ASME Conference Presenter Attendance Policy and Archival Proceedings

2018;():V08BT00A001. doi:10.1115/IMECE2018-NS8B.

This online compilation of papers from the ASME 2018 International Mechanical Engineering Congress and Exposition (IMECE2018) 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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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: Measurements of Thermophysical Properties

2018;():V08BT10A001. doi:10.1115/IMECE2018-87268.

Air-rich soft materials are widely used in textile products, such as clothes and towels, because they exhibit good heat-retaining properties. Quantification of the heat-retaining properties of materials is necessary for product design engineering. Here, the behavior of heat transfer in the layer structure of the material is evaluated to formulate its kinetics. Such evaluation can address the barriers to appropriate design. The heat transfer kinetics of the multilayered structure of the materials are evaluated by assessing the surface temperature of the outer layers. The evaluation equation for kinetics is formulated by applying the fundamental relationship of heat transfer, which is represented by thermal conductivity and the heat transfer coefficient. In the experimental evaluation, a simple wind tunnel was developed using a blower, hot plate, and digital radiation temperature sensor. The temperature of the hot plate was set at three levels. In the evaluation of surface temperature, the quantity of infrared ray was measured using the digital radiation temperature sensor, because it could be used without mechanically influencing the specimen. The surface temperature of the materials was measured by changing the number of layers from one to eight. In the evaluation of heat transfer kinetics, some properties of the conductivity and the transfer were identified by the formulated relationship for the kinetics of the layered structure and the numerical technique of inverse analysis. It was found that the heat conductivity of the material and heat conductivities between the layers can be identified by the examination of surface temperature variation caused by the change in the number of layers. Then, the crush effect of air-rich structures can be assessed by compressing the material and then analyzing the behavior change in heat transfer caused by the crush. The difference between the observed results and those obtained without the crush of air-rich structure was significant. Thus, we concluded that the physical properties of heat transfer in a multilayered structure of air-rich soft materials can be identified using the surface temperature change in the material resulting from the number of layers. Therefore, it is important to measure its behavior without the crush of the air-rich structure to evaluate the most natural state of the material appropriately.

Topics: Heat transfer
Commentary by Dr. Valentin Fuster
2018;():V08BT10A002. doi:10.1115/IMECE2018-87496.

Conventional heat transfer fluids such as water, ethylene glycol, and mineral oil, that are used widely in industry suffer from low thermal conductivity. On the other hand, diamond has shown exceptional thermal properties with a thermal conductivity higher than five times of copper and about zero electrical conductivity. To investigate the effectiveness of nanodiamond particles in traditional heat transfer fluids, we study deaggregated ultra-dispersed diamonds (UDD) using X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). Furthermore, nanodiamond nanofluids were prepared at different concentrations in deionized (DI) water as the base fluid. Particle size distribution was investigated using TEM and the average particle size have been reported around 6 nm. The thermal conductivity of nanofluids was measured at different concentrations and temperatures. The results indicate up to 15% enhancement in thermal conductivity compared with the base fluid and thermal conductivity increases with temperature and particle loading. The viscosity raise in the samples have been negligible.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Methods in Computational Heat Transfer

2018;():V08BT10A003. doi:10.1115/IMECE2018-86113.

The melting of quartz ingot undergoes solid-liquid phase transition, free-surface, large deformation and other complex flow. Thermal field is the fundamental driving factor during the process. Thus, new method of computing the complex flow and thermal field simultaneously needs to be developed. An integrated method of the finite volume method (FVM) and smoothed particle hydrodynamics (SPH) is proposed to combine the advantages of SPH in the complex flow and FVM in the thermal calculation. The method, a solver conjugate scheme, is implemented through the data exchange between the FVM sub-solver and the SPH sub-solver. The sub-solver of FVM focuses on thermal calculation, and SPH concentrates on complex flow with free-surface and large deformation. The inverse distance weighted (IDW) interpolation and spatial matching are employed to translate data from FVM to SPH and from SPH to FVM separately. The mechanism how the heater temperature affects the thermal field is investigated. The conclusion is that the increasing heater temperature affects the hot zone by raising the sidewalls temperature mainly, thus employing additional heating or cooling ways for controlling the temperature of the sidewalls is an efficient direction to optimize the hot zone design.

Topics: Melting , Quartz
Commentary by Dr. Valentin Fuster
2018;():V08BT10A004. doi:10.1115/IMECE2018-86425.

In this study, three-dimensional numerical simulations are performed to investigate heat transfer enhancement in multi-harmonic micro-scale wavy channels. The focus is on the influence of channel surface-topography, modeled as multi-harmonic sinusoidal waves of square cross-sectional area, on the enhancing mechanisms. A single-wave device of 0.5 mm × 0.5 mm × 20 mm length, is used as baseline, and new designs are built with harmonic-type surfaces. The channel is enclosed by a solid block, with the bottom surface within the sinusoidal region being exposed to a 47 W/cm2 heat flux. The numerical solutions of the governing equations for an incompressible laminar flow and conjugate heat transfer are obtained via finite elements. By using the ratio of the Nusselt number for wavy to straight channels, a parametric analysis — for a set of cold-water flowrates (Re = 50, 100, and 150) — shows that the addition of harmonic surfaces enhances the transfer of energy and that such ratio achieves the highest value with wave harmonic numbers of n = ±2. Use of a performance factor (PF), defined as the ratio of the Nusselt number to the pressure drop, shows that, surprisingly, the proposed wavy multi-harmonic channels are not as efficient as the single-wave geometries. This outcome is thought to be, primarily, due to the uncertainty associated with the definition of the Nusselt number used in this study, and establishes a direction to investigate the development of a more accurate definition.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A005. doi:10.1115/IMECE2018-86831.

Considering that radiative heat transfer is encountered in many engineering and industrial applications, significant efforts have been applied during the last decades for the development of relevant numerical methodologies. In this study, such an inhouse academic radiative heat transfer method is presented in brief, whereas it is evaluated against a geometrically complex furnace. The proposed solver depends on the time-dependent RTE (Radiative Transfer Equation) aiming to predict radiative heat transfer in general enclosures through absorbing, emitting, and either isotropically or anisotropically scattering gray media. Spatial discretization is obtained with a node-centered finite-volume method on three-dimensional tetrahedral or hybrid unstructured grids. Increased accuracy is succeeded with a second-order scheme. The final steady-state solution is obtained with an iterative procedure, based on an explicit second-order accurate in time four-stage Runge-Kutta method and accelerated mainly via parallel processing and an agglomeration multigrid scheme. The proposed solver is assessed against an experimental three-dimensional furnace case, incorporating many of the geometric complexities encountered in industrial furnace systems. The predicted numerical results, regarding the incident wall fluxes, are compared with the available experimental data, revealing a satisfactory agreement and consequently demonstrating the proposed code’s potential to predict accurately radiative heat transfer in complex enclosures.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Multi-Phase and Passive Enhanced Heat Transfer

2018;():V08BT10A006. doi:10.1115/IMECE2018-86195.

To improve the cooling performance of disc brake systems, cross-drilled holes penetrating across the rubbing discs are separately introduced into a commercial radial vane brake disc (as reference) and a novel X-lattice cored brake disc. Prototype samples of both the reference and cross-drilled brake discs are fabricated. A rotating test rig is designed and constructed to characterize and compare the cooling performance of the brake discs with infrared thermography. Within the typical operating range of a vehicle, e.g., 200–1000 rpm, the experimental results show that the introduction of cross-drilled holes can substantially enhance brake disc cooling. For the radial vane brake disc, the overall Nusselt number is enhanced by 31%–44%; for the X-lattice cored brake disc, the cross-drilled holes only lead to 9%–18% enhancement. As the radial vane brake disc and the X-lattice cored brake disc with cross-drilled holes exhibit similar cooling performance, flow through the cross-drilled holes has a more prominent effect on the former than the latter. Corresponding fluid flow and heat transfer mechanisms underlying the enhanced heat transfer by cross-drilled holes and the different effects of cross-drilled holes on the two distinct brake discs are explored. The experimental comparison and the thermo-fluidic physics presented in this paper are beneficial for engineers to further improve disc brake cooling.

Topics: Convection , Disks , Brakes
Commentary by Dr. Valentin Fuster
2018;():V08BT10A007. doi:10.1115/IMECE2018-86449.

Natural Convection heat transfer from horizontal rectangular fin array with various knurling patterns is studied experimentally to find the effect of varying surface roughness on the heat transfer rate. The experimental parametric study is performed to investigate the effect of knurl produced surface roughness of fin on heat transfer rate. The parameters like knurling height from base, knurling depth and fin spacing might affect the flow characteristics and hence it is investigated to find the effect on heat transfer coefficient. The knurling is usually accomplished using one or more very hard rollers that contain the reverse of the pattern to be imposed. The result of this study shows that there are some important geometric factors related to knurling affecting the design of fin arrays and also heat transfer augmentation of natural convection heat transfer is observed.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A008. doi:10.1115/IMECE2018-87123.

Natural convection in a square cavity filled with water-Al2 O3 nanofluid is studied numerically. Upper, lower, and left surfaces are insulated. Right wall is at low temperature, while two heat sources are kept at high temperature. The sources are vertically attached to the horizontal walls of a cavity . A uniform magnetic field is applied in a horizontal direction. Effective thermal conductivity and viscosity of nanofluids are obtained using Koo-Kleinstreuer model which implements the Brownian motion of nanoparticles effect. Steady state laminar regime is assumed. The conservation of mass, momentum, and energy equations are solved using finite volume method. The numerical results are reported for the effect of Rayleigh number, solid volume fraction, and Hartmann number on the streamlines as well as the isotherms. In addition, the results for average Nusselt number are presented for various parametric conditions. This study is presented in the following ranges, Rayleigh number from 103 to 105, Hartmann number from 0 to 60, and solid volume fraction from 0 to 0.06, while the Prandtl number which represents water is kept constant at 6.2. The results showed that heat transfer rate decreases with the rise of Hartmann number and increases with the rise of Rayleigh number, and volume fraction. Moreover, results showed that heat sources positions, lengths and intensities have crucial effect on heat transfer rate. Additionally, the effect of nanofluids type was studied, it was found that water-Cu nanofluid enhances the heat transfer better than water-Al2O3, water-CuO and water-TiO2 nanofluids.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A009. doi:10.1115/IMECE2018-87356.

Saturated pool boiling heat transfer of water is investigated experimentally on copper surfaces with nanoparticle coatings at atmospheric pressure. The coatings are generated by an electrophoretic deposition method (EPD). Three modified surfaces are prepared with gold nanoparticles of 0.20 mg, 0.25 mg and 0.30 mg, respectively. During the deposition, ethanol works as the solvent while the electrical potential and deposition time are controlled as 9.5 V and 30 min, respectively. The experimental results show that heat transfer coefficients (HTC) and critical heat fluxes (CHF) are enhanced on the modified surfaces. HTC increases with decreasing thickness of the coating, while CHF increases with increasing thickness of the coating. CHFs of EPD-0.20 mg, EPD-0.25 mg and EPD-0.30 mg are 93 W/cm2, 123 W/cm2 and 142 W/cm2, respectively, which are increased by 7%, 41% and 63% compared with the smooth surface. EPD-0.20 mg performs the best on heat transfer, with a maximum enhancement of around 60%. At the end, a brief review about mechanistic models of heat transfer at low and moderate heat fluxes is provided, based on which, the reasons why heat transfer is enhanced are discussed.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A010. doi:10.1115/IMECE2018-87958.

A radial design of a passive heat sink for cooling LED illumination devices is analyzed numerically in order to identify the geometric shape that promotes better heat dissipation rates. Natural convection with the surrounding is considered during the operation of the heat sink. Due to the fact that natural convection is the main mechanism of heat transfer, the shape of the heat sink has a high influence in the heat dissipated. An analysis of the influence of different parameters of a heat sink is conducted in the presented study.

The radial heat sink under analysis consists in a flat disc with rectangular fins on it, and the fins are distributed with a radial longitudinal orientation in a circular row arrangement. The number of rows can vary but there is a constant relation of two times the number of fins between the number of fins in an inner row and the next outer row. In order to find a correct configuration to improve the dissipation of heat, parameters like the number of fins, the length of the fins and the separation between fins are studied.

The average Nusselt number and thermal resistance for each geometric configuration are compared. The output analysis provides the best shape for a maximum heat transfer.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A011. doi:10.1115/IMECE2018-88571.

The scope of combining two wettability regions is to impact the droplet dynamic behaviors, manipulate the droplets’ mobility and enhance condensation heat transfer. Hydrophobic-hydrophilic hybrid patterns can promote the heat transfer, droplet-renewal frequency and enhance the droplets’ removal during condensation. With regard of condensation on hybrid surfaces, the geometry of the patterns has a significant influence on droplets departure frequency and heat transfer performance. Therefore, different patterns geometries (circle, ellipse, and diamond) have been developed on horizontal copper tubes at atmospheric pressure. All the patterns have the same size, and the same identical gap as well between the adjacent patterns. Results show that the diamond hybrid surface has the best performance compared with ellipse, circles hybrid surfaces at the same pattern area with same neighbor gap between two patterns and complete dropwise However, the circle and ellipse hybrid surfaces outperform lower performance compared to complete dropwise surface. The heat transfer rate for the diamond hybrid surface is 15% higher than complete dropwise surface when the gap is 0.5mm. This study clearly demonstrated the effect of pattern’s geometry regarding maximum condensation heat transfer rate and droplet departure frequency.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Nanoscale Heat Transport in Practical Systems

2018;():V08BT10A012. doi:10.1115/IMECE2018-86617.

Experiment and simulation studies were performed to investigate the flow characteristics of pressure-driven Nitrogen flow in the micro-channels of Printed Circuit Heat Exchanger (PCHE). The core of the PCHE was made using diffusion bonding method with ten stainless steel 316L plates, where hemispherical 1 mm in diameter channels were chemically etched. On one of the plates, four-teen more channels, 1 mm in diameter, were milled to make pressure taps to measure local pressure drops. Then, one inlet tube and four-teen tubes for pressure tabs were attached by welding on the top and sides of PCHE core, respectively. The PCHE was connected to Nitrogen tank with pressure regulator, Coriolis flowmeter and differential pressure gauge, and data was acquired with DAQ system.

By varying the velocity of Nitrogen gas from 1 to 35 m/s, differential pressure drops were measured between two different locations. The local pressure drops were analyzed theoretically and pressure loss coefficients could be calculated in straight and serpentine channels, respectively. In addition, simulation work using ANSYS Fluent was also performed to understand flow characteristics especially at corners of channels.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A013. doi:10.1115/IMECE2018-88657.

In the Suspended ThermoReflectance (STR) technique a microcantilever is heated with a laser power at the free end of the microcantilever and as heat propagates through it, another laser is used to measure the temperature along the beam.[1] In this paper, the heat equation is solved for two-dimensional heat flow in the microcantilever to determine the material’s thermal conductivity and heat capacity. Two of the dimensions of the microcantilever, width and length, are significantly greater than the third dimension, the thickness, leading to the two-dimensional approximation. Two boundaries along the length of the structure and one boundary along the width are assumed to be under Dirichlet boundary conditions, while the other boundary has Neumann condition. The Neumann or flux condition has a Gaussian profile due to the nature of laser beam intensity. The heat equation is solved using under 3 different flux conditions: (1) Steady-state, (2) Transient, and (3) Periodic. A steady-state condition mimics the experimental condition when a continuous wave laser is used to heat the microcantilever’s tip. A transient condition is possible when quickly removing or adding the continuous wave laser’s flux from the microcantilever’s tip using a chopper. Finally, a periodic condition can be achieved when an electro-optic modulator is utilized experimentally. Closed form analytical expressions are evaluated against the finite element model and experimental results for microcantilever beams and micro-structures of Si that have lengths on the order of a mm, width on the order of 100 microns, and thicknesses of 1 micron or less.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Numerical Analysis and Performance Assessment of Energy Systems

2018;():V08BT10A014. doi:10.1115/IMECE2018-87758.

Utilizing analytical models at the initial stages of Stirling engine (SE) development is a common approach since the cost could be excessive when experimental (i.e., building prototypes) or even numerical (i.e., using Computational Fluid Dynamics (CFD)) approaches are taken first. One of the well-known analyses in this area is the adiabatic analysis that assumes working fluid to be an ideal gas, and adiabatic expansion and compression processes in the power cylinder. Although adiabatic analysis neglects pressure loss in the cycle, it still predicts operating envelope and performance with a better accuracy compared to isothermal (Schmidt) analysis. This study considers the adiabatic analysis that was originally developed for conventional, reciprocating displacer SE configuration, and aims to adapt it for an innovative, rotary displacer SE configuration. The analysis enables to present pressure-volume diagrams, and estimates the amount of generated work and the efficiency. The results, when compared to that of the ideal Schmidt analysis, indicate up to 4.6% lower values of the generated work, suggesting a significant difference between the two ideal assumptions.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A015. doi:10.1115/IMECE2018-88288.

A comprehensive study is conducted to evaluate the heat transfer characteristics of laminar nanofluid flow in an annular tube. Thermo-physical properties of the nanofluid is considered to be variable and for the inner and outer walls, there exists serrated surface roughness. The study focuses on the velocity distribution, friction factor and Nusselt number. All results are compared with those for the smooth channel and constant property nanofluid as well. The results show that the tube with serrated wall experiences greater maximum velocity. Moreover, decrease in velocity gradient and some other thermal characteristics result in decrease in average Poiseuille and Nusselt numbers for the rough tube with variable-property fluid.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Posters

2018;():V08BT10A016. doi:10.1115/IMECE2018-88083.

Silicon carbide (SiC) is a useful semiconductor material due to its high thermal conductivity (λ), low reactivity, and high strength. These properties also make it an ideal nuclear fuel cladding material. Because heat transfer in SiC is dominated by phonons, there is value in understanding how different phonon branches contribute to λ. To accomplish this, it is useful to run simulations which employ fewer phonon branches than normally exist. In materials where phonons dominate heat transport, such as SiC, the Monte Carlo method as applied to phonon transport is suitable for estimating λ. This work uses the Monte Carlo method to estimate λ of 3C-SiC using four phonon branches, namely, transverse acoustic (TA), longitudinal acoustic (LA), transverse optical (TO), and longitudinal optical (LO). By adding branches into the simulation and measuring λ, the individual contributions to λ from each branch can be determined.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A017. doi:10.1115/IMECE2018-88532.

The heat and flow characteristics of mist/steam two-phase flow in U-shaped internal cooling passage of gas turbine blade are studid numerically in this paper. The standard k-ε model was used as the turbulence model combined with the DPM model to calculate the influence of mist/steam mass ratio and mist diameter on flow and heat transfer of U-passage with different shaped ribs. The result indicates that under the same working condition, the U-shaped channel with 45 deg. V-shaped ribs has better heat transfer performance than other channels and heat transfer non-uniformity of the U-shaped channel with 75 deg. ribs is the worst among all channels studied in this paper. The heat transfer performance of the U-shaped channel with V-shaped ribs is higher than that of the channel with paralleled ribs. As for the mist/steam cooling in U-shaped passage with same ribs structure, heat transfer non-uniformity increases with the increasing of heat transfer performance. When mists diameter increases from 5μm to 15μm, the heat transfer performance of the Second-Flow-Passage increases obviously and the heat transfer non-uniformity increases at the same time. The heat transfer performance has not been further enhanced when the mists diameter continuously increases after mist diameter are larger than 10μm.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A018. doi:10.1115/IMECE2018-88548.

Shaft cooling based on a loop thermosiphon is an ideal method for cooling of motorized spindles since it transfers heat with high efficiency and does not require an external power supply. In this study, an experiment was conducted on an R134a single-loop thermosiphon when the evaporation and condensation sections were on the same pipe. Results indicated that the single-loop thermosiphon was still operational with a minimum average thermal resistance of 0.51 W/°C when the filling ratio (FR) was 40%. The temperature distribution of the test specimen was determined predominantly by the amount of heating power, and not the mode. The optimum liquid filling ratio was 40% – 60% under this special condition, and both the thermal resistance and the heat transfer limit increased with the increase of FR in this range. The maximum temperature of the 150SD motorized spindle decreased 29% with the use of the R134a shaft cooling structure.

Topics: Cooling
Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Professor Frank Kreith Memorial Symposium: Advances in Heat Transfer, Energy Systems, and Sustainability

2018;():V08BT10A019. doi:10.1115/IMECE2018-87614.

Across the U.S., electricity production from coal-fired generation is declining while use of renewables and natural gas is increasing. This trend is expected to continue in the future. In the Rocky Mountain region, this shift is expected to reduce emissions from electricity production while increasing emissions from the production and processing of oil and gas, with significant implications for the level, location, and timing of the air pollution emissions that are associated with these activities. In turn, these emissions changes will affect air quality in the region, with impacts on ground-level ozone of particular concern. This study aims to evaluate the tradeoffs in emissions from both power plants and oil and gas basins resulting from contrasting scenarios for shifts in electricity and oil and gas production through the year 2030. The study also incorporates federal and state-level regulations for CH4, NOx, and VOC emissions sources. These regulations are expected to produce significant emissions reductions relative to baseline projections, especially in the oil and gas production sector. Annual emissions from electricity production are estimated to decrease in all scenarios, due to a combination of using more natural gas power plants, renewables, emissions regulations, and retiring old inefficient coal power plants. However, reductions are larger in fall, winter, and spring than in summer, when ozone pollution is of greatest concern. Emissions from oil and gas production are estimated to either increase or decrease depending on the location, scenario, and the number of sources affected by regulations. The net change in emissions thus depends on pollutant, location, and time of year.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A020. doi:10.1115/IMECE2018-87915.

Metal foams enhance heat transfer rates by providing significant increase in wetted surface area and by thermal dispersion caused by flow mixing induced by the tortuous flow paths. Further, jet impingement is also an effective method of enhancing local convective heat transfer rates. In the present study, we have carried out an experimental investigation to study the combined effect of the two thermal performance-enhancement mechanisms. To this end, we conducted a set of experiments to determine convective heat transfer rates by impinging an array of jets onto thin metal foams attached on a uniformly heated smooth aluminum plate simulating a high heat-dissipating chip. The metal foams used were high porosity aluminum foams (ε∼0.94–0.96) with pore densities of 5 ppi, 10 ppi and 20 ppi (ppi: pores per inch) with thicknesses of 19 mm, 12.7 mm and 6.35 mm, respectively. With the jet-to-foam distance (z/d) set to zero, we conducted experiments with values of jet-to-jet spacing (x/d = y/d) of 2, 3 and 5. The jet plate featured an array of 5 × 5 cylindrical jet-issuing nozzles. The normalized jet-to-jet distance was varied by changing the jet diameter and keeping the jet center-to-center distance constant. Steady state heat transfer and pressure drop experiments were carried out for Reynolds number (based on jet diameter) ranging from 2500 to 10000. We have found that array impingement on thin foams leads to a significant enhancement in heat transfer compared to normal impingement over smooth surfaces. The gain in heat transfer was greatest for the 20 ppi foam (∼2.3 to 2.8 times that for the plain surface smooth target). However, this enhancement came at a significant increase of about 2.85 times in the plenum static pressure. With the pressure drop penalty taken into consideration, the x/d = 3 jet plate for the 20 ppi foam and x/d = 2 jet plate for the 10 ppi foam were found to be the most efficient cooling designs amongst the 18 cooling designs investigated in the present study.

Topics: Metal foams , Porosity
Commentary by Dr. Valentin Fuster
2018;():V08BT10A021. doi:10.1115/IMECE2018-88107.

The study summarized in this paper links a model of thermal energy storage (TES) unit performance to a subsystem model including heat exchangers that cool down the storage at night when air temperatures are low; this cool storage is subsequently used to precool the air flow for a power plant air-cooled condenser during peak daytime air temperatures. The subsystem model is also computationally linked to a model of Rankine cycle power plant performance to predict how much additional power the plant could generate as a result of the asynchronous cooling augmentation provided by this subsystem. The goal of this study is to use this model to explore the parametric effects of changing phase change material (PCM), melt temperature, and the energy input and rejection control settings for the system. With this multi-scale modeling, the performance of the TES unit was examined within the context of a larger subsystem to illustrate how a high efficiency, optimized design target can be established for specified operating conditions that correspond to a variety of applications. Operating conditions of interest are the mass flow rate of fluid through the flow passages within the TES, the volume of the TES, and the amount of time the system remains in the extraction process in which thermal energy is inputted to the device by melting PCM, and the PCM melt temperature. These conditions were varied to find combinations that maximized efficiency for a 50 MW power plant operating in the desert regions of Nevada during an average summer day. By adjusting the flow rate within the fluid flow passages and the volume of the TES to achieve complete melting of the PCM during a set extraction time, indications of the parametric effects of system flow, melt temperature, and control parameters were obtained. The results suggest that for a full-sized power plant with a nominal capacity of 50 MW, the kWh output of the plant can be increased by up to 3.25% during the heat input/cold extraction period, depending on parameter choices. Peak power output enhancements were observed to occur when the system operated in the extraction phase during limited hours near the peak temperatures experienced throughout a day, while total kWh enhancement was shown to increase as the extraction period increased. For the most optimized conditions, cost analyses were performed, and it was estimated that the TES system has the potential to provide additional revenue of up to $1,366 per day, depending on parameter choices as well as the local cost of electricity. Results obtained to date are not fully optimized, and the results suggest that with further adjustments in system parameters, weather data input, and control strategies, the predicted enhancement of the power output can be increased above the results in the initial performance predictions reported here.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Radiative Heat Transfer and Radiative Properties of Energy Systems

2018;():V08BT10A022. doi:10.1115/IMECE2018-86386.

The radiation fractional function is the fraction of black body radiation below a given value of λT. Edwards and others have distinguished between the traditional, or “external”, radiation fractional function and an “internal” radiation fractional function. The latter is used for simplified calculation of net radiation from a non-gray surface when the temperature of an effectively black source is not far from the surface’s temperature, without calculating a separate total absorptivity. This paper examines the analytical approximation involved in the internal fractional function, with results given in terms of the incomplete zeta function. A rigorous upper bound on the difference between the external and internal emissivity is obtained. Calculations using the internal emissivity are compared to exact calculations for several models and materials. A new approach to calculating the internal emissivity is developed, yielding vastly improved accuracy over a wide range of temperature differences. The internal fractional function can be useful for certain simplified calculations.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A023. doi:10.1115/IMECE2018-87023.

A novel non-imaging Fresnel-lens-based solar concentrator-receiver system has been investigated to achieve high-efficiency photon and heat outputs with minimized effect of chromatic aberrations. Two types of non-imaging Fresnel lenses, a spot-flat lens and a dome-shaped lens, are designed through a statistical algorithm incorporated in MATLAB. The algorithm optimizes the lens design via a statistical ray-tracing methodology of the incident light, considering the chromatic aberration of solar spectrum, the lens-receiver spacing and aperture sizes, and the optimum number of prism grooves. An equal-groove-width of the Poly-methyl-methacrylate (PMMA) prisms is adopted in the model. The main target is to maximize ray intensity on the receiver’s aperture, and therefore, achieve the highest possible heat flux and output concentration temperature. The algorithm outputs prism and system geometries of the Fresnel-lens concentrator. The lenses coupled with solar receivers are simulated by COMSOL Multiphysics. It combines both optical and thermal analyses for the lens and receiver to study the optimum lens structure for high solar flux output. The optimized solar concentrator-receiver system can be applied to various devices which require high temperature inputs, such as concentrated photovoltaics (CPV), high-temperature stirling engine, etc.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Single-Phase Enhanced Heat Transfer: Applications and Experiments

2018;():V08BT10A024. doi:10.1115/IMECE2018-87345.

This paper concentrates on comparing dimples to improve the heat transfer rate from extended surfaces under forced convection conditions. Dimples are milled on the surface of the fins while keeping the exposed surface area between the various designs as constant. Spherical dimples, ellipsoidal dimples, cylindrical dimples, and pyramidal dimples are selected as part of the paper. Experimental results are compared with results obtained from simulation. The paper concludes that surface modifications improve the heat transfer rates. The paper also compares the thermal performance of various shapes of dimples.

Topics: Heat transfer
Commentary by Dr. Valentin Fuster
2018;():V08BT10A025. doi:10.1115/IMECE2018-88335.

In this study, a new type of tube inserts, named wedge-shaped wavy-tape insert, which is designed from bionics based on the movement of cuttlefish, is reported. The numerical simulation was carried out to investigate the effects of wedge-shaped wavy-tape insert arrangements on the heat transfer and flow characteristics of laminar flow in a circular tube under constant heat flux conditions. Details of the flow structures in the circular tube with wedge-shaped wavy-tape inserts which are arranged in same phase (S-type wavy tape) and different phase (D-type wavy tape) were presented and analyzed respectively. Then stereoscopic particle image velocimetry (Stereo-PIV) measurements on the flow structures were conducted to verify the numerical results. The flow structures obtained through simulations and PIV measurements agree well. It was observed that the arrangements of wedge-shaped wavy-tape inserts have a significant influence on the thermo-hydraulic performance. The average friction factor enhancement ratio f/f0 of D-type wavy tape were about 14%–20% lower than S-type wavy tape, but average heat transfer enhancement ratio Nu/Nu0 of D-type wavy tape were about 7%–14% higher than S-type wavy tape. The best performance evaluation criterion of D-type wavy tape could be improved to 3.02. The result shown the wedge-shaped wavy-tape insert is a promising technique for laminar convective heat transfer enhancement.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A026. doi:10.1115/IMECE2018-88377.

The circular, liquid jet impingement provides a convenient way of cooling surfaces. To effectively cool the devices inside the electric vehicle, a rotating jet impingement cooling system is designed to evaluate the potential of the jet impingement for high heat flux removal. The liquid used for jet impingement is automatic transmission fluid. The jet impingement system consists of a rotating pipe with two nozzles and a cylindrical ring which is attached to the heat source. To reduce the computational loads, first, the CFD simulation for a laminar flow inside the pipe is carried out to estimate the flow velocities at the nozzle exits. Then, the rotating jet impingement cooling of a cylinder with a uniform surface temperature is investigated numerically for stable, unsubmerged, uniform velocity, single phase laminar jets. The numerical simulation using the commercial code is performed to determine the heat flux removal performance over the cylindrical surface. The numerical results are compared with the empirical formula and experimental measurements from the literature. Furthermore, the effects of the Reynolds number and pipe rotation on the jet impingement cooling performance are also investigated.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A027. doi:10.1115/IMECE2018-88567.

Nowadays, cooling of electronic chips is one of the most serious challenges due to the exponential growth in the demand of increasingly powerful computer systems; the overheating of these components has become a problem of high importance. For this reason, the new cooling technologies such as liquid cooling systems replace the conventional air-cooling systems to avoid the effect of hotspots generated on a chip. To make matters worse, the current use of video games is requiring a tremendous amount of energy dissipation, over passing the cooling requirements of CPUs. Therefore, in this paper a new geometry is proposed to keep cool the graphic processor unit (GPU) in a CPU, using water as the working fluid. The main aim of the design is to enhance the heat dissipation in the GPU, decrease the pressure drop during the cooling process and reduce the amount of material used to build the waterblock. A numerical simulation solves the energy and momentum equations. The thermal performance of the proposed geometry is compared with a commercial heat sink geometry previously characterized. The results for the new geometry show that greater heat dissipation is not reached (results are about the same as the results for the commercial geometry) but due to the modification made, there is less pressure drop, while reducing the size of the waterblock. These results make this new geometry quite a good candidate for the new state of the art of cooling waterblocks.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Single-Phase Enhanced Heat Transfer: Numerical Studies

2018;():V08BT10A028. doi:10.1115/IMECE2018-86354.

Gas turbine blades are subjected to elevated heat loads due to high temperature gases exiting the combustor section. Complex internal and external cooling techniques are employed in blades to protect them from the hot gases. Blades are equipped with internal cooling passages which are connected to each other by 180-degree bends. The coolant flow is typically from blade root-to-tip and blade tip-to-root. Further, since the blades are subjected to rotation, the fluid dynamics and heat transfer inside these serpentine channels get modified. Under the influence of Coriolis force and centrifugal buoyancy force induced by rotation, the heat transfer for radially outward flow enhances on the trailing side (pressure side) and reduces on the leading side (suction side). A reverse trend in heat transfer is observed for radially inward flow. This heat transfer trend leads to non-uniform blade temperature leading to increase in thermal-stresses. Prolonged operation under critical thermal stresses can lead to significant damage and increase in maintenance and overhaul. This paper presents a novel 8-passgae serpentine design, where passages are arranged along the chord of the blade which has similar heat transfer coefficient distribution on both leading and trailing walls. Detailed heat transfer coefficients were measured using transient liquid crystal thermography under stationary and rotating conditions. Heat transfer experiments were carried out for Reynolds numbers ranging from 14264 to 83616 under stationary conditions. Rotation experiments were carried out at Rotation number of 0.05. Heat transfer enhancement levels of approximately two times the Dittus-Boelter correlation (for developed flow in smooth tubes) were obtained under stationary conditions. Under rotating conditions, we found that the heat transfer levels on the leading and trailing sides were similar to each other and with the stationary condition. Some differences in heat transfer were observed on local level, when rotation cases were compared against the stationary cases.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A029. doi:10.1115/IMECE2018-86355.

Porous media like open celled metal foams inherently provide a high heat transfer area per unit volume due to their interconnected cellular structure and are lightweight. High pore density metal foam because of its small overall dimensions and micro feature size shows promise in thermal packaging of compact electronics. An experimental study was carried out to evaluate thermal performance of high porosity (95%) and high pore density (90 PPI) copper foam of size 20 mm × 20 mm × 3 mm in buoyancy induced flow conditions and compared with a baseline smooth surface. The enhanced surface showed about 15% enhancement in average heat transfer coefficient over the baseline case. To optimize the performance further, the foam sample was cut into strips of 20 mm × 5 mm × 3 mm and attached symmetrically on the central 20 mm2 base surface area with inter-spacing of 2.5 mm. This new configuration led to further 15% enhancement in heat transfer even with 25% lesser heat transfer area. This is significant as heat transfer is seen as a strong function of permeability to flow through the structure over heat conduction through it. To test this hypothesis, a third configuration was tested in which the strips were further cut into blocks of 4 mm × 4 mm × 3 mm and attached in a 3 × 3 array on to the base surface. Here, only 36% of the central 20 mm2 base surface area was covered with foam. The heat transfer performance was found to be within ± 10% of the initial metal foam configuration, thereby, supporting the hypothesis. Performance was seen to decrease with increase in inclination from 0° to 30° to 90° with respect to the vertical.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A030. doi:10.1115/IMECE2018-86430.

Gas turbine blades are subjected to elevated heat loads due to highly turbulent hot gases exiting the combustor section. Several internal and external cooling techniques are used to protect the blades from such hostile environment. Trailing edge of a turbine blade is usually cooled with array of staggered cylindrical pins, which connects the pressure and suction side internal walls and hence provide improved structural integrity. However, the heat transfer enhancement levels for array of pin-fins is generally lower than jet impingement and ribbed channels. In this study, we present a three-tier impingement cooling design for blade trailing-edge and part of mid-chord region. In this design, pressure and suction side internal walls are subjected to oblique jet impingement. Three different configurations have been studied where we have systematically varied the jet diameters and number of jets in an array for different tiers. Numerical simulations have been carried out for different flow conditions, which corresponds to Reynolds numbers (based on 1st-passage jet diameter) ranging between 3000 and 46000. First two plenums had high levels of heat transfer due to oblique jet impingement, where the suction side internal wall representative surface, had higher heat transfer compared to the pressure side internal wall. Third tier had the lowest heat transfer due to triangle-like configuration where jets were almost parallel to pressure and suction side surfaces, and hence their effectiveness was lower than the oblique jet impingement in upstream two tiers.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A031. doi:10.1115/IMECE2018-86432.

High porosity metal foams are known for providing high heat transfer rates, as they provide significant increase in wetted surface area as well as highly tortuous flow paths to coolant flowing over fibers. Further, jet impingement is also known to offer high convective cooling, particularly on the footprints of the jets on the target to be cooled. Jet impingement, however, leads to large special gradients in heat transfer coefficient, leading to increased thermal stresses. In this study, we have tried to use high porosity thin metal foams subjected to array jet impingement, for a special crossflow scheme. One aim of using metal foams is to achieve cooling uniformity also, which is tough to achieve for impingement cooling. High porosity (92.65%) and high pore density (40 pores per inch, 3 mm thick) foams have been used as heat transfer enhancement agents. In order to reduce the pumping power requirements imposed by full metal foam design, we developed two striped metal foam configurations. For that, the jets were arranged in 3 × 6 array (x/d = 3.42, y/d = 2), such that the crossflow is dominantly sideways. This crossflow scheme allowed usage of thin stripes, where in one configuration we studied direct impingement onto stripes of metal foam and in the other, we studied impingement onto metal and crossflow interacted with metal foams. Steady state heat transfer experiments have been conducted for a jet plate configuration with varying jet-to-target plate distance z/d = 0.75, 2 and 4. The baseline case was jet impingement onto a smooth target surface. Jet diameter-based Reynolds number was varied between 3000 to 11000. Enhancement in heat transfer due to impingement onto thin metal foams has been evaluated against the enhancement in pumping power requirements. For a specific case of z/d = 0.75 with the base surface fully covered with metal foam, metal foams have enhanced heat transfer by 2.42 times for a concomitant pressure drop penalty of 1.67 times over the flow range tested.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A032. doi:10.1115/IMECE2018-86558.

Solar thermal panels’ heat enhancement through cooling techniques is important for the effective use of the panels. This study is performed on a simulated internal cooling channel of a solar thermal cell with an artificial technique using angled dimpled rough end-wall and exploring the combination of the different geometrical surface to enhance the heat transfer from the wall. Circular and oval shape dimples combination arranged in staggered form are tested. However, the oval geometrics are varied typical to flow direction. The following combinations of circular and oval dimpled are therefore examined (1) 90° circular by 90° oval dimples to the mainstream (2) 90° circular by 60° oval dimples to the mainstream (3), 90° oval by 90° circular dimples to the mainstream and (4) 60° oval by 90° circular to the mainstream. All of which are having pitch/depth ratio, P/δ of 6, dimple centre to centre, P, of 30 mm, and print diameter, D, of 20 mm (for both circular and oval shape), oval small diameter of 10 mm. These combinations are tested for three aspect ratios of 0.049, 0.035 and 0.0249. This study is conducted for a Reynolds number range of 1,000–11,000, and local and averaged heat transfer coefficient values are presented for all the geometries. Pressure drops are measured along the mainstream of the smooth and dimpled channel end-wall and friction factors are calculated. The combination of the 60° oval and 90° circular dimple surface exhibits the best performance of all the cases considered, a moderate pressure drop was also observed compared with others like a combination of pin fins, ribs-protrusions, grooves etc. These values were higher or comparable to the best-performing dimple geometries commonly used for the internal cooling process.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A033. doi:10.1115/IMECE2018-86616.

Heat exchangers are widely used in heating and cooling devices. The primary challenge is to improve the efficiency of the heat transfer equipment. Researchers have utilized various techniques to achieve this goal. Using twisted tapes could significantly increase the heat transfer rate from a circular surface due to turbulence generated from swirl flow. To enhance the heat transfer rate by twisted tape, two types of arrangements namely: (i) plain twisted tape and (ii) altered twisted tape geometries are used. These arrangements result in swirl flows. For improving heat transfer through swirl flow, some important parameters such as Reynolds number, external surface temperature, friction factor, inlet pressure, and surface heat flux are also considered. To identify the aftereffect of the velocity of inlet water, several parameters namely: (i) external surface temperature, (ii) inlet pressure, (iii) external surface heat flux and (iv) twist ratio are varied. A numerical modelling using k-ε method is performed to evaluate the effects of turbulence from the twisted tape on the heat transfer rate. The objective is to analyze the improvement of heat transfer effectiveness due to the swirl flow. The change in the values of the resulting Reynolds number by changing the inlet fluid velocity from 0.1 ms−1 to 0.7 ms−1 and rotational speed from 200 rpm to 600 rpm is studied. It is observed that for such changes heat transfer increases by 17 percent. It is also observed that heat transfer is directly proportional to inlet pressure and inversely proportional to the increment of twist ratio. The rate of heat transfer increased from 17 percent to 19 percent when the angular velocity of the twisted tape is changed from the 0 rpm to 600 rpm while the velocity of the water inside the pipe is held constant at 0.7 ms−1. Higher heat transfer rate is observed with high inlet pressure. Likewise, higher value of the Nusselt number is observed with higher rotational speed of the twisted tape and higher velocity at the pipe inlet. In addition, it is also observed that when the twist ratio is changed from 4 to 6, the rate of heat transfer is diminished by 6 percent.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A034. doi:10.1115/IMECE2018-87029.

This work is aimed towards studying and analyzing the heat transfer performance in a novel 3D graphene-carbon nanotube (CNT) pillared structure. Although both graphene and CNT are known to have high thermal conductivity in in-plane and along the axis, respectively, they have low thermal conductivities in the other directions. Hence, the 3D graphene-CNT structure will have high thermal conductivities in both in-plane and out-of-plane directions due to the pillared architecture. It can be applied to small-scale electronic devices for high efficient heat dissipation and/or exchange. The pillared structure consists of few-layer graphene (FLG) and bundles of CNTs. CNT bundles connect between two sheets of FLG. The heat transfer performance of the structure was investigated through a continuum model by COMSOL Multiphysics. Parameter studies were conducted to determine the optimum graphene-CNT configuration, including number of CNTs in each bundle, number of bundles in the structure, distance between bundles (a.k.a. inter-pillar distance “IPD”), length of CNT, and the arrangement of CNT bundles. Results of the simulations concluded that (1) the reduced IPD could prevent the in-plane heat spreading, (2) the increased number of CNTs could enhance the axial-direction thermal transport, and (3) the arrangement of CNT bundles between FLG sheets (e.g. shifting one row of CNT bundles) has minor impacts on the overall heat transfer performance of the structure.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A035. doi:10.1115/IMECE2018-87780.

To minimize the computational and optimization time, a numerical simulation of 3D microchannel heat sink was performed using surrogate model to achieve the optimum shape. Latin hypercube sampling method was used to explore the design space and to construct the model. The accuracy of the model was evaluated using statistical methods like coefficient of multiple determinations and root mean square error. Thermal resistance and pressure drop being conflicting objective functions were selected to optimize the geometric parameters of the microchannel. Multi objective shape optimization of design was conducted using genetic algorithm and the optimum design solutions are presented in the Pareto front. The application of the surrogate methods has predicted the performance of the heat sink with the sufficient accuracy employing significantly lower computational resources.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A036. doi:10.1115/IMECE2018-88273.

A numerical investigation of three-dimensional conjugate heat transfer was performed to quantify the thermal and hydraulic performance of an inter-connected parallel and counter flow mini-channel heat sink under laminar flow condition and within the single-phase regime. The aspect ratio (height/width) and the hydraulic diameter of the mini-channel were 0.33 and 750μm respectively. Three different widths of the inter-connector were selected to analyze the effect of cross flow for Reynolds number ranging from 150 to 1044, at a constant heat flux (20 W/cm2). To understand the fluid flow and heat transfer mechanism inside the inter-connector and their effects on overall thermal performance of the heat sink, Nusselt number (Nu), friction factor, pumping power, and overall thermal resistance were analyzed. Results show that the inter-connector has significantly higher effect on counter flow mini-channel heat sink than parallel flow mini-channel heat sink.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A037. doi:10.1115/IMECE2018-88570.

The increase in the power of chips and microchips has resulted in the generation of heat fluxes to be dissipated of the order of 100 W/cm2 in very small areas [1], therefore, dissipating this heat has become a priority for the proper functioning of these dispositives. Thus, the proposition of new geometries and dissipation methods has become an area of great interest in scientific research. This research presents the analysis of a new geometry for a heat sink capable of dissipating very high energy flows by means of liquid cooling. The analyzes are based on previous analyzes of serpentine type geometries, where the heat flux to dissipate was 10 W/cm2 [2]. The operating conditions, such as velocity and pressure drop, as well as heat transfer are analyzed. Water is used as the dissipation fluid at an inlet velocity of 0.1 m/s. The geometry to be analyzed, called “Aztec Geometry,” is a radial type geometry that was originally designed for fuel cells, and has small fins arranged in three radial stripes. The results indicate that the pressure drop is on the order of 85 Pa, which is less than the pressure drop when radial coil microchannels are used (between 100 and 870 Pa). The dissipated heat is larger than the heat dissipated in radial coil microchannels (205 W versus 145 and 194 W), proving that the proposed radial geometry has a greater dissipation capacity at a lower cost than previously proposed geometries in the market.

Topics: Heat , Geometry
Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Thermal Analysis of Industrial Equipment and Systems Operating Under Extreme Process Conditions

2018;():V08BT10A038. doi:10.1115/IMECE2018-87049.

A steady state sensible performance analysis of multi-pass cross-flow finned-tube heat exchangers is reported. The investigation considers various flow circuiting, such as counter cross-flow, parallel cross-flow, and cross-flow where the tube-side flow is in parallel. A previously developed matrix approach is used to evaluate the heat exchanger performance in each tube pass. The equations required to model the thermal performance of these configurations are presented, and the thermal performance is compared for each type of flow circuiting. Thereafter a parametric study on cross-flow heat exchanger performance is performed by varying physically significant parameters such as number of transfer units (NTU) and capacity rate ratios, and the graphical results for each type of flow circuiting are presented both for both two-pass and three-pass arrangements. A consistent criterion is proposed for each case, wherein increasing the NTU beyond a certain threshold value does not significantly improve heat exchanger thermal performance.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A039. doi:10.1115/IMECE2018-87788.

Assuring that food products have acceptable quality and are safe to consume requires maintaining adequate nutrition levels and fulfilling consumer expectations. Quality losses can lead to food waste, resulting in increased economic costs and low consumer confidence. Therefore, quality expectations should be maintained at an acceptable level for consumer purchase and consumption. It is well known that a cold environment reduces the respiratory activities and kinematics of nutritional degradation. The cooling temperature is critical since lower than recommended cold temperatures may cause chill damage. Therefore, the food industry intensively employs cold storage methods to slow respiration rates, inhibit harmful bacterial growth, reduce water loss, and prolong shelf life in order to maintain product nutritional value and quality. Improving product cooling efficiency will reduce energy costs that are a significant expense for fruit and vegetable processors. Understanding the cooling process is key to the development of new technology and processes. However, most natural food products are not conformed to simple geometric shapes or uniform properties and distributions. Thus, the cooling process of an agricultural product (cucumbers) was investigated in this study. The study was conducted in a packing house, where the cooling temperature of the cucumbers was recorded by placing multiple thermocouples in the produce after boxing and palletizing as well as cold storage. The test results showed that individual produce cooling was relatively easy to predict. However, boxed and palletized cucumber cooling showed significant variations. For example, the temperature of the cucumbers changed depending on their location in the box in addition to the box location on the stack. In the case of boxed produce cooled by natural convection cooling, the temperature changed from 25 to 18 °C after three hours. However, in the case of palletized tunnel cooled, the temperature change ranged from 25 to 11 °C and 25 to 18 °C after nearly three hours of cooling. Indeed, the temperature differences indicated that the cooling rate has significant variations depending on the location of the produce. Some parts of the pallet received more direct contact with the forced cold air than other parts. Thus, it is very important for produce processors to understand cooling system performance. The study emphasized that efficient use of energy is one of the areas that can have not only significant cost savings but can also improve produce shelf life, reduce food waste, and maintain consumer confidence.

Topics: Cooling
Commentary by Dr. Valentin Fuster
2018;():V08BT10A040. doi:10.1115/IMECE2018-88635.

Convective heat transfer coefficient and its interdependency with various key parameters is analyzed for turbulent multi-jet impingement. Air is used as the working fluid impinging on the flat surface via a three-nozzle arrangement. A thorough investigation of velocity and temperature distribution is performed by varying Nozzle Velocity, Height over Diameter ratio (H/D) and Spacing over Diameter ratio (S/D). Convective heat transfer coefficient, average impingement surface temperature, and heat transfer rate are calculated over the impingement surface. It was found that higher S/D ratios result in higher local heat transfer coefficient values near stagnation point. However, increased spacing between the neighboring jets results in less coverage of the impingement surface reducing the average heat transfer. Lower H/D ratios result in higher heat transfer coefficient peaks. The peaks for all three nozzles are more uniform for H/D ratios between 6 and 8. For a fixed nozzle velocity, heat transfer coefficient values are directly proportional to nozzle diameter. For a fixed H/D and S/D ratio, heat transfer rate and average impingement surface temperature increase as the nozzle velocity increases until it reaches a limiting value. Further increase in nozzle velocity causes drop in heat transfer rate due to ingress of large amounts of cold ambient air in the cooking space.

Topics: Turbulence
Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Thermal Management of Battery Systems

2018;():V08BT10A041. doi:10.1115/IMECE2018-86081.

Phase-change materials (PCMs) are a useful alternative to more traditional methods of thermal management of Li-ion batteries in electric or hybrid-electric vehicles. PCMs are materials which absorb large amounts of latent heat and undergo solid-to-liquid phase change at near-constant temperature. The goal of the research is to experimentally investigate the thermal properties of a novel shape-stabilized PCM/HDPE composite extruded filament. The extruded filament can then be used in a 3D printer for custom PCM/HDPE shapes. The PCM used in the study is PureTemp PCM 42, which is an organic-based material that melts around 42° C. Four PCM/HDPE mixtures were investigated (all percentages by mass): 20/80, 30/70, 40/60, and 50/50. Preliminary findings include differential scanning calorimeter (DSC) measurements of melting temperature and latent heat as well as scanning electron microscope (SEM) pictures of filament composition.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A042. doi:10.1115/IMECE2018-87923.

Li-ion based energy storage devices have highly temperature dependent characteristics such as performance, life-cycle, efficiency and safety. Large temperature gradient within a cell results in thermal stresses and nonuniform current density leading to accelerated degradation. This adversely affects the life cycle of the cell due to capacity and power fade. There are similar issues due to large temperature variation within a battery pack. Operation of Li-ion cell outside the desirable temperature range also leads to lower efficiency, degradation and safety related issues. Different thermal management approaches have been proposed and demonstrated in past. The present work focuses specifically on minichannel based liquid cooling for conducting a parametric study. Minichannels have been found effective in various thermal management applications due to their simple construction and high convective heat transfer. In past, minichannels have been proposed and used in battery thermal management. However, designing of such systems has been somewhat arbitrary without considering various factors and trade-offs involved. There is a lack of rigorous studies for determining various parameters related to thermal management system that would result in adequate thermal management in a cost-effective manner. In the present work, a comprehensive parametric study has been carried out on the minichannel based liquid cooling for thermal management of Li-ion battery pack. A simplified computationally efficient numerical simulation-based approach has been used to conduct parametric study for optimizing the design and operating parameters of the thermal management system.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Thermal Management of Electronic Equipment

2018;():V08BT10A043. doi:10.1115/IMECE2018-86730.

In recent years, semiconductor industry has manufactured processors which can be socketed and installed using specially designed retention mechanisms. Due to increased power and I/O capabilities for processors from generation to generation, the number of pins on the socket is increasing. This pin number increase is translated directly to increased retention loading force on thermal management solutions for reliable electrical contact and thermal interface material actuation. For recent generation of Intel® Xeon® Scalable Processor Family, a maximum retention force of 1334 N (300 lbf) needs to be transferred to the socket via thermal solution i.e. heat sink or cold plate. In liquid cooling applications, this high loading requirement calls for a stiffer cold plate.

At the same time, other regulatory and thermal requirements such as burst pressure and thermal performance need to be satisfied. A liquid cooled thermal solution was developed for the Intel® Xeon® Scalable Processor Family Platform. This thermal solution considers a modular bracket design which allows changing the material responsible for the load application on the thermal solution for a stronger and/or lighter one, without impacting the thermal performance due to material selection. This paper presents the design strategy, numerical analysis, test fixture setup for mechanical and thermal analysis, and prototype test results for mechanical and thermal performance of designed cold plates. This paper will be helpful to guide the thermal community to design a liquid cooled thermal solution for future generation of processors in data center applications and as well as for different electronic components.

Topics: Design , Testing
Commentary by Dr. Valentin Fuster
2018;():V08BT10A044. doi:10.1115/IMECE2018-88497.

In typical data centers, the servers and IT equipment are cooled by air and almost half of total IT power is dedicated to cooling. Hybrid cooling is a combined cooling technology with both air and water, where the main heat generating components are cooled by water or water-based coolants and rest of the components are cooled by air supplied by CRAC or CRAH. Retrofitting the air-cooled servers with cold plates and pumps has the advantage over thermal management of CPUs and other high heat generating components. In a typical 1U server, the CPUs were retrofitted with cold plates and the server tested with raised coolant inlet conditions. The study showed the server can operate with maximum utilization for CPUs, DIMMs, and PCH for inlet coolant temperature from 25–45 °C following the ASHRAE guidelines. The server was also tested for failure scenarios of the pumps and fans with reducing numbers of fans and pumps. To reduce cooling power consumption at the facility level and increase air-side economizer hours, the hybrid cooled server can be operated at raised inlet air temperatures. The trade-off in energy savings at the facility level due to raising the inlet air temperatures versus the possible increase in server fan power and component temperatures is investigated. A detailed CFD analysis with a minimum number of server fans can provide a way to find an operating range of inlet air temperature for a hybrid cooled server. Changes in the model are carried out in 6SigmaET for an individual server and compared to the experimental data to validate the model. The results from this study can be helpful in determining the room level operating set points for data centers housing hybrid cooled server racks.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A045. doi:10.1115/IMECE2018-88690.

The goal of this research is to present an analytical model of nanostructures and study the effects of their geometry on the performance of micro channels. The pressure drop experienced by micro channels is of interest as it presents a limit on forced convection heat transfer. This work will demonstrate how the presence of nanostructures alleviates pressure drop and results in enhanced cooling capabilities. Multiple transient analyses were performed in ANSYS FLUENT to ascertain performance characteristics of microchannels without the presence of hydrophobic nanostructures. The results were compared to the analytical model developed in this study.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Thermal Transport Across Hard/Soft Interfaces

2018;():V08BT10A046. doi:10.1115/IMECE2018-86497.

The understanding of nanoscale heat transfer across solid-liquid interfaces poses similar challenges as solid-solid interfaces; however, the higher mobility of liquid particles increases the complexity of this problem. It has been observed that liquid particles tend to form organized structures in the vicinity of solid surfaces; additionally, the formation of such structures has been reported to correlate with heat transfer across interfaces. Classical molecular dynamics simulations were used to investigate the behavior of liquid water in contact with crystalline and amorphous silicon. The in-plane and out-of-plane structure of interfacial water was characterized under different artificial wettability conditions, i.e., the silicon-water interaction potentials were calibrated to reproduce a wide range of wettability conditions. The change in the vibrational density of states was analyzed in order to quantify the mismatch between modes on both sides of the solid-liquid interfaces. Linear response theory was used to calculate the thermal boundary conductance at the different interfaces and a correlation was found between surface chemistry and heat transfer.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A047. doi:10.1115/IMECE2018-86722.

Experimental data of thermal contact conductance (TCC) between two metallic rough surfaces versus the applied load (pressure) distinctly exhibit non-linear behavior that can be split into two regimes with two distinct slopes. When the load is small, the rate of change of TCC with load is linear with a small slope. At intermediate loads, this slope increases. A third slope has been exhibited in some cases at extremely high loads — one in which the slope decreases again. In this study, two types of analysis are conducted on a simplified model system comprised of a single asperity compressed by two flat surfaces. The first analysis assumes one-dimensional heat conduction across the asperity, resulting in a fin-equation type model. In the second analysis, two-dimensional heat conduction through the asperity is considered, and the governing steady state heat conduction equation is solved numerically. Results show that the first two slopes at low and intermediate loads can be captured by both models. However, when the asperity is significantly depressed (high load regime) and deformed, the experimental behavior of the third reduced slope can only be captured by the two-dimensional numerical model. This implies that when the asperity deforms significantly, multi-dimensional heat transport becomes a critical limiting factor for the TCC.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A048. doi:10.1115/IMECE2018-87195.

The binary eutectic mixtures of sugar alcohols, which can maintain their high latent heat of fusion while extending the range of melting points for more flexible utilizations, have attracted increased attention. The eutectic mixture of erythritol and xylitol, with a melting point of 82 °C and a latent heat of fusion of 270 kJ/kg, has been identified as a promising latent heat storage material at the temperature range around 80 °C. In comparison to the pure components, the changes in thermal conductivity of mixture sugar alcohols are of great interest, which are investigated in this work with emphasis on the interfacial heat transfer across erythritol and xylitol molecules. Molecular dynamics simulations were performed to study the nanoscale heat transfer over an artificial interface between two crystal layers of erythritol and xylitol in contact with each other. Based on the non-equilibrium molecular dynamics method and eHEX algorithm, a constant heat flux was imposed over the simulated box. The dependence of the erythritol-xylitol interfacial thermal resistance on the system length was studied by adapting different system lengths. With increasing the length from 26 to 78 Å, the interfacial thermal resistance was predicted to decrease from 5.5 × 10−10 to 3.8 × 10−10 m2·K/W, which then becomes nearly unvaried while further increasing the system length to over 100 nm. The knowledge on the interfacial thermal resistance will help understand the changes in thermal conductivity of bulk mixtures of sugar alcohols.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A049. doi:10.1115/IMECE2018-87764.

We employ molecular dynamics simulations to explore the effect of tensile strain on the thermal conductivity of carbon nanotube (CNT)-graphene junction structures. Two different types of CNT-graphene junctions are simulated; a perfect seamless junction between CNT and graphene with complete sp2 covalent bonds, and a CNT-graphene junction with mixed sp2/sp3 covalent bonds are studied. The most interesting phenomenon observed in the present research study is that the thermal conductivity of CNT-graphene junction structures increases with an increase in mechanical strain. For the case of CNT-graphene junction structure with pillar height of 50 nm and inter-pillar distance of 15 nm, the thermal conductivity is improved by 22.4% when 0.1 tensile strain is imposed. It is observed that the thermal conductivity improvement is enhanced when a larger graphene floor is placed between junctions since larger graphene floor allows larger deformation (larger tensile strain) in the junction. In addition, the thermal conductivity of CNT-graphene junction structures with pure sp2 bonds is observed to be higher than the thermal conductivity of CNT-graphene junction structures with mixed sp2/sp3 bonds regardless of the amount of tensile strain. The obtained results will contribute to the development of flexible electronics by providing a theoretical background on the thermal transport of three dimensional carbon nanostructures under deformation.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A050. doi:10.1115/IMECE2018-88642.

The temperature evolution of nanoparticle packings on a substrate under high laser power is investigated both experimentally and via numerical simulations. Numerical modeling of temperature distributions in copper nanoparticle packings on a glass substrate is performed and results are compared with experiment under 2.6 kW/cm2 laser power. A coupled electromagnetic-heat transfer model is implemented to understand the nanoparticle temperature distribution. Very good agreement between the coupled electromagnetic-heat transfer model and the experimental results is obtained by matching the interfacial thermal conductance, G, between the nanoparticles using the experimental result in the coupled electromagnetic-heat transfer model.

Commentary by Dr. Valentin Fuster

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

2018;():V08BT10A051. doi:10.1115/IMECE2018-86290.

Novel technologies have always been an indispensable part of the scientific enterprise and a catalyst for new discoveries. The invisible radiation patterns of objects are converted into visible images called thermograms or thermal images. Thermal images can be utilized to estimate the ripeness of some fruits which do not change their color from yellow to green when they are ripe. Thermal imaging techniques are very helpful since color and fluorescent analytical approaches cannot be applied to these fruits. In this work, it is shown that different ripeness levels of avocado (Hall type) using a non-destructive method called thermal imaging, in two dimensional spaces. The work is based on the fact that fruits have different specific heat capacities at different temperatures, thus making their thermal images clear indicators of ripeness.

Topics: Imaging
Commentary by Dr. Valentin Fuster
2018;():V08BT10A052. doi:10.1115/IMECE2018-86929.

This paper reports the experimental and numerical studies on the effects of rotating speed and blowing ratio on the film cooling performance of the hole near the leading edge on the suction side of the turbine blade. The chord and height of the blade are 60mm and 80mm respectively. The film hole with diameter of 0.8mm is located in the mid span on the suction side at axial location of 8%. The injection angle of the hole is 45° to the suction surface of the blade and is nearly perpendicular to the axial direction. Both experimental and numerical studies were carried out with rotating speeds of 300rpm, 450rpm and 600rpm, and with blowing ratios of 0.5, 1.0, 1.5 and 2.0. CO2 was used as the coolant. Experimental data was measured by applying the Thermochromic Liquid Crystal (TLC) technique and the Stroboscopic Imaging Technique. Mainstream and coolant were heated to 308K and 318K respectively. Numerical studies were performed to assist the analysis of the experimental results. The SST turbulence model was applied in the simulations. Results show that the film cooling performance of the hole near the leading edge is different from that of the hole further downstream on the suction side. This is because the direction of the jet is nearly perpendicular to the axial direction, which increases the effect of the Coriolis force. Besides, the mainstream from leading edge also has effects on film cooling performance. With the increase of the blowing ratio, the film coverage area and spatially averaged film cooling effectiveness increase first and then decrease. The maximum film coverage and averaged film cooling effectiveness appear at blowing ratio of 1.0 and rotating speed of 300rpm. Moreover, the upward deflection angle of the film trajectory increases slightly with the increase of the blowing ratio. Higher rotating speed intensifies the deflection of the film trajectory. Therefore, the film coverage and the averaged film cooling effectiveness decrease rapidly.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A053. doi:10.1115/IMECE2018-86976.

In the current study, the influence of different rotation conditions on the flow behavior is experimentally investigated by a new system which is designed for time-resolved PIV measurements of the smooth channels at rotation conditions. The Reynolds number equals 15000 and the rotation number ranges from 0 to 0.392 with an interval of 0.098.

This new time-resolved Particle Image Velocimetry system consists of a 10 Watts continuous laser diode and a high-speed camera. The laser diode can provide a less than 1mm thickness sheet light. 6400 frames can be captured in one second by the high-speed camera. These two parts of the system are fixed on a rotating disk. In this case, the relative velocity of flows in the rotating smooth square channel can be measured directly to reduce the measurement error. This system makes high-speed camera close to the rotating channel, which allows a high resolution for the measurements of main stream. In addition, high accuracy and temporal resolution realize a detailed analysis of boundary layer characteristics in rotation conditions. Based on this system, experimental investigation has been undertaken. Results are presented of the evolution of velocity and boundary layer thickness at various rotation numbers and different circumferential positions.

Topics: Flow (Dynamics)
Commentary by Dr. Valentin Fuster
2018;():V08BT10A054. doi:10.1115/IMECE2018-87183.

This experiment measures the temperature and the velocity field synchronously in the boundary layer in a rotating smooth, wall-heated channel using hot-wire. The Reynolds number based on the bulk mean velocity and hydraulic diameter is 19000 and the rotation numbers are 0, 0.07, 0.14, 0.21, 0.28 and 0.35. Four streamwise stations (X/D = 4.06, 5.31, 6.56, 7.81) were investigated. To calibrate the parallel-array hot-wire probe, a heating section is added to the original wind tunnel that could only calibrate the hot-wire at room temperature. Different gas temperatures at the outlet could be obtained by changing the heating power of the heating section. The velocity profiles and the temperature profiles are obtained. It can be seen that the viscous sublayer also exists when the wall is heated, thus the viscous sublayer profile method is also valid when the wall is heated. It is found that the velocity profile near the leading side is more sensitive to the change of rotation number and X/D than the velocity profile near the trailing edge. The critical rotation number phenomenon of velocity profile has also been found in present work. By comparing with the previous work without the wall heated, the influence of both kinds of buoyancy under this condition is discussed. Some explanations are given for the experimental results.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A055. doi:10.1115/IMECE2018-87258.

Engine turbine blades operate at a high speed of rotation and are subjected to high temperature and pressure prevailing gas from the combustion chamber, making the working condition very harsh. In particular, the leading edge of the blade, which is directly subjected to high-temperature gas impacts, is the hottest part of the turbine. Therefore, it is of great importance to improve the protection of the blade leading edge and enhance the understanding of this part of the flow field and temperature field. This paper will focus on the phenomenon of wake deflection and study the film cooling characteristics of the turbine blade under rotating condition. The characteristics of pressure surface and suction surface of the blade are verified by numerical simulation. The contents cover the influence of the film hole diameter, pitch, blowing ratio, rotation number and the development process, the film cooling efficiency on the outflow of coolant film. The result shows that Coriolis force, centrifugal force and secondary flow induced by rotation will change the mainstream flow along the blade, which will lead to changes of pattern concerning the development of the film on the blade surface. In the process of wake development, deflection occurs in different directions at different positions, and the greater the rotation number is, the more obvious the degree of deflection will be.

Studying the model with film holes on the leading edge of the blade, these phenomena can be observed along the downstream on the pressure and suction surfaces. Also, models with film holes independently set on the pressure and suction surfaces can be used as proof of these features. At the same time, this paper studies the flow and heat transfer characteristics of the leading-edge gas film under rotating condition and focuses on the influence of rotation on the outflow and the development processes of the wake. The gas film cooling models in rotating state of different film hole diameters and film hole radial spacing will also be compared to further understand the flow and heat transfer characteristics of film cooling on the leading edge of the blade.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Transport Phenomena in Manufacturing and Materials Processing

2018;():V08BT10A056. doi:10.1115/IMECE2018-86144.

In the present work, the deformation behavior in metallic film subjected to ultra-short laser heating is investigated. Static thermo-elastic behavior is predicted for 100 nm thin film of either single layer or multiple layers. The temperature distribution is estimated from dual-phase lag non-Fourier heat conduction model. The maximum temperature after single pulse is achieved 730 K. The temperature profile for this pulse laser is used to compute elastic stress and distortion field following the minimization of potential energy of the system. In the present work, the simulation has been proposed by developing 3D finite element based coupled thermo-elastic model using dual phase lag effect. The experimental basis of transient temperature distribution in ultra-short pulse laser is extremely difficult or nearly impossible, the model results have been validated with literature reported thermal results. Since the temperature distribution due to pulse laser source varies with time, the stress analysis is performed in incremental mode. Hence, a sequentially coupled thermo-mechanical model is developed that is synchronized between thermal and mechanical analysis in each time steps of transient problem. The maximum equivalent stress is achieved 0.3 GPa. Numerical results show that the predicted thermal stress may exceeds the tensile strength of the material and may lead to crack or damage the thin film.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A057. doi:10.1115/IMECE2018-86729.

Alloy parts fabricated by the selected laser melting (SLM) additive manufacturing process generally contain many defects. Non-destructive Positron Annihilation Lifetime Spectroscopy (PALS) measurements were applied to evaluate these defects. The two-component positron lifetime method was used to analyze the evolution of two types of defects, mono-vacancy and vacancy cluster.

Stainless steel 316 SLM samples were prepared using two sets of SLM processing parameters. For SLM samples, the temperature effect of heat treatment was examined by PALS. The effect of plastic deformation is also examined using PALS.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A058. doi:10.1115/IMECE2018-86736.

The application of laser processing as a surface treatment method on oxide dispersion strengthened (ODS) Fe-14Cr ferritic alloys, Fe-14Cr-3W-0.3Ti-xY2O3 (x = 0.3, 0.6, 0.9) (wt%), was examined in this paper. The ODS ferritic alloys with different amount of Y2O3 particles were prepared by mechanical milling and subsequently consolidated by spark plasma sintering (SPS). The effect of surface laser processing on the corrosion behavior was investigated for these ODS alloys with different oxide contents. The corrosion behaviors of SPS consolidated ODS samples with subsequent laser melting/solidification were examined by the means of electrochemical tests and compared with the untreated ODS samples in salt water. Results indicated that for samples without laser treatment, powders are mainly in their elemental state. However, after laser processing, the formation of passive layer and the improvement in the corrosion resistance are noticeable. CALculation of PHAse Diagrams (CALPHAD) calculations were used to identify the equilibrium phases and compared well with the experimental results.

Topics: Lasers , Alloys , Corrosion
Commentary by Dr. Valentin Fuster
2018;():V08BT10A059. doi:10.1115/IMECE2018-87995.

Air jet impingement technology receives considerable attention due to its high performance for heat transfer enhancement in thermal equipment, providing high heat transfer rates. Due to its inherent characteristics of high average heat transfer coefficients and uniformity of the heat transfer over the impinging surface, this technology is implemented in a variety of engineering applications and industrial processes, such as reflow soldering, drying of textile, cooling of turbojet engine blades and fusion reactors. Multiple jet impingement involves several variables such as: jets arrangement, jet diameter, nozzle-to-surface distance, nozzle shape, jet-to-jet spacing, jet velocity and Reynolds number, among others. However, the total control of all these parameters is still one of the remarkable issues of the thermal design of jet impingement systems. In some industries that have implemented this technology in their processes, such as reflow soldering, the range of values of these variables are established through empiricism and “trial and error” techniques. To improve the process and to reduce time and costs, it is fundamental to define accurately all the process parameters in order to obtain an optimized design with a high degree of control of the heat transfer over the target surface. To perform an accurate and complete study of the multiple jet impingement variables for a specific application, the development of both experimental and numerical studies is fundamental in order to obtain reliable results. In that sense, this work reports the project and construction of a purpose-built test facility which has been commissioned, using a PIV system. This experimental setup is based on the oven used in the reflow soldering process. The optimization of the multiple jets geometry which is integrated in the experimental setup is herein described and discussed both experimentally and numerically. The numerical simulation of the jet impingement inside the oven was conducted using the ANSYS software, specially designed to predict the fluid behavior. Regarding the relevance of the multiple jet impingement, this work intends to improve the knowledge in this field and to give reliable and scientifically proved answers to the industries that apply this technology in their processes.

Topics: Air jets
Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Two Phase Transport in Energy Systems and Non-Equilibrium and Dynamic Energy Systems

2018;():V08BT10A060. doi:10.1115/IMECE2018-86561.

Prediction of evaporation rates from spent fuel pools of nuclear power plants in normal and post-accident conditions is of great importance for the design of safety systems. A severe accident in 2011 Fukushima nuclear power plant caused failure of cooling systems of its spent fuel pools. The post-accident evaporation from the spent fuel pools of Fukushima units 2 and 4 is compared to a model based on analogy between heat and mass transfer which has been validated with a wide range of data from many water pools including a spent fuel pool. Calculations are done with two published estimates of fuel decay heat, one 25 % lower than the other. The model predictions are close to the evaporation using the lower estimate of decay heat. Other relevant test data are also analyzed and found in good agreement with the model.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A061. doi:10.1115/IMECE2018-86571.

Accuracy of numerical simulation of non-equilibrium steam condensation is strongly influenced by a condensation model, i.e. a nucleation rate model and a droplet growth model. Numerical studies of steam condensation in Laval nozzles show that the choice of the condensation model has a significant influence on nucleation rate, position of nucleation zone and consequently steam wetness and the droplet size in the nozzle outlet.

It is necessary to model the transition area between rotating-rotor and stationary part-stator in numerical simulations of steam flow in steam turbines. For this purpose, “Stage” and “Frozen rotor” rotor-stator interface models are widely used.

The aim of the present work has been to analyze how the numerical modeling of the rotor-stator transition area together with the condensation model influences the result of numerical simulation of flow with non-equilibrium steam condensation in the low pressure part of steam turbine of large power output.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A062. doi:10.1115/IMECE2018-86607.

In the current study, the performance of a high temperature, cylindrical heat pipe under various operating conditions is investigated numerically. To find the appropriate geometrical and working parameters of the heat pipe, a two-dimensional axisymmetric model is developed to describe the vapor and liquid flows and heat transfers in the vapor core, the wick, and the wall regions. Sodium and stainless steel are selected as the working fluid, the wick material, and the container material. The compressibility of the vapor and viscous dissipation are taken into account. In the wick region, the Darcy–Brinkman–Forchheimer model is applied to simulate the liquid sodium characteristics. The effect of wick type, heat input, and operating temperature are studied on the overall performance of the heat pipe as well as vapor and liquid pressure drops. Screen wick, sintered powder wick and felt wick are selected. The results showed that, for the selected wick types, the sintered powder wick resulted in the largest liquid pressure drop and the felt wick resulted in the lowest thermal resistance. In addition, the influence of operating temperature on thermal resistance diminishes with increasing temperature.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A063. doi:10.1115/IMECE2018-87752.

This work aims to investigate pool boiling heat transfer enhancement by using nanostructured surfaces. Two types of nanostructured surfaces were employed, gold nanoparticle-coated surfaces and alumina nanoparticle-coated surfaces. The nanostructured surfaces were fabricated by an electrophoretic deposition technique, depositing nanoparticles in a nanofluid onto smooth copper surfaces under an electric field. N-pentane and acetone were tested as working fluids. Compared to the smooth surface, the pool boiling heat transfer coefficient has been increased by 80% for n-pentane and acetone. Possible mechanisms for the enhancement in heat transfer are qualitatively provided. The increase in active nucleation site density due to multiple micro/nanopores on nanoparticle-coated surfaces is likely the main contributor. The critical heat flux on nanostructured surfaces are approximately the same as that on the smooth surface because both smooth and modified surfaces show similar wickability for the two working fluids.

Commentary by Dr. Valentin Fuster
2018;():V08BT10A064. doi:10.1115/IMECE2018-88507.

Continuous provision of quality supply air to data center’s IT pod room is a key parameter in ensuring effective data center operation without any down time. Due to number of possible operating conditions and non-linear relations between operating parameters make the working mechanism of data center difficult to optimize energy use. At present industries are using computational fluid dynamics (CFD) to simulate thermal behaviour for all types of operating conditions. The focus of this study is to predict Supply Air Temperature using Artificial Neural Network (ANN) which can overcome limitations of CFD such as high cost, need of an expertise and large computation time.

For developing ANN, input parameters, number of neurons and hidden layers, activation function and the period of training data set were studied. A commercial CFD software package 6sigma room is used to develop a modular data center consisting of an IT pod room and an air-handling unit. CFD analysis is carried out for different outside air conditions. Historical weather data of 1 year was considered as an input for CFD analysis. The ANN model is “trained” using data generated from these CFD results. The predictions of ANN model and the results of CFD analysis for a set of example scenarios were compared to measure the agreement between the two.

The results show that the prediction of ANN model is much faster than full computational fluid dynamics simulations with good prediction accuracy. This demonstrates that ANN is an effective way for predicting the performance of an air handling unit.

Commentary by Dr. Valentin Fuster

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