, a calibrated mid-infrared camera was used to acquire images of radiation intensity including soot and carbon dioxide in the 2–5μm wavelength range. The mole fraction of oxygen in the oxidizer varied from 21% to 100% with co-flowing inverse flame burner used to stabilize the flames. The characteristics of axial and radial radiation intensity distribution in different oxygen enhanced conditions are compared and analyzed. The results indicated that oxygen enhancement broadens the radial range of inner blue reaction zone and stretches the axial height of the plume zone. Similar to radial peak radiation intensity value and the growth rate of radial radiation intensity in different axial heights from X = 1D to X = 3D (X: axial height above the burner along the flame centerline; D: diameter of oxidizer exit), the peak value of radiation intensity and the growth rate of radiation intensity along the flame centerline both have a positive linear relationship with the oxygen mole fraction in the oxidizer.

Commentary by Dr. Valentin Fuster
2016;():V008T10A025. doi:10.1115/IMECE2016-65369.

We demonstrate workings of a near-field thermal rectification device that uses phase change material to achieve asymmetry in heat transfer. We exploit the temperature dependent dielectric properties of VO2 due metal-insulator transition near 341 K. The device operates near the critical temperature of the phase change material. Analogous to an electrical diode, heat transfer coefficient is very high in one direction (forward bias) while it is very small when the polarity of temperature gradient is reversed (reverse bias). Rectification as high as 15 can be obtained for minimal temperature difference of 5 K. We show that high rectification is achieved by using 1-D triangular and rectangular surface gratings. The rectification factor is dramatically enhanced in the near-field due to the spectral mismatch between dissimilar materials for the negative polarity.

Commentary by Dr. Valentin Fuster
2016;():V008T10A026. doi:10.1115/IMECE2016-66780.

Controlling the properties of the nanostructures requires use of proper characterization methods. There are many techniques available such as microscopy, time-resolved laser-induced-incandescence or light scattering methods that can be used for characterization of nanostructures. While direct observation such as microscopy is possible for some applications, the indirect characterization is carried out through measurements of structures’ emission or scattering behavior as in the laser-induced-incandescence and light scattering methods. Characterization of soot aggregates is well studied and is often classified as an inverse problem that can be formulated as a parameter estimation problem, where parameters defining the aggregate such as average size and number of nanoparticles are estimated. Estimations based on the scattering behavior can be questionable unless these parameters are directly observed by other methods. Instead of presenting a single estimate, Bayesian credible intervals would be a better option when indirect methods such as light scattering are used. The objective of this work is to investigate the strengths and weaknesses of the Bayesian approach based on numerical light scattering experiments considering soot aggregates as an example. Light scattering behavior of the soot aggregates is obtained with discrete dipole approximation, considering unpolarized light.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Fundamentals of Single Phase Convection

2016;():V008T10A027. doi:10.1115/IMECE2016-65065.

This paper deals with the results of a simulative study of free convective heat transfer in the enclosure having different shapes. Problem has been characterized with the constant temperature on lower and upper walls while side walls have been considered as adiabatic walls. This study has been conducted for finding the shape of enclosure having maximum heat transfer rate considering different values for the aspect ratio and the Grashof number. Steady state natural convection problem has been formulated for all enclosures having laminar flow of air (at Pr = 0.7). Values for the aspect ratio vary from 0.2 to 0.5 while for the Grashof number from 10e4 to 10e8. ANSYS 14.0 has been used for modelling and simulation and for concluding study in the terms of Nusselt Number.

Commentary by Dr. Valentin Fuster
2016;():V008T10A028. doi:10.1115/IMECE2016-65144.

Heat transfer in a laminar confined oscillating slot jet impinging on an isothermal surface is numerically investigated. A uniform inlet velocity profile, oscillating with an angle φ, is used at the jet exit. The angle φ changes in a sinusoidal form. The height-to-jet width ratio is fixed at 5. The working fluid is air with constant physical properties corresponding to Prandtl number, Pr, equal to 0.74 at ambient conditions. Reynolds number, Re, is defined based on the jet hydraulic diameter and is varied in the self-stable range between 100 and 400. Strouhal number, St, is also varied between 0.05 and 0.75. Oscillating the jet at Reynolds number equal to 100 showed no heat transfer improvement over the steady state case, regardless of the used Strouhal number values. The vortices generated by the oscillation were too weak and could barely reach the wall. The flow showed a high vulnerability to severe oscillations which drastically reduced the jet heat removal ability. The vorticity contours showed a perfect symmetry which resulted in instantaneous and average Nusselt number distributions that are symmetric about the center of the isothermal surface at x = 0. The average stagnation Nusselt number, Nu0, decreased by about 1.25% as Strouhal number is increased from 0.4 to 0.625 then dipped by 44.1% as St is further increased to 0.75, a fact that was attributed to reduction in the bulk momentum by the relatively high frequency. With Reynolds number at 250, the lowest two frequencies corresponding to St of 0.05 and 0.1, resulted in a flow field that is more developed to the right side of the channel, a phenomenon that was linked to the direction of the first jet swing. The corresponding average Nusselt number distributions were consequently asymmetric, with a significant shift to the right. This asymmetric behavior gradually disappeared as the frequency is increased. At St of 0.4 and 0.5, the average stagnation Nusselt number Nu0, showed a 2.2% increase over the steady jet case. As Strouhal number is further increased beyond 0.5, the average Nu0 gradually decreased, since the oscillation period became too short for a vortex to be strong enough to reach the wall. For Reynolds number set at 400, the oscillating condition at the inlet engaged the jet into flapping. The jet showed a tendency to a permanent lean towards one side of the channel, for all used frequencies. Flapping was more one-sided which led to a shift in the average Nusselt number distribution at low frequencies. As Strouhal number is increased to 0.75, flapping became more stable and the generated vortices were expectedly weaker due to the higher frequency. Also, at this Strouhal number value, the average Nu distribution showed the best symmetry with a 2.45% improvement of the average stagnation Nusselt number, over that of the steady state case.

Commentary by Dr. Valentin Fuster
2016;():V008T10A029. doi:10.1115/IMECE2016-65321.

We studied the forced convection heat transfer performance and pressure drop of high permeability metal cellular porous media in air flow using a 3-dimensional thermofluid computation code. The temperature and velocity distributions in the air flow region, local heat transfer coefficient, and local heat flux on the surface of the porous media were numerically calculated for steady air flow by changing the parameters of the pore size and air velocity. The cellular porous media were modeled by pin array, cube geometry, and truncated octahedron geometry using thin wires. The diameter of the wires was 0.1 mm, and the pore per inch (PPI) was 5–50. The relations between the Nusselt number using the volumetric heat transfer coefficient and the Reynolds number were obtained from our calculation results, and we compared them with conventionally proposed experimental correlations. Also, the pressure drop calculation result was compared with conventionally proposed experimental correlations. The following results were obtained. The local heat transfer coefficient and local heat flux on the surface of porous media were small near the joint positions of the wires of the cellular porous media because of the thermal boundary layer. The volumetric heat transfer coefficient and pressure drop agreed with conventionally proposed experimental correlations within errors of twice the volumetric heat transfer coefficient and pressure drop. The relation between the heat transfer rate per unit volume and the heat transfer area per unit volume agreed with the convection heat transfer correlation for a tube bundle.

Commentary by Dr. Valentin Fuster
2016;():V008T10A030. doi:10.1115/IMECE2016-65540.

Natural convective heat transfer from the top and bottom surfaces of a thin circular isothermal horizontal plate which, in general, has a centrally placed adiabatic section has been numerically investigated. The temperature of the plate surfaces is higher than the temperature of the surrounding fluid. The range of conditions considered is such that laminar, transitional, and turbulent flow occurs over the plate. The heat transfer from the upper and lower surfaces of the plate as well as the mean heat transfer rate from the entire surface of the plate have been considered. The flow has been assumed to be axisymmetric and steady. The k-epsilon turbulence model with account being taken of buoyancy force effects has been used and the solution has been obtained using the commercial CFD solver ANSYS FLUENT©. The heat transfer rate from the heated plate has been expressed in terms of a Nusselt number based on the outside plate diameter and the difference between the plate temperature and the fluid temperature far from the plate. The mean Nusselt number is dependent on the Rayleigh number, the ratio of the diameter of the inner adiabatic section to the outer plate diameter, and the Prandtl number. Results have only been obtained for a Prandtl number of 0.74, i.e., effectively the value for air. The variations of the mean Nusselt number averaged over both the upper and lower surfaces and of the mean Nusselt numbers for the upper surface and for the lower surface with Rayleigh number for various adiabatic section diameter ratios have been studied. The use of a reference length scale to allow the correlation of these mean Nusselt number-Rayleigh number variations has been investigated.

Topics: Convection
Commentary by Dr. Valentin Fuster
2016;():V008T10A031. doi:10.1115/IMECE2016-65716.

A numerical study of natural convective heat transfer from an upward facing, heated horizontal isothermal surface imbedded in a large flat adiabatic surface has been undertaken. On the heated surface is a series of triangular shaped waves. Laminar, transitional, and turbulent flow conditions have been considered. The flow has been assumed to be two-dimensional and steady. The fluid properties have been assumed constant except for the density change with temperature giving rise to the buoyancy forces. This was with treated using the Boussinesq approach. The numerical solution has been obtained using the commercial CFD solver ANSYS FLUENT©. The k-epsilon turbulence model with full account being taken of buoyancy force effects has been employed. The heat transfer rate from the heated surface expressed in terms of a Nusselt number is dependent on the Rayleigh number, the number of waves, the height of the waves relative to the width of the heated surface, and the Prandtl number. This study obtained results for a Prandtl number of 0.74 which is effectively the value for air. An investigation of the effect of the Rayleigh number, the dimensionless height of the surface waves, and the number of surface waves on the Nusselt number has been undertaken.

Topics: Waves , Convection
Commentary by Dr. Valentin Fuster
2016;():V008T10A032. doi:10.1115/IMECE2016-66136.

Micro-electro-mechanical systems (MEMS) offer vast applications and those involving fluid flow/gas flows typically operate in the slip flow regime, where the normal non-slip condition assumptions for boundary conditions are not valid. In this study, two-dimensional numerical simulations of continuum and slip flows for U-shaped microchannels were performed to evaluate flow characteristics by means of the ANSYS-FLUENT software. In order to model slip condition existing at the solid-liquid interface of microchannels, a user defined subroutine was linked to the software. The effect of Reynolds number and geometric parameters such as the bend shape and the distance between legs on fluid flow and heat transfer characteristics were examined in detail. The computational results showed that increasing either the slip length or Reynolds number decreased the average friction factor, while the distance between legs does not have any effect on it. Moreover, it was found that the averaged Nusselt number would increase with Reynolds number and the slip length, but increasing the distance between legs decreased the averaged Nu for square bend compared to its negligible increase for circular bend.

Commentary by Dr. Valentin Fuster
2016;():V008T10A033. doi:10.1115/IMECE2016-66189.

In this paper a numerical investigation on laminar forced convection flow of a water-Al2O3 nanofluid in a rectangular microchannel, taking into account the viscous dissipation, is accomplished. A constant and uniform heat flux on the external surfaces has been applied and a single-phase model approach has been employed. The analysis has been performed in steady state regime for particle size in nanofluids equal to 38 nm. The CFD commercial code Ansys-Fluent has been employed in order to solve the 3-D numerical model. The geometrical configuration under consideration consists in a duct with a rectangular shaped crossing area. A steady laminar incompressible flow with viscous dissipation and different nanoparticle volume fractions has been considered. The base fluid is water and nanoparticles are made up of alumina (Al2O3). Thermo-physical properties of the nanofluid are considered constant with temperature. The length the edge and height of the duct are 0.030 m, 1.7 × 10−7 and 1.1 × 10−7 m, respectively. A constant and uniform heat flux q on the top wall is applied, the others are adiabatic and at the inlet section uniform temperature and velocity profiles are assumed. The results showed the increase of the convective heat transfer coefficients, in particular, for high concentration of nanoparticles and for increasing values of Reynolds number. However, the disadvantages are represented by the growth of the wall shear stress and the required pumping power, observed in particular, at high particle concentrations.

Commentary by Dr. Valentin Fuster
2016;():V008T10A034. doi:10.1115/IMECE2016-66572.

The objective of this study is to compare the fluid flow and the heat transfer characteristics between a 2-D planar and a 3-D circular wall jet along the stream wise direction. The experiments are performed at a Reynolds number of 5540 for non-dimensional streamwise distance ranging from 0 to 40. The hot wire anemometer is used to quantify the velocity distribution on the jet spread and the local maximum velocity decay along the stream wise direction. Liquid Crystal Thermography (LCT) technique is used to map the surface temperature and the semi-infinite approximation methodology is used for extracting the heat transfer coefficient. From the results it is observed that, the 2-D planar wall jet shows lesser distribution of RMS values in the near field and better heat transfer performance than that of the 3-D circular wall jet.

Commentary by Dr. Valentin Fuster
2016;():V008T10A035. doi:10.1115/IMECE2016-67196.

In case of natural heat convection from a horizontal plate fin heat sink, heat transfer rates highly depend on the geometric parameters. It is observed that if the fin height is very low, fresh cooler air may not be able to reach middle parts of the heat sink causing an ineffective use of the extended heat transfer area. Using a validated numerical model of an underperforming heat sink, various ways of improving heat sink geometry has been investigated. The tried approaches include leaving gaps in the length of the fins in different patterns, adding two different shape pin fins in the channels between the plate fins and raising the height of the fins on the edges. The last approach is shown to be effective in improving heat transfer by blocking the side flows over the heat sink. By numerical simulations, causes of the unwanted in-channel longitudinal vortices were also investigated in detail with the help of powerful flow visualization capability of Computational Fluid Dynamics.

Commentary by Dr. Valentin Fuster
2016;():V008T10A036. doi:10.1115/IMECE2016-67486.

Convective heat transfer from suddenly expanding annular pipe flows are numerically investigated within the steady laminar flow regime. A parametric study is performed to reveal the influence of the annular diameter ratio, k, the Prandtl number, Pr, and the Reynolds number, Re, over the following range of parameters: k = {0, 0.5, 0.7}, Pr = {0.7, 1, 7, 100}, and Re = {25, 50, 100}. Heat transfer enhancement downstream of the expansion plane is only observed for Pr > 1. Peak wall-heat-transfer-rates always appear downstream of the flow reattachment point, in the case of suddenly expanding round pipe flows, i.e. k = 0. However, for suddenly expanding annular pipe flows, i.e., k = 0.5 and 0.7, peak wall-heat-transfer-rates always appear upstream of the flow reattachment point. The observed heat transfer augmentation is more dramatic for suddenly expanding annular flows, in comparison with the one observed for suddenly expanding pipe flows. For a given annular diameter ratio and Reynolds number, increasing the Prandtl number, always results in higher wall-heat-transfer-rates downstream the expansion plane.

Topics: Convection , Pipe flow
Commentary by Dr. Valentin Fuster
2016;():V008T10A037. doi:10.1115/IMECE2016-67640.

The steady-state flow field and temperature distribution inside a thermal cycling test chamber with nonuniform perforated plate are investigated both numerically and experimentally. Porous zones are set up by pressure loss analogy to simplify the perforated plate. Boussinesq approximation and low-Re model are used in the simulation. The numerical result shows both forced convection and natural convection contribute to the fluid flow and heat transfer. For uniform perforated plate, the temperature at the given height always increases from the center line to the walls. And from top to bottom of the cycling chamber, temperature increases around the center line while decreases near the walls. Based on that, two cases of nonuniform perforated plates with the same ratio of open area and different holes distribution are examined to improve the temperature uniformity in test chamber. The results show that both average temperature and standard temperature deviation are effected significantly by nonuniform perforated plate. The latter experiment is performed with the optimal perforated plate under the same condition of Re = 4.1 × 104, Gr = 1.8 × 1011. The experiment results are obtained by Constant Temperature Anemometry and agree with the numerical simulation.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Gas Turbine Heat Transfer

2016;():V008T10A038. doi:10.1115/IMECE2016-66059.

The pocket cavity is generated at the transition part between the low pressure turbine (LPT) and outlet guide vane (OGV) in a gas turbine engine. Because the important connection with OGV, the heat transfer and fluid flow need to be investigated and analyzed. In the present work, a simplified triangular pocket cavity is built and heat transfer and fluid flow are investigated experimentally and numerically. Liquid Crystal Thermography (LCT) is employed to measure the heat transfer over the pocket surface with Reynolds number ranging from 54,054 to 135,135. In addition, two fillets with different radii are designed to investigate the flow structures over the pocket surface. The turbulent flow details are provided by numerically calculations based on the commercial software Fluent 15.0 with a validated turbulence model. Based on the results, the highest heat transfer value is located in the downstream boundary of the pocket cavity where the strongest flow impingement happens. The smaller fillet radius presents a higher heat transfer peak value and also induces stronger recirculating flow inside the pocket cavity. Considering the design requirement in the rear part of a gas turbine, i.e., to decrease the heat transfer peak value, a larger fillet radius is recommended for practical design. The heat transfer and flow details also provide a reliable reference for gas turbine engine design.

Commentary by Dr. Valentin Fuster
2016;():V008T10A039. doi:10.1115/IMECE2016-66783.

Cylindrical pins, often called pin fins, are used to create turbulence and promote convective heat transfer within many devices, ranging from computer heat sinks to the trailing edge of jet engine turbine blades. Previous experiments have measured the time-averaged heat transfer over a single pin as well as the flow fields around the pin. However, in this study, focus is placed on the instantaneous heat flux around the centerline of a low aspect-ratio pin within an array. Time-mean and unsteady convective heat flux are measured around the circumference of an isothermal heated test pin via a microsensor located at the surface. The pin is positioned at various locations within a staggered array in a large-scale wind tunnel. Reynolds numbers from 3,000 to 50,000, based on pin diameter and maximum velocity between pins, are tested with a streamwise spacing of 1.73 diameters between rows, a spanwise spacing of 2 diameters, and a pin height of 1 diameter. The time-averaged and standard deviation of convective heat flux around the pin is higher over most of the pin surface for pins in downstream row positions of an array relative to the first row pin, except in the wake which has similar levels for all rows. For a given pin position in the array, as the Reynolds number increases, the point of minimum heat transfer moves circumferentially upstream on the pin fin, corresponding to earlier transition of the pin boundary layer. Also, for a given Reynolds number, the minimum heat transfer point on the pin circumference moves upstream for pins further into the array, due to the high turbulence levels within the array which cause early transition. For a single pin row with no downstream pins, heat transfer fluctuations are very high on the backside of the pin due to the significant unsteadiness in the pin wake, but heat transfer fluctuations are suppressed for a pin with downstream rows due to the confining effects of the close spacing. The results from this study can be used to design pin-fin arrays that take advantage of unsteadiness and increase overall convective heat transfer for various industry components.

Commentary by Dr. Valentin Fuster
2016;():V008T10A040. doi:10.1115/IMECE2016-67029.

Vane heat transfer distributions have been acquired on an aft loaded vane with a large leading edge over a range of turbulence conditions and across a range of Reynolds numbers. The large leading edge was designed to reduce heat transfer levels around the vane stagnation region and provide an opportunity to internally cool the region using a double wall cooling method. Heat transfer measurements were acquired in a linear cascade using a constant heat flux technique. The cascade was designed in a four vane, three full passage configuration with inlet bleeds flows and exit tailboards shaped along streamlines. Heat transfer measurements were acquired at exit chord Reynolds numbers of 500,000, 1,000,000, and 2,000,000 over seven turbulence conditions. The turbulence conditions included a low turbulence condition (Tu ≈ 0.7%), a small grid (M = 3.175 cm) at far and near locations (Tu ≈ 3.5% & 7.9%), a larger grid (Tu ≈ 8.0%), an aero-combustor closely coupled to the cascade and with a decay spool in between (Tu ≈ 13.5% and 9.3%) as well as with a new very high turbulence generator (Tu ≈ 17.4%). Heat transfer levels in the stagnation region are correlated in terms of approach flow Reynolds number and turbulence conditions and compared with recent large cylindrical leading edge test surface data using the TRL parameter. The surface heat transfer measurements are presented at different Reynolds numbers in terms of Stanton number based on exit conditions. These comparisons provide useful information on the level of turbulence augmentation in laminar regions of the flow as well as the onset location and length of transition. Midspan surface static pressure distributions were acquired at all the conditions and were used as a basis to determine experimental isentropic Mach number distributions. These data are reported in part but were also used to help generate the free-stream boundary condition for a boundary layer calculation. Predictive comparisons generated from boundary layer calculations (STAN7) using an algebraic turbulence model (ATM) and a well-known transition model (Mayle) are provided. At low turbulence levels the close comparisons provide confidence in the experimental technique. At higher turbulence levels the comparisons may provide a better indication of the physics of response of vane heat transfer to the external turbulence. These data are expected to help clarify the physics of vane heat transfer at very high turbulence levels.

Commentary by Dr. Valentin Fuster
2016;():V008T10A041. doi:10.1115/IMECE2016-67655.

The present investigation considers the effects of special roughness patterns on impingement target surfaces to improve the effectiveness and surface heat transfer augmentation levels of impingement jet array cooling. This investigation utilizes various sizes, distributions, shapes, and patterns of surface roughness elements for impingement cooling augmentation. In total, fifteen different test surfaces are considered, either with cylinder small roughness, triangle small roughness, or rectangle small roughness element shapes. Six of these test surfaces also employ large roughness elements with rectangular shapes (along with either triangle or rectangle small roughness elements). Tests are performed at impingement jet Reynolds numbers of 900 and 11000. Nusselt number variations for the small cylinder roughness show different trends with streamwise development and changing roughness height, compared to target plates with small rectangle roughness and small triangle roughness. In general, this is because roughness elements which contain surface shapes with sharp edges generate increased magnitudes of vorticity with length scales of the order of the roughness element diameter. Such generation is not always present in an abundant fashion with the small cylinder roughness because of the smooth contours around each roughness element periphery. Such effects are illustrated by several data sets, including Nusselt numbers associated with the small cylinder roughness with a height of 0.250D at a turbulent Reynolds number of 11000.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Heat and Mass Transfer in Built Environment: Buildings, Cities, and Transportation

2016;():V008T10A042. doi:10.1115/IMECE2016-67431.

One of the most important requirements for building performance is energy saving and recovering and they are chased developing new strategies for the reduction of energy consumption, due to the heat flux transmitted through buildings envelopes. This work examines a prototypal ventilated roof numerically using a two-dimensional model in Ansys Fluent. Only a single flap of the roof is analyzed because its structure is geometrically and thermally symmetrical. The objective of this work is to study the thermal and fluid dynamic behaviors of a ventilated roof for different configurations of the exit section of the ventilated channel. The model is evaluated in air flow, considering a k-ε turbulence model to give the governing equations. Results are a function of an assigned heat flux on the top wall of the ventilation layer. They are analyzed studying temperature and air velocity distributions. The profiles of wall temperature and air velocity along the cross sections and longitudinal sections of the ventilated layer consider the different effects of the various geometric configurations. The results for different considering configuration detect that the ridge form and the outlet reservoir dimensions do not influence the thermal behavior inside the channel whereas a smaller outlet section determines higher wall temperature and lower air velocity in the channel.

Topics: Fluid dynamics , Roofs
Commentary by Dr. Valentin Fuster
2016;():V008T10A043. doi:10.1115/IMECE2016-67765.

The use of Phase Change Materials (PCMs) in asphalt pavement mixtures potentially offers a solution for regulating extreme temperatures that can cause thermally-induced rutting in pavement systems. The primary objective of this study is to fundamentally understand the effect on the heat transfer and maximum surface temperature in flexible pavement systems that includes PCMs. In particular, we consider a pavement structure in which PCM is embedded in the asphalt-concrete layer with varying volume fractions.

Our simulation results show that the pavement system embedded with PCMs yield lower surface temperature values than systems without PCM (maximum temperature decrease is 1.5°C for the distributed PCM with a volume fraction of 30%). Further, we observe a higher temperature drop through the PCM-embedded asphalt layer compared to a pavement without PCM, and regions possessing temperature values less than 45°C that may help to reduce the thermally induced rutting problems. The simulation yields another interesting result: increasing PCM volume fraction beyond 60% results in higher surface temperature values. This increase in the maximum surface temperature may be explained by the fact that the PCM used in the simulation has a lower thermal conductivity than that of the asphalt-concrete that ultimately results in a lower effective thermal conductivity value for the system. Finally, we observe that an increase in the effective thermal conductivity yields lower surface temperature for the PCM embedded pavement system.

Commentary by Dr. Valentin Fuster
2016;():V008T10A044. doi:10.1115/IMECE2016-67800.

Energy consumption and thermal management have become key challenges in the design of large-scale data centers, where perforated tiles are used together with cold and hot aisles configuration to improve thermal management. Although full-field simulations using computational fluid dynamics and heat transfer (CFD/HT) tools can be applied to predict the flow and temperature fields inside data centers, their running time remain the biggest challenge to most modelers. In this paper, response surface methodology based on radial basis function is used to significantly reduce the running time for generating a large set of generations during a two-objective minimization process which uses the genetic algorithm as its main engine. Three design parameters including mass flow inlet, inlet temperature, and server heat load are investigated for a two-objective optimization. The goal is to minimize both the temperature difference and the maximum temperature inside the data center and search for a range of design parameters that satisfy both of these objectives. Numerous radial basis function models are studied and compared. Discussion on a more preferred scheme for the response surface construction is provided. Finally, a graph of Pareto font is generated showing the set of optimal designs in the objective space, and Pareto design validation is also performed.

Commentary by Dr. Valentin Fuster
2016;():V008T10A045. doi:10.1115/IMECE2016-67816.

People spend most of their time indoors. A comfortable indoor environment is thus essential for the occupants’ good health and productivity. Buildings are responsible for about half of a modern society’s total energy consumption. HVAC (Heating, Ventilation and Air-Conditioning) which is often used to provide thermal comfort to the occupants, in turn accounts for a major proportion of this energy demand. Minimising HVAC energy consumption will thus result in great economic benefits. It also contributes beneficially to the issue of sustainable future and climate change, by reducing fuel burning. Natural ventilation can be used to help reduce significantly HVAC energy demand. Solar chimney (thermal chimney) is a device which absorbs solar radiation to heat the air. The heated air, becoming buoyant, rises through the chimney’s passage and induces further air currents. When fitted to a building, solar chimney can thus induce fresh outside air to flow through it for ventilation. As a very useful ventilation device, solar chimney has been the subject of many studies. However, due to the complex non-laminar, non-isothermal flow and heat transfer involved, there are still many factors affecting a solar chimney’s performance (measured by the induced flow rate of air, for instance) not yet considered, especially regarding 3-dimensional computational modelling in real-sized building settings. This work thus investigates computationally natural ventilation induced by a roof-mounted solar chimney through a real-sized 3-dimensional room, using a commercial CFD (Computational Fluid Dynamics) software package which employs the Finite Volume Method. Chien’s turbulence model of low-Reynolds-number K-ε is used in a Reynolds Averaged Navier-Stokes (RANS) formulation. Thus, the full set of Reynolds-Averaged governing equations pertaining to non-isothermal, buoyancy induced, incompressible, steady, turbulent flow of air near standard conditions at sea level, coupled with equations describing the Chien’s turbulence model, are solved, with appropriate boundary conditions. No further simplifying assumptions are made. Grid convergence tests are conducted to make sure that the grid patterns used are appropriate. Adequate numerical convergence is allowed; this often requires that relative changes in the successive iterated solutions be less than 0.0001. Accumulation errors resulting from massive or lengthy computation are also carefully monitored and minimized. 64-bits precision is used throughout. It is found that entrance geometry to the chimney’s channel affects significantly the ventilation rate, especially at higher solar heat flux, with rounded entrance resulting in higher rate. But these entrance-geometry effects also vary significantly with location of the room’s inlet-opening which in its turn affects the flow path before the chimney’s entrance.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Heat Pipes

2016;():V008T10A046. doi:10.1115/IMECE2016-66440.

The heat transfer capacity of a PHP is tremendously high and is finding many applications such as in electronic cooling. In order to maximize its heat transfer potential, the working parameters of a PHP have to be set to the right values. The present work deals with the optimization study of a part-unit-cell model of a Pulsating Heat Pipe (PHP) comprising of a single meniscus oscillating between evaporator and adiabatic sections. The parameters considered for this study are the effective length of the evaporator section, the evaporator temperature and the fluid fill ratio. All the numerical studies on PHP till date make the approximation of incompressibility of working fluid. However, recent experimental studies by M.Rao et al. [1] have shown the importance of compressibility effects on the working of a PHP. The present work involves a compressible phase change heat transfer model, based on the Volume-of-Fluid solver. The compressible model is incorporated into open source CFD solver OpenFOAM. This solver is validated in stages by Ghanta and Pattamatta [2] and the part-unit cell of the PHP is validated against the existing experimental results of M. Rao et al [1] and contrast is made with an incompressible solver, to emphasise the importance of considering the compressibility effects. Following validation of the compressible phase change solver, a parametric study explaining the effects of the above mentioned parameters on the objective functions and working of the PHP is performed, which forms the basis for the optimization presented in this work. Accordingly, the ratio of evaporator to the adiabatic length (Le/La) is varied between 2 and 10, the evaporator superheat between 5 and 20 and the fluid filling ratio is varied between 35–80 %. A multi-objective optimization problem is set-up taking the maximum vapour pressure attained and working time (the time for which the working fluid is in contact with the part unit cell of the PHP) as the objective functions. Models are created using two different methods — Kriging and Response Surface Approximation (RSA). The models are optimized using multi-objective Genetic Algorithm, coded in MATLAB. Both the models used predicted the same optimum values, with a variation of 0.01%. The optimum values point at a fluid fill ratio of 79.5%, evaporator excess temperature of 7.89 and an evaporator section of length seven times that of the adiabatic section. The same is also validated with results of numerical simulation at the optimal point. In majority of the works presented so far, the maximum vapour pressure alone is taken as a benchmark for the performance of the PHP. To elucidate the importance of considering working time as an objective function, a single objective optimization study was also performed, with only the maximum pressure as the objective function. The results of single objective optimization showed a deviated optimal point, with similar optimal pressure value as that of multi-objective optimization, but working time reduced by half. Hence by not considering the working time of PHP as an objective function, the optimal point generated results in only half the maximum heat transfer that can otherwise be attained with different parameters.

Commentary by Dr. Valentin Fuster
2016;():V008T10A047. doi:10.1115/IMECE2016-66566.

In this paper, a miniature loop heat pipe (mLHP) with a flat evaporator is illustrated and investigated experimentally, with water as the working fluid. The mLHP can be applied for the mobile electronics cooling, such as tablet computers and laptop computers, with a 1.2 mm thick ultra-thin flat evaporator and a thickness of 1.0 mm for the vapor line, liquid line and condenser. A narrow sintered copper mesh in the liquid line and a part of the condenser as the secondary wick can promote the flow of the condensed working fluid back to the evaporator. The experimental results showed that the mLHP could start up successfully and operate stably at low heat load of 3 W in the horizontal orientation, and transport a high heat load of 12 W (the heat flux of 4 W/cm2) with the evaporator temperature below 100 °C in different test orientations by natural convection, showing good operational performance against gravity field. The minimum mLHP thermal resistance of 0.32 K/W was achieved at the input heat load of 12 W in the horizontal orientation.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Heat Transfer in Energy Systems: Applications

2016;():V008T10A048. doi:10.1115/IMECE2016-65410.

In this paper we report the main advances made by our research group on the heat transfer performance of complex stream architectures embedded in a conducting solid. The immediate application of this review work deals with ground-coupled heat pumps. Various configurations are considered: U-shaped with varying spacing between the parallel portions of the U, serpentines with three elbows, and trees with T- and Y-shaped bifurcations. In each case the volume ratio of fluid to soil is fixed. We determine the critical geometric features that allow the heat transfer density of the stream-solid configuration to be the highest that it can be. In the case of U-tubes and serpentines, the best spacing between parallel portions is discovered, whereas the vascular designs morph into bifurcations and angles of connection that provide progressively greater heat transfer rate per unit volume. Next we move to more complex underground structures, connecting several heat pumps to the same fluid loop. We conclude by comparing the merits of the two options.

Commentary by Dr. Valentin Fuster
2016;():V008T10A049. doi:10.1115/IMECE2016-65653.

Heat exchangers are present in a variety of processes and industries. Increasing system efficiency is the most effective method and one of the greatest concerns in reducing energy consumption. In this paper we applied an integrated design approach to heat exchangers design, which combines the Integrated Multi-Scale Robust Design (IMRD) with the Grey Relational Analysis (GRA). As a case study, a double-pipe heat exchanger was used.

The IMRD performs the horizontal integration in the Process-Structure-Property-Performance (P-S-P-P) relationship through forward modeling and inductive exploration processes, while the vertical integration in the P-S-P-P relationship is accomplished by adopting localization and homogenization concepts.

For the proposed application into heat exchangers, the IMRD explores solution spaces and suggests feasible solution ranges for improving the thermal-hydraulic performance, while the GRA evaluates the relative importance of design variables in the heat exchanger.

In the preliminary study, it is found that the feasible solution range is significantly reduced for maximizing the heat transfer rate, compared to the equally balanced function, while the feasible solution range is less sensitive in minimizing annular pump power. To validate the IMRD simulation results from a CFD model are used.

Commentary by Dr. Valentin Fuster
2016;():V008T10A050. doi:10.1115/IMECE2016-65833.

A three-dimensional model focusing on fluid flow, heat transfer, species transport and chemical reaction is investigated in a commercial metal-organic chemical vapor deposition (MOCVD) reactor. The key reaction pre-exponential factor is improved to yield more reasonable results matching the experiment data. The growth rate and growth uniformity are carefully investigated with the premixed and non-premixed inlets, as well as with the various temperatures, flow rates and V:III ratios. The susceptor of the reactor is divided into Zone A, Zone B and Zone C according to the heater alignment. The results reveal that the premixed inlet leads to a more uniform growth rate than the non-premixed inlet does. Temperature change of the inlet gas has a negligible influence on the growth rate and uniformity. A larger flow rate and/or lower V:III ratio result in increase of the growth rate and uniformity. However, growth uniformity of the particular zones shows different variable-dependent tendency. The conclusions can be instructive for high-efficiency and better-quality manufacture in industry production with a balance between the growth rate and the growth uniformity.

Commentary by Dr. Valentin Fuster
2016;():V008T10A051. doi:10.1115/IMECE2016-65883.

The purpose of the present work was to investigate numerically the effect of the top and/or bottom blind openings on the convective heat transfer from a window fitted with a double-layered top down-bottom up honeycomb blind system. Top down-bottom up systems that utilize so-called honeycomb (or cellular) blinds can be opened at the top and/or the bottom. When a honeycomb blind is fully closed there are two or more vertical blind portions and a series of horizontal or nearly horizontal blind portions which join the vertical portions and form a column of cells. This gives the blind system its honeycomb or cellular structure. When opening a honeycomb blind the vertical portions of the blind bend or fold allowing the overall height of the blind to decrease. A double-layered honeycomb blind is constructed with three vertical blind portions and two columns of cells. A recessed window has been considered in the present study and only the convective heat transfer from the window to the surrounding room has been investigated. The surfaces of the blind are assumed to offer no resistance to heat transfer. The commercial CFD solver ANSYS FLUENT© has been used to obtain the solution. Over the range of parameters considered in this study, both laminar and turbulent flow can occur. The k-ε turbulence model has been used in obtaining the solutions. The convective heat transfer rate from the inner surface of the window, expressed in terms of a mean Nusselt number based on the window height and the difference between the window and the air temperatures, will depend on the Rayleigh number, also based on the window height, and the difference between the window and the air temperatures, the dimensionless top and bottom blind openings, and the dimensionless window recess depth. Variations of the mean Nusselt number with Rayleigh number for various values of these other parameters have been obtained and the results used to study how these other parameters affect the window heat transfer rate.

Commentary by Dr. Valentin Fuster
2016;():V008T10A052. doi:10.1115/IMECE2016-66106.

Ammonothermal crystal growth technique is one of the most effective methods used for growing Gallium Nitride (GaN) crystals. GaN crystals have wide applications in light emitting diodes (LEDs) or UV lasers. Three-dimensional large eddy simulations (LES) of natural convection in a laterally heated cylindrical reactor, using the commercial computational fluid dynamics (CFD) software ANSYS FLUENT, are presented for a Rayleigh number of Ra = 8.8 × 106. The objective of the current calculations is to understand the effect(s) of opening area of the baffle on the flow pattern and temperature distribution inside the reactor. The baffles considered in this study are annular hollow discs with different opening areas. Three cases with total opening areas of 40%, 25% and 100% (baffle-less) are considered. Velocity and temperature distributions across the different planes and lines, are analyzed in order to obtain information on the flow and heat transfer processes (temperature maps) resulting from various baffle openings.

Commentary by Dr. Valentin Fuster
2016;():V008T10A053. doi:10.1115/IMECE2016-66380.

To reduce computational time for simulation of natural convection in open cavities, it is quite common to use a domain restricted to the cavity with approximate boundary conditions at the cavity opening. It had been shown that such approach leads to quite accurate solutions for high Rayleigh number (Ra) flows. Such approach has been extended to flows involving radiative heat transfer as well. However, it is important to note that the effect of radiation on the accuracy of restricted domain approach has not been evaluated. In the present work, a comparison of Nusselt numbers is obtained by restricted domain approach with those obtained by using extended domain approach. The convective as well as radiative Nusselt numbers are considered for comparison for various values of Ra and radiation conduction parameter (Nr). It is observed that the accuracy of the restricted domain approach varies with the radiation conduction parameter as well and the approach is found to be quite accurate for high values of Nr.

Commentary by Dr. Valentin Fuster
2016;():V008T10A054. doi:10.1115/IMECE2016-66449.

Internal Y-shaped bifurcation has been proved to be an advantageous way on improving thermal performance of microchannel heat sinks according to the previous research. Metal foams are known due to their predominate performance such as low-density, large surface area and high thermal conductivity. In this paper, different parameters of metal foams in Y-shaped bifurcation microchannel heat sinks are designed and investigated numerically. The effects of Reynolds number, porosity of metal foam, and the pore density (PPI) of the metal foam on the microchannel heat sinks are analyzed in detail. It is found that the internal Y-shaped bifurcation microchannel heat sinks with metal foam exhibit better heat transfer enhancement and overall thermal performance. This research provides broad application prospects for heat sinks with metal foam in the thermal management of high power density electronic devices.

Commentary by Dr. Valentin Fuster
2016;():V008T10A055. doi:10.1115/IMECE2016-66663.

The flow and heat transfer in a sudden expansion followed by sudden contraction channel are widely applied in industry, and it is also a classic problem for theoretical study. In this article, the SIMPLE algorithm with QUICK scheme were used to study the flow and heat transfer in a sudden expansion followed by sudden contraction channel. The nonlinear characteristics and temperature field were investigated for various Reynolds number and geometrical dimension. The results show that the temperature field evolves from symmetric to asymmetric state with the increasing Re. When Re ≥ Rec, the flow loses stability and from symmetric to asymmetric via a symmetry-breaking bifurcation; when the Reynolds number continues to increase, the fluid flow and heat transfer oscillation. The nonlinear characteristics of flow and heat transfer within the channel is further analyzed.

Commentary by Dr. Valentin Fuster
2016;():V008T10A056. doi:10.1115/IMECE2016-66671.

As significant fluid machinery, canned motor pumps are widely applied in industrial field. The typical characteristic of canned motor pump is that the fluid comes into the narrow gap and affects the performance of canned motor. The coolant flow in the narrow annular gap between rotor and stator cans belongs to Taylor-Couette-Poiseuille flow which has been investigated for a long time while the thermal design is a key function of internal narrow gap annular flow of canned motor. However, the temperature distribution prediction of canned motor deviates from the experiments, especially in the high-capacity canned motor due to the large shear rate of fluid and eddy-current loss of motor’s can. According to the researcher’s work, the significant work lies in the heat transfer coefficient that different researchers give various numerical prediction and experimental measurement. It brings big challenge in thermal design of high-capacity canned motor pump. In this paper, the author focuses on the reason why the heat transfer coefficient is remarkably lower than that other’s forecast. In this paper, the heat transfer behavior of the boundary layer near surfaces in the annular flow is investigated by using the commercial fluid dynamic (CFD) method. Firstly, the Naiver-Stocks (N-S) equations and energy conservation equation are employed for modeling the flow and heat transfer behavior, and the k-ω turbulent model is used for solving the flow control equations. Secondly, the fluid domain is described by a simplified geometrical model: two concentric cylinders with finite gap length. Thirdly, numerical approach is used to analyze the subject with tools of Solidworks, ICEM CFD and Ansys Fluent. Two parameters are analyzed in the research, namely the rotating speed and the wall heat flux, without considering the fluid viscous dissipation and thermal contact resistance. Numerical simulation results indicate that Taylor vortex exists in the flow regime, and the temperature distribution is affected by both the rotating speed and the wall heat flux, named thermal barrier effect under large heat flux condition. The thermal barrier effect lies in that the temperature gradient of interface decreases compared to the peak value of temperature gradient near the surface, so that the heat transfer coefficient is reduced remarkably. This effect leads to the temperature prediction deviates from the experiment measurement.

Commentary by Dr. Valentin Fuster
2016;():V008T10A057. doi:10.1115/IMECE2016-66769.

This paper focuses on an approach to predict the temperature of a Photovoltaic panel under varying irradiation conditions in Cordoba, Colombia. The thermal model developed considers a heat transfer analysis in order to estimate the performance of a photovoltaic solar system due to local temperature variation. The heat transfer model analyzes the photovoltaic cell as a system exposed to radiation and natural convection by carrying out a first law energy balance which takes into account the radiation energy from the sun that hits the panel and the energy lost from the photovoltaic cell through natural convection and radiation. To determine the natural convection heat transfer coefficient, the Grashof number was employed along with Nusselt and Rayleigh number in a dimensionless form. The model has been implemented in the Matlab-Simulink platform that allows to establish a specific empirical correlation among the Nusselt number and Rayleigh for PV statics panels operating under natural convection condition. This experimental process consists in an iterative adjust of the theoretical equations of natural convection with experimental data gathered from a real PV module operation. The variables measured were the surface temperature, the environmental temperature and the solar irradiation provided by a pyranometer. It is found a good agreement between the radiation behavior and the predicted temperature. The higher values of the irradiation and environmental temperature coincides with predicted and observed PV surface temperatures and the thermal performance of the panel. The mean absolute error of the model was 3.09 K and the root mean square deviation 3.47 K.

Commentary by Dr. Valentin Fuster
2016;():V008T10A058. doi:10.1115/IMECE2016-66960.

The quest to achieve higher heat transfer rate, smaller size and minimum pressure drop is a main area of focus in the design of heat exchangers. Plate heat exchangers are one of viable candidates to deliver higher heat duties but still have a drawback of higher pressure drop due to long restricted flow path. Motivated by demand of miniaturization and cost reduction, a novel design of tubular microchannel heat exchanger for single phase flow employing ammonia water mixture is proposed. Numerical simulation of unit fluid domain is conducted in ANSYS Fluent. Parametric study of the different flow geometries is evaluated in terms of Nusselt number and pressure drop. The salient features of the design include ultra-compact size with higher heat transfer rate and acceptable pressure drop.

Commentary by Dr. Valentin Fuster
2016;():V008T10A059. doi:10.1115/IMECE2016-67288.

Nanofluids often exhibit superior heat transfer characteristics when compared with conventional heat transfer fluids. The increase in thermal conductivity due to the presence of various nanoparticles was experimentally examined using commercially available equipment that utilizes the two thickness method. The thermal conductivity of 10 and 30 nm aluminum oxide nanoparticles suspended in distilled water at concentrations of 2% and 5% was measured for a temperature range of 15°C to 70°C in increments of 5°C. For a 2% concentration of 10 nm aluminum oxide the experimentally derived thermal conductivity deviated from the theoretical thermal conductivity predicted by Maxwell by an average of 1.55%. The average percent increase in the thermal conductivity of the base fluid due to the presence of 10 nm aluminum oxide nanoparticles was found to be 4.17 and 4.90% for concentrations of 2 and 5% respectively. The presence of 30 nm nanoparticles resulted in a greater discrepancy with the theoretical model developed by Maxwell, regardless of concentration. In addition, the presence of 10 nm aluminum oxide nanoparticles resulted in a greater increase in thermal conductivity when compared with 30 nm aluminum oxide nanoparticles. In addition, the thermal conductivity of a base fluid dispersed with multi-walled carbon nanotubes (MWNTs) with an outer diameter ranging from 13–18 nm and a length ranging from 3–30 micrometers (μm) was examined. The presence of a 0.2% concentration of MWNTs resulted in an average increase in thermal conductivity of 0.31%. Unfortunately, there was a large standard deviation in the results for the MWNTs and significant fluctuations with temperature. While this experimental methodology may be sufficient for metal based nanofluid particles it may be undesirable for fluids enhanced by MWNTs.

Commentary by Dr. Valentin Fuster
2016;():V008T10A060. doi:10.1115/IMECE2016-67563.

Flow assurance is critical in offshore oil and gas production. Thermal insulation is an effective way to reduce heat loss from subsea pipelines and avoid the formation of hydrates or wax deposits that could block the flowlines. This paper presents a hybrid thermal insulation model with a combination of phase change material (PCM) and conventional insulating layers. The idea is to use PCM to store thermal energy with normal oil and gas production and release heat back to the fluids during a shut-in operation. Melting and solidification of the PCM layer is analyzed for different thicknesses at both working and shut-in conditions. The model is developed numerically using a Finite Volume Method (FVM) and an enthalpy porosity technique. It accounts for heat conduction with liquid-solid phase changes, as well as natural convection in the PCM. In this study, paraffin is implemented as PCM with temperature dependent properties while Aerogel is used as the conventional insulation layer. The results show that ticker PCM layer than conventional insulating layer can significantly improve thermal insulation performance, with extended cool-down time during flow line shut in.

Commentary by Dr. Valentin Fuster
2016;():V008T10A061. doi:10.1115/IMECE2016-67882.

In this study tube bundle Transport Membrane Condenser (TMC) has been studied numerically. The tube walls of TMC based heat exchangers are made of a nano-porous material and has a high membrane selectivity which is able to extract condensate pure water from the flue gas in the presence of other non-condensable gases (i.e. CO2, O2 and N2). Low grade waste heat and water recovery using ceramic membrane, based on separation mechanism, is a promising technology which helps to increase the efficiency of boilers and gas or coal combustors. The effects of inclination angles of tube bundle, different flue gas velocities, and the mass flow rate of water and gas flue have been studied numerically on heat transfer, pressure drop and condensation rates. To assess the capability of single stage TMC heat exchangers in terms of waste heat and water recovery at various inlet conditions, a single phase multi-component model is used. ANSYS-FLUENT is used to simulate the heat and mass transfer inside TMC heat exchangers. The condensation model and related source/sink terms are implemented in the computational setups using appropriate User Defined Functions (UDFs).

Commentary by Dr. Valentin Fuster
2016;():V008T10A062. doi:10.1115/IMECE2016-68001.

Influences of different SOFA ratios on NOx emission in a tower pulverized coal fired boiler that burners are arranged in the front and the rear wall are investigated in this paper. The front wall is arranged with three layers of burners, and the rear wall is arranged with two layers of burners. The upper layers are the SOFA nozzles. We adopt the method of adding SOFA to reduce NOx emission, and analyze the influence of SOFA on the internal combustion and NOx emissions for pulverized coal boiler. The results show that the addition of SOFA makes the pulverized coal fired boiler form a reduction zone in the main combustion zone, which can inhibit the NOx production increase, so as to achieve the goal of reducing NOx emissions. And the results show that, it is not true that the more SOFA ratio, the less NOx emissions. In fact, the percentage of SOFA has an optimal value, and below or above of this value, NOx yield will increase. Through comparison of different ratios of SOFA distribution modes with the furnace temperature, O2, CO and NOx, we analyze the influence of SOFA ratio on the internal combustion for pulverized coal boiler, and provide some guidance and bases for the optimization of other similar units.

Commentary by Dr. Valentin Fuster
2016;():V008T10A063. doi:10.1115/IMECE2016-68004.

The combustion mechanism of pulverized coal in a DRB-4Z burner are analyzed and the temperature distribution, char burnout and CO production in the burner outlet area are obtained. The gas phase turbulence model is the Realizable k-ε two equation model, and radiation heat transfer model is P-1 radiation model. The discrete phase model is used to simulate the force and motion trajectory of the pulverized coal particles, and the stochastic model is used to simulate the flow of coal particles. The combustion model is non-premixed combustion model, and the devolatilization model is two competing rates model; char combustion model is kinetics/diffusion-limited model. Numerical results revealed the mechanism of pulverized coal devolatilization and char combustion, and the solution may give reference to air arrangement of the same type of burners.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Heat Transfer in Energy Systems: Design and Performance Analysis

2016;():V008T10A064. doi:10.1115/IMECE2016-65441.

Modeling of heat loss from offshore buried pipelines is one of the prime concerns for Oil and Gas industries. Offshore Oil and Gas production and thermal modeling of buried pipelines in arctic regions are challenging tasks due to environmental conditions and hazards. Flow properties of Oil and Gas flowing through the pipelines in arctic regions are also affected due to freezing around pipelines. Solid formation in the production path can have serious implications on production. Heavy components of crude oil start to precipitate as wax crystal when the fluid temperature drops. Gas hydrates also form when natural gas combines with free water at high pressure and low temperature. Pipeline burial and trenching in some offshore developments are now one of the prime methods to avoid ice gouge, ice cover, icebergs, and other threats. Long pipelines require more thermal management to deliver production to the sea surface. Significant heat loss may occur from offshore buried pipelines in the forms of heat conduction and natural convection through the seabed. The later can become more prominent where the backfill soil is loose or sandy. The aim of this paper is to provide an insight of modeling and conducting the experiments using different parameters with numerical analysis results support to investigate the heat loss from offshore buried pipelines. This paper also provides validation of the outputs from benchmark tests with analytical models available for theoretical shape factor at constant temperature and constant heat flux boundary conditions. These theoretical models have limitations such as the assumption of uniform soil properties around the buried pipeline, isothermal outer surface of the buried pipeline and soil surface. Degree of saturation of surrounding medium can play a significant role in the thermal behavior of fluid travelling through the backfill soil. This paper presents several steady states and transient response analysis describing some influential geotechnical parameters along with test procedures and numerical simulations using CFD to model the heat loss for different parameters such as burial depth, backfill soil, trench geometries etc. This paper also shows the transient response for several shutdown (cooldown) tests performed in the saturated sand medium. The statistical and uncertainty analysis performed from the experimental outputs also ensure the legitimacy of the experimental model. The outcomes of this research will provide valuable experimental data and numerical predictions for offshore pipeline design, heat loss from buried pipelines in offshore conditions, and efficient model to mitigate the flow assurance issues e.g. wax and hydrates.

Commentary by Dr. Valentin Fuster
2016;():V008T10A065. doi:10.1115/IMECE2016-65729.

Thermoelectric effects of size of microchannels on an internally cooled Li-ion battery cell is investigated in this paper. The liquid electrolyte was flowed as the coolant through rectangular microchannels embedded in the positive and negative electrodes. The effects of size of microchannels on the thermal and electrical performances of a Li-ion (Lithium-ion) battery cell were studied by carrying out 3D transient thermal analysis. Six different cases were designed according to the ratio of the width of the microchannels to the width of the cell from 0 to 0.5. The effects of inlet velocity of electrolyte flow, inlet temperature of electrolyte flow, and size of the microchannels were studied on the temperature uniformity inside the battery cell, maximum temperature inside the battery cell, and cell voltage. The results showed that increasing the size of the microchannels enhances the thermal performance of the battery cell; however, it causes slight decrease on the cell voltage (less than 2%). Comparison between the case with width ratio of 0.5 (Case 6) with the case without microchannel (Case 1) showed that this internal cooling method can decrease the maximum temperature of the battery up to 11.22K, 9.36K, and 7.86K for the inlet temperature of electrolyte flow of 288.15K, 298.15K, and 308.15K, respectively. Furthermore, the case with width ratio of 0.5 (Case 6) has up to 77% better temperature uniformity compare with the case with width ratio of 0.1 (Case 2). Increasing the inlet temperature of electrolyte flow enhances the temperature uniformity up to 33% and increases the cell voltage up to 3%, but it keeps the battery on higher temperatures. Furthermore, increasing the inlet velocity of electrolyte flow from 0.01m/s to 0.01m/s enhances the thermal management of the battery cell by decreasing the temperature inside the battery up to 8.09K, 6.75K, and 5.67K for the inlet temperature of electrolyte flow of 288.15K, 298.15K, and 308.15K respectively. Furthermore, it improves the temperature uniformity up to 89% and decreases the voltage less than 1%.

Commentary by Dr. Valentin Fuster
2016;():V008T10A066. doi:10.1115/IMECE2016-66772.

The design criteria of converter cooling system for a 2.5 MW permanent magnet direct-drive wind turbine generator were investigated. Two (2) distribution networks with pipe sizes of DN40 and DN50 were used as basis for fluid flow analysis. The theoretical system pressure drop and system volume flow rate of converter cooling system were calculated using the governing equations of mass conservation, pump performance curve and distribution network characteristics. The system of nonlinear equations was solved using multivariable Newton-Raphson method with the solution vector determined using LU decomposition method. Numerical results suggest that the DN50 pipe provides a pressure drop limit of less than 300 Pa/m in the converter cooling system better than the pressure drop obtained from a DN40 pipe. The system volume flow rate of DN50 pipe was found to be above the operating limit of heat exchanger requirement of 135.30 L/min which needs to dissipate heat with a minimum of 50 kW.

Commentary by Dr. Valentin Fuster
2016;():V008T10A067. doi:10.1115/IMECE2016-66901.

Heat transfer in an oscillating water column in the transition regime of pool boiling to bubbly flow is investigated experimentally and theoretically. Forced oscillations are applied to water via a frequency controlled dc motor and a piston-cylinder device. Heat transfer is from the electrically heated inner surface to the reciprocating flow. The heat transfer in the oscillating fluid column is altered by using stainless steel scrap metal layers (made off open-cell discrete cells) which produces a porous medium within the system. The effective heat transfer mechanism is enhanced and it is due to the hydrodynamic mixing of the boundary layer and the core flow. In oscillating flow, the hydrodynamic lag between the core flow and the boundary layer flow is somehow significant. At low actuation frequencies and at low heat fluxes, heat transfer is restricted in the single phase flows. The transition regime of pool boiling to bubbly flow is proposed to be a remedy to the stated limitation. The contribution by the pool boiling on heat transfer appears to be the dominant mechanism for the selected low oscillation amplitudes and frequencies. Accordingly the regime is a transition from pool boiling to bubbly flow. Nucleate-bubbly flow boiling in oscillating flow is also investigated using a simplified thermodynamic analysis. According to the experimental results, bubbles induce highly efficient heat transfer mechanisms. Experimental study proved that the heater surface temperature is the dominant parameter affecting heat transfer. At greater actuation frequencies saturated nucleate pool boiling ceases to exist. Actuation frequency becomes important in that circumstances. The present investigation has possible applications in moderate sized wicked heat pipes, boilers, compact heat exchangers and steam generators.

Commentary by Dr. Valentin Fuster
2016;():V008T10A068. doi:10.1115/IMECE2016-66999.

The usage of compressed air generated by supercharger or turbocharger by automotive Original Equipment Manufacturers (OEM) is growing with the aim to increase engine performance by increasing the density of the air charge being drawn into the cylinder. Denser air coupled with more fuel pulled into the combustion chamber results in increased engine performance. The inlet air is heated during compression which can cause pre-ignition, which leads to reduced engine functionality. The charge air cooler (CAC) is a heat exchanger introduced to extract heat created during the compression process. Previous research developed a 3-D Computational Fluid Dynamics (CFD) model using the k-epsilon turbulent model with near wall treatment to resolve turbulence in the small channels of the CAC. [1] The present research uses a refined computational scheme with a Large Eddy Simulation (LES) model to solve local data as a function of time and location and correlates the result to the experimental measurements, as well as compare to the k-epsilon approach. Using LES resulted in the ability to correlate any portion of the experimental data and take a closer look at local heat transfer between the outside surface of the tube and the cooling air. Large Eddy Simulation for heat transfer gave more information required for design of CACs which is difficult to collect for various operating conditions by experiment. The overall benefit presented is a validated simulation methodology that predicts condensation, which is then used to evaluate and design CACs that function outside the condensate formation zone during various vehicle operation modes.

Commentary by Dr. Valentin Fuster
2016;():V008T10A069. doi:10.1115/IMECE2016-67660.

In this paper, a novel geometry is proposed for evaporators that are used in Organic Rankine Cycles. The proposed geometry consists of employing successive plenums at several length-scale levels, creating a multi-scale heat exchanger. The channels at the lowest length-scale levels were considered to have their length given by the thermal entrance-length. Numerical simulations based on turbulent flow correlations for supercritical R134a and water were used to obtain performance indicators for new heat exchangers and baseline heat exchangers. The relationship between the size of the channels at one level, k, with respect to the size of the channels at the next level, k + 1, is based on generalization of the “Murray’s law.” In order to account for the variation of the temperature and heat transfer coefficient in the entrance region, a heat transfer model was developed. The variation of the brine and refrigerant temperatures along each pipe was considered. Using the data on pumping power and weight of metal structures, including that of all the plenums and piping, the total present cost was evaluated using a cost model for shell-and-tube heat exchangers. In addition to the total present cost, the data on overall thermal resistance is also used in identifying optimal heat exchanger configurations. The main design variables include: tube arrangement, number of channels fed from plenum, and number of rows in the tube bank seen by the outside fluid. In order to assess the potential improvement of the new evaporator designs, baseline evaporators were designed. The baseline evaporator designs include long tubes of the same diameter as those of the lowest length-scale levels, placed between one inlet and one outlet. The baseline evaporator designs were created from the new evaporator designs by simply removing most of the internal plenums employing tubes much longer than their entrance length, as they would currently be used. Consistent with geothermal applications, the performance of new heat exchanger designs was compared to that of baseline heat exchanger designs at the same flow rates. For some operating conditions it was found that the new heat exchangers outperform their corresponding baseline heat exchangers.

Commentary by Dr. Valentin Fuster
2016;():V008T10A070. doi:10.1115/IMECE2016-68085.

Fresh water withdrawal for thermoelectric power generation in the U.S. is approximately 139 billion gallons per day (BGD), or 41% of total fresh water draw, making it the largest single use of fresh water in the U.S. Of the fresh water withdrawn for the power generation sector, 4.3 BGD is dissipated to the atmosphere by cooling towers and spray ponds. Dry-cooled power plants are attractive and sometimes necessary because they avoid significant withdrawal and consumption of freshwater resources that could otherwise be used for other purposes. This could become even more important when considering the potential effects of climate change (1). Additional benefits of dry-cooling include power plant site flexibility, reduced risk of water scarcity, and faster permitting (reducing project development time and cost). However, dry-cooling systems are known to be more costly and larger than their wet-cooling counterparts. Additionally, without the benefit of additional latent heat transfer through evaporation, the Rankine cycle condensing (cold) temperature for dry-cooling is typically higher than that for wet-cooling, affecting the efficiency of power production and the resultant levelized cost of electricity (LCOE).

The Advanced Research Projects Agency - Energy (ARPA-E) has developed a technoeconomic analysis (TEA) model for the development of indirect dry-cooling systems employing steam condensation within a natural gas combined cycle power plant. The TEA model has been used to inform the Advanced Research in Dry-Cooling (ARID) Program on the performance metrics needed to achieve an economical dry-cooling technology. In order to assess the relationship between air-cooled heat exchanger (ACHX) performance, including air side heat transfer coefficient and pressure drop, and power plant economics, ARPA-E has employed a modified version of the National Energy Technology Laboratory (NETL) model of a 550 MW natural gas combined cycle (NGCC) plant employing an evaporative cooling system. The evaporative cooling system, including associated balance of system costs, was replaced with a thermodynamic model for an ACHX with the desired improved heat transfer performance and supplemental cooling and storage systems. Monte Carlo simulation determined an optimal ACHX geometry and associated ACHX cost. Allowing for an increase in LCOE of 5%, the maximum allowable additional cost of the supplemental cooling system was determined as a function of the degree of cooling of the working fluid required. This paper describes the methodologies employed in the TEA, details the results, and includes related models as supplemental material, while providing insight on how the open source tool might be used for thermal management innovation.

Commentary by Dr. Valentin Fuster
2016;():V008T10A071. doi:10.1115/IMECE2016-68173.

Since 2006, The Center for Innovation and Applied Technology (CIAT) at Cooper Union for the Advancement of Science and Art has been developing a system to use thermal pollution to heat the growth medium of green roofs. CIAT is researching various apparatus and techniques, including shell-and-tube and shell-and-coil heat exchangers, to improve its heated ground agricultural projects. There are limited recorded observations on shell-and-coil heat exchangers; therefore a laboratory work station was created of interchangeable components to test the efficiency of a variety of coil designs.

This paper discusses the data collected on temperature, pressure, and flow rates for a straight tube and two different helical coils. The analysis of this data indicates the superiority of a helical coil design when compared to a straight tube design with respect to both rating and heat transfer rate. The same data analysis has lead to preliminary observations on how the contour properties of a helical coil influence the heat transfer rate through a coil. The authors intend to further this helical coil research to develop a useful mathematical model for determining efficient designs for shell-and-coil heat exchangers.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Heat Transfer in Energy Systems: Energy Conversion

2016;():V008T10A072. doi:10.1115/IMECE2016-65151.

The ever-increasing power throughput and ever-decreasing size of modern electronics, specifically power electronics, requires more advanced packaging techniques and materials to maintain thermal limits and sustain mechanical life. Specific applications with known operating conditions for these components can realize added benefits through a tailored thermal-mechanical-electrical optimized assembly, potentially utilizing niche material classes. Without losing any expected functionality, solid-liquid phase change materials could be incorporated into the device structure to reduce peak temperature and/or suppress high-cycle fatigue problems commonly found at die-attachment interfaces. The purpose of this study was to investigate, through model-based design and analysis, the impact of using organic phase-change materials (PCMs) at two strategic locations in the standard device stack. The results suggest noteworthy life improvement (40%) is possible when optimizing for a given melt point material. Additionally, further improvements were predicted through future material enhancements, namely thermal conductivity and latent heat.

Commentary by Dr. Valentin Fuster
2016;():V008T10A073. doi:10.1115/IMECE2016-65263.

As parabolic trough systems with high concentration ratios become feasible, convective heat transfer enhancement is expected to play a significant role in improving the thermal and thermodynamic performance of these systems. In this paper, the thermal performances of a high concentration ratio system using three different types of nanofluids were investigated. A system with a geometric concentration ratio of 113 and a rim angle of 80° was used in this study. The nanofluids considered were copper-Therminol®VP-1, silver-Therminol®VP-1 and Al2O3-Therminol®VP-1 nanofluid. For each nanofluid, the volume fraction of the nanoparticles in the base fluid was varied from 0–6%. The numerical solution was obtained using a finite volume based computational fluid dynamics tool. Temperature dependent properties were used for both the base fluid and the nanoparticles. An actual receiver heat flux boundary condition obtained using Monte Carlo ray tracing was coupled to the computational fluid dynamics code to model the thermal performance of the receiver. Results show that for each nanofluid used, the thermal performance of the receiver improves significantly. The thermal efficiency increases by about 12.5%, 13.9% and 7.2% for the copper-Therminol®VP-1, silver-Therminol®VP-1 and Al2O3-Therminol®VP-1 nanofluids, respectively as the volume fraction increases from 0 to 6%. The thermal efficiency improvement with silver-Therminol®VP-1 was the highest of the considered nanofluids owing to the relatively higher thermal conductivity of silver.

Commentary by Dr. Valentin Fuster
2016;():V008T10A074. doi:10.1115/IMECE2016-66340.

Current study analyzes dynamic instability of evaporator tube array at heat recovery steam-generator (HRSG) that encounters repetitive tube vibration failure. The tube array experiences turbulent swirling flue-gas. The analysis according to ASME criteria predicts critical instability velocities at 26.2 m/s, dimensionless reduced velocity factor at 85.7 and dimensionless mass damping at 50.2. These levels create large response of high vibration amplitude of tube reflecting strong coupling between tube structure and exhaust gas. CFD model for exhaust gas flow regime upstream tube array predicts large variation in velocity. The model is not validated but results agree with experience of repetitive tube failure within the high velocity profile sections. The calculated natural frequency of tube is 6 Hz, dimensionless reduced mass damping factor of tube is found at 243 meeting ASME criterion of greater than 64. Thus, synchronous vortex shedding vibration will not occur at the tube. Last, HRSG encounters structural vibration, cracks and high noise level at stack side. Fundamental acoustic frequency and vortex shedding frequency are calculated at 65 Hz and 134 Hz, respectively. These values don’t meet 80–120% range. Thus acoustic vibration noise will not occur.

Commentary by Dr. Valentin Fuster
2016;():V008T10A075. doi:10.1115/IMECE2016-67230.

The riser tube solar receiver of a circulating fluidized bed solid particle absorption solar thermal energy system was numerically modeled for analyzing hydrodynamic and heat transfer behaviors of the solid particles in the riser. Hydrodynamics of the model is validated by comparing radial distribution of void fractions with an experimental study. For the heat transfer from the opaque walls of the receiver that is heated to high temperatures by the solar rays concentrated by the heliostat field, a simple fractional model is used in which radiative transfer is neglected and total heat flux is distributed to phases according to the instantaneous volume fractions at the boundary cells. MFIX: Multiphase Flow with Interphase eXchanges code of NETL is used with a 2.5D Eulerian-Eulerian computational model for transient simulations. The 2.5D grid is a combination of planar cells and cylindrical cells with the determined optimum fraction of planar cells of 0.15. For the solar receiver riser, transient and time averaged results of void fraction and gas and solid phase temperature distributions were numerically obtained and analyzed.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Heat Transfer in Energy Systems: Fundamentals

2016;():V008T10A076. doi:10.1115/IMECE2016-67260.

The use of extended surfaces or fins is very common for enhancing the heat transfer between a prime surfaces and surrounding environment. The applications cover both scenarios where the prime surface is either at a higher or at a lower temperature than the surrounding environment. In the first case, only sensible heat transfer occurs whereas the latter is typical for refrigeration and air conditioning applications where both sensible and latent heat transfer occur.

The performance of a fin is well described through a dimensionless parameter called fin efficiency. The efficiency is represented graphically in form of charts as a function of another dimensionless parameter called the fin parameter. The objective of the dimensionless presentation is that it provides the solution to a class of problems. However, this is true only for the dry fins because such charts for wet fins are for a set of particular operating conditions (i.e. temperature and psychrometric data). Thus, a separate chart is required if operating conditions are changed. The objective of present study is to investigate the possibility of developing the fin efficiency charts in the form which are independent of the operating conditions, thus a single chart covering all possible operating conditions. The finite element formulation is used to account for the actual nonlinear psychrometric relationships.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Heat Transfer in Multi-Phase Systems

2016;():V008T10A077. doi:10.1115/IMECE2016-65357.

Effective Thermal Conductivity (ETC) of particulate beds is an important property to many processes in industries such as pharmaceutical, food, nuclear and casting and solidification technologies. This paper presents an experimental research that examines the dependence of the ETC of soil due to changes in the average temperature of the particulate beds, and the stresses on the particles (as derived from the pressure on the top face of the beds).A uni-axial cylindrical experimental system was composed. The ETC was measured by the experimental system while either the pressure on the particulate beds or the average temperature of the beds was changed.

Commentary by Dr. Valentin Fuster
2016;():V008T10A078. doi:10.1115/IMECE2016-65598.

As a kind of unconventional gas reservoirs, shale gas reservoirs are full of potential to develop and have attracted global attention. Accompanying the exploiting of shale gas, a large amount of drilling cuttings contaminated by the oil-based drilling fluid are generated inevitably. How to deal with the drilling cuttings in a environmental-friendly way is tough especially for offshore oilfield. So it is important to investigate this aspect deeply and develop methods to clean the contaminated drilling cuttings. As is known to all, the thermal desorption technology has outstanding performance in oily cuttings cleaning. This paper bases on a kind of mechanical-thermal cuttings cleaning apparatus where the contaminated drilling cuttings are heated up by friction heat produced by the friction between the cuttings and the agitating vanes. And the harmful substance is separated from the cuttings in the agitated and high temperature flow field. This thesis investigates the fundamental of the energy conversion in the frictional process, infer formulas analyzing the thermo-physical phenomena and quantitatively model the energy conversion and thermal transmission accompanying the friction.

Firstly, the principle of heat transfer and the law of conservation of energy are employed to investigate the natural law of the energy conversion in the frictional process. Based on the investigation, taking the liquid bridge between the oily cuttings and the agitating vane into account, this paper deduces the physical equations and the frictional energy model to calculate the total frictional heat, heat density and temperature distribution.

Following up the frictional model, in the Eulerian-Lagrangian coupling framework, this paper develops a parallel numerical platform of computational fluid dynamics combined with discrete element method (CFD-DEM). In the coupling approach, the gas motion is solved at the computational grid level while the solid motion is resolved at the particle-scale level. Furthermore, the coupling approach is extended with the frictional energy model. The numerical platform can calculate the dense gas-solid motion in the fluidizing apparatus, the convective heat transfer between gas and solid phase, and the conductive heat transfer between particles. Based on the platform, the mechanical-thermal energy conversion and the convective heat transfer between gas and oily cuttings, and the conductive heat transfer between cuttings and the agitating vanes are investigated. Meanwhile an experiment is conducted. By comparing the numerical results with the experiment data, the paper can come to the conclusion that how to dispose the nonlinear parameters such as the friction contact area, the friction coefficient and the normal pressure is the key to accurately model the energy conversion and the heat transmission. What’s more, it can be understood that the convective heat transfer between gas and solid phase play an important role in the heat transmission.

Commentary by Dr. Valentin Fuster
2016;():V008T10A079. doi:10.1115/IMECE2016-65708.

In this paper, both experimental and numerical studies have been performed on the convective boiling heat transfer of the Ethanol-in-Polyalphaolefin (PAO) Nanoemulsions inside a heat exchanger of twelve 1mm diameter mini-channels that was subjected to a uniform heat flux at its outer surface. The heat transfer characteristics and the pressure drop of the Ethanol/PAO nanoemulsion was studied experimentally, meanwhile, the volume of fraction (VOF) model with Pressure-Velocity coupling based Semi Implicit Method for Pressure Linked Equations (SIMPLE) iterative algorithm is employed to simulate the same experimental conditions numeircally. The results reveal that the convective boiling heat transfer coefficient of the nanoemulsion can be greatly enhanced upon the nucleation of ethanol nanodroplets inside, in which a maximum 50% enhancement compared to pure PAO base fluid can be achieved under current test conditions. However, the thermal conductivity and viscosity of the nanoemulsions has an insignificant effect on convective boiling heat transfer coefficient based on the experimental results. The ANSYS FLUENT simulation results also agree well with the experimental data. The Ethanol-in-PAO nanoemulsion could function as a good alternative conventional working fluid in two phase heat transfer applications.

Commentary by Dr. Valentin Fuster
2016;():V008T10A080. doi:10.1115/IMECE2016-66606.

Fluid flow with particles are found in many engineering applications such as flows inside lab-on-a-chips and heat exchangers. In heat exchangers, nanofluids or base fluids mixed with nanoparticles are applied to be used as the working fluid instead of the traditional base fluids which have low thermal-physical properties. The nanoparticle diameters are in the range from 1 to 100 nanometers are mixed with the traditional base fluids before they are applied inside the heat exchangers and the nanofluids have been proved continually that they enhance heat transfer rates of the heat exchangers. Turbulent and laminar nanofluid flows have shown different enhancements in different conditions. This work focused on comparing different turbulent nanofluid simulations which used the computational fluid dynamics, CFD, with different multiphase models. The Realizable k-ε turbulence model coupled with three multiphase models; Volume of Fluid (VOF) model, Mixture model and Eulerian model, were considered and compared. The heat exchanger geometry in the work was rectangular as in the electrical device application and the nanofluid was a mixture between Al2O3 and water. All simulated results, then, were compared with experimental results. The comparisons showed that numerical results did not deviate from each other but their delivered-time consumptions and complications were different. If one develops his own code, Eulerian model was the most complicated while Mixture model and Eulerian model consumed longer performing times. Although the Eulerian model delivered-time consumption was long but it provided the best results, so the Eulerian model should be chosen when time consumption and errors play important roles. From this ordinary study, the first significant step of in-house program developments has started. The time consumption still indicated that the high performance computers should be selected, and properties obtained from the experimental studies should be imported to the simulation to increase the result accuracy.

Commentary by Dr. Valentin Fuster
2016;():V008T10A081. doi:10.1115/IMECE2016-67795.

This research paper specifically focuses on experimentally characterizing and elaborating the effect of z-aligned carbon nanofibers (CNFs) on the through-thickness (i.e., z-direction) thermal conductivity of paraffin wax. The z-aligned CNF network present within the paraffin sample was hypothesized to provide a thermally-conductive nanostructure throughout the sample thickness, thereby increasing the thermal conductivity and the thermal energy charging/discharging capabilities of the paraffin wax. It was further hypothesized that the effectiveness of this thermally-conductive nanostructure was strongly related to both CNF alignment and CNF concentration.

To experimentally analyze the respective impact of CNF concentration (measured as a percentage of sample weight) and CNF alignment on the through-thickness thermal conductivity, z-aligned CNF-modified paraffin wax samples with various CNF concentrations were manufactured and compared with unmodified (i.e. control) paraffin wax samples and unaligned CNF-modified paraffin wax samples; the concentration of CNF-reinforcement was tested at both 0.1wt.% and 0.3wt.%. The through-thickness thermal conductivities were characterized for all samples using a steady-state parallel plate testing device and the results were compared and discussed against the experimental parameters. It was found that both CNF alignment and concentration had a strong influence on the improvement of through-thickness thermal conductivity of paraffin wax.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: High Heat Flux and Enhanced Heat Transfer

2016;():V008T10A082. doi:10.1115/IMECE2016-65446.

In this experimental work, a flow field test system was installed to investigate the impact of vortex generators on the flow structure and heat transfer of air flow in a horizontal channel. Three different configurations of vortex generators, a small single delta winglet pair, a large single delta winglet pair, and two delta winglet pairs developed in a V-formation array were fitted vertically on an aluminum plate and tested in a small wind path system of open circuit with horizontal test section of dimensions 70 mm (width) × 35 mm (height) × 1600 mm (length). An axial AC fan was used to supply the flow of air through the test section. The air flow was cooling the flat plate which had embedded electric heating constructed as a layered structure. Temperature distributions along the heated plate were measured using thermocouples to obtain the Nusselt numbers. The effect of three different attack angles, 15°, 30°, and 45° of the selected VGs were investigated in this work. The experimental results showed that under the tested Reynolds number of 10145, the presence of vortex generators had considerable effect on temperature distribution, pressure drop and heat transfer augmentation in the channel flow. Compared with the plain channel; the heat transfer rate was enhanced by (31.9% – 51.0%), (30.8% – 53.7 %), and (18.2 % – 36.2%) while the pressure drop increased by (1.8% – 11.0%), (4.5% – 35.4%), and (6.0 % – 30.0%) with the small single delta winglet pair, the large single delta winglet pair, and two pairs deployed in a V-formation array, respectively.

Commentary by Dr. Valentin Fuster
2016;():V008T10A083. doi:10.1115/IMECE2016-66564.

An experimental study using Liquid crystal thermography technique is conducted to study the convective heat transfer enhancement in jet impingement cooling in the presence of porous media. Aluminium porous sample of 10 PPI with permeability 2.48e−7 and porosity 0.95 is used in the present study. Results are presented for two different Reynolds number 400 and 700 with four different configurations of jet impingement (1) without porous foams (2) over porous heat sink (3) with porous obstacle case (4) through porous passage. Jet impingement with porous heat sink showed a deterioration in average Nusselt number by 10.5% and 18.1% for Reynolds number of 400 and 700 respectively when compared with jet impingement without porous heat sink configuration. The results show that for Reynolds number 400, jet impingement through porous passage augments average Nusselt number by 30.73% whereas obstacle configuration enhances the heat transfer by 25.6% over jet impingement without porous medium. Similarly for Reynolds number 700, the porous passage configuration shows average Nusselt number enhancement by 71.09% and porous obstacle by 33.4 % over jet impingement in the absence of porous media respectively.

Commentary by Dr. Valentin Fuster
2016;():V008T10A084. doi:10.1115/IMECE2016-66683.

Optical networks are a critical element of contemporary communications infrastructure, due to their efficacy in transmitting high-speed data over large distances. Photonic integrated circuits (PICs) offer compelling advantages in terms of performance and miniaturization, but the increase in power density of these components, coupled with shrinking packaging restrictions, presents a significant thermal management challenge. This has driven the need for the integration of liquid-based microfluidic cooling artefacts into next generation PIC packages. Liquid micro-jets are emerging as candidate primary or secondary heat exchangers for such packages, however the thermal behavior of confined, low Reynolds number liquid slot jets is not comprehensively understood. This investigation utilized a hot foil technique to experimentally determine the influence of implementing jet outlet modifications — in the form of tabs and chevrons — as techniques for passive control and enhancement of single-phase convective heat transfer. The investigation was carried out for slot jets in the laminar flow regime, with a Reynolds number range, based on the conventional slot jet hydraulic diameter, of 100 to 500. The investigation was carried out with a slot jet aspect ratio of 4, and a fixed confinement height to hydraulic diameter ratio (H/Dh) of 1. It was found that all outlet modifications increased local and area-averaged Nusselt number compared to a conventional slot jet. Modifications to the major axis (or long edge) of the slot jet were most effective, achieving increases in area-averaged Nusselt number of up to 61%. It was also determined that the location and magnitude of Nusselt number peaks within the slot jet stagnation region, could be passively controlled and enhanced through the application of outlet tabs at varying locations, allowing for more flexible targeted hotspot cooling. Therefore, it was concluded that enhancements in an integrated microjet cooling artefact can be achieved through passive geometry devices, without compromising the stringent packaging restrictions of such systems, such as confinement height and nozzle geometry.

Commentary by Dr. Valentin Fuster
2016;():V008T10A085. doi:10.1115/IMECE2016-66717.

High heat flux is very dangerous for electronic heat transfer, such as IGBT (Insulated Gate Bipolar Transistor) cooling. In order to explore and master the heat transfer and hydraulic characteristics for IGBT cooling, experiments have been carried out to study the situation mentioned above in a flat plate heat sink, which was designed for high heat flux IGBT cooling. The geometrical parameters of the test section are as follows: outline dimension 229 mm × 124 mm × 30 mm; flow channels of 229 mm × 3 mm × 4 mm in total of 20. The experiments performed at atmospheric pressure and with inlet temperatures of 25–35°C, heat fluxes of 3.5–18.9 kW/m2. The influence of temperatures, heat fluxes on IGBT surface temperature and the cooling effect of the liquid cold plate have been investigated under a range of flow rates of 280–2300 kg/m2s. It was found that the heat transfer enhancement was very obvious using this kind of small sized channel for IGBT cooling, which was tens of times of the effect than air cooling or triple of the effect than that in normal sized channels. And the heat transfer enhancement increases with increasing heat fluxes and flow rates, while it decreases with increasing inlet temperatures. Most of the experimental results show good cooling effect as expected. However, it is dangerous for the cooling system under high heat fluxes when the system starts or stops suddenly, when the Respond Time (RT) is less than 5 seconds to cut off heated power. Also, the cooling performance is bad when the heat fluxes increased greatly, which is considered as abnormal situation in operating. The effect on IGBT surface temperature of heat flux is more obvious when the average Nusselt Number is smaller. For hydraulic characteristics observed, it was found that the flow friction increased with flow rates increasing, but the pressure drops of heated flow channels ahead were slightly larger than those back, especially under large flow rates conditions. That is because the temperatures of flow heated in channels ahead are lower than those back, which causes the fluid viscosity to be higher. At last, this paper suggested a series of method for enhancing heat transfer in flat plate heat sink, and also gave some ways to avoid heat transfer dangerous situations for IGBT cooling, which can provide a basis for thermodynamic and hydraulic calculation of flat plate heat sink design and lectotype.

Commentary by Dr. Valentin Fuster
2016;():V008T10A086. doi:10.1115/IMECE2016-67164.

When certain fractal geometries are used in the design of fins or heat sinks the surface area available for heat transfer can be increased while system mass can be simultaneously decreased. The Sierpinski carpet fractal pattern, when utilized in the design of an extended surface, can provide more effective heat dissipation while simultaneously reducing mass. In order to assess the thermal performance of fractal fins for application in the thermal management of electronic devices an experimental investigation was performed. The first four fractal iterations of the Sierpinski carpet pattern, used in the design of extended surfaces, were examined in a forced convection environment. The thermal performance of the Sierpinski carpet fractal fins was quantified by the following performance metrics: efficiency, effectiveness, and effectiveness per unit mass. The fractal fins were experimentally examined in a thermal testing tunnel for a range of Reynolds numbers. As the Reynolds number increased, the fin efficiency, effectiveness and effectiveness per unit mass were found to decrease. However, as the Reynolds number increased the Nusselt number was found to similarly increase due to higher average heat transfer coefficients. The fourth iteration of the fractal pattern resulted in a 6.73% and 70.97% increase in fin effectiveness and fin effectiveness per unit mass when compared with the zeroth iteration for a Reynolds number of 6.5E3. However, the fourth iteration of the fractal pattern resulted in a 1.93% decrease in fin effectiveness and 57.09% increase in fin effectiveness per unit mass when compared with the zeroth iteration for a Reynolds number of 1.3E4. The contribution of thermal radiation to the rate of heat transfer was as high as 62.90% and 33.69% for Reynolds numbers of 6.5E3 and 1.3E4 respectively.

Commentary by Dr. Valentin Fuster
2016;():V008T10A087. doi:10.1115/IMECE2016-67514.

Two-phase spray cooling has been an emerging thermal management technique offering high heat transfer coefficients (HTCs) and critical heat flux (CHF) levels, near-uniform surface temperatures, and efficient coolant usage that enables to design of compact and lightweight systems. Due to these capabilities, spray cooling is a promising approach for high heat flux applications in computing, power electronics, and optics. The two-phase spray cooling inherently depends on saturation temperature-pressure relationships of the working fluid to take advantage of high heat transfer rates associated with liquid-vapor phase change. When a certain application requires strict temperature and/or pressure conditions, thermophysical properties of the working fluid play a critical role in attaining proper efficiency, reliability, or packaging structure. However, some of the commonly used working fluids today, including refrigerants and dielectric liquids, have relatively poor properties and heat transfer performance. In such cases, utilizing binary mixtures to tune working fluid properties becomes an alternative approach.

This study aimed to conduct an initial investigation on the spray cooling characteristics of practically important binary mixtures and demonstrate their capability for challenging high heat flux applications. The working fluid, water/2-propanol binary mixture at various concentration levels, specifically at x1 (liquid mass fraction of 2-proponal in water) of 0.0 (pure water), 0.25, 0.50, 0.879 (azeotropic mixture) and 1.0, represented both non-azeotropic and azeotropic cases. Tests were performed on a closed loop spray cooling system using a pressure atomized spray nozzle with a constant liquid flow rate at corresponding 20°C subcooling conditions and 1 Atm pressure. A copper test section measuring 10 mm × 10 mm × 2 mm with a plain, smooth surface simulated high heat flux source. Experimental procedure involved controlling the heat flux in increasing steps, and recording the steady-state temperatures to obtain cooling curves in the form of surface superheat vs heat flux. The obtained results showed that pure water (x1 = 0.0) and 2-propanol (x1 = 1.0) provide the highest and lowest heat transfer performance, respectively. At a given heat flux level, the HTC values indicated strong dependence on x1, where the HTCs depress proportional to the concentration difference between the liquid and vapor phases. The CHF values sharply decreased at x1≥ 0.25.

Commentary by Dr. Valentin Fuster
2016;():V008T10A088. doi:10.1115/IMECE2016-67723.

This paper studies the variation of the streamwise vortex circulation resulting from a delta wing vortex generator. A delta wing vortex generator is employed in the common flow down configuration, this generates an anti-clockwise vortex over the right wing. Two different vortex generators with angle of attack 15° and 30° were considered in this study for a range of Reynolds numbers from 750 to 1500. The average Nusselt number was observed to increase with increasing Reynolds number and angle of attack. The circulation around the vortex core was calculated at different streamwise locations behind the vortex generator. The circulation of the vortex was observed to decrease in the down-stream direction. For a given Reynolds number and angle of attack, circulation at all streamwise locations was averaged in order to compare it with the trends observed by the averaged Nusselt number. The variation in averaged Circulation was identical to the Nusselt number. The vortex center locations were used to plot the trajectories by applying a least squares second order polynomial fit to the data.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Multi-Phase Heat Transfer

2016;():V008T10A089. doi:10.1115/IMECE2016-65236.

Turbulent heat transfer for flow of water-air mixture driven by moving walls in a cubical heat sink is investigated. One wall is maintained at an elevated temperature, while the vertical walls are at a low temperature. The cubical enclosure functions as a heat sink using water-air mixture with no phase change. Different arrangements for wall motion are considered, which include 1 to 4 moving walls. As the number of moving walls increases, the flow and heat transfer become more complex. In general, the flow reveals complex and multi-scale structures with an unsteady and evolving nature. The larger structure of the flow is resolved using Large Eddy Simulation, while the sub-grid scales are captured by the dynamic k-equation eddy-viscosity model. The focus of this work is on thermal field and heat transfer as affected by the complex flow field generated by multiple moving walls. The results indicate that the Nusselt number for the heat sink varies from 5202.8 to 7356.1, depending on the number of moving walls. Contours of fluid temperature, liquid volume fraction, local and average values of Nusselt number are among the results presented in this paper.

Commentary by Dr. Valentin Fuster
2016;():V008T10A090. doi:10.1115/IMECE2016-65345.

In this work, high-density polyethylene/multi-walled carbon nanotubes (HDPE/MWCNTs) nanocomposites containing various filler loadings (i.e., 0.5∼16.0 wt.%) were prepared with their thermal conductivities determined using a laser-based analyzer. It was found that although the nanocomposite’s thermal conductivity increased with elevated MWCNT content, the enhancement degree lowered gradually. Rheology and microstructure characterizations were performed to reveal the morphology origin of gradually weakened thermal-conductivity enhancement. The dynamic rheology measurements showed that all nanocomposites exhibited higher storage modulus (G′), loss modulus (G″) as well as complex viscosity (η*) compared with the neat HDPE. More interestingly, the plateau of the flow regime formed at low frequency ranges with MWCNT loadings higher than 2.0 wt.% suggested the formation of the MWNCT network structures within the nanocomposites. The existence of such structures was further verified by the Cole-Cole curves obtained from the rheology testing and MWCNT distribution states from scanning electron microscope (SEM) results. The formation of MWCNT network lowered the degree of thermal-conductivity enhancement in such a way that it gave a larger possibility for MWCNTs to agglomerate, which led to phonon scattering that reduced the nanocomposite’s thermal conductivity.

Commentary by Dr. Valentin Fuster
2016;():V008T10A091. doi:10.1115/IMECE2016-66222.

Electrohydrodynamic (EHD) conduction pumps generate pressure to drive dielectric liquids via the electrical Coulomb force exerted within heterocharge layers of finite thickness in the vicinity of the electrodes. By applying an external electric field in a dielectric liquid, the heterocharge layers form due to the net charges as a result of the process of enhanced dissociation of neutral molecules versus the recombination of the generated ions. EHD conduction pumping can be applied to enhance and control mass and heat transfer of both isothermal and nonisothermal liquid and two-phase fluid, with many advantages such as simple design, no moving parts and low power consumption. It also shows its potential as an active control technique for flow distribution for multi-scale systems in both terrestrial and microgravity environment. Flow distribution control based on EHD conduction pumping mechanism was previously investigated in macro-scale. This study experimentally examines its capability in controlling two-phase flow distribution between two parallel meso-scale evaporators. The working fluid was refrigerant HCFC-123. It has been found that an EHD conduction pump could effectively control the two-phase flow distribution via adjusting the flow rate in each branch line, and facilitate the recovery from dry-out condition in two-phase system.

Commentary by Dr. Valentin Fuster
2016;():V008T10A092. doi:10.1115/IMECE2016-66240.

Modern-day microprocessors consist of over one billion integrated circuits on silicon chips as small as a human fingernail. Normal operation of this circuitry produces an enormous amount of heat on a very small footprint. Dissipating this heat is a very challenging task, perhaps the largest roadblock to continued increases in computing technology. Microchannel heat sinks utilizing either single-phase flow or phase-change are an effective means of cooling stacked 3-D microelectronics. A roadblock to practical implementation of microchannels is the presence of flow instabilities. The asymmetric saw-toothed microchannel heat sink is proposed to address this issue. Deep reactive-ion etching is used to produce channels comprised of asymmetric sawtoothed structures that alter the local flow structure within the microchannel. All experiments are conducted using the dielectric fluid, FC-72. Each microchannel array has a footprint of 1 cm × 1 cm, comprised of thirty-four channels etched into a silicon wafer. A series of thin film serpentine copper heaters is fabricated on the other side of the silicon wafer to provide a uniform heat flux boundary condition. Experimental information is presented for a range of mass fluxes from 381 to 1777 kg/m2s, and inlet subcooling from 5°C to 20°C. Parameters presented and analyzed includes boiling curves, onset of boiling (ONB), averaged two-phase heat transfer coefficient.

Topics: Microchannels
Commentary by Dr. Valentin Fuster
2016;():V008T10A093. doi:10.1115/IMECE2016-66864.

Considering the need of performance control in engineering systems, this work presents a methodology to predict the controlling variables to control the performance of an induced draft cooling tower. At first, the set of experiments have been conducted with the variation of mass flow rate of water and air under identical ambient conditions. The experimental data for temperatures at different locations has been collected using data acquisition system (by National Instruments) in conjunction with LABVIEW™. Thereafter, relevant 3rd order empirical correlations of range and approach have been developed using the experimental readings. Depending upon the pertinent requirement, it is required to operate the cooling tower at certain combination of mass flow rate of water and air to fulfill the required output. Based upon the user requirement, the correlations are further employed to construct relevant constraint functions using the least square technique. In order to meet a desired performance (say either a given range, approach or optimum operation) of the cooling tower, the retrieval of design variables (water and air flow rates) has been carried out using an inverse optimization methodology to ensure minimum power consumption. The Genetic Algorithm (GA) is used as an optimization algorithm that minimizes the objective function along with given constraint. The optimization algorithm simultaneously predicts the possible combination of mass flow rate of water and air (control or design variables) in order to meet the given requirement. Further, the methodology avoids multiple combinations of controlling variables that satisfies a particular requirement. Therefore, the user can select an optimum combination that results in minimum power consumption. Moreover, if the cost involved in the cooling tower is considered, it is directly proportional to the range (difference between water inlet and outlet temperatures), whereas, at the same time, the cost is inversely proportional to the approach (difference between outlet water temperature and inlet air wet bulb temperature). In many applications like HVAC (heating, ventilating and air conditioning), chillers, cold storage plants and many more, lower cooling water temperature (at system inlet) is preferable in order to enhance the system efficiency. On the other hand, lower water outlet temperature from the cooling tower for a given water inlet temperature (at tower inlet) means either high range of the tower or low approach, consequently increasing the tower operating cost. Therefore, in order to save the cost involved in cooling tower operation, a compromise between the range and the approach has to be maintained to achieve an optimum performance. So, this method can be also used to predict the optimum operating parameters ensuring the possible optimum performance from the cooling tower under a given set of operating conditions.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Multiscale Computational Heat Transfer Modeling and Simulation

2016;():V008T10A094. doi:10.1115/IMECE2016-67818.

This work provides a detailed description of the setup and execution of an experiment employing Magnetic Resonance Thermometry (MRT) techniques for measuring the three-dimensional temperature field of a fully turbulent jet mixing with a cross flow. The proposed methodology has the flexibility of applying different thermal boundary conditions — adiabatic and conductive — by varying the materials used in the test section as well as varying the temperatures of the mixing flows. The experiment described in this paper employs a standard magnetic resonance imaging system comparable to those used in medical radiology departments worldwide. A series of MR scans with both isothermal and thermal mixing conditions were conducted and results are presented with sub-millimeter resolution across the measured 3D domain of interest within one degree Celsius. The methodology presented here holds unique advantages over conventional techniques because measurements can be acquired without introducing flow disturbances and in regions without any optical access. When coupled with other established MR-based measurement techniques, MRT provides large, robust data sets that can be used for validation, design, and insight into system thermal performance for complex, turbulent flows. The materials and components employed in this work cost approximately $13,900, and the experimental setup and data collection required approximately 48 hours.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Poster

2016;():V008T10A095. doi:10.1115/IMECE2016-66236.

A Computational Fluid Dynamics (CFD) study of heat enhancement in helically grooved tubes was carried out by using a 3-dimensional simulation with the STARCCM+ simulation package software. The k-ε model selected for turbulent flow simulation and the governing equations were solved by using the finite volume method. Geometric models of the current study include 3 rectangular grooved tubes with different groove width (w) and depth (e) which varies from 0.2 mm to 0.6 mm for the same tube length of 2.0m and diameter of 7.1 mm. The simulations were performed in the Reynolds number (Re) range of 4000–10000 with a uniform wall heat flux of 3150 w/m2 applied as a boundary condition on the surface of each tube. The purpose of this research is to investigate the effect of different groove dimensions on the thermal performance and pressure drop of water inside the grooved tubes and clarify the structural nature of the flow in regards to flow swirl and turbulent kinetic energy distributions. It was found that the highest performance belongs to the groove with these dimensions (w = 0.2 mm and e = 0.2 mm) which was considered for further study. Then, for these same groove dimensions four pitch size to tube diameter (p/D) ratios ranging from 1 to 18 were simulated for the same 2.0 m length tube. The results for Nusselt number (Nu) and friction factor (f) showed that by increasing the (p/D) ratio both the Nu numbers and the friction factors (f) values decrease. With a smaller pitch length (p) the turbulence intensity generated by the internal groove was also found to increase. The physical behavior of the turbulent flow and heat transfer characteristics were observed by contour plots which showed an increasing swirl flow and turbulent kinetic energy as p/D decreases. With an increase of the Nu number for smaller p/D ratio, a penalty of a higher pressure drop was obtained. The results were validated with a previous experimental work and the average error between the experimental and CFD Nu numbers and f were 13% and 8% respectively. A higher level of turbulent kinetic energy is observed near the grooves, as compared to the smooth areas of the pipe surface away from the grooves, which are expected to lead to higher levels of heat transfer. The effect of pitch length (p) on the flow pattern were plotted by streamlines along the tubes, by decreasing the pitch size (p/D ratio) an increase in the swirl is noticed as evidenced by the plots of the path lines. Finally, empirical correlations for Nusselt number and friction factor were provided as a function of p/D and Re number. This study indicates that the incorporation of the internal groove, of particular dimensions, can lead to an improvement of performance in heat exchanger devices. A limited variation of the groove dimensions was conducted and it was found that the values of Nu and f do not improve with an increase of (w) nor with that of (e) from 0.2–0.6 mm.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Thermal Management of Solar and Alternative Energy Equipment

2016;():V008T10A096. doi:10.1115/IMECE2016-65012.

This paper presents the analysis of a compact heat exchanger design for application to a supercritical CO2 (SCO2) Rankine cycle waste energy conversion cycle. In this paper a compact heat exchanger using a multi-pass wavy channel configuration with surface area density β = 1222 m2/m3 and overall surface efficiency of 50% is analyzed using the NTU-ε method. Due to the high pressures used in the SCO2 Rankine cycle (high side of 20 MPa low side of 12.4 MPa) the variability of the specific heat of SCO2 leads to thermal pinch which must be accounted for in the modeling. Heat transfer augmentation is accomplished using porous media Silica particles on the low-side (12.4 MPa, a.k.a. hot fluid stream) of the SCO2 heat exchanger. Results for heat transfer area versus duty, temperature approach versus heat transfer area, and, effectiveness versus duty are presented. Parametric results for entropy generation and Second Law considerations are presented in order to place a realistic bound on the analysis. Effects of porous flow on exit temperature, temperature approach and effectiveness are summarized. Results of this study can be used to guide design and development of compact heat exchanger selection for renewable energy waste heat recovery applications.

Commentary by Dr. Valentin Fuster
2016;():V008T10A097. doi:10.1115/IMECE2016-66039.

The world is still dependent on fossil fuels as a continuous and stable energy source, but rising concerns for depletion of these fuels and the steady increase in demand for clean “green” energy have led to the rapid growth of the renewable energy field. As one of the most available energy sources with high energy conversion efficiency, solar energy is the most prominent of these energies as it also has the least effect on the environment. Flat plate collectors are the most common solar collectors, while their efficiency is limited by their absorber’s effectiveness in energy absorption and the transfer of this energy to the working fluid. The efficiency of flat plate solar collectors can be increased by using nanofluids as the working fluid. Nanofluids are a relatively recent development which can greatly enhance the thermophysical properties of working fluids. In the present study, the effect of using Al2O3/Water nanofluid as the working fluid on the efficiency of a thermosyphon flat-plate solar collector was experimentally investigated. The results of this experiment show an increase in efficiency when using nanofluids as the working fluid compared to distilled water. It was found that Al2O3/water nanofluids are a viable enhancement for the efficiency of flat-plate solar collectors.

Commentary by Dr. Valentin Fuster
2016;():V008T10A098. doi:10.1115/IMECE2016-66375.

Computational Fluid Dynamics (CFD) study is conducted to determine turbulent fluid flow and temperature profiles in rectangular ribbed channels of solar air heater. The results show significant effect of Reynolds number and ribs height and pitch on turbulence and heat transfer rates. When heat flux is defined at the bottom wall, the temperature values increase rapidly near the ribs due to stagnant zones. The heat transfer coefficients are lower at these locations. When heat flux is specified at the top wall, the variation in heat transfer coefficient is relatively smooth. From the research work, the channel containing ribs of 3mm and pitch 40mm are determined suitable due to higher heat transfer rates.

Commentary by Dr. Valentin Fuster
2016;():V008T10A099. doi:10.1115/IMECE2016-68179.

A design team at the Cooper Union for the advancement of Science and Art has developed and patented a robust thermoelectric-based point of use power generation system with no moving parts that is designed to be clamped onto the outer wall of a steam or hot water pipe [1]. Furthermore, in 2013 The Cooper Union for the Advancement of Science received patents for The Bimetallic Leaf Spring and Clamping Device which was designed so that it can compensate for the expected positive expansion and contraction of the thermoelectric power generation system.

This paper presents different design concepts evaluated during the development of the clamp and theoretical models for determining the coefficient of thermal expansion of the design concepts. Furthermore, the paper presents experimental results from testing different variations of the selected design concept. Finally, a theoretical thermal expansion model with experimentally obtained parameters is presented. The final clamp design compensates for the expansion and contraction of the thermoelectric power generation system.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Thermal Transport Under High Temperature and/or Pressure Conditions

2016;():V008T10A100. doi:10.1115/IMECE2016-65547.

This paper presents the results of an analysis of a hybrid cascaded Methyl Linoleate / Supercritical (SCO2) / Transcritical CO2 / R-410A cycle for extreme environment refrigeration applications. The particular application of this cascaded CO2 refrigeration cycle stems from a space exploration application of a Venus lander mission. The payload of the Venus lander is subject an extremely harsh environment, i.e. the objective is to maintain a 1 cubic meter payload cavity at 35 °C, with dissipation of 500 W to an environmental temperature of 465 °C. Complicating the situation is the Venus local atmosphere is 9 MPa, and the atmosphere is mainly comprised of CO2 (95.5% by volume, 3.5% N2 by volume). Because this temperature is so high, to stay under the saturation dome we need some fairly exotic fluids to do a normal vapor compression system. Some of the only fluids with critical points allowing for this particular application are sulfuric acid and Fatty Acid Methyl Ester (FAME) type bio-diesels such as Methyl Linoleate (MLL). The actual heat rejection process and throttling processes are the primary challenges of this research topic. Results of a COP comparison and a lift curve are carried out in order to determine efficiency and guide feasibility of realizing the actual hardware to be used in the cycle.

Commentary by Dr. Valentin Fuster
2016;():V008T10A101. doi:10.1115/IMECE2016-66037.

This research aims to investigate the effect of ambient pressure on the burning rate and heat release rate (HRR) of n-heptane pool fire. The experiments were performed in a large-scale altitude chamber of size 2 m×3 m×4.65 m under series of pressure, 24kpa, 38 kPa, 64 kPa and 75 kPa to 90 kPa. A round steel fuel pans of 34 cm in diameter and 15 cm in height was chosen for the pool fire tests. The fuel pan was filled with 99% pure liquid n-Heptane. Experimental results show that the burning rate increases rapidly after ignition until it reaches to the peak, and then maintains at a relatively stable stage. It decreases gradually until the flame extinguishes. The burning time is longer at lower pressure. The mean mass burning rate at the steady burning stage increases exponentially with pressure as Pα, with α = 0.68. HRR curve has a similar trend with the burning rate. The maximum HRR increases from 27kW to 62kW as the pressure rises from 24kPa to 90kPa. It is concluded that the ambient pressure has a significant effect on the fire heat release rate, and will further influent on other fire parameters.

Commentary by Dr. Valentin Fuster
2016;():V008T10A102. doi:10.1115/IMECE2016-66171.

Non-isothermal suddenly expanding annular pipe flows of a shear-thinning non-Newtonian fluid are numerically studied within the steady laminar flow regime. The power-law constitutive equation is used to model the shear-thinning rheology of interest. A parametric study is performed to reveal the influence of annular-nozzle-diameter-ratio, k, power-law index, n, and Prandtl numbers over the following range of parameters: k = {0, 0.5}; n = {1, 0.6}; and Pr = {1, 10, 100}. Heat transfer enhancement, i.e., wall heat transfer rates higher than the fully developed ones downstream of the expansion plane, is observed only for Pr = 10 and 100. In the case of Pr = 1, wall heat transfer rates monotonically increase to the fully developed value. Higher Pr, k, and n values, in general, result in more significant heat transfer enhancement downstream of the expansion plane. Further, shear-thinning non-Newtonian flows display two local peak wall heat transfer rates, in comparison with only one peak value in the case of Newtonian flows.

Commentary by Dr. Valentin Fuster
2016;():V008T10A103. doi:10.1115/IMECE2016-66972.

In today’s fast growing world where availability of energy has become a major concern, the cost of performance demands optimum heat exchange performance over extended periods of operational times. Fouling is one major factor that drastically affects heat exchanger performance. Most of the oil & gas processing plants in the Middle East are located in deserts. Due to scarcity of water most of the installed heat exchangers are air-cooled. These heat exchangers are at high risk of low performance due to dusty/sticky particulate fouling. In order to identify possible active/passive methods to control or ideally eliminate particulate fouling, as a first step, it is desirable to know exact morphology of such particulate fouling. This study presents morphological characterization of selected fouling samples from eight different installed fin fan heat exchangers. The scanning electron microscope (SEM) tests are carried out to determine standard characteristics and size of sample foulant powder. Variability in sizes and shapes is found between samples perhaps due to different working temperature ranges of the selected heat exchangers. The semi quantitative sample composition measured by energy dispersion x-ray micro analysis was as following: 26.50% Si, 26.12% Ca, 10.07% C and 9% Al with traces of Fe, Na, Mg, Cl, and some other salts. X-ray diffraction analysis revealed presence of quartz, calcite and alumina with traces of halite and hematite. The diversity of these fouling samples reflects complexity with respect to their potential removal and effects on heat transfer.

Topics: Heat exchangers
Commentary by Dr. Valentin Fuster
2016;():V008T10A104. doi:10.1115/IMECE2016-66987.

In this work we investigate the effect of molecular alignment on thermal conductivity (k) enhancement of polyethylene/graphene nanoplatelet (PE/GNP) composites. Enhancement of thermal conductivity of polymers can pave way for their application in heat exchangers leading to significant energy savings as processing of polymers is more energy efficient than metals. Such energy savings will drive down costs and will have the additional benefit of considerably reducing the environmental effects of energy production. Such high k polymers will also enable improved thermal management in electronic devices in servers, automobiles, high brightness LEDs and mobile applications. Stretching is known to induce alignment of molecular chains in a polymer system thereby increasing thermal conductivity. In this work we explore mechanical stretching of polyethylene-graphene nanocomposites to enhance their k.

Commentary by Dr. Valentin Fuster
2016;():V008T10A105. doi:10.1115/IMECE2016-68049.

The reliability of experimental data are important for heat exchanger design and evaluation. In the present paper, we extended the concept of Critical Heat Balance Error (CHBE) to a general imbalanced heat exchanger with thermal capacity ratio great than 1. Based on the principle of positive entropy generation in experiment, were analytically expressed the CHBE under the influence of different thermal capacity ratios. Interestingly, we found the same analytical expression as previous research which is, CHBE = −(1 − τ)(1 − ε), where ε and τ are heat exchanger efficiency and inlet temperature ratio, respectively. Therefore, we claim this analytical filter can be used for a general heat exchanger with any thermal capacity configuration.

Commentary by Dr. Valentin Fuster

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