ASME Conference Presenter Attendance Policy and Archival Proceedings

2018;():V08AT00A001. doi:10.1115/IMECE2018-NS8A.

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presenter attendance policy, if a paper is not presented at the Conference by an author of the paper, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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: Applications of Computational Heat Transfer

2018;():V08AT10A001. doi:10.1115/IMECE2018-86575.

Due to the rapid growth in IT demands over the past few decades, the market for data centers also increases dramatically. However, thermal management remains a big issue in the design of large-scale data centers. Although best practices are deployed to utilize perforated tiles together with the hot and cold aisles configuration to improve the thermal management, thermal hotspots are inevitable in IT racks, which causes equipment failures and signal interruptions. Thermal hotspots in air-cooled data centers are due to many factors such as insufficient cold air supply from the raised-floor plenum, air recirculation from hot aisle into cold aisle, airflow non-uniformity at the perforated tiles, etc. One of the ways to mitigate such issues is to uniformly distribute the cold air by properly controlling the airflow rate through perforated tiles. In this study, a validation study of the tile airflow and the rack airflow rate ratio of 20% is carried out using an adopted tile model. Also, several turbulence models are thoroughly investigated, and recommendations are provided for the most accurate and less time-consuming turbulence model when applying to a single rack model.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A002. doi:10.1115/IMECE2018-86682.

As research continues into the generation IV advanced nuclear reactors, exploration of liquid sodium as a coolant, or Sodium Fast Reactors (SFRs), coupled to supercritical CO2 (sCO2) Brayton cycles are currently underway. Liquid sodium offers unique and beneficial fluid properties that can achieve higher efficiencies and longer equipment lifespans compared to conventional water cooled reactors. Coupling sodium with sCO2 matches well with sodium’s temperature profile and is less reactive with sodium when compared to water used in standard Rankine cycles. To achieve commercial viability, methods for developing diffusion-bonded Hybrid Compact Heat Exchangers (H-CHX) to couple SFRs with sCO2 Brayton cycles are being developed. This paper includes thermal-hydraulic analysis of these fluids to quantify thermal and pressure stresses within the H-CHX for use in determining a structurally sound design. Two models for predicting the temperature profiles within a practical H-CHX channel design are presented. The first is a 1-D heat transfer model employing heat transfer correlations to provide both bulk fluid and wall temperatures. The second is a 3-D computational fluid dynamics model (CFD) providing a three-dimensional temperature profile, but at a significantly increased simulation time. By comparing the results of the two models for specific design conditions, significant temperature deviation is shown between the models at a short channel length of 10 cm. However, for longer channel lengths, although the 1-D model neglected the strong axial conduction on the sodium side, it generally shows good agreement with the CFD model. Thus, for any practical H-CHX designs, the findings reveal both simulation methods can be used to extrapolate the temperature gradient along the channel length for use in designing a H-CHX, as well as predicting the overall size and mass of the heat exchanger for component costing.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A003. doi:10.1115/IMECE2018-86716.

A combined Computational Fluid Dynamics (CFD) and experimental approach is presented to determine (calibrate) the external convective heat transfer coefficients (h) around a partially-filled water tank cooled in a climactic chamber. A CFD analysis that includes natural convection in both phases (water and air) was performed using a 2D-axisymmetric tank model with three prescribed average heat transfer coefficients for the top, side and bottom walls of the tank. The commercial CFD code ANSYS-Fluent™, along with User-Defined Functions (UDFs), were utilized to compute and extract temperature vs. time curves at five different thermocouple locations within the tank. The prescribed h values were then altered to match experimentally obtained temperature-time data at the same locations. The calibration was deemed successful when results from the simulations exhibited match with experimental data within ±2°C for all thermocouples. The calibrated h values were finally used in full-scale 3D simulations and compared to the experimental data to test their accuracy. Predicted 3D results were found to agree with experimental results within the error of the calibration, thereby lending credibility to the overall approach.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A004. doi:10.1115/IMECE2018-86874.

Recent advancements in medical technology have included engineering thermal ablation probes, a minimally invasive cancer treatment aimed to heat up cancerous cells. Currently, probes meant to treat hepato-cellular carcinoma (HCC), commonly known as liver cancer, are limited to tumors up to 5 cm across. Consequently, the effectiveness of ablation treatment decreases considerably for tumors beyond this range. Unlike most probes that are stationary, a novel design by Han et al. intends to extend beyond this range via a dynamic probe. We present a mathematical heat transfer model in which the spatial- and time-dependent heat source probe is represented by an ad hoc combination of traveling wave solutions. Specifically, 1D and 2D simulated results for the heat transfer of the dynamic probe are presented in this paper for selected input parameters. This preliminary mathematical model paves the way for optimizing the dynamic thermal ablation probe in future work.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A005. doi:10.1115/IMECE2018-87066.

The bay cooling of a specific new turboprop engine is investigated in this paper. The new ATP turboprop engine has additional jets with hot air stream close to the PT. This considerably increases the temperature inside the first nacelle compartment in the hot engine part around the engine combustion chamber. In order to achieve the optimal temperature conditions for engine parts inside the nacelle in the critical operating regime (triple red line), a new bay cooling system is proposed. Using the existing standard (National Advisory Committee for Aeronautics) NACA inlet at the front of the nacelle, two additional groups of ribs on rear part of front nacelle compartment and standard nacelle gaps (around exhausts), the temperature in the front part of the nacelle is decreased bellow the critical temperature for installed devices and engine parts (gear box etc.) in this compartments. Using a 3D CFD model of the first compartment of the nacelle is analyzed using the software ANSYS. The boundary conditions for this CFD simulation are obtained from ground testing of the turboprop engine.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A006. doi:10.1115/IMECE2018-87139.

A combined computational/ experimental analysis is conducted to investigate the cooldown behavior of a surrogate engine mount assembly. The engine mount in an automobile is often in the close proximity of the catalytic converter, and may heat up significantly during operation of the vehicle. When the vehicle is parked after operation, the mount cools due to heat loss by natural convection and radiation. The objective of this study is to develop a model that is capable of accurately predicting the spatio-temporal evolution of the mount temperature during this cooldown process. Carefully controlled experiments were first conducted, during which temperatures were recorded at 41 different locations. A Computational Fluid Dynamics (CFD) model that includes natural convection and radiation was next developed to simulate the same experiments. The simulations were conducted using roughly 5–6 million control volume (cells). The mesh was generated using ANSA™ and parallel computations of the governing equations were conducted using Ansys-Fluent™. The CFD results were found to agree with the measured temperatures to within a few tens of degrees. The discrepancies may be attributed to differences in initial conditions (measured versus numerical) and due to the fact that thermal contact resistances were neglected. However, the study revealed that to obtain reasonably close agreement, one must use very small time step sizes — small enough to sufficiently resolve the rapidly changing unsteady natural convection patterns — making such computations extremely time-consuming.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A007. doi:10.1115/IMECE2018-87319.

During metal cutting, it is well known that the cutting temperature has great influence on the machined surface integrity, especially on the residual stress and machining defects. At present, a lot of analytical modeling work has been done on the cutting temperature of tool, chips and workpiece machined by the side cutting edge during end milling process. To the workpiece surface machined by the bottom cutting edge, the study of temperature modeling is rarely reported. Besides, as a new kind of particulate metal matrix composites (MMCs) with improved mechanical and physical properties, the machining study of in-situ TiB2/7050Al MMCs is not many and no analytical temperature modeling of MMCs has been published up to now. Our study aims to establish an analytical cutting temperature model of workpiece machined by the bottom cutting edge in end milling in-situ TiB2/7050Al MMCs. In this model, the moving heat source method was applied. To meet the actual cutting process, the effect of heating time was also taken into account. With validation, the temperature model shows good agreement with experimental results. It was found that the heat partition ratio conducted from the shear plane heat source to the workpiece increased linearly as thermal number increased, due to the influence of increasing heat conducted into chip by the side cutting edge. The proposed cutting temperature model was of great significance for both the temperature modeling work of end milling and study of Al-MMCs.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A008. doi:10.1115/IMECE2018-88468.

The blowpipe is used to transmit hot blast air in blast furnace operation, which is continually manipulated and part of a high-temperature and high-pressure environment. In order to optimize blowpipe functionality and reliability, computational fluid dynamics (CFD) was applied to simulate the flow pattern of hot blast air, to generate details of input conditions for mechanical simulation of thermal stress, and to help identify areas of failure corresponding to high stresses and plastic strain. In this investigation, parametric studies were conducted to study the effects of thermal paper thickness, thermal paper length, and refractory thickness on the thermal and stress distributions. The results of this investigation can offer useful information for new blowpipe designs with reduced failure and better reliability.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: CMS: Applied Combustion

2018;():V08AT10A009. doi:10.1115/IMECE2018-86172.

Heat transfer measurements on a heated curved thin sheet are performed by infrared thermography. The evolution of the temperature field is recorded to calculate the heat flux by using the two-dimensional unsteady heat balance equation. The thermal conduction term is estimated by the projection relationship between the curved surface of the thin sheet and the horizontal plane. Natural convection is neglected during the estimation of this heat flux. Unlike the traditional means of heat flux measurement, this method is non-intrusive and can measure the heat flux distribution within a curved space, allowing an easier evaluation of the errors due to radiation and tangential conduction. An electrical resistance foil with known power are applied as the heating source to compare the calculated heating power with the actual recorded power, the max relative error for different heating powers is about 10 %, which verified of the feasibility of the method. Considering possible applications, three different domestic gas cookers are used to heat three different curved thin pans, and then, in each case, the heat flux of the burners is analyzed. From the heat flux distribution of the three gas cookers, some heating characteristics such as heating power, maximum and average heating flux are investigated to help optimize the designs of the gas cookers, avoiding local overheating and low uniformity of heat distribution.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A010. doi:10.1115/IMECE2018-86691.

In the steel continuous casting process, cooling water is directly injected through multiple rows of nozzles to remove heat from the slab to allow the slab to solidify in secondary cooling. Effective heat removal from the slab without causing slab cracking and deformation is desired. The present study focuses on developing a reliable numerical model which can accurately predict the impingement and heat transfer between water droplet and solid slab. The flat fan atomizer is chosen as a representative nozzle to be simulated. The spray pattern on the slab surface, as well as the impingement behaviors of water droplets, are obtained through an Eulerian-Lagrangian approach. The wall jet model coupled with modified evaporation rate depending on the droplet Weber number has been applied in the numerical model. A series of parametric studies have been performed to investigate the effects of spray direction, standoff distance, and distance between adjacent nozzles on the impingement heat transfer process. Simulation results reveal that intense cooling effects can be found in the center of the spray, where the concentration of droplets is the highest regardless of the spray direction. Double the standoff distance can reduce the heat transfer coefficient on slab surface by 10%. Finally, the distance between two adjacent nozzles should be adjusted to be smaller than the standoff distance in order to avoid the “fountain” effect induced by the collision of the two neighboring wall jets.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A011. doi:10.1115/IMECE2018-87834.

This paper represents an analytical model for predicting mineral particle redistribution of coal blending during pulverized coal (PC) combustion in a pulverized coal-fired boiler. The objective of this research is to develop a computer program to perform the mass balance of total minerals after transformation during combustion. A MATLAB code was developed for coal blending mineral redistribution from single coal mineral redistribution in modular approach based on relative Hardgrove Grindability Index (HGI) of coals. The calculations of the single coal number of ash particles before and after combustion both for excluded and included minerals from the single coal proximate analysis, Malvern analysis, Computer Controlled Scanning Electron Microscopy (CCSEM) analysis, density and composition analysis were designed in a submodule. Utilizing single coal sub-module, the calculations of coal blending number of ash particles before and after combustion both for excluded and included minerals were designed in a module of MATLAB code. The blending modeling was designed to blend up to five sub-bituminous coals. Calculations were made for typical boiler combustion conditions ranging from 1,500K to 2,500K as flame temperature. The organically-associated ash content or mineral grains of each coal smaller than 1 micrometer was not included in the calculation of redistribution modeling. Coal particle fragmentation of blended coal was considered as same as single coal and size dependent phenomena. Partial coalescence model was assumed as more likely to occur. Blended coal was assumed to follow additive rule applied to mineral mass percentage based on sizes and mineral phase regardless grinding of coals separately or after blending if the HGI difference between highest and lowest HGI of coals arranged in ascending order stands within five. The modeling was demonstrated for KPU: AVRA and AVRA: Solntsevsky with specific blending ratio 80:20 and 20:80 respectively. The model for blended coal was validated by the mass balance of minerals before and after combustion. The resulting simplified particle size distribution of mass fraction of KPU: AVRA shows good agreement with experimental results of Kentucky #9 coal because of having a larger amount of included minerals of KPU coal. The model for blended coal mineral redistribution before and after combustion will be developed for the HGI difference between highest and lowest HGI of coals arranged in ascending order becomes greater than five and validated by minerals mass balance before and after combustion. This modeling will be used to predict number of mineral particles and its sizes that is a key parameter as to predict the problems like fouling and slagging and the related reduction of boiler efficiency. The results from this study will be further carried out to investigate ash deposition rates in post-boiler heat exchangers.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A012. doi:10.1115/IMECE2018-87932.

This paper investigates the combustion performance of a commercial cooktop burner operating on natural gas and renewable biogas. Various blends of carbon dioxide and methane are used to simulate biogas and fed as fuel to the cooktop burners. Combustion operation on standard pipeline natural gas is taken as a reference for comparison with other fuel classes. In this study, different configurations of cooktop burners available in the market were investigated to establish similarities and differences. Based on the current regulations and testing standards, a protocol for testing and evaluating the cooktop burner combustion performance was generated and adopted in this research. Experimental investigation of the flame characteristics, ignition properties, cooking efficiency, and emissions (CO, NOx, UHC) were studied as a function of gas composition. The results indicate that, based on the overall performance of the cooktop burners, up to 5% CO2 can be added to pipeline natural gas without impacting operation. Different methodologies of analyzing emissions were compared with each other, which can provide insight into future emission regulations on open-air residential or light industrial burners.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A013. doi:10.1115/IMECE2018-88042.

An experimental investigation was conducted to correlate thermal characteristics with primary reference fuel (PRF) using an “isothermal” flow reactor. Objective of the investigation was to assess whether or not thermal characteristics measured in a radiant-heated flow reactor could serve as an indicator of fuel octane number. The experimental set-up consisted of a radiant furnace and a pyrex-tube test section inside. The pyrex tube was fitted with thermocouples alongside the tube wall. Four PRF compositions of iso-octane and n-heptane were considered: 0, 65, 85 and 100% of iso-octane by volume; noted as PRF0, 65, 85 and 100, respectively. The test conditions reported in the paper set the fuel-air mixture temperature to 180 °C at the inlet of the test section and the radian furnace temperature to 345 °C. The equivalence ratio was set in the range 0.93 to 2.0. For a pre-set PRF and equivalence-ratio condition, the experiments were run with fixed mixture velocities over the range 0.019 m/s to 0.400 m/s. Over the conditions tested, the thermocouples recorded two temperature oscillations along the flow reactor for each of PRF0, 65 and 85 mixtures. Both oscillation locations moved downstream when PRF number was increased and the two oscillation locations merged when PRF was set to 85. No temperature oscillations were recorded for experiments with PRF100 mixture. The results suggest that the temperature oscillation locations from the experiments using isothermal flow-reactors can be used to correlate fuel octane number.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A014. doi:10.1115/IMECE2018-88111.

Autoignition in commercial and residential gas appliances is typically a phenomenon to be avoided. The autoignition temperature for a particular fuel, defined as the minimum temperature at which spontaneous ignition will occur without an external source of energy, is often used to characterize this phenomenon. In the design of combustion systems, it is used to demarcate conditions where autoignition may occur. In an emerging class of residential and commercial heating, cooling, and power generation appliances, preheating air and fuel can provide an effective means of boosting the overall energy efficiency by recuperating residual energy in the exhaust and reinvesting it back into the thermodynamic process. In such applications, the design question to answer is: How much can the air and fuel be preheated without autoignition? The autoignition temperature, often determined experimentally and can vary as much as 100°C for methane, may not be the most useful metric in this context. This work describes the results of a recent experimental investigation into the preheat limits for autoignition of air and natural gas with the aim of recuperating as much heat as possible in a heat pump. The experimental apparatus consisted of an air-fuel mixer supplying preheated mixture to a radiant burner. The air was first heated in excess of 750°C, cool natural gas was injected into and mixed with the hot-air stream, and all while avoiding autoignition. The current capability to predict autoignition in such applications a priori was also assessed using available chemical kinetic models and numerical simulations.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A015. doi:10.1115/IMECE2018-88117.

In the steelmaking process, reheating furnaces are used to reheat steel slabs to a target rolling temperature. The bottom intermediate zone inside the reheating furnace plays a decisive role in controlling the slab temperature distribution before slabs enter the soaking zone. Efforts to maintain a uniform slab surface temperature and thus enhance product quality require a good understanding of the furnace’s operation. However, traditional physical experiments are costly and have high risks as well. In this study, a three-dimensional steady-state computational fluid dynamics (CFD) model was developed to investigate the flow field in the bottom intermediate zone of a full-scale reheating furnace. The commercial software ANSYS Fluent® was used to solve the transport equations to predict the flame length, heat transfer, and gas temperature near the slab. Total input mass flow rate, preheated air temperature, and air/fuel ratio were selected to investigate the comprehensive influence of the furnace’s performance, which can be evaluated from the flame length, flame angle, and average gas temperature near the slab. Importantly, an orthogonal experimental design was conducted to optimize the evaluation factors by considering the multi influencing factors simultaneously. The simulation results indicate that a higher mass flow rate produces a lower upwards flame angle, which can prevent the hot spot detected on the slab surface. A higher preheated air temperature leads to a higher average gas temperature in this furnace; meanwhile, the flame becomes shorter by enhancing the air-fuel ratio.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A016. doi:10.1115/IMECE2018-88390.

The cost and quality of aluminum produced by the reduction process are strongly dependent on heat treated (baked) carbon anodes. A typical aluminum smelter requires more than half a million tons of carbon anodes for producing one million ton of aluminum. The anode baking process is very energy intensive, approximately requires 2GJ of energy per ton of carbon anodes. Moreover, pollutant emissions such as NOx and soot formation are of major concern in the aluminum anode baking furnace. The current study aims at developing an accurate numerical platform for predicting the combustion and emissions characteristics of an anode baking furnace. The Brookes and Moss model, and the extended Zeldovich mechanism are employed to estimate soot and NOx concentration, respectively. Considering a fire group of three burner bridges, one after the other in the fire direction, combustion and emissions features of these three firing sections are interrelated in terms of oxidizer’s concentration and temperature. In the present study, considering this interconnection, the effect of diluted oxygen concentration at elevated oxidizer’s temperature (∼1200°C), which are the key features of the moderate or intense low oxygen dilution (MILD) combustion are analyzed. It is observed that by circulating some of the exhaust gases through the ABF crossovers, oxygen dilution occurs which results in higher fuel efficiency, lower pollutant emissions, and more homogeneous flow and temperature fields.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A017. doi:10.1115/IMECE2018-88688.

Liquid water or steam injection is a technique that has been used for years to reduce NOx primarily by reducing the flame temperature which reduces thermal NOx. There is also evidence to suggest it reduces NOx by modifying the flame chemistry. While it is well proven for reducing NOx, there are some potential disadvantages including reduced thermal efficiency, flame instability, and increased emissions of other pollutants such as CO and unburned hydrocarbons. Water/steam injection has been used in a wide range of applications, particularly in boilers and gas turbines. Much less information is available on using this technique in process heaters which have some key differences compared to most combustors which include a highly varying fuel composition and natural draft to provide the combustion air. This paper will consider how water or steam may be injected into process burners including some predictive methods for determining NOx.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: CMS: Combustion Power Systems

2018;():V08AT10A018. doi:10.1115/IMECE2018-86410.

In order to investigate the performance and emissions behavior of a high compression ratio Compression Ignition (CI) engine operating in Partially Premixed Charge Compression Ignition (PPCI) mode, a series of experiments were conducted using a single cylinder naturally aspirated engine with a high-pressure rail fuel injection system. This included a moderately advanced direct injection strategy to attempt PPCI combustion under low load conditions by varying the injection timing between 25° and 35° Before Top Dead Center (BTDC) in steps of 2.5°. Furthermore, during experimentation the fuel injection pressure, engine speed, and engine torque (through variance of the fuel injection quantity) were kept constant. In-cylinder pressure, emissions, and performance parameters were measured and analyzed using a zero-dimensional heat release model. Compared to the baseline conventional 12.5° BTDC injection, in-cylinder pressure and temperature was higher at advanced timings for all load conditions considered. Additionally, NOx, PM, CO, and THC were higher than conventional results at the 0.5 N-m load condition. While PM emissions were lower, and CO and THC emissions were comparable to conventional injection results at the 1.5 N-m load condition between 25° and 30° BTDC, NOx emissions were relatively high. Hence, there was limited success in beating the NOx-PM tradeoff. In addition, since Start of Combustion (SOC) occurred BTDC, the resulting higher peak combustion pressures restricted the operating condition to lower loads to ensure engine safety. As a result, further investigation including Exhaust Gas Recirculation (EGR) and/or variance in fuel Cetane Number (CN) is required to achieve PPCI in a high compression ratio CI engine.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A019. doi:10.1115/IMECE2018-87911.

Emissions compliance during engine start-up conditions is a major obstacle for current automotive manufacturers across global markets. The challenges to meeting emissions targets are both due to increasingly stringent regulations and the difficulty in developing control strategies for a high degree-of-freedom and highly non-linear system. Online extremum-seeking (ES) methods offer a promising alternative to traditional optimization based on design-of-experiment based automotive calibration. With extremum-seeking methods, results from all prior experiments are used to intelligently and efficiently generate the next iteration of the control parameter(s). In this work, the applicability of the online extremum-seeking method is explored to optimize five performance variables (injection timing for two injection events, the injection fuel mass divided between the first and second injection events, air-fuel equivalence ratio and exhaust cam timing) to minimize brake specific fuel consumption while imposing different constraints on NOx emissions. The experiments were conducted using a production turbocharged four-cylinder gasoline engine with an advanced fuel injection system. The results show the utility of the ES strategy to quickly identify optimal control parameter combinations and the emissions and engine performance improvements during the calibration process. The results also demonstrate the dramatic benefit of the ES calibration strategy in terms of test time required.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A020. doi:10.1115/IMECE2018-88569.

Operational characteristics of an air breathing Rotating Detonation Combustor (RDC) fueled by natural gas-hydrogen blends are discussed in this paper. Experiments were performed on a 152 mm diameter uncooled RDC with a combustor to inlet area ratio of 0.2 at elevated inlet temperature and combustor pressure while varying the fuel split between natural gas and hydrogen over a range of equivalence ratios. Experimental data from short-duration (∼6sec) tests are presented with an emphasis on identifying detonability limits and exploring detonation stability with the addition of natural gas. Although the nominal combustor used in this experiment was not specifically designed for natural gas-air mixtures, significant advances in understanding conditions necessary for sustaining a stable, continuous detonation wave in a natural gas-hydrogen blended fuel were achieved. Data from the experimental study suggests that at elevated combustor pressures (2–3bar), only a small amount of natural gas added to the hydrogen is needed to alter the detonation wave operational mode. Additional observations indicate that an increase in air inlet temperature (up to 204°C) at atmospheric conditions significantly affects RDC performance by increasing deflagration losses through an increase in the number of combustion (detonation/Deflagration) regions present in the combustor. At higher backpressure levels the RDC exhibited the ability to achieve stable detonation with increasing concentrations of natural gas (with natural gas / hydrogen-air blend). However, losses tend to increase at intermediate air preheat levels (∼120°C). It was observed that combustor pressure had a first order influence on RDC stability in the presence of natural gas. Combining the results from this limited experimental study with our theoretical understanding of detonation wave fundamentals provides a pathway for developing an advanced combustor capable of replacing conventional constant pressure combustors typical of most power generation processes with one that produces a pressure gain.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A021. doi:10.1115/IMECE2018-88659.

Swiss Roll Combustor of 1 W capacity for micro gas turbine engine is operated with premixed hydrogen air mixture at ultra-lean equivalence ratio. The reaction zone under consideration has volume of 60 mm3. The reactant passage and product passage are coiled around the reaction zone facilitating the recovery of heat loss, by preheating the reactants. The reactants are entered through an increasing cross-sectional area passage from 0.6mm × 5mm inlet to 1.5mm × 5mm outlet, thereby reducing the velocity levels in the reactant passage, facilitating stable combustor operation. The combustor performance parameters, temperature levels, pattern factor and emissions are measured is operated at ultra-lean equivalence ratio of 0.12 to lean equivalence ratio of 0.43, for premixed hydrogen air combustion. The results are compared at similar (not same) equivalence ratios for constant area reactant passage. The visual inspection shows stable flame front in the combustion zone for variable area passage and extended flame front in the constant area passage combustor. However, the combustor performance deteriorates drastically above equivalence ratio of 0.43, leading to hot spots generation on walls.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: CMS: Sprays and Emissions

2018;():V08AT10A022. doi:10.1115/IMECE2018-86372.

Using the integral formulation of the conservation equations as in our previous work, we can determine the drop size and its distributions in liquid sprays in co- and cross flow of air. The energy balance dictates that the initial kinetic energy of the gas and injected liquid be distributed into the final surface tension energy, kinetic energy of the gas and droplets, and viscous dissipation incurred. The mass and energy balance for the spray flows render to an expression that relates the drop size to all of the relevant parameters, including the gas- and liquid-phase properties and velocities. The results agree well with experimental data and correlations for the drop size. The solution also provides for drop size-velocity cross-correlation, leading to drop size distributions based on the gas-phase velocity distributions. These aspects can be used in estimating the drop size for practical applications, in synthesizing the data as a function of relevant variables, and also in integration into CFD for atomization algorithm.

Topics: Jets , Cross-flow
Commentary by Dr. Valentin Fuster
2018;():V08AT10A023. doi:10.1115/IMECE2018-87353.

Air traffic increases and growing concerns about the environment raised interests in the study of ways to reduce pollutants emissions. One reason for combustor and downstream components damage is non-uniform distribution of fuel due to dirtiness or injector damage, increasing NOx and CO emissions due to higher and lower temperature zones. Hot spots also reduce components live. Fuel injection angle change with injector life and combustion behaviors also change with this parameter. Present work report CFD simulations of combustion in the combustion chamber of a CMF56-3 gas turbine engine, to evaluate influence of injection angle on pollutant emissions and combustion temperature. Concerning engine power setup, International Civil Aviation Organization Landing and Take-Off cycle (100%, 85%, 30% and 7% engine power) were used. From the studied injection angles, lowest temperature is for 58° and that angle also produced the lowest NOx for power setups lower than 85%. 70° produced higher NOx emissions. For CO, 58° had higher emissions and 70° lower. CO2 reduces for lower injection angles, opposite to UHC. Lower angles had better results, having 3% reduction in NOx with a reduction of 10° of the injection angle. Temperature also reduces 4% with a 10° injection angle reduction.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A024. doi:10.1115/IMECE2018-87940.

Cold-flow spray researchers have an array of diagnostic tools to extract meaningful information on spray characteristics. The efficacy of many of these tools, however, depends heavily on calibration, alignment, and human operation. This can lead to large discrepancies in data values for seemingly identical setups between workers. The application of experimental data to numerical models is thereby hindered due to inconsistencies in results caused by experimental error. Previously, an attempt was made to produce a “standard spray” through the use of a research simplex atomizer (RSA). As manufacturing processes and diagnostic tools have improved, the research simplex atomizer is being revisited.

Here, a new research simplex atomizer has been investigated. Fundamental datasets captured from detailed test conditions are presented to provide benchmark data with the intention of other workers testing the reproducibility of the results. Preliminary findings between laboratories show good agreement in droplet size measurements.

Further, emphasis is placed on the sensitivity of laser diagnostics used and the effect their operation can incur. To satisfy the requirements of a measurement standard, it is paramount that all workers adhere to similar diagnostic configurations and detail their operating parameters.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A025. doi:10.1115/IMECE2018-88618.

Recent studies have shown that addition of nano-sized particles to liquid fuels could significantly enhance major combustion characteristics such as burning rate and ignition delay. Colloidal suspensions are known to have enhanced optical properties and thermal conductivity compared to neat liquids; however, in the case of colloidal fuels, the main mechanism responsible for such enhanced properties is not well understood. To better understand these phenomena, colloidal suspensions of jet fuel and different types of carbon-based nanomaterials (carbon nanoparticles, multi-walled carbon nanotubes, and graphene nanoplatelets) prepared at different particle loadings were experimentally tested for their thermal conductivities. Colloidal suspensions of nanotubes showed higher conductivity compared to that of graphene and nanoparticle. This could justify higher burning rate of these fuels. Furthermore, and to differentiate between the effects of thermal conduction and radiation, droplet evaporations tests were carried out on colloidal suspensions of carbon nanoparticle under forced convection and in the absence of any radiation source. It was found that the presence of nanoparticle in jet fuel initially increases evaporation rate. However, a reduction in evaporation rate was observed at higher concentration as a result of particles agglomeration.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Fundamentals of Boiling and Condensation I

2018;():V08AT10A026. doi:10.1115/IMECE2018-86965.

Explosive boiling occurs when a liquid film contacts with the wall at extremely high temperature, which is detrimental to continuous heat transfer process. In this paper, five kinds of nanostructured surfaces with equal distance between neighboring nano-concaves and flat surface are set up to study the explosive boiling of liquid argon on copper surface. For all the five cases with concave nanostructured surface, the ratio of concave nanostructured surface area to flat surface area is kept as a constant. The temporal and spatial distributions of temperature, atomic motion and number density are recorded to study the effects of different nanostructured surface designs on explosive boiling. From the perspective of reducing explosive boiling, the most favorable nanostructured surface is determined.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A027. doi:10.1115/IMECE2018-87741.

The bubble departure radius is a very important parameter for bubble dynamics during boiling heat transfer. In this study, experiments of highly subcooled nucleate pool boiling of FC-72 were conducted on two different sized silicon chips (chip S 2 × 2 and chip S 1 × 1) in short-term microgravity and normal gravity conditions by utilizing the drop tower in Beijing. During the experimental study, bubble dynamics were captured by a high-speed digital camera. From the images at the bubble departure moment, the bubble departure radius was obtained. Although the traditional force balance model is modified through the addition of a Marangoni force, it still cannot precisely predict the bubble departure radius in the microgravity condition, especially in the low heat flux regime. By using the advancing contact angle measured from the bubble departure moment instead of the static contact angle, and considering the bubble asymmetry due to the small bubble coalescence and the surrounding liquid motion, a revised force balance model is proposed. It can predict the experimental bubble departure radius within a deviation of ±3.8% for both silicon chips in the whole heat flux range.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A028. doi:10.1115/IMECE2018-87890.

Wettability gradient in radial direction and evaporation rate gradient can cause droplet motion on a solid surface. Here a theoretical model is proposed. Besides, an equation of droplet velocity is derived on a solid surface. We consider the wettability and evaporation rate gradients are mainly caused by the chemical composition and surface roughness, only along the radial direction. Surface tension at the liquid-vapor interface is constant as it is assumed that the temperature does not change during the whole process. Thus, Marangoni effect induced by the liquid-vapor surface tension gradient is neglected. Besides, as droplet size is set as less than the capillary length (Display Formulal=γ/ρg), the gravity effect is ignored as well. The velocity at the droplet center on a gradient surface along the radial direction is half of that along the x-direction. With the simulation of water droplet, the center velocity decreases with time and the droplet radius increases at the beginning part and then decreases.

Topics: Drops , Evaporation
Commentary by Dr. Valentin Fuster
2018;():V08AT10A029. doi:10.1115/IMECE2018-87991.

Recent studies of droplet spreading on nanostructured surfaces have demonstrated that the fluid motion and wicking effects impact the morphology of the liquid on the nanostructured surface and the thermophysics of the vaporization process. In the investigation summarized here, models of the spreading mechanism, and mechanisms of heat transport to the interface of a spreading droplet are used to explore the interaction of these mechanisms during the droplet vaporization process on nanostructured hydrophilic surfaces. Exploration of the trends in the model predictions and their comparison with experimental data suggests that the wickability of such surfaces causes an impinging droplet to quickly spread to form a thin liquid film with a somewhat curved interface. This liquid film has a mean thickness in the range of 10–100 microns near the contact line at the outer perimeter of the droplet footprint. If the surface is highly superheated, bubble nucleation and a nucleate boiling mechanism may augment conduction across the liquid film to facilitate evaporation. However, physical arguments and data from droplet evaporation experiments suggest that nucleation in the interstitial spaces of the nanoporous layer may be suppressed as a result of the extremely small size of those spaces. The role of these different mechanisms and the stages of the vaporization process for impinging droplets is discussed in detail. This exploration indicates that the wickability effect on droplet spreading strongly enhances the droplet evaporation heat transfer.

Topics: Drops , Evaporation
Commentary by Dr. Valentin Fuster
2018;():V08AT10A030. doi:10.1115/IMECE2018-87998.

Effective heat transfer techniques benefit the development of nuclear and fossil fuel powered steam generators, high power electronic devices, and industrial refrigeration systems. Boiling dissipates large heat fluxes while keeping a low and a constant surface temperature. However, studies of the fluid behavior surrounding the bubble and the heat transfer near the contact-line are scare due to difficulties of flow visualization, chaotic conditions, and small length scales. The preset study shows the simulation of bubble growth over a heated surface from conception to departure. The computation of mass transfer with interfacial temperature gradients leads to proper bubble growth rates. Models to include the interface sharpness uncover the dynamic and thermal interaction between the interface and the fluid. Results indicate that the nucleation of a bubble (in water at 1 atm with 6.2 K wall superheat) has an influence region of 2Db (where Db is the departure bubble diameter). In addition, results reveal a thin thermal film near the interface that increases the heat transfer at the contact-line region. Numerical bubble growth rates compare well with experimental data on single bubble nucleation.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Fundamentals of Boiling and Condensation II

2018;():V08AT10A031. doi:10.1115/IMECE2018-86228.

This paper presents a theoretical model of the moisture condensation of ambient air flowing over a cold heat sink. When ambient air flows over a cold heat sink, three-dimensional conservation equations of momentum, energy, and mass should be used to predict the heat and mass transfer of ambient air to determine the condensation rate. In this paper, a simplified model is developed to predict moisture condensation from ambient air flowing over a cold heat sink under the boundary condition of a constant baseplate temperature. The model can be used to predict effects of inlet velocity, relative humidity, incoming flow temperature, and fin geometry. The model demonstrates that the increasing inlet velocity and relative humidity could help to enhance the condensation rate. The model can also be used to reveal the variation of condensation rate over cold fins in terms of fin geometry parameters. The significance of this model is that it can be readily applied to predict mass and heat transfer behavior in phase change processes incurred from ambient air flowing over complex geometries of cold surfaces.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A032. doi:10.1115/IMECE2018-88088.

When vapor bubbles are subjected to suddenly reduced pressure or immediate subcooling, it may rapidly condense, rupture, and generate cavitation corrosions. This phenomenon often occurs behind the blade of a rapidly rotating propeller or on any surface vibrating in liquid with sufficient amplitude and acceleration. In this article, we reported cavitation and its corrosive collapse occurring in capillary tubes, called pulsating heat pipes. Visualization images of cut and opened tubes show that internal copper surface was seriously etched after a certain period of operation. Sub-millimeter etching pits are observed on the tube internal surface. Copper particles in size of a few hundred micrometers are also found in the reclaimed operating fluid. Starting from this finding, the temperature effect of performance is analyzed to understand the cavitation occurrence and collapse. Pulsating heat pipe requires a certain temperature difference between the evaporator and condenser sections, typically > 10°C, to generate continuous two-phase oscillating movements. However, during the transient startup period, this temperature difference could reach as high as 50°C. Large saturation temperature difference, associated with highly turbulent two-phase flow, drives the saturated vapor bubbles from the hot evaporation region to the subcooled environment in less than 100ms. During the rapid condensation, the accelerated shrinking vapor bubbles create interface instability, followed by forming a strong impingement jet to etch the solid pipe wall. The collapse of cavitation is associated with the generation of acoustically tinkling signals that are often heard during most of the operating pulsating heat pipe.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Fundamentals of Liquid/Solid Phase Change (Icing/Deicing, Solidification)

2018;():V08AT10A033. doi:10.1115/IMECE2018-88078.

Previous efforts to model the effectiveness of heat input and extraction from a thermal storage unit have generally been based on the definition of a constant conductance of heat from the working fluid to the phase change storage material. In order to capture the effects of changing thermal resistance between the working fluid and melt front location, this paper presents a method using a resistor network analogy to account for thermal conductance as a function of melt fraction. This expression for thermal conductance is then implemented in an existing numerical framework. Results are validated by comparing calculations for a single unit cell using a quasi-steady Stefan problem approach, a finite difference scheme, and more general form solutions from literature. The variable approach is then compared with an average value for overall thermal conductivity, U, to characterize the performance of a thermal energy storage unit consisting of a series of these unit cells. Overall effectiveness in the thermal energy storage device is found to be within 0.6% agreement when comparing these methods, though local percent deviation can be as high as 113%. Depending on the needed accuracy and use case for such a numerical framework, suggestions are provided on whether an average value for U is sufficient for characterizing such a thermal energy storage device. Discussion is also provided on the flexibility of the computation schemes described by testing the sensitivity of the results via changes in dimension-less input parameters.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Fundamentals of Multiscale Modeling

2018;():V08AT10A034. doi:10.1115/IMECE2018-86947.

A multiscale modeling that integrates electronic scale ab initio quantum mechanical calculation, atomic scale molecular dynamics simulation, and continuum scale two-temperature model description of the femtosecond laser processing of nickel film at different thicknesses is carried out in this paper. The electron thermophysical parameters (heat capacity, thermal conductivity, and electron-phonon coupling factor) are calculated from first principles modeling, which are further substituted into molecular dynamics and two-temperature model coupled energy equations of electrons and phonons. The melting thresholds for nickel films of different thicknesses are determined from multiscale simulation. Excellent agreement between results from simulation and experiment is achieved, which demonstrates the validity of modeled multiscale framework and its promising potential to predict more complicate cases of femtosecond laser material processing. When it comes to process nickel film via femtosecond laser, the quantitatively calculated maximum thermal diffusion length provides helpful information on choosing the film thickness.

Topics: Nickel , Lasers , Melting , Heating
Commentary by Dr. Valentin Fuster
2018;():V08AT10A035. doi:10.1115/IMECE2018-87009.

A multi-scale method combining the finite volume model (FVM) considering Darcy-Brinkman formulation with grand conical Monte Carlo (GCMC) is built to study the process of CO2 adsorption in 13X zeolite particle bed. The saturation adsorption capacities and adsorption heat in FVM method are calculated by Langmuir model and linear fitting formula, respectively. The GCMC method is used to obtain the parameters of Langmuir model and linear fitting formula. The multi-scale method overcomes the shortcomings of the saturation adsorption capacities restricted by level of experimentation or empirical formula. The relationship between adsorption heat and adsorption amount is also obtained. The value of adsorption heat is no longer treated as the constant value or obtained from the empirical formula. The effects of velocity, particle size, porosity and thermal conductivity of particle on CO2 adsorption in13X zeolite particle bed are investigated. The results show that the saturation adsorption time decreases with increased velocity, porosity and thermal conductivity of particle, while increases with increased particle size. The peak of temperature difference between the solid and gas phase increases with increased inlet velocity, porosity and particle size, while decreases with thermal conductivity of particle. The temperature difference trends uniformity and the peak of temperature difference moves towards to the outlet of adsorption bed with adsorption time processing. The adsorption bed with a higher inlet velocity, porosity and thermal conductivity of particle, and smaller particle size is recommended to improve the adsorption bed performance.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Fundamentals of Single Phase Convection

2018;():V08AT10A036. doi:10.1115/IMECE2018-87152.

The unconventional gas reservoir has attracted more and more attention as the shale gas greatly expands worldwide energy supply, for which the gaseous fluid transport in complex porous domain is one important process as the shale gas is extracted. The apparent permeability of porous media is one important parameter in the related numerical model, however, its determination is still challenging. The apparent permeability varies with gas pressure, the porous media properties and gas–solid interactions based on the previous studies. For the slip gas flows, the velocity slip at the gas-solid interface in confined porous space is one significant difference compared with that on macro scale, which is caused by the gas rarefaction effect. In this work, a pore-scale LB model is established to simulate the gaseous fluid flow in the confined porous media. An effective curved boundary treatment is adopted for the porous surface and the validation test shows that the present model has superiority in capturing the slip phenomenon on the curved surfaces. Based on the numerical predictions, the different influential factors on the permeability of confined porous media are thoroughly studied, for which the gas rarefaction effect is considered.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A037. doi:10.1115/IMECE2018-88662.

In advanced heat transfer courses, a technique exists for reducing a partial differential equation, where the dependent variable is a function of two independent variables, to an ordinary differential equation where that same dependent variable becomes a function of only one. The key to this technique is finding out what the functional form of the similarity variable is to make such a transformation. The difficulty is that the form of the similarity variable is not intuitive, and many heat transfer textbooks do not reveal how this variable is found in classical problems such as viscous and thermal boundary layer theory. It turns out that one way to find this variable is by utilizing the integral technique. By employing the integral technique to boundary layer theory, it will be shown that when the approximate functional relationship for the dependent variable (temperature, velocity, etc) can be represented by an nth order polynomial, the similarity variable can be found very simply. This is seen to be a good tool especially in heat transfer education, but may have applications in research as well. The approach described here is a variation of a well-known technique used for isothermal momentum boundary layer consideration.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Gas Turbine Heat Transfer and Cooling

2018;():V08AT10A038. doi:10.1115/IMECE2018-86501.

With recent advancements in the field of additive manufacturing, the design domain for development of complicated cooling configurations has significantly expanded. The motivation of the present study is to develop high-performance impingement cooling designs catered towards application’s requiring high rates of heat removal, e.g. gas turbine blade leading edge and double-wall cooling, air-cooled electronic devices etc. Jet impingement is a popular cooling technique which results in high convective heat rates. In the present study, jet impingement is combined with strategic roughening of the target surface, such that a combined effect of impingement-based and curved-surface area based enhancement in heat transfer coefficient could be achieved. Traditionally, for surface roughening, cylindrical and cubic elements are used. We have demonstrated, through our steady-state experiments, a novel “concentric” shaped roughness element design which has resulted in about 20–60% higher effectiveness compared to smooth target jet impingement, for jet-to-target spacing of one jet diameter. The cubic shaped roughened target yielded about 20% to 40% enhancement in effectiveness, and the cylindrical shaped roughened target yielded 10% to 30% enhancement. Through the plenum pressure measurements, it was found that the addition of the micro-roughness elements does not result in a discernable increment in pressure losses, compared to the standard impingement on the smooth target surface. Hence, the demonstrated configuration with the highest heat transfer coefficient also resulted in the highest thermal hydraulic performance.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A039. doi:10.1115/IMECE2018-86887.

Modeling the heat transfer characteristics of the highly turbulent flow in gas turbine film cooling is important for better engineering solutions to the film cooling system design. URANS, LES, DES and modified DES models capability in simulating film cooling with a density ratio of 2.0 and blowing ratio of 1.0 are studied in this work. Detailed comparisons of simulation results with experimental data regarding the near-field and far-fields are made. For near field predictions, DES gives decent prediction with a 21.4 % deviation of centerline effectiveness, while LES and URANS have deviation of 33.6% and 51.2% compared to the experimental data. Despite good predictions for near field, DES under predicts the spanwise spreading of counter rotating vortex pair and temperature field, therefore it over predicts the centerline effectiveness in the far field. To compensate for this shortcoming of DES, the eddy viscosity in the spanwise direction is increased to enhance spanwise-diffusion of the cooling jets. The modified DES prediction of overall centerline effectiveness deviates 12.4% from experimental data, while LES, unmodified DES and URANS predictions deviate 10.8%, 31.9% and 46.9%. The modified DES model has adequate predictions of vortices evolutions which URANS modeling lacks and consumes significant less computational time than LES. It can be said that the modified DES model results in satisfactory film cooling modeling with a moderate computational cost and time.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A040. doi:10.1115/IMECE2018-87169.

To meet the demand of thermal protection in aero engines, this paper presents a novel compact cross-flow air-air heat exchanger based on the Cooled Cooling Air (CCA) technology. This novel air-air heat exchanger consisting of 4 × 10 serpentine tubes (4.4 mm I.D., 5.0 mm O.D., stainless steel type 321) was designed using the classic Logarithmic Mean Temperature Difference (LMTD) method. Experimental verification has been done to research the hydraulic and heat transfer performance of the heat exchanger. The results show that the 1.48 kg serpentine tube air-air heat exchanger can cool the high pressure compressor bleeding air by 200 K at the mass flow rate of 0.05 kg/s using bypass duct cold air. Comparisons between calculated and experimental data have been done and good agreement between them was obtained in both flow resistance and heat transfer characteristics. Thus, the LMTD method could be well adopted in designing compact air-air heat exchanger for aero-engines. A new empirical heat transfer coefficient correlation for the tube outside is obtained using Wilson plot method, and it can be helpful designing heat exchanger with similar structures. This research is a great proof of CCA’s feasibility in terms of theory and practice.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A041. doi:10.1115/IMECE2018-87876.

Turbine airfoils are subject to strong secondary flows that produce total pressure loss and high surface heat transfer in the airfoil passage. The secondary flows arise from the high overall flow turning acting on the incoming boundary layer, as well as the generation of a horseshoe vortex at the leading edge of the airfoil. Prediction of the effects of secondary flows on endwall heat transfer using steady Reynolds-averaged Navier-Stokes (RANS) approaches has so far been somewhat unsatisfactory, but it is unclear whether this is due to unsteadiness of the secondary flow, modeling assumptions (such as the Boussinesq approximation and Reynolds analogy), strongly non-equilibrium boundary layer behavior in the highly skewed endwall flow, or some combination of all. To address some of these questions, and to determine the efficacy of higher-fidelity computational approaches to predict endwall heat transfer, a low pressure turbine cascade was modeled using a wall-modeled Large Eddy Simulation (LES) approach. The result was compared to a steady Reynolds-stress modeling (RSM) approach, and to experimental data. Results indicate that the effect of the unsteadiness of the pressure side leg of the horseshoe vortex results in a broad distribution of heat transfer in the front of the passage, and high heat transfer on the aft suction side corner, which is not predicted by steady RANS. However, the time-mean heat transfer is still not well predicted due to slight differences in the secondary flow pattern. Turbulence quantities in the blade passage agree fairly well to prior measurements and highlight the effect of the strong passage curvature on the endwall boundary layer, but the LES approach here overpredicts turbulence in the secondary flow at the cascade outlet due to a thick airfoil suction side boundary layer. Overall, more work remains to identify the specific model deficiencies in RSM or wall-modeled LES approaches.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: General

2018;():V08AT10A042. doi:10.1115/IMECE2018-87032.

This paper performs a numerical study of forced convection heat transfer in a square enclosure with four identical stationary cylinders with single inlet and outlet ports. The ratio of the diameter of the cylinder to the length of the enclosure is kept constant at 0.1 with a fixed spacing between the cylinders. The enclosure walls are adiabatic while the cylinders are maintained at a constant temperature. The governing equations are solved for laminar, steady state and incompressible flow for different fluids namely air, water, and ethylene glycol. The study aims to determine the effect of varying Reynolds number (5 ≤ Re ≤ 100) and fluid properties (0.7 ≤ Pr < 200) on heat transfer rate and flow characteristics. The results of the study are presented in terms of streamlines, isotherm contours, and surface-averaged Nusselt numbers. The 2-D modeling and simulation have been conducted using ANSYS 16.0.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Heat Transfer Analysis in Waste Heat Recovery Systems

2018;():V08AT10A043. doi:10.1115/IMECE2018-86532.

This present work is to investigate the effects of chrome plating in reciprocating air compressors that result in reduction of power consumption. Reciprocating air compressors are the most commonly used compressors for domestic and industrial purposes to give required air output in terms of free air delivery, delivery temperature and maximum working pressure. This study also develops a better understanding on the effect of honing in the cylinder which reduces the surface roughness in the cylinder liner and results in greater air output. Cylinders are made of graded cast iron. The cylinder liner was honed to a thickness of about 0.26 mm and hard chrome plated to the same thickness. The honing improves the volumetric efficiency and hard chrome plating reduces the power consumption. The adequacy of this model can be verified using thermal image analysis, which includes the various temperature distribution plots around the compressor components. Further delivery temperature, actual displacement and free air delivery pressure are the parameters that conclude the deviation in actual and experimental values. Power consumption and efficiency owe for the major expenditures and maintenance for Reciprocating air compressors. This paper suggests the need of hard chrome plating to a compressor cylinder that resulted in annual power savings of about 25%. The increase in volumetric efficiency was about 20–30% from the actual conditions.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A044. doi:10.1115/IMECE2018-86844.

A thermodynamic analysis and optimization of a newly-conceived combined power cycle were conducted in this paper for the purpose of improving overall thermal efficiency of power cycles by attempting to minimize thermodynamic irreversibilities and waste heat as a consequence of the Second Law. The power cycle concept comprises a topping advanced recompression supercritical carbon dioxide (sCO2) Brayton cycle and a bottoming transcritical carbon dioxide (tCO2) Rankine cycle. The bottoming cycle configurations included a simple tCO2 Rankine cycle and a split tCO2 Rankine cycle. The topping sCO2 recompression Brayton cycle used a combustion chamber as a heat source, and waste heat from a topping cycle was recovered by the tCO2 Rankine cycle due to an added high efficiency recuperator for generating electricity. The combined cycle configurations were thermodynamically modeled and optimized using an Engineering Equation Solver (EES) software. Simple bottoming tCO2 Rankine cycle cannot fully recover the waste heat due to the high exhaust temperature from the top cycle, and therefore an advance split tCO2 Rankine cycle was employed in order to recover most of the waste heat. Results show that the highest thermal efficiency was obtained with recompression sCO2 Brayton cycle – split flow tCO2 Rankine cycle. Also, the results show that the combined CO2 cycles is a promising technology compared to conventional cycles.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A045. doi:10.1115/IMECE2018-86896.

Solar power is a clean source of energy, i.e. it does not generate carbon dioxide or other air pollutants. In 2017, solar power produced only 0.6 percent of the energy used in the United States, according to the Energy Information Administration. Consequently, more solar energy should be implemented, such as in solar water heaters.

This research took place in Riverside, Southern California where there is an abundance of solar energy. In house uniquely designed and assembled solar tubes were used in designing a mini solar water heating system. The mini solar water heating system was set to operate under either natural or forced convection. The results of running the system under forced convection then under natural convection conditions are reported and discussed in the article. In addition, comparison of using two different solar water storage systems are reported: the first was water; the second storage medium was a combination of water and gravel. Since water heaters are extensively used for residential purposes, this research mimicked the inefficiencies in residential use and is compared with ideal operating conditions. The performance of the different cases studied is evaluated.

Topics: Solar energy , Water , Heating
Commentary by Dr. Valentin Fuster
2018;():V08AT10A046. doi:10.1115/IMECE2018-87565.

Strict regulations are set up in various parts of the world with respect to vehicular emissions by their respective government bodies forcing automakers to design fuel-efficient vehicles. Fuel economy and carbon emission are the main factors affecting these regulations. In this competitive industry to make fuel efficient vehicles and reduce Green House Gas (GHG) emissions in internal combustions has led to various developments. Exhaust Heat Recovery System (EHRS) plays a vital role in improving powertrain efficiency. In this system, heat rejected by the engine is reused to heat the vehicle fluids faster (like engine coolant, engine oil, etc) also reducing harmful gases emitted. In internal combustion engines, generally only 25% of the fuel energy is converted into useful power output and approximately 40% of it is lost in exhaust heat. Certain studies show that by using the EHRS, the power output can be increased to 40% and the heat loss can be reduced to as much as 25%. The purpose of this study is to make use of this lost energy and convert most of it into useful energy. The thermodynamic properties and fuel consumed during the warmup period were analyzed to measure the improvement in the engine efficiency. The design was implemented on a Briggs and Stratton Junior 206cc engine. This system includes the use of heat exchangers. The main goal of this study is to develop a robust EHRS design and compare it with the baseline engine configuration to see the thermal and fuel economy improvement.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Heat Transfer in Electronic Equipment

2018;():V08AT10A047. doi:10.1115/IMECE2018-86876.

Magnetic gears are non-contact means of torque transmission which utilize the interaction of magnetic fields in place of the meshing teeth of mechanical gears to achieve a change in rotational speed and scale up/down the torque. A subscale magnetic gearbox featured a radial flux focusing arrangement consisting of three main rotors in the active region called inner, cage and outer rotors. In this arrangement, ferromagnetic cage rotor poles modulate flux between the inner rotor and outer rotor permanent magnets to achieve the gear reduction. Replacing the solid metal bars with laminated stacks for the cage modulating pieces as well as retaining pieces of the inner and outer rotor magnets reduces eddy current losses in the axial direction, a main source of losses in magnetic gears, while preserving the magnetic flux directed in the radial direction. Both of these features are key for overall system performance.

Given the potential of demagnetization of the permanent magnets and damage to the components at high temperature, multiphysics thermal analysis is conducted on a subscale flux focusing magnetic gearbox to predict temperature distribution and thermal stresses. A conjugate heat transfer (CHT) method is used in a 3D academic code, FLUENT, to predict heat flux and the coupled non-adiabatic external flow field and temperature field on the inner, cage and outer rotor with a Finite Volume Method (FVM). Thermo-elastic behavior of the laminated components are assigned through anisotropic materialistic characters in a finite element method (FEM), where the thermal and centrifugal stresses are calculated.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A048. doi:10.1115/IMECE2018-87479.

Thermal management in data centers has become more and more important due to the rapid growth in power density in modern data centers. Computational fluid dynamics (CFD) is proved to be a very useful tool in data center design and analysis. However, the previous papers always utilize k-epsilon model, and has never studied on the effect of other turbulence models. This paper will demonstrate the difference between various turbulence models in terms of accuracy and computational time. The data center investigated in this paper has a floor area of 900 ft2 and comprises one rack, one CRAC unit, and several perforated tiles. This paper mainly investigates the effect of various turbulence models on CFD simulation in data center. The Turbulence model is believed to be a possible factor to improve the CFD results. The most suitable turbulence model will be identified based on a balance in both accuracy and computing resource requirements. Four turbulence models were investigated in this paper. The present investigation suggested that A&S 1-equation model yield the best accuracy and required the least computational time. Hence, 1-eqaution model should be the preferable turbulence model for CFD simulation in data center in the future.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A049. doi:10.1115/IMECE2018-87481.

This study presents the convective heat transfer coefficient of 0.05 wt.% diamond nanofluids containing functionalized nanodiamond dispersed in a base fluid deionized (DI) water flowing in a conduction cold plate under turbulent flow conditions, experimentally. The conduction cold plate was heated via six cartridge heaters with a constant heat transfer rate. The primary experimental study has been implemented to investigate the thermal conductivity of diamond nanofluids which showed a higher effective thermal conductivity than that of the base fluid. In addition, nanofluid was flowed in a closed system with heating at the heat exchanger and cooling via a cooling tank to keep the inlet temperature constant to explore the convection heat transfer properties of diamond nanofluids. Results indicate that the convective heat transfer coefficient and Nusselt number of diamond nanofluid are higher than that of the DI water in a same flow rate, and these properties increased with increase in Reynolds number.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A050. doi:10.1115/IMECE2018-87989.

A two-wavelength thermoreflectance (2WTR) imaging technique is developed to conduct steady-state temperature measurement of miniature electronic devices, such as micro-scale gold resistors. Compared with traditional single wavelength thermoreflectance (TR) imaging requiring comparison of TR signals from a target under heated and unheated conditions, 2WTR method obtains temperature information from heated target under operation directly. Therefore, 2WTR is not affected by movement of a heated target due to thermal expansion. Note that thermal expansion of targets between heated and unheated conditions is a main constraint of current TR imaging of miniature targets. In addition to the low sensitivity to the target movement, the new 2WTR can provide even higher temperature resolution than single wavelength TR by appropriately selecting the adopted two wavelength to have different signs of TR coefficients. With this new TR imaging technique, we successfully measure temperature distribution of a microscale gold resistor under steady-state operation, which are challenging to be obtained by traditional single wavelength TR method.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Heat Transfer in HVAC Systems and Air Quality and Comfort in Confined Spaces

2018;():V08AT10A051. doi:10.1115/IMECE2018-87507.

The accumulated heat and humidity inside occupied refuge alternatives (RAs) can impose risk of heat stress to the occupants. The accumulated heat could be from the metabolic and environmental sources. For hot mines, the high ambient temperature makes it more difficult to dissipate heat accumulated inside the RA. A cooling system is then needed to reduce the interior heat and humidity. Two types of cooling systems were tested out for their cooling capacity. One cooling system is a portable, battery-powered, air conditioning system and the other is a portable cryogenic air supply. During the testing, the mine air temperature surrounding the RA was elevated to and maintained at 85°F to simulate hot mine environment. The tests demonstrated that both cooling systems were able to control the air temperature inside the RA even though they did not last the entire duration of a 96-hour test. This paper provides an overview of the test methodology and findings as well as guidance on improving the performance of both cooling systems, including: optimizing the cooling cycle for the battery-powered AC system and increasing the flow rate and tank storage capacity for the cryogenic system. The information in this publication is useful for RA manufacturers and mines to develop the cooling systems that will enable providing the life sustaining environment in mines with elevated temperatures.

Topics: Cooling systems
Commentary by Dr. Valentin Fuster
2018;():V08AT10A052. doi:10.1115/IMECE2018-87632.

It is well recognized in the literature that thermal sensation and comfort are dependent on both core and skin temperatures. In particular, some regions of the human skin, such as the forehead, have a higher density of thermal receptors, giving a higher sensitivity to the skin temperature. Some studies suggest that the forehead skin temperature and its rate ofchange alone could potentially be a good indicator of one’s overall thermal comfort. To validate this claim, an idea for a smart sensor which would be able to read the occupants’ forehead temperature and other environmental parameters in a proximal way is here considered. Moreover, with the aim of exploiting the system not only in lab or test facility environments but, considering the 4.0 revolution, also in the building automation context, a non-invasive solution has been searched so as the occupants are not disturbed while the measurement is performed. Therefore, in this study, a new cheap and smart mechatronic sensor device for a non-invasive measurement of the occupants’ thermal comfort is proposed. The main components consist of a central unit, i.e. microprocessor, a small infrared sensor for thermal imaging, i.e a Lepton infrared camera by FLIR, as well as other sensors for measuring distance, humidity and temperature. The setup was imagined as the sensor being placed on the top of each desk, so it is not easily obstructed by a laptop or a similar object that can be found on top of the working surface. After the conceptual hardware definition and software development, an accurate experimental calibration has been performed exploiting an ad-hoc developed set-up based on a hot plate with an emissivity factor similar to the one of the human skin and with adjustable temperature. Finally, a first design for embedding the whole smart mechatronic system in a unique box has been developed and built.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A053. doi:10.1115/IMECE2018-88660.

This paper details the design of an experiment to indirectly measure the thermal conductivity, k, of prototype samples consisting of various mixtures of aerogel and concrete for the purpose of better insulative value and lighter weight. A “hot box” apparatus was designed based on ASTM C1363. It was constructed primarily out of 2” rigid extruded polystyrene insulation and designed to force the majority of the heat generated in the enclosure through the concrete composite test samples. Several samples with well documented k values were tested to calibrate the apparatus. After calibration, three prototype aerogel composite samples were tested. The results showed that the higher the ratio of aerogel to concrete yielded a lower thermal conductivity as would be expected. The sample with no aerogel yielded a k-value of 0.0936 Btu/hrft°F, whereas a sample with 1.5 parts of aerogel-to-concrete mix yielded a 0.0488 Btu/hrftoF k-value. The average uncertainty is ± 28.8%. This is a first step in determining the feasibility of this unique composite concrete mix into new and existing construction.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Heat Transfer in Multiphase Systems

2018;():V08AT10A054. doi:10.1115/IMECE2018-86137.

In this study, an experimental investigation was carried out to explore the heat transfer characteristics of the smooth water wall tube of an ultra-supercritical circulating fluidized bed (CFB) boiler. The ranges of the test pressure, mass flux, and heat flux were 23–32 MPa, 550–1200 kg·m−2·s−1, and 200–560 kW·m−2, respectively. The material of the tube used in the test was 12 Gr1MoVg. The diameter and wall thickness were 30 and 5.5 mm, respectively. The length of the test section was 2 m. The effects of the pressure, mass flux, heat flux, buoyancy, and flow acceleration on the heat transfer characteristics were analyzed. The formulas of the heat transfer coefficient were fitted, and the existing classical formula was used to evaluate the experimental data. The mechanism of heat transfer enhancement and deterioration of the tube were also investigated. Results showed that at the area of supercritical pressure, the wall temperature gradually increased with the increase of enthalpy in the pseudo-enthalpy region and sharply increased with the increase of enthalpy in the low-enthalpy region (enthalpy < 1200 kJ kg−1) and high-enthalpy region (enthalpy > 2400 kJ kg−1). This phenomenon indicated that heat transfer enhancement occurs near a pseudo-critical point. The increase of heat flux resulted in rapid heat transfer deterioration. Thereafter, the wall temperature rose immediately. The deterioration was delayed with the increase of mass flux and pressure. The effect of buoyancy and flow acceleration on the heat transfer concentrated on the pseudo-critical temperature of the fluid. Among the five selected heat transfer correlations, the Jackson and Bishop correlations agreed well with the experimental data.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A055. doi:10.1115/IMECE2018-86586.

A general correlation is presented for predicting maximum heat transfer coefficient for surfaces submerged in gas-fluidized beds. It has been verified with data for horizontal and vertical cylinders and spheres in beds of a wide variety of particles and gases. The gases include air, cryogens, methane, CO2, ammonia, and R-12. The range of parameters includes: heat transfer surface diameter 0.05 to 220 mm, particle diameter 31 to 15000 μm, pressure 0.026 to 0.95 MPa, and temperature 13 to 1028 °C. The 363 data points from 53 sources are predicted with a mean absolute deviation of 16.2 %. Several other correlations were also compared to the same data but had much larger deviations.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A056. doi:10.1115/IMECE2018-86589.

Heat transfer to two-component gas-liquid mixtures is needed in many industries but there is lack of a well-verified predictive method. A correlation is presented for heat transfer during flow of gas-liquid non-boiling mixtures in horizontal tubes. It has been verified with a wide range of data that includes: tube diameters 4.3 to 57 mm, pressures from 1 to 4.1 bar, temperatures from 12 to 62 °C, gravity < 0.1 % to 100 % earth gravity, liquid Reynolds number from 9 to 1.2E5, and ratio of gas and liquid velocities from 0.24 to 9298. The 946 data points from 18 sources are predicted with mean absolute deviation of 19.2 %. The same data were compared to several other correlations; they had much larger deviations.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A057. doi:10.1115/IMECE2018-86590.

A general correlation is presented for heat transfer during flow of gas-liquid mixtures flowing in vertical channels prior to dryout. It has been verified with a wide range of data that include upwards and downwards flow in heated and cooled tubes, annuli, and rectangular channels. The data are from 19 studies and include 14 gas-liquid mixtures with a very wide range of properties. The parameters include pressure 1 to 6.9 bars, temperature 16 to 115 oC, liquid Reynolds number from 2 to 127231, superficial gas and liquid velocities up to 87 and 13 m/s respectively, and ratio of superficial gas and liquid velocities 0.03 to 1630. The 1022 data points are predicted by the new correlation with mean absolute deviation (MAD) of 18.1 %. Several other correlations were also compared to the same data and had much larger deviations.

Topics: Heat transfer
Commentary by Dr. Valentin Fuster
2018;():V08AT10A058. doi:10.1115/IMECE2018-87382.

Direct contact condensation occurs when a vapor comes in contact with the liquid of the same fluid and is accompanied by very high heat transfer coefficients compared to the conventional heat exchanging processes. Many researchers have investigated the direct contact condensation of steam jets in a pool of subcooled water. In the last decade, the potential of flowing liquid as an enhanced heat transfer medium in comparison with the stationary pool of liquid was explored by various researchers. Also, in some configurations of staged combustion cycle based rocket engine, the oxygen-rich gas is injected into flowing liquid oxygen to improve the heat transfer characteristics. Hence, there is a need to investigate the direct contact condensation of vapor jets in a cross flow of liquid. A two-fluid particle based multiphase formulation with thermal phase change model has been implemented in the present investigation to capture the direct contact condensation phenomena. The data obtained from numerical simulations are validated with the experimental results of Clerx et al., [1]. Further, studies on plume shapes, interfacial area and pressure amplitudes are reported.

Commentary by Dr. Valentin Fuster
2018;():V08AT10A059. doi:10.1115/IMECE2018-88490.

Oscillating flows and multiphase heat transfer processes frequently occur in many engineering and scientific applications and systems, as is the case in enhanced geothermal energy, CO2 sequestration and storage, and in evaporation in soil, to name a few. Nevertheless, modeling of such flows is a rather challenging task due to the complex interfacial dynamics among different phases and solid porous structures. Over the decades, several types of Lattice Boltzmann (LB) models for multiphase flows have been developed under different physical pictures, for example the color-gradient model, Single-Relaxation-Time (SRT) pseudopotential model, and the HSD model. In this study, a pseudopotential Multiple-Relaxation-Time (MRT) LBM simulation will be utilized to simulate incompressible oscillating flow and condensation in 2D porous media. Initially, the model will be used to optimize the porous structure in order to have the maximum condensation rate of water vapor. Subsequently, the effects of contacting angle, wettability, oscillating frequency and phase angle to the heat flux, the temperature field of porous media, and the condensation rate will be discussed. Moreover, a multiscale approach will be considered in order to couple the heat transfer in macroscale applications. It is expected that such an approach will provide a different perspective regarding the engineering applications involved with oscillating flow and multiphase heat transfer processes.

Commentary by Dr. Valentin Fuster

Heat Transfer and Thermal Engineering: Heat Transfer in Passive Thermal Control Systems

2018;():V08AT10A060. doi:10.1115/IMECE2018-88634.

Electrocaloric (EC) cooling technology, which has reversible temperature change of a polarizable material in an adiabatic condition with the application and/or removal of an electric field, exhibits some great advantages for efficient solid-state refrigeration. However, many challenges still exist in EC cooling technology. One of the main challenges is how to control the heat transfer direction. Some of the reported device types require movement of EC material by step motor or fluid media by pump back and forth between heat source and heat sink for controlling heat transfer direction. The other device designs utilize thermal diodes by adjusting their thermal conductivity to control heat transfer direction. Here we report a solid-state electrocaloric refrigeration using unimorph beam structure which has temperature change due to EC effect and bending behavior due to converse piezoelectric effect. The new device design can eliminate problems of fluid medium loss, friction, high thermal conductivity ratio requirement and external system assistance, etc., existed in the previously reported EC cooling device types. An analytical model is also derived by considering multi-physical phenomenon. The model shows that the temperature change is a combinatorial result from the couplings of thermal, electric and mechanical field in the device.

Topics: Refrigeration
Commentary by Dr. Valentin Fuster

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