bluuebunny/crossref_metadata_2025 huggingface dataset:
Comprehensive Numerical Modeling of Thermoelectric Devices Applied to Automotive Exhaust Gas Waste-Heat Recovery
Authors: Reddy B. V. K. , Barry Matthew , Li John , Chyu Minking K.
Published: December 2013

This study investigates using numerical methods the performance of thermoelectric devices (TEDs) integrated with heat exchangers and applied to automotive exhaust gas waste-heat recovery. Air as an exhaust gas and water as a cooling fluid are used. The effects of temperature-dependent properties of materials (TE elements, ceramic plates, connectors, insulation materials and fluids) and interface electrical and thermal contact resistances on TED’s performance are included in the analysis. Additionally, the fluid heat exchangers and the insulation materials are modeled using a porous media approach. The response of hot and cold fluid inlet temperatures (Thi, Tci) and flow rates, number of modules N, permeability of heat exchangers and TE materials type on TED’s hydro-thermoelectric characteristics is studied. An increase in either Thi or a decrease in Tci is resulted in an enhancement in TED’s performance. The addition of modules is shown a significant effect on heat input Qh and power output P0 predictions; however, a minimal impact on efficiency η is displayed with N. For instance, at Thi = 873.15 K and Tci = 353.15 K with clathrate n-Ba8Ga16Ge30 and p-PbTe material’s combination, compared to single module case, TED with four modules showed 3.77- and 3.7-fold increase in P0 and Qh, respectively. In the studied 1–4 modules range, the cold fluid flow rate and the permeability of heat exchangers are exhibited a negligible effect on TED’s P0 and η, whereas the hot fluid flow rate is shown an appreciable change in η values. Further, when Thi is less than 500 K, TED with bismuth-tellurides showed a higher performance when compared to the clathrates and lead-tellurides materials combination.
Effect of Condenser Temperature on Pulsating Heat Pipe Performance
Authors: Hansen Nick , VerSteeg John , Michna Gregory J.
Published: December 2013

Pulsating heat pipes (PHPs) excel at transferring heat efficiently over a small area. As electrical components continue to miniaturize, heat flux is increasingly important in thermal management. In this work, the effect of condenser temperature in a PHP was explored. Significantly reduced thermal resistance in the PHP was achievable by increasing the condenser temperature. It was found that for a given heater input, the evaporator temperatures with a 30°C condenser temperature were lower than with a 20°C condenser temperature. It is hypothesized that this is the result of more favorable fluid properties (viscosity and vapor pressure) at those temperatures. It is therefore possible, in some cases, to reduce the temperature of the device being cooled by placing the condenser in a warmer environment.
Natural Convection of Heat Transfer Fluid (Therminol VP-1) in Square Cavity Heated From Below
Authors: Paul Titan C. , Morshed A. K. M. M. , Fox Elise B. , Visser Ann E. , Bridges Nicholas J. , Khan Jamil A.
Published: December 2013

Heat transfer fluid (HTF) plays an important role in the efficiency and cost effectiveness of solar thermal collector. From several choices, Therminol VP-1 (eutectic mixture of diphenyl oxide and biphenyl) are successfully used as heat transfer fluid in the collector field of parabolic trough plants. This paper experimentally analyzes the buoyancy driven heat transfer performance of Therminol VP-1 in a square enclosure with uniformed heating from below and for a Rayleigh number up to 1.11×108. Thermophysical properties such as density, viscosity, and thermal conductivity of Therminol VP-1 were also measured experimentally. The results show that the density, viscosity, and thermal conductivity decrease with temperature within the measured temperature range 10–60°C. The obtained convective heat transfer coefficient was lower than the De-Ionized (DI) water, whereas the dimensionless Nusselt number was observed higher than DI water, which is because of the low thermal conductivity (approximately 25% of DI water) of Therminol VP-1.
Compact Model Based Microfluidic Controller for Energy Efficient Thermal Management Using Pin-Fin Enhanced Micro Gap
Authors: Han Xuefei , Joshi Yogendra
Published: December 2013

Over-cooling of electronic devices and systems results in excess energy consumption, which can be reduced by closely linking cooling requirements with actual power dissipation. A thermal model-based flow rate controller for single phase liquid cooled three-dimensional (3D) stacked chips, using pin-fin enhanced micro gap was studied in this paper. A thermal compact model of a two-layer pin fin enhanced micro gap was developed, which ran 105 times faster than using full-field computational fluid dynamics/heat transfer (CFD/HT) method, with reasonable accuracy and spatial details. This was used in conjunction with a flow rate control strategy to provide the needed amount of liquid to cool the heat sources to the desired temperature range. An example case study shows that the estimated energy savings in pump power is about 27% compared with pumping fluid at a constant flow rate.
Probing the Mysteries of Spider Silk’s Uncharacteristically High Thermal Diffusivity
Authors: Munro Troy , Xing Changhu , Ban Heng , Copeland Cameron , Lewis Randolph
Published: December 2013

Spider silks exhibit excellent strength, stiffness, and toughness simultaneously, a feat unachievable in most synthetic, structural materials. It has recently been reported that the thermal conductivity of dragline silk is comparable to copper, which is uncharacteristically high for a biomaterial. In order to develop a fundamental understanding of the high thermal properties of spider silk, further research must be made to explore how the structure and organization of spider silk proteins affects heat transfer characteristics. Synthetically produced silks created from spider silk proteins obtained from transgenic sources can be used to determine these protein structure effects by varying protein content and process treatments. This initial study determined the thermal properties of synthetic spider silk created from transgenic goat’s milk proteins using the transient electrothermal method (TET). Results show that the thermal properties of the synthetic silk are lower than the natural spider silk but vary based on the process treatment, and that the annealing of the gold film coated on the fiber has no effect on the measured thermal properties. These results provide a framework for further research on the protein content effect and its role in thermal properties.
Metamaterial Window Glass for Adaptable Energy Efficiency
Authors: Heltzel Alex , Mann Tyler , Howell John R.
Published: December 2013

A computational analysis of a metamaterial (MTM) window design is presented for the purpose of increasing the energy efficiency of buildings in seasonal or cold climates. Commercial low-emissivity windows use nanometer-scale Ag films to reflect infrared energy, while retaining most transmission of optical wavelengths for functionality. An opportunity exists to further increase efficiency through a variable emissivity implementation of Ag thin-film structures. 3-D finite-difference time-domain simulations predict nonlinear absorption of near-infrared energy, providing the means to capture a substantial portion of solar energy during cold periods. The effect of various configuration parameters is quantified, with prediction of the net sustainability advantage. MTM window glass technology can be realized as a modification to current, commercial low-emissivity windows through the application of nanomanufactured films, creating the opportunity for both new and after-market sustainable construction.
Numerical Simulation of an Industrial Fluid Catalytic Cracking Regenerator
Authors: Tang Guangwu , Silaen Armin , Wu Bin , Zhou Chenn Q. , Agnello-Dean Dwight , Wilson Joseph , Meng Qingjun , Khanna Samir
Published: December 2013

Fluid catalytic cracking (FCC) is one of the most important conversion processes in petroleum refineries, and FCC regenerator is a key part of an FCC unit to recover the solid catalyst activity by burning off the deposited coke on the catalyst surface. In modern FCC units, regenerator is a cylindrical vessel. Carrier gas transports the solid catalyst from the stripper and feeds the catalyst into the regenerator through catalyst distributors. The catalyst is fluidized by the air that is injected into the regenerator through air rings in the bottom part of the cylindrical vessel. A three-dimensional multi-phase, multi-species reacting flow computational fluid dynamics (CFD) model was established to simulate the flow inside an FCC regenerator. The two phases involved in the flow are gas phase and solid phase. The Euler-Euler approach, where the two phases are considered to be continuous and fully inter-penetrating, is employed. The model includes gas-solid momentum exchange, gas-solid heat exchange, gas-solid mass exchange, and chemical reactions. Chemical reactions incorporated into the model simulate the combustion of coke which is present on the catalyst surface. The simulation results show a good agreement with plant data.
Nanofluid Pendant Droplet Evaporation
Authors: Gerken William J. , Oehlschlaeger Matthew A.
Published: December 2013

Nanofluids, stable colloidal suspensions of nanoparticles in a base fluid, have potential applications in the heat transfer, combustion and propulsion, manufacturing, and medical fields. Experiments were conducted to determine the evaporation rate of room temperature, millimeter-sized pendant droplets of ethanol laden with varying (0–3%) weight percentages of 40–60 nm aluminum nanoparticles (nAl). High-resolution droplet images were collected as a function of time for the determination of D-square law evaporation rates. Results show an asymptotic decrease in droplet evaporation rate with increasing nAl loading. The evaporation rate decreases by approximately 15% at around 1% to 3% nAl loading relative to the evaporation rate of pure ethanol, a reduction greater than can be explained by reduction in the vapor pressure of an ideal nanofluid mixture by Raoult’s law. It is hypothesized that the reduction in evaporation rate could be due to two phenomena: 1) the reduction in the ethanol volume fraction available for evaporation due to an interfacial layer on the immersed nanoparticle surface and 2) the aggregation of nanoparticles within the droplet and at the droplet surface, reducing the liquid diffusion rate to the surface and the liquid volume fraction at the surface available for evaporation.
The Effect of Ballistic Electron Transport on Copper-Niobium Thermal Interface Conductance
Authors: Cheaito Ramez , Duda John C. , Beechem Thomas E. , Ihlefeld Jon F. , Hattar Khalid , Piekos Edward S. , Misra Amit , Baldwin Jon K. , Hopkins Patrick E.
Published: December 2013

The thermal conductivities of 1μm copper-niobium multilayer films of different period thicknesses are measured by time–domain thermoreflectance at room temperature. The values for thermal conductivity are then used to calculate the thermal conductance between Cu/Nb interfaces using a series resistors model. Results show that Cu/Nb interface conductance increases with the decrease in period thickness reaching a value as high as 20 GWm−2K−1 for a 1×1 Cu/Nb multilayer. At shorter period thicknesses, ballistic electron transport dominates the thermal transport across this interface resulting in high interface conductance. The results are well described by a model that accounts for both ballistic and diffusive transport of electrons. This model assumes that an electron on one side of a metal-metal multilayer may not scatter at the interface but rather move ballistically on to the adjacent material and scatter in the adjacent material.
Experimental Study of a Closed-Loop Thermosyphon Operating With Slurries of a Microencapsulated Phase-Change Material
Authors: Lamoureux Alexandre , Baliga B. Rabi
Published: December 2013

An experimental investigation of steady, laminar, fluid flow and heat transfer in a vertical closed-loop thermosyphon operating with slurries of a microencapsulated phase-change material (MCPCM) suspended in distilled water is presented. The MCPCM particles consisted of a solid-liquid phase-change material (PCM) encapsulated in a thin polymer resin shell. Their effective diameter was in the range 0.5 to 12.5 micrometers, and had a mean value of 2.5 micrometers. The melting and freezing characteristics and the latent heat of fusion of the PCM were determined using a differential scanning calorimeter. The effective density of the MCPCM was measured, and the effective thermal conductivity of the slurries was determined using a published correlation. In the range of parameters considered, it was determined that the slurries exhibit non-Newtonian behavior. The closed-loop thermosyphon consisted of two vertical straight pipes, joined together by two vertical semi-circular 180-degree bends made of the same pipe. An essentially constant heat flux was imposed on a portion of one of the vertical pipes. The wall temperature of a portion of the other vertical pipe was maintained at a constant value. The outer surfaces of the entire thermosyphon were very well insulated. Calibrated thermocouples were used to measure the outer-wall-surface temperature at numerous points over the heated portion and the bulk temperature of the slurry at four different locations. A special procedure was formulated, benchmarked, and used to deduce the mass flow rate of the slurries in the thermosyphon. The investigation was conducted with slurries of MCPCM mass concentration 0% (pure distilled water), 7.471%, 9.997%, 12.49%, 14.95%, and 17.5%. The results are presented and discussed.
A Critical Review on the Determination of Convective Heat Transfer Coefficient During Condensation in Smooth and Enhanced Tubes
Authors: Dalkiliç Ahmet Selim , Celen Ali , Awad Mohamed M. , Wongwises Somchai
Published: December 2013

Heat exchangers using in-tube condensation have great significance in the refrigeration, automotive and process industries. Effective heat exchangers have been rapidly developed due to the demand for more compact systems, higher energy efficiency, lower material costs and other economic incentives. Enhanced surfaces, displaced enhancement devices, swirl-flow devices and surface tension devices improve the heat transfer coefficients in these heat exchangers. This study is a critical review on the determination of the condensation heat transfer coefficient of pure refrigerants flowing in vertical and horizontal tubes. The authors’ previous publications on this issue, including the experimental, theoretical and numerical analyses are summarized here. The lengths of the vertical and horizontal test sections varied between 0.5 m and 4 m countercurrent flow double-tube heat exchangers with refrigerant flowing in the inner tube and cooling water flowing in the annulus. The measured data are compared to theoretical and numerical predictions based on the solution of the artificial intelligence methods and CFD analyses for the condensation process in the smooth and enhanced tubes. The theoretical solutions are related to the design of double tube heat exchangers in refrigeration, air conditioning and heat pump applications. Detailed information on the in-tube condensation studies of heat transfer coefficient in the literature is given. A genetic algorithm (GA), various artificial neural network models (ANN) such as multilayer perceptron (MLP), radial basis networks (RBFN), generalized regression neural network (GRNN), and adaptive neuro-fuzzy inference system (ANFIS), and various optimization techniques such as unconstrained nonlinear minimization algorithm-Nelder-Mead method (NM), non-linear least squares error method (NLS), and Ansys CFD program are used in the numerical solutions. It is shown that the convective heat transfer coefficient of laminar and turbulent condensing film flows can be predicted by means of theoretical and numerical analyses reasonably well if there is a sufficient amount of reliable experimental data. Regression analysis gave convincing correlations, and the most suitable coefficients of the proposed correlations are depicted as compatible with the large number of experimental data by means of the computational numerical methods.
A Critical Review on the Determination of Pressure Drop During Condensation in Smooth and Enhanced Tubes
Authors: Dalkiliç Ahmet Selim , Celen Ali , Awad Mohamed M. , Wongwises Somchai
Published: December 2013

Heat exchangers using in-tube condensation have great significance in the refrigeration, automotive and process industries. Effective heat exchangers have been rapidly developed due to the demand for more compact systems, higher energy efficiency, lower material costs and other economic incentives. Enhanced surfaces, displaced enhancement devices, swirl-flow devices and surface tension devices improve the heat transfer coefficients in these heat exchangers. This study is a critical review on the determination of the condensation heat transfer coefficient of pure refrigerants flowing in vertical and horizontal tubes. The authors’ previous publications on this issue, including the experimental, theoretical and numerical analyses are summarized here. The lengths of the vertical and horizontal test sections varied between 0.5 m and 4 m countercurrent flow double-tube heat exchangers with refrigerant flowing in the inner tube and cooling water flowing in the annulus. The measured data are compared to theoretical and numerical predictions based on the solution of the artificial intelligence methods and CFD analyses for the condensation process in the smooth and enhanced tubes. The theoretical solutions are related to the design of double tube heat exchangers in refrigeration, air conditioning and heat pump applications. Detailed information on the in-tube condensation studies of heat transfer coefficient in the literature is given. A genetic algorithm (GA), various artificial neural network models (ANN) such as multilayer perceptron (MLP), radial basis networks (RBFN), generalized regression neural network (GRNN), and adaptive neuro-fuzzy inference system (ANFIS), and various optimization techniques such as unconstrained nonlinear minimization algorithm-Nelder-Mead method (NM), non-linear least squares error method (NLS), and Ansys CFD program are used in the numerical solutions. It is shown that the convective heat transfer coefficient of laminar and turbulent condensing film flows can be predicted by means of theoretical and numerical analyses reasonably well if there is a sufficient amount of reliable experimental data. Regression analysis gave convincing correlations, and the most suitable coefficients of the proposed correlations are depicted as compatible with the large number of experimental data by means of the computational numerical methods.
Scaling of Nusselt Number for Digitized Heat Transfer at All Axial Distances
Authors: Zhang Peter , Mohseni Kamran
Published: December 2013

The heat generation rates of modern electronic systems have increased to a point where conventional forms of thermal management are no longer sufficient. In this paper, Digitized Heat Transfer (DHT) is examined as one of the proposed solutions for high heat flux thermal management. Nusselt number is used to quantify the heat transfer capabilities of the flow while Re, Pr, x/H, and droplet aspect ratio are identified as the relevant nondimensional parameters that influence the shape and magnitude of Nu throughout a heated channel. With the intention of providing a single curve to represent the heat transfer in any digitized flow, a scaling constant, f2, for Nu at axial distances greater than one circulation length is found. This scaling is combined with a previously identified scaling constant for the first circulation length using an inverse tangent weighting function. The two different scalings are applied to the Nu curve for heat transfer to a digitized flow and the result is a single curve that can approximately predict Nu at any axial position if the flow parameters are known. From the fitting functions identified, it is found that extremely long droplets will exhibit higher steady state Nu that is at least three times greater than the Nu value of the equivalent continuous flow.
Experimental Study of Water Vapor Absorption Into Lithium Bromide (LiBr) Solution Constrained by Superhydrophobic Porous Membranes
Authors: Isfahani Rasool Nasr , Moghaddam Saeed
Published: December 2013

An experimental study on absorption characteristics of water vapor into a thin lithium-bromide (LiBr) solution flow is presented. The LiBr solution flow is constrained between a superhydrophobic vapor-permeable wall and a solid surface that removes the heat of absorption. As opposed to conventional falling film absorbers, in this configuration, the solution film thickness and velocity can be controlled independently to enhance the absorption rate. The effects of water vapor pressure and cooling surface temperature on the absorption rate are studied. An absorption rate of approximately 0.005 kg/m2s was measured at a LiBr solution channel thickness and flow velocity of 160 μm and 4 mm/s, respectively. The absorption rate increased linearly with the water vapor driving potential at the tested solution channel thickness. The high absorption rate and the inherently compact form of the proposed absorber promise compact small-scale waste heat or solar-thermal driven cooling systems.
3D Thermal Resistance Network Method for the Design of Highly Integrated Packages
Authors: Boteler Lauren , Smith Andrew
Published: December 2013

There is a continual market pull in the electronics industry for smaller products with more capabilities, creating a growing need for 3D stacked electronics. This work presents a generic, easy to use approach, to estimate the thermal performance in a generic NxMxP stack using 3D heterogeneous integrated packaging (3D HIP) approach as a baseline. 3D HIP is a microfabrication packaging technology that helps facilitate chip stacking. While this work is demonstrated utilizing the 3D HIP geometry, the technique is easily adapted to most packaging approaches, both 3D and planar. A low order model has been developed with a combination numerical-analytical approach and a 3D resistor network to estimate the chip temperatures. The resistor network solves quickly in MATLAB, enabling fast, iterative thermal analyses and design through the parametric studies of the chip dimensions, number of chips, chip layout, material types, cooling solutions, etc. The model has been validated against full 3D numerical models in COMSOL for a number of conditions including variation of chip dimensions, substrate thickness, number of chips, and material types. The temperature difference between the resistor network model and the COMSOL model was always within 5%. This method can be utilized to identify potential cooling approaches based on the power dissipation per chip and the packaging approach and also to determine the maximum temperatures of each chip. The code achieves significant time saving as compared to full FEA models while providing similar results.
Effective Thermal Conductivity of Lithium Ion Battery Electrodes Employing Fully Resolved Simulations for Use in Volume Averaged Models
Authors: Vadakkepatt Ajay , Trembacki Bradley L. , Mathur Sanjay R. , Murthy Jayathi Y.
Published: December 2013

Simulations of lithium ion batteries on a cell level are usually performed with volume averaging methods that employ effective transport properties. Bruggeman’s model, which is widely used to determine these effective properties, is solely based on the volume fraction of these porous electrodes. However, other factors like the topology and microstructure of electrodes also play a crucial role in determining effective properties. In this paper, a general derivation of the effective thermal conductivity of multiphase materials, which can be correlated with these factors, is derived using the volume averaging technique. For demonstration, three-dimensional microstructures of various porous materials are reconstructed from scanned images. These images are used to generate fully-resolved finite volume meshes representing the various constituents. The resulting mesh is then employed for numerical analysis of thermal transport, results from which are used for correlating the effective thermal conductivity with various parameters describing the microstructure. It is shown that commonly used power law exponents in the Bruggeman model for effective thermal conductivity must be recalibrated to fit the effective thermal conductivity computed from these detailed simulations.
Critical Aspects of Efficient Waste Heat Recovery From Low-Temperature Wet Industrial Exhaust
Authors: Skop Helen , Pezzuto Jim , Oleynikov-White Valeriy G.
Published: December 2013

About 60% of unrecovered waste heat in US is low temperature waste heat (<230°C). In case of exhaust flows that contain water vapor over 20% by mass (baking, drying, biofuel production) the latent heat of the “wet component” plays a key role in the process of energy recovery and makes such a recovery economically feasible. Low temperature sources of waste heat have a few specific features, so majority of available techniques developed for high temperature waste heat recovery cannot be successfully applied to justify the cost-effective benefits. The paper discusses the basic requirements for appropriate equipment development along with possible options for heat and water recovery.
Numerical Simulation of Solidification of Colloidal Suspensions Inside a Differentially-Heated Cavity
Authors: El Hasadi Yousef M. F. , Khodadadi J. M.
Published: December 2013

Development of the solid-liquid interface, distribution of the particle concentration field, as well as the development of thermo-solutal convection during solidification of colloidal suspensions in a differentially-heated cavity is investigated. The numerical model is based on the one-fluid-mixture approach combined with the single-domain enthalpy-porosity model for phase change. The linear dependence of the liquidus concentration of the nanoparticles was assumed. A colloidal suspension consisting of water and copper, and alumina nanoparticles were considered. In the current investigation, the nanoparticle size selected was 2 nm. The suspension was solidified unidirectionally inside a square differentially-heated cavity that was cooled from the left side. It was found that the solid-liquid interface changed its morphology from a planar shape to a dendritic one as the solidification process proceeds in time, due to the constitutional supercooling that resulted from the increased concentration of particles at the solid-liquid interface rejected from the crystalline phase. Initially, the flow consisted of two vortices rotating in opposite directions. However, at later times only one counter clockwise rotating cell survived. Changing the material of the particle to alumina results in crystallized phase with a higher concentration of particles if it is compared to that of the solid phase resulted from freezing the copper-water colloidal suspension. Decreasing the segregation coefficient destabilize the solid-liquid interface, and increase the intensity of the convection cell with respect to that of the case of no particle rejection. At slow freezing rates, the crystal phase resulted consisted of lower particle content if it is compared to that resulted from higher freezing rate.
Vortex Heat Transfer Enhancement in Narrow Channel by Oval Dimples Arrangement
Authors: Isaev Sergey , Chudnovsky Yaroslav , Leontiev Alexander , Kornev Nikolai , Hassel Egon
Published: December 2013

There are many passive techniques of heat transfer enhancement ranging from surface (2D) to volumetric (3D) vortex generators, however only a few of them are capable to provide a reliable increase in a heat transfer rate overrunning the increase in pressure losses. One of such successful techniques is the profiling of a heat transfer surface with the regulated arrangement of 3D cavities (dimples). The authors explored that the deviation of the dimple geometry from the spherical shape affects the flow structure and thermal and hydraulic performance of the dimpled wall. Detailed numerical simulation of fluid flow and heat transfer has been performed in the narrow channel with the 2.5 × 0.33 cross section normalized by the equivalent diameter of the dimple footprint at the constant Reynolds number Re = 10,000 and the constant heat flux through the dimpled wall. The oval dimple geometry was varied by changing the aspect ratio of the dimple footprint from 1 to 4.5 keeping the same footprint area. In the course of the numerical study, the optimal geometry, the arrangement and the orientation of oval dimples on the heated surface to achieve the superior thermal and hydraulic performance over the spherical cavities are established. Numerical results of local and integral heat transfer characteristics enhanced with the visual representation of the generated vortices clearly illustrated the flow restructuring and an increase in the thermal and hydraulic performance.
Exploration of Hands-On Discovery Pedagogy in Heat Transfer
Authors: Diller Thomas E. , Williams Chris
Published: December 2013

Recent research in the development of the “Thermal and Transport Concept Inventory” test (TTCI) has shown that, despite completing several related courses, students have significant misconceptions of heat transfer principles such as the differences between heat, energy and temperature. This lack of conceptual understanding limits students’ problem-solving abilities (and thus their transition to expertise) and their ability to transfer knowledge to other courses and contexts. This research demonstrates how this problem can be addressed by integrating hands-on workshops into a traditional heat transfer lecture course. The workshops are designed to actively engage students in exploration and discovery using authentic problems. Using heat flux sensors allows students to physically observe abstract phenomena that cannot be easily observed.
Numerical Study and Optimization of GaN Thin-Film Growth by MOCVD Method
Authors: Fang H. S. , Pan Y. Y. , Wei J. A. , Liu S. , Zhang Z. , Zheng L. L.
Published: December 2013

Light-emitting diode (LED) is considered as the “green light” of the twenty-first century, and the white high-power LED is mainly achieved by the excitation of yellow fluorescent powder with GaN-based blue light. Therefore, the quality of GaN films directly influences the reliability, light efficiency and durability of the Led devices. In the paper, a coupled model has been developed and applied on the simulation of transport phenomena and chemical kinetics during the GaN growth process by a vertical metal-organic chemical vapor deposition (MOCVD) reactor. The effects of the carrier gas type, gas flow rate, and the disk rotation rate on the species distributions, GaN deposition rate and temperature field are investigated. The results indicate that nitrogen is better than hydrogen as carrier gas in consideration of the GaN deposition rate, and that, at the current range of the growth parameters, fast crystal rotation rate and gas inlet velocity are favorable for the large deposition rate and for the improvement of the averaged growth uniformity. However, the edge effect becomes more critical. The results also show that an intermediate gas inlet velocity and a fast disk rotation rate are better conditions from an averaged evaluation of the deposition rate and growth uniformity. The analyses have provided important guide for a practical GaN thin-film growth.
Spectral Control of Near-Field Radiation Through Surface Plasmon Polariton Interference
Authors: Hirashima Daisuke , Hanamura Katsunori
Published: December 2013

Through interference of surface plasmon polaritons (SPPs), near-field radiation transfer between pillar-array-structured surfaces was enhanced compared with that between plane surfaces. Even in nanoscale channels between the pillars, the SPPs could propagate, and then a kind of interference and resonance took place according to the depth of the channel between the pillars. With decreasing pillar height, the frequency at maximum radiation transfer was shifted to the high-frequency side. That is, spectral control of near-field radiation could be achieved using pillar-array-structured surfaces.
Reduced Order Modeling and Compression of Data Produced by Simulations of Transient and Periodic Heat Transfer Processes
Authors: Blanc Trevor J. , Jones Matthew R. , Gorrell Steven E. , Duque Earl P. N.
Published: December 2013

Reduced Order Modeling may be used to obtain compact and computationally efficient representations of complex dynamic systems. The objective of this paper is to demonstrate the application of reduced order modeling techniques to systems undergoing thermal transients. In this paper, a reduced order model is defined as a spectral method in which the dominant features of a spatially and temporally varying temperature profile are represented using a relatively small set of basis vectors. Although various approaches are possible, reduced order modeling generally relies on the use the singular value decomposition of a matrix containing representative data to generate an orthonormal basis for the process to be modeled. The results presented in this paper illustrate reduced order modeling of periodic and transient heat transfer in an axisymmetric system. Measures demonstrating the accuracy and computational savings associated with the use of reduced order modeling are presented.
Modeling and Trajectory Optimization of Water Spray Cooling in a Liquid Piston Air Compressor
Authors: Saadat Mohsen , Shirazi Farzad A. , Li Perry Y.
Published: December 2013

An efficient and sufficiently power dense air compressor/expander is the key element in a Compressed Air Energy Storage (CAES) approach. Efficiency can be increased by improving the heat transfer between air and its surrounding materials. One effective and practical method to achieve this goal is to use water droplets spray inside the chamber when air is compressing or expanding. In this paper, the air compression cycle is modeled by considering one-dimensional droplet properties in a lumped air model. While it is possible to inject water droplets into the compressing air at any time, optimal spray profile can result in maximum efficiency improvement for a given water to air mass ratio. The corresponding optimization problem is then defined based on the stored energy in the compressed air and the required input works. Finally, optimal spray profile has been determined for various water to air mass ratio using a general numerical approach to solve the optimization problem. Results show the potential improvement by acquiring the optimal spray profile instead of conventional constant spray flow rate. For the specific compression chamber geometry and desired pressure ratio and final time used in this work, the efficiency can be improved up to 4%.
Optimal Control Experimentation of Compression Trajectories for a Liquid Piston Air Compressor
Authors: Shirazi Farzad A. , Saadat Mohsen , Yan Bo , Li Perry Y. , Simon Terry W.
Published: December 2013

Air compressor is the critical part of a Compressed Air Energy Storage (CAES) system. Efficient and fast compression of air from ambient to a pressure ratio of 200–300 is a challenging problem due to the trade-off between efficiency and power density. Compression efficiency is mainly affected by the amount of heat transfer between the air and its surrounding during the compression. One way to increase heat transfer is to implement an optimal compression trajectory, i.e., a unique trajectory maximizing the compression efficiency for a given compression time and compression ratio. The main part of the heat transfer model is the convective heat transfer coefficient (h) which in general is a function of local air velocity, air density and air temperature. Depending on the model used for heat transfer, different optimal compression profiles can be achieved. Hence, a good understanding of real heat transfer between air and its surrounding wall inside the compression chamber is essential in order to calculate the correct optimal profile. A numerical optimization approach has been proposed in previous works to calculate the optimal compression profile for a general heat transfer model. While the results show a good improvement both in the lumped air model as well as Fluent CFD analysis, they have never been experimentally proved. In this work, we have implemented these optimal compression profiles in an experimental setup that contains a compression chamber with a liquid piston driven by a water pump through a flow control valve. The optimal trajectories are found and experimented for different compression times. The actual value of heat transfer coefficient is unknown in the experiment. Therefore, an iterative procedure is employed to obtain h corresponding to each compression time. The resulted efficiency versus power density of optimal profiles is then compared with ad-hoc constant flow rate profiles showing up to %4 higher efficiency in a same power density or %30 higher power density in a same efficiency in the experiment.
A Validated Two-Phase Flow Large Eddy Simulation Methodology
Authors: Xiao Feng , Dianat Mehriar , McGuirk James J.
Published: December 2013

A robust two-phase flow LES methodology is described, validated and applied to simulate primary breakup of a liquid jet injected into an airstream in either co-flow or cross-flow configuration. A Coupled Level Set and Volume of Fluid method is implemented for accurate capture of interface dynamics. Based on the local Level Set value, fluid density and viscosity fields are treated discontinuously across the interface. In order to cope with high density ratio, an extrapolated liquid velocity field is created and used for discretisation in the vicinity of the interface. Simulations of liquid jets discharged into higher speed airstreams with non-turbulent boundary conditions reveals the presence of regular surface waves. In practical configurations, both air and liquid flows are, however, likely to be turbulent. To account for inflowing turbulent eddies on the liquid jet interface primary breakup requires a methodology for creating physically correlated unsteady LES boundary conditions, which match experimental data as far as possible. The Rescaling/Recycling Method is implemented here to generate realistic turbulent inflows. It is found that liquid rather than gaseous eddies determine the initial interface shape, and the downstream turbulent liquid jet disintegrates much more chaotically than the non-turbulent one. When appropriate turbulent inflows are specified, the liquid jet behaviour in both co-flow and cross-flow configurations is correctly predicted by the current LES methodology, demonstrating its robustness and accuracy in dealing with high liquid/gas density ratio two-phase systems.
Study of Deformation of Water-Cooled Laser Mirror Used in High Power Laser System
Authors: Hu Panpan , Zhu Haihong , He Chongwen , Yin Jie , Ke Linda
Published: December 2013

The transient thermal deformations of laser water-cooled mirror surface with minichannels have been numerically studied. The theoretical results show that fluid flow has a great influence on temperature distribution and thermal deformation. The maximum of temperature and thermal deformation appear in the downstream area, which is different from the previous research results. Meanwhile, experiments with different working conditions are conducted to validate the numerical simulation, and the numerical results agree well with the experimental data. The emulation method of thermal deformation of water-cooled mirror used in this study is proved to be effective research method.
Physics of Membrane-Based Desorption Process From LiBr Solution Flow in Microchannels
Authors: Isfahani Rasool Nasr , Moghaddam Saeed
Published: December 2013

This study investigates the physics of water desorption from a lithium bromide (LiBr) solution film. The study was conducted on a membrane-based desorber in which the solution flows through an array of microchannels capped by a porous membrane. The membrane allows the vapor to exit the flow and retains the liquid. The solution film velocity and thickness as well as the solution and vapor pressures are independently controlled. Effects of different parameters such as wall temperature, solution and vapor pressures, solution flow velocity, and the solution inlet temperature on desorption rate were studied. Two different mechanisms of desorption are observed and analyzed. These mechanisms consisted of: (1) direct diffusion of water molecules out of the solution and their subsequent flow through the membrane and (2) formation of water vapor bubbles within the solution and their exit through the membrane. Direct diffusion was the dominant desorption mode at low surface temperatures and its magnitude was directly related to the vapor pressure, the solution concentration, and the heated wall temperature. Desorption at the boiling regime was predominantly controlled by the solution flow pressure. Overall, an order of magnitude higher desorption rate compare to a previous study on a membrane-based desorber was achieved.
Comparisons of Radiative Heat Transfer Calculations Using Spherical Harmonics and K-Distributions
Authors: Cai Jian , Modest Michael F.
Published: December 2013

A new nongray radiation modeling library for combustion gases has been implemented in OpenFOAM. The spectral models for single species include gray, correlation tables and narrowband k-distributions. Mixing models for k-distributions include the multiplication and uncorrelated mixture models. Radiative transfer equation solvers for the library include spherical harmonics such as P1, SP3 and SP5 as well as the optically thin approximation. The performance of the different solution methods is compared for accuracy and speed as a tool for future model strategy selection.
Investigation of Thermal Properties in Nanofluids for Thermal Energy Storage Applications
Authors: Zabalegui Aitor , Tong Bernadette , Lee Hohyun
Published: December 2013

Phase change materials (PCMs) are promising for thermal energy storage applications, but low thermal conductivity limits their heat exchange rate with a working fluid. The nanofluid approach has been established as a method of thermal conductivity enhancement, but particle addition may have an adverse effect on specific energy storage capacity. Latent heat reduction beyond traditional theory has been observed experimentally for carbon nanotubes dispersed in paraffin wax. Nanofluid latent heat and effective thermal conductivity were analyzed to investigate the effects of particle addition on thermal properties affecting PCM energy storage performance. It is shown that particle diameter significantly impacts nanofluid latent heat, with smaller particles generating greater degrees of reduction, but has a negligible effect on thermal conductivity. A method to approximate nanofluid latent heat of fusion is presented, considering the diameter-dependent reduction observed.
Prediction of f and Nu During Laminar-to-Turbulent Transition: Case of Flow in a Tube Containing a Twisted Tape
Authors: Date A. W. , Jagad Pankaj I.
Published: December 2013

In a straight pipe (or, duct) flow, the f and Nu vs Re characteristics over transition range of Reynolds numbers (typically, 2300 ≤ Re ≤ 4000) demonstrate abrupt and sharp departures from tendencies under fully laminar and fully turbulent regimes. This characteristic behaviour is quite competently captured by the low Turbulence Reynolds number (Ret) two-equation turbulence model(s) over all flow regimes without requiring any regime-dependent modifications to the governing equations. In contrast, the experimentally determined f and Nu characteristics of flow in a tube containing twisted tape do not demonstrate sharp departures from tendencies in laminar and turbulent regimes. As a result, the so called transition regime of Reynolds numbers cannot be easily identified. The purpose of the present paper is to explore if these very special characteristics can be predicted by low Ret, k-ε model of turbulence by computing over a large range 500 ≤ Re ≤ 30000.
The Concept Design of Tornado Like Jet Condenser Heat Exchanger
Authors: Kiknadze G. I. , Gachechiladze I. A. , Barnaveli T. T.
Published: December 2013

The concept design and fabrication of cost-effective and resource-saving Tornado Like Jet Condensers Heat Exchangers is described. Tornado Like Jet (TLJ) Technologies are utilizing the features of the streams of the continuous medium over the surfaces with dimples of double curvature inducing the secondary twisted vortexes self organization. (TLJ) Technologies are characterized by high functional efficiency of heat and mass exchange. The project is based on theoretical and experimental results obtained by the authors of the project in past years in development of a (TLJ) Technologies package.
Flow and Heat Transfer Characteristics in Ribbed Channel Using Lattice Boltzmann Method
Authors: Sharma Prateek , Mondal Bittagopal , Biswas Gautam
Published: December 2013

In order to improve the efficiency of the gas turbines and power plants, researchers have aimed to reach higher turbine inlet temperatures. There is always a metallurgical limit for highest temperature, as the materials pertaining to turbine cannot withstand very high temperature due to change in material properties. Deformation, creeping and even melting of turbine blades may occur. To alleviate these, researchers have been trying to evolve the cooling systems for turbine blades. Two major cooling strategies involve (a) external cooling and (b) internal cooling. In case of internal cooling, a layer of air or some coolant is made to flow through small passages inside the blade. Both the systems remove heat from the blade and keep the blade temperature under the metallurgical limit. The present work is aimed at modeling the internal cooling passages of the gas turbine blades. The same geometry can throw light on the performance of cooling passages used in electronic devices. Taking these two applications into consideration, it becomes necessary to study flow and heat transfer past bluff-bodies and in ribbed channels. In the present work, the fluid flow behavior and heat transfer characteristics in a rectangular channel with staggered ribs mounted on both walls are analyzed using the lattice Boltzmann method (LBM). This study is carried out for the fluid with Prandtl number Pr = 0.7 and a wide range of Reynolds numbers (10 ≤ Re ≤ 120). The computational strategy is applied in various test cases and validated with the results reported in the literature. The unsteady flow behaviors, such as, instantaneous streamlines, vortex shedding frequency and phase plots are reported. For the ribbed channel (with staggered ribs), the heat transfer is predicted with the help of isotherms, local Nusselt number distribution and average Nusselt number.