bluuebunny/crossref_metadata_2025 huggingface dataset:
An Investigation Into the Effects of Steam Condensation on Fluid Distribution When Occurring on the Tube Side of a Miniature Shell and Tube Heat Exchanger
Authors: MacLeod Gregory D.
Published: April 2009

A hypothesis is evaluated for a miniature shell and tube heat exchanger that the distribution of flow through the tubes is non-uniform when steam condenses inside the tubes. It is believed that due to the small tubing size, surface tension effects, generally negligible in larger exchangers, will have a noticeable effect on distribution of condensate through the tube bundle. This hypothesis was tested using a custom-built miniature shell and tube heat exchanger. The unit consisted of nineteen 0.094” OD tubes (0.010” wall thickness) in a 3/4” OD shell. The effect of both angle of inclination (0°, 45° and 90°) and steam flow regime (loosely defined as low, medium and high) on fluid distribution were investigated. Initial results proved that the flow distribution during condensation on the tube side was non-uniform; within a given trial, each tube produced a significantly different amount of condensate. Furthermore, while at a horizontal angle this non-uniformity was observed to be sporadic with respect to tube location. A tube that produced little condensate in one trial might produce a substantial amount of condensate in a subsequent trial. With increasing angle of inclination, the amount of fluid condensed became more consistent with respect to tube location within the bundle. The experiments were meant to be a preliminary investigation to either prove or disprove the hypothesis. As experimental results did not disprove the hypothesis, future study is recommended. More research into the effects of angle and flow rate on distribution should be conducted. Additionally, the effect of tube size should also be studied. If surface tension is the true explanation for the observed phenomena, it is expected that as the tube size increases, the amount of mal-distribution will be minimized.
Computational Analysis of Gas Flow and Heat Transport Phenomena in Monolithic Structures for High Temperature Processes
Authors: Selimovic Faruk , Bruun Tor , Sunde´n Bengt
Published: April 2009

High-temperature catalytic processes such as partial oxidation of Methane (POX) and steam Methane reforming (SMR) may benefit from use of reactor systems using monolithic honeycomb structures. Hereby, process performance is enhanced through more efficient heat transfer and considerable smaller reactor foot-prints than for conventional reactor concepts. Compact ceramic heat exchange structures may also be an interesting option for increasing the energy efficiency of high temperature processes in general. One example is single cycle turbines where these structures can be used as recuperators. The purpose of this paper is to describe modelling of gas flow pattern and heat transfer in reactors and heat exchangers with monolithic based structures. This technology is currently under development in a partnership of European companies and academia, with financial support from the EC and Swiss Government. The mathematical model developed for heat transfer and flow maldistribution has been used for counter-current checkerboard channel-arrangement. Pressure drop has been analyzed both experimentally and numerically (computation fluid dynamics, CFD). Power density has been shown to depend on various reactor parameters. Channel geometry, inlet gas temperature difference and channel wall thickness have been calculated to find the influence on power density.
Modelling of Flyash Water Mixture Flows
Authors: Ternik Primozˇ , Marn Jure
Published: April 2009

Present paper deals with modelling of a laminar flow of shear-thickening non-Newtonian fluid. First, approach with the Quadratic model to rheological modelling of such a fluid is presented. Secondly, the laminar flow of non-Newtonian fluid in a pipe bend is studied by numerical means to obtain the pressure loss coefficient prompted by disagreement between the empirical correlations and numerically obtained results. Finally, the comparison between two rheological models is presented.
Homogenization of a Conductive and Radiative Heat Transfer Problem, Simulation With CAST3M
Authors: El Ganaoui K. , Allaire G.
Published: April 2009

We are interested in conductive and radiative transfer of energy in the core of gas cooled reactors. Two scales characterize the problem: macroscopic and microscopic. We want to consider the domain like an equivalent homogenous medium. So we use homogenization theory to compute the effective macroscopic properties which take into account the microscopic structure. We first present a full mathematical study of a simpler conduction problem with non linear boundary condition and its simulation with the CEA’s (French Atomic Energy Commissariat) computer code CAST3M. Then we present the homogenization of the real physical problem (including radiative boundary condition).
Modeling the Transport Phenomena in Moving 3-D Dual-Beam Laser Keyhole Welding
Authors: Zhou J. , Tsai H. L. , Wang P. C.
Published: April 2009

In recent years, laser-beam welding using two laser beams, or dual-beam laser welding, has become an emerging welding technique. Previous studies have demonstrated that it can provide benefits over conventional single-beam laser welding, such as increasing keyhole stability, slowing down cooling rate and delaying the humping onset to a higher welding speed. It is reported that the dual beam laser welding can significantly improve weld quality. However, so far the development of the dual-beam laser welding technique has been limited to the trial-and-error procedure. In this study, the objective is to develop mathematical models and the associated numerical techniques to investigate the transport phenomena, such as heat transfer, metal flow, keyhole formation and weld pool shape evolutions during the moving three-dimensional dual-beam laser keyhole welding. Detailed studies have been conducted to determine the effects of key parameters, such as laser-beam configuration on weld pool fluid flow, weld shape, and keyhole dynamics. Some experimentally observed phenomena, such as the changes of the weld pool shape from oval to circle and from circle to oval during the welding process are predicted and can be well explained by the present model.
Drawdown-Effect of Lightpipes in Silicon Wafer Surface Temperature Measurements
Authors: Qu Yan , Puttitwong Ekachai , Howell John R. , Ezekoye Ofodike A. , Ball Kenneth S.
Published: April 2009

Lightpipe radiation thermometers (LPRTs) have been widely used for temperature measurement in the semiconductor industries. According to the International Technology Roadmap for Semiconductors 2004 (ITRS), temperatures for semiconductor wafer processing should be measurable to within an uncertainty of ± 1.5°C at 1,000 °C with temperature calibration traceable to ITS (international temperature standard)-90. To achieve this uncertainty, there are several issues associated with LPRTs to be resolved. The “draw-down effect” is the one that will be examined in this paper. We discuss this effect both experimentally and numerically in the temperature range of 500°C to 900°C.
Isothermal Solidification of Micro Layers of Molten Aluminum Alloys
Authors: Zhao Hui , Sekulic Dusan P.
Published: April 2009

Isothermal solidification of micro layers of aluminum binary alloys has been analyzed experimentally and theoretically. An in-situ real time monitoring of the behavior of molten eutectic, and sub-eutectic Al-Si alloys on a reactive Al substrate have been conducted using the hot stage microscopy. All tests were conducted in a high purity nitrogen background atmosphere. The heating ramp rates were in the range of 20 K/min to 50 K/min, the peak temperature was in the range between 858 K and 873 K, and the cooling rate during quench was 100 K/min. A transient moving boundary diffusion model of Si transport across the liquid/solid interface has been corroborated with empirical findings. A heuristic explanation of the cause of isothermal solidification and a comparison of experimental data and numerical predictions convincingly illustrate that (1) slow solid state diffusion into the substrate and (2) a much faster diffusion within the liquid phase are both the key controlling factors of solidification kinetics. The margin of an agreement between modeling predictions and empirical data is strongly influenced by an uncertainty in the estimation of diffusion characteristics across the interface. Phenomena considered are critical for the magnitude of erosion/dissolution of substrate during controlled atmosphere aluminum brazing processes; hence they are essential for the integrity of resulting metal-metal bonds facilitated by brazing.
Confinement Effects in Two-Dimensional Silicon Structures
Authors: Pascual-Gutie´rrez Jose´ A. , Murthy Jayathi Y. , Viskanta Raymond
Published: April 2009

Two-dimensional silicon structures are currently attracting a great deal of attention due to their potential application in the electronic and energy sectors. Most published works have employed simple face-centered cubic (fcc) models in determining dispersion curves and density of states for silicon. In this paper we address confinement effects in silicon using a two- and three-body environment-dependent interatomic potential (EDIP). Dispersion curves for silicon thin films under free-standing boundary conditions are theoretically computed by means of the dynamical equation. We show how size confinement causes the emergence of new energy levels and a flattening of the dispersion curves, explaining the reduction of phonon group velocities with respect to bulk, and the change in the volumetric specific heat. Our results indicate when confinement effects begin to play a primary role in the dynamical behavior of the structure and allow the prediction of the number of atomic layers above which a silicon film can be considered thick in terms of its dynamical behavior.
Fluid Flow Characteristics for Partially-Confined Compact Plain-Plate-Fin Heat Sinks
Authors: Wang M. P. , Wu T. Y. , Horng J. T. , Lee C. Y. , Hung Y. H.
Published: April 2009

A series of experimental investigations with a stringent measurement method on the study of the fluid flow behavior for confined compact heat sinks in forced convection have been successfully conducted. In the present study, a theoretical model to effectively predict the velocity and pressure drop for partially-confined heat sinks has been successfully developed. The air velocities flowing into heat sink Us through side bypass U1 and top bypass U2 for various 0.47<H/Hc<1 ratios are evaluated, where H/Hc is the ratio of the heat sink height to channel height. The maximum and average deviations of the velocities predicted by the present model from the experimental data are less than 20.31% and 13.13%, respectively, for confined compact heat sinks. Besides, the results show a good agreement between the predicted results and the experimental data of the pressure drop for the cases of H/Hc = 1. Nevertheless, the relative deviation of the predictions from the experimental data becomes more significant with decreasing H/Hc ratio, i.e., increasing the top bypass of confined compact heat sink. A new modified correlation of pressure drop including the H/Hc effect is presented. The maximum and average deviations of the results predicted by the new correlation from the experimental data are 14.48% and 7.72%, respectively.
Experimental Investigation of an Electro-Adsorption Chiller
Authors: Ng Kim Choon , Wang Xiaolin , Gao Lizhen , Chakarborty Anutosh , Sai Maung Aye
Published: April 2009

A comprehensive experiment has been conducted on a novel electro-adsorption chiller (EAC) with a rated cooling capacity of 120 W (uniform heat flux of about 4.7 W/cm2). At these rated conditions, it produces a heating load surface temperature of 23°C, about 10 degree below that of the heating-load temperature. The coefficient of performance (COP) of the prototype EAC is measured to be about 0.84.
Experimental Investigations of the Adsorption of NH3 on Silica Gel-Based Adsorbent
Authors: Wang Xiaolin , Zimmermann Wolfgang , Ng Kim Choon , Gao Lizhen , Keller Ju¨rgen U.
Published: April 2009

The silica gel-water working pair has been commonly used for commercial adsorption chillers due to the environmental benign refrigerant and low desorption temperature (less than 85°C). However, the application has been constrained due to the vacuum working condition and Ice point. This motivates researchers to investigate alternative working pairs. The silica gel-based adsorbents - ammonia working pairs have been found to be the most promising alternative. The isotherms and heats of adsorption of the working pair are essential to be investigated for designing the adsorption reactor and predicting the chiller performance. A novel sensor-gas calorimeter has been used to simultaneously measure the adsorption isotherm and heats of adsorption. The experimental results for adsorption of ammonia on the pure silica gel and silica gel treated with different weight percentage of calcium chlorine are presented.
Use of Liquid Film Evaporation in Biporous Media to Achieve High Heat Flux Over Large Areas
Authors: Semenic Tadej , Lin Ying-Yu , Catton Ivan
Published: April 2009

Boiling characteristics of three biporous and one monoporous sintered wick are tested. The monoporous wick has the same wick thickness as a comparable biporous wick. Diameters of the clusters of the comparable biporous wick are equal to the powder diameter of the monoporous wick. A second biporous wick has the same configuration as the first, but is sintered in a thicker layer. The third biporous wick that is tested has smaller cluster sizes then the first two. All three biporous wicks have clusters sintered from powder with the same size distribution. The results demonstrate the advantages of a biporous capillary structure. All biporous wicks reached higher critical heat flux (CHF) then the monoporous wick. Experiments show that larger clusters are better than smaller. Comparing two different wick thicknesses, we can see that even though there is a dryout region inside the thick wick, it is still able to continuously remove heat at constant superheat. No sudden changes in superheat are seen. This process of heat removal is not possible with the thin wick. The working fluid in all runs is methanol. 4-mm thick wick with powder diameter ranging from 53 to 63 microns and cluster diameter ranging from 500 to 707microns is able to remove 377W/cm2 at temperature difference 110°C. A partial pressure inside the test chamber at this heat flux is 0.68atm and the interface temperature 167°C.
Thermophysical Properties of Monoporous Sintered Copper
Authors: Lin Ying-Yu , Semenic Tadej , Catton Ivan
Published: April 2009

Thermophysical properties of monodispersed-sintered copper are measured. An apparatus to measure effective thermal conductivity of dry and wet samples is built. It is calibrated using bulk samples with known thermal conductivity. Permeability is measured based on flow resistance though the porous samples. Velocity at different pressure drops is measured and the permeability calculated using Darcy’s law. The experiment is performed using water and silicone oil as working liquids. The error of the measurement is less then five percent. Capillary pressure for all samples is measured based on amount of liquid that is held by the porous sample. The Young-Laplace relationship is used to relate capillary pressure to effective pore radius. Porosity of the samples is calculated by measuring the dimension of samples and weighing the amount of liquid in fully saturated samples. Thermal conductivity and capillary pressure are found to decrease as powder diameter increases; permeability and porosity increases with powder diameter.
Independent Hybrid Power Plant “PEMFC+MEMS” With Use of Molecular Ceramic Membranes to Separate CO and H2
Authors: Soudarev A. V. , Souryaninov A. A. , Konakov V. G. , Molchanov A. S.
Published: April 2009

As analysis of thermal-technical parameters of the existing polymer exchange membrane fuel cells (PEMFC) indicated, their electrical efficiency is not above 32–37% which is due to relatively high (10–15%) electric power consumption to cover own needs. Its major percentage falls on pump and compressor drive (air, fuel, water supply) using the AC electric engines connected via converter to FC. A real alternative allowing the efficiency increase up to 45% and higher is to apply hybrid plants when an AC turboelectric generator (TEG) is built into the thermodynamic cycle, the latter operating at the expense of utilization of the FC reagent stream power. TEG is a micro turbocompressor with incorporated turbo generator manufactured on the basis of the micro electric-mechanical system (MEMS) technology. The numerical study over the hybrid cycle effectiveness revealed that the optimum efficiency is ensured provided the TEG power does not exceed 12–15% of the total hybrid power plant power. Considering a value of the PEMFC mean power of around 8, a need arises in TEG of 500 to 1500W power to operate as a part of hybrid engine. Among various auxiliaries involved into the PEMFC, there should be devices that ensure getting target values in terms of hydrogen purity, a dominant synthetic gas fraction, at the FC inlet. A need to get and maintain hydrogen purity on the level of 99.99% is related with that if CO content in mixture is higher 0.01%, then a normal operation of FC fails due to “poisoning” effect of the platinum-containing catalysts of the FC electrodes. To forestall this, the palladium molecular membranes are now typically applied which causes the filtered flow temperature limitations within values not exceeding 500–550°C. At the same time, PEMFC in most cases must operate on air and syngas produced by reforming, with their temperature amounting to 800–900°C. To provide this, we need to have ceramic molecular membranes (CMM) made of a ceramic support in which macropores nano pores are formed (characteristic size of less 0.3nm), the latter achieved through application of a complex of various chemical and physical processes. In the paper presented, findings of numerical studies over a hybrid engine plant are provided, this hybrid plant (PEMFC + MEMS) as compared with alternatives to existing and offered schemes, and, also, test data on the zeolite-based support CMM are demonstrated.
A Thermal Transport and Non-Equilibrium Deposition Model in AlN Sublimation Growth Process
Authors: Wu Bei , Zhang Hui
Published: April 2009

Sublimation vapor transport method is a widely used technique for production of bulk crystals, such as SiC and AlN. A one-step reaction with two vapor species, i.e. aluminum (Al) vapor and nitrogen (N2) gas, is usually assumed for AlN sublimation growth with diffusion-controlled growth mechanism. However, vapor species generation/consumption is determined by surface reactions, which do not depend on the concentration gradient, but on concentration itself. Thus, the flux at the interfaces is controlled not only by the Fick’s law, but by the surface reaction. In this paper, inductively heated AlN sublimation growth process is simulated to predict the heat generation and temperature field in the growth system. The effects of coil position on heat and mass transfer are investigated. A non-equilibrium growth model considering surface reaction on the source/seed surfaces, diffusion within the boundary layers and vapor transport between source and seed is developed to predict the growth rates at different operating conditions. The predicted results are compared with the experimental data and the results from a traditional diffusion model, which assumes thermodynamic equilibrium on the solid/vapor surface/interface and vapor diffusion through bulk gas. The conditions under which the new model will provide the same as the one obtained by the diffusion model are identified.
Transient Heat Transfer Experiments in Complex Passages
Authors: Poser Rico , von Wolfersdorf Jens , Semmler Klaus
Published: April 2009

Transient heat transfer experiments were performed in a model of a multi-pass gas turbine blade cooling circuit. The inner surface of the Plexiglas model was coated with thermochromic liquid crystals in order to determine the internal heat transfer coefficients. A change in inlet temperature is applied using a pre-cooled heat exchanger. As for simple geometries the analytical solution of Fourier’s equation can often be directly used for data evaluation, one ought to pay attention to complex passages. The reason has to be seen that the flow in complex passages has to be characterized by local and time dependent fluid temperatures. As a direct consequence data evaluation might be limited to small evaluation areas especially far downstream. Otherwise the uncertainties in the heat transfer results will increase substantially. In the present study the sensitivity of the transient method for complex passages has been analyzed theoretically and applied experimentally.
Numerical and Experimental Analysis for Laser Surface Densification of Plasma Sprayed Coatings
Authors: Wu J. , Choi J. , Zhang S. , Hilmas G.
Published: April 2009

Advanced ceramics, suitable to fabricate ultra-high temperature ceramic components for structural applications and thermal protection systems, are not easily prepared by the plasma spray technique due to their extremely high melting temperature. How to prepare the materials with high density is a challenging research task. In this study, applying a laser surface treatment technique for the densification of zirconium diboride, the influence of laser power and beam diameter on the microstructure and mechanical properties of the coatings are examined both numerically and experimentally. Using a two dimensional mathematical model, which was developed incorporating melting, solidification, and evaporation phenomena, the microstructural characteristics during solidification are predicted via tracking the solid-liquid interface. For the mathematical model, volume-of-fluid technique is incorporated to track the free surface, while the surface force as a body force instead of a boundary condition. Typical laser processing parameters have been obtained for the desired both porosity reduction and microstructure from the model and the predicted results are compared with the experimental results.
Steady State Analysis of Heated Soil Vapor Extraction Process With Air Sparging
Authors: Mohan Das P. M. , Amano R. S. , Roy T. , Jatkar J.
Published: April 2009

Heated Soil Vapor Extraction (HSVE), developed by Advanced Remedial Technology is a Soil remediation process that has gained significant attention during the past few years. HSVE along with Air sparging has been found to be an effective way of remediating soil of various pollutants including solvents, fuels and Para-nuclear aromatics. The combined system consists of a heater/boiler that pumps and circulates hot oil through heating wells, a blower that helps to suck the contaminants out through the extraction well, and air sparging wells that extend down to the saturated region in the soil. Both the heating wells and extraction wells are installed vertically in the saturated region in contaminated soil and is welded at the bottom and capped at the top. The heat source heats the soil and the heat is transported inside the soil by means of conduction and convection. This heating of soil results in vaporization of the gases, which are then absorbed by the extraction well. Soil vapor extraction cannot remove contaminants in the saturated zone of the soil that lies below the water table. In that case air sparging may be used. In air sparging system, air is pumped into the saturated zone to help flush the contaminants up into the unsaturated zone where the contaminants are removed by SVE well. In this analysis an attempt has been made to predict the behavior of different chemicals in the unsaturated and saturated regions of the soil. This analysis uses the species transport and discrete phase modeling to predict the behavior of different chemicals when it is heated and absorbed by the extraction well. Such an analysis will be helpful in predicting the parameters like the distance between the heating and extraction wells, the temperature to be maintained at the heating well and the time required for removing the contaminants from the soil.
Heat Transport Characteristics in Closed Loop Oscillating Heat Pipes
Authors: Wang Shuangfeng , Nishio Shigefumi
Published: April 2009

Heat transport rates of micro scale SEMOS (Self-Exciting Mode Oscillating) heat pipe with inner diameter of 1.5mm, 1.2mm and 0.9mm, were investigated by using R141b, ethanol and water as working fluids. The effects of inner diameter, liquid volume faction, and material properties of the working fluids are examined. It shows that the smaller the inner diameter, the higher the thermal transport density is. For removing high heat flux, the water is the most promising working fluid as it has the largest critical heat transfer rate and the widest operating range among the three kinds of working fluids. A one-dimensional numerical simulation is carried out to describe the heat transport characteristics and the two-phase flow behavior in the closed loop SEMOS heat pipe. The numerical prediction agrees with the experimental results fairly well, when the input heat through was not very high and the flow pattern was slug flow.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.
Numerical Investigation of Thermofluid Flow Characteristics With Phase Change Against High Heat Flux in Porous Media
Authors: Yuki K. , Abei J. , Hashizume H. , Toda S.
Published: April 2009

This study numerically evaluates thermofluid flow characteristics in porous media by a newly developed “modified two-phase mixture model” applying a two-energy model instead of an one-energy model. In a single-phase flow case, thermal nonequilibrium between a solid phase and a fluid phase is observed in the area where inlet heat conducts from a heating wall and further convective heat transfer is more active. Though the degree of thermal nonequilibrium has a positive correlation with the increase in flow velocity and inlet heat flux, the degree is very low and can be ignored, from an engineering perspective. In a case of two-phase flow, the thermal nonequilibrium is remarkable in the two-phase region because the solid-phase temperature in this region is far beyond saturation temperature. A difference between these two models is obvious especially in the two-phase flow case, so that the numerical simulation with the two-energy model is indispensable under the high heat flux conditions of over 1MW/m2.
Heat Transfer in Ultrafast Laser Tissue Welding
Authors: Kim Kyunghan , Guo Zhixiong , Kumar Sunil
Published: April 2009

The objective of this research is to develop an appropriate model for simulating the transient heat transfer processes in tissue welding subject to irradiation of ultrashort laser pulses. The ultrafast laser tissue welding process is modeled in three steps. First, there is an immediate local temperature response due to radiation absorption during an ultrashort time period. The transient discrete ordinate method is employed to simulate the ultrashort laser pulse transport in tissue. The temporal radiation field is obtained and the lumped method is used for predicting the local temperature response. After a stable local temperature profile is achieved, the second step starts, in which the hyperbolic heat conduction model is adopted to describe the heat transfer. The thermal wave behavior is observed. It is found that the hyperbolic wave model predicts a higher temperature rise than the classical diffusion model. After about five thermal relaxation times the thermal wave behavior is substantially weakened and the heat diffusion predominates. The heat diffusion equation can accurately describe the heat transfer thereafter.
Nucleate Boiling Flow Simulation With Coupling of Eulerian and Lagrangian Methods
Authors: Koncˇar Bosˇtjan , Kljenak Ivo , Mavko Borut
Published: April 2009

Subcooled boiling flow was simulated by combining the two-fluid model of the CFX-4.4 code and a Lagrangian bubble-tracking model. At present, both models are coupled “off-line” via the local bubble Sauter diameter. The two-fluid model simulation with the CFX-4.4 code provides local values of turbulent kinetic energy field of the liquid phase, which is used as an input for the bubble-tracking model. In the bubble-tracking model, vapour is distributed in the liquid in the form of individually tracked bubbles. The result of the Lagrangian simulation is a non-homogeneous distribution of local Sauter diameter, which is used in the two-fluid model to predict the interfacial forces and interfacial transfer rates of mass and heat transfer. The coupled approach requires a few iterations to obtain a converged solution. The results of the proposed approach were validated against boiling flow experiments from the literature. A good agreement between measured and calculated radial profiles of void fraction and bubble diameter was obtained.
A New Transient Bio-Heat Model of the Human Body
Authors: Salloum M. , Ghaddar N. , Ghali K.
Published: April 2009

A new mathematical multi-segmented model based on an improved Stolwijk model is developed for predicting nude human thermal and regulatory responses within body segments and the environment. The passive model segments the body into the 15 cylindrical parts. Each body part is divided into four nodes of core, skin, artery blood, and vein blood. The body nodes interact with each other through convection, perfusion and conduction. In any body element, the blood exiting the arteries and flowing into the capillaries is divided into blood flowing in the core (exchanges heat by perfusion in the core) and blood flowing into the skin layer (exchanges heat by perfusion in the skin). The model calculates the blood circulation flow rates based on exact physiological data of Avolio [1], real dimensions, and anatomic positions of the arteries in the body. The circulatory system model takes into consideration the pulsatile blood flow in the macro arteries with its effect on the convective heat transport. The inclusion of calculated blood perfusion in both the tissue and the skin, based on the arterial system model and the heart rate is unique for the current model. The bio-heat human model is capable of predicting accurately nude human transient physiological responses such as the body’s skin, tympanic, and core temperatures, sweat rates, and the dry and latent heat losses from each body segment. The nude body model predictions are compared with published theoretical and experimental data at a variety of ambient conditions and activity. The current model agrees well with experimental data during transient hot exposures. The nude human model has an accuracy of less than 8% for the whole-body heat gains or losses and ±0.48°C for skin temperature values.
Analysis of Microwave Heating for Composite Dielectric Food Substances Supported on Ceramic Materials
Authors: Basak Tanmay , Meenakshi A.
Published: April 2009

A detailed theoretical analysis has been carried out to study efficient heating of 1D composite dielectric samples due to microwaves. Current study involves processing of beef with oil layers with/without support and three cases are considered where oil layer is followed by beef layer (case 1), beef layer is followed by oil layer (case 2) and oil-beef layers are exposed to microwaves at both the sides (case 3). For cases 1 and 2, microwaves are incident at the left face only and the support is generally attached with the oil layer. A preliminary analysis has been carried out for beef-oil composite without any support for all cases and it is observed that identical average power in beef sample occurs for small thickness of oil layer irrespective of either oil or beef directly exposed to microwaves (case 1 or 2) and for greater thicknesses of oil layer, the food composite would exhibit greater average power for case 1. The maxima in average power corresponding to resonances occur at various sample thicknesses for all cases with and without supports and two dominant resonance modes R1 and R2 are considered where the average power at R1 mode is greater than that at R2 mode for all cases. The detailed spatial distribution for various cases illustrates that for small oil thicknesses, heating rate is less and greater heating rate would correspond to larger oil thicknesses. However, the excessive heating in beef sample may correspond to thermal runaway which are also illustrated by ΔTb (difference between the maximum and minimum values of temperature) in beef samples vs time plot. The similar analysis has been extended for all cases with oil layer directly attached with ceramic supports (Al2O3 and SiC). Based on the detailed analysis, the suitability of the support would be guided by factors such as optimal oil thickness, uniform heating and enhanced thermal processing within the beef sample.
Numerical Simulation of a Strongly Heated Gas Flowing Upward in a Vertical Tube Using a k–ε Model
Authors: Richards Adam H. , Spall Robert E. , McEligot Donald M.
Published: April 2009

A two-layer k-ε model is used to model a strongly heated, low-Mach number gas flowing upward in a vertical tube. Heating causes significant property variation and thickening of the viscous sublayer, consequently a fully developed flow does not evolve. Two-equation turbulence models generally perform poorly under such conditions. However, in the present work, a two-layer k-ε model is shown to accurately predict this flow through adjustment of a model constant related to the viscous sublayer thickness.
Numerical Study of Transport and Reaction Phenomena in GaN Vapor Phase Epitaxy
Authors: Cai D. , Zheng L. L.
Published: April 2009

A vapor phase epitaxy (VPE) system has been designed to grow high quality gallium nitride layers under the deposition temperature of 990°C and the pressure range of 200–800 Torr. For the better understanding of the deposition mechanism of GaN layers, a numerical model that is capable of describing multi-component fluid flow, gas/surface chemistry, conjugate heat transfer, thermal radiation, and species transport, has been developed to help in design and optimization of the epitaxy growth system. The vacuum area between heaters and reactor tube is simulated as a solid body with small thermal conductivity and totally transparent to radiative heat transfer. Simulation results were compared to the experimental data to examine the temperature distribution achieved inside the growth reactor. To optimize operating parameters, the reaction mechanism for GaN in the VPE system has been identified, and the comprehensive computational simulations have been performed to study the temperature distribution, species mixing process, ammonia decomposition process and GaN deposition rate distribution on the substrate. Parametric studies have been performed to investigate the effects of operational and geometric conditions, such as temperature, reacting/carrier gas flow rate and distance between the substrate and the nozzle, on species mixing process and GaN deposition uniformity. The relationship between gas flow rate and III/V ratio achieved on the substrate will be established.
Natural Convection Inside a Square Cavity Heated From Below and Symmetrically Cooled at Both Sides: Effects of Various Dirichlet Boundary Conditions at the Bottom Wall
Authors: Roy Satyajit , Basak Tanmay
Published: April 2009

A numerical study is performed to investigate the steady laminar natural convection flow in a square cavity with uniformly and non-uniformly heated bottom wall, and adiabatic top wall maintaining constant temperature of cold vertical walls. A penalty finite element method with bi-quadratic rectangular elements has been used to solve the governing mass, momentum and energy equations. The numerical procedure adopted in the present study yields consistent performance over the range of parameters (Rayleigh number Ra, 103 ≤ Ra ≤ 105 and Prandtl number Pr, 0.7 ≤ Pr ≤ 10) with respect to continuous and discontinuous Dirichlet boundary conditions. Non-uniform heating of the bottom wall produces greater heat transfer rate at the center of the bottom wall than uniform heating case for all Rayleigh numbers but average Nusselt number shows overall lower heat transfer rate for non-uniform heating case. Critical Rayleigh numbers for conduction dominant heat transfer cases have been obtained.
Limitations of Photoacoustic Measurement of Burn Depth
Authors: Viator John A. , Jacques Steven L.
Published: April 2009

Noninvasive burn depth measurements would allow clinicians to manage burn injury better and improve treatment outcomes. Additionally, knowledge of the burn depth would allow surgeons to excise thermally damaged tissue without harming the underlying healthy tissue which is the source of epithelial cells important for proper healing response. We propose a photoacoustic method for inducing acoustic waves in burns. We used an Nd:YAG laser coupled to an optical fiber probe to deliver laser light to burn injury. Subsequent acoustic wave analysis results in burn depth profiling. We test ex vivo pig skin and optical diffusion theory to extrapolate these measurements to determine the maximum depth determined by this probe. We found that our probe can determine burn depths up to 2.8 mm. We propose changes to extend this depth to about 5 mm, the full thickness of human skin.
Numerical Investigation on Electroosmotic Transport in Porous Media
Authors: Yang Z. , Peng X. F. , Wang B. X.
Published: April 2009

A numerical investigation was conducted to explore the laminar electroosmotic heat and mass transport in a single cell or pore of a regular 2-D porous structure with the typical scale of order 100μm. The influence of the ratio, f, of the dielectric constants of the fluid, εl, to that of solid matrix, εs, on the electroosmotic flow was studied. It was found that the larger f was the more electroosmotic flow was enhanced. A comparison between the electroosmotic and presser-driven flows was made under different Reynolds numbers conditions. The heat transfer in a single cell was also considered under the condition of no heat conduction along the flow direction and the results showed that the effective thermal conductivity was significantly influenced by Reynolds number.
Inverse Estimation of Surface Temperature in Nanoscale Using the Artificial Neural Network
Authors: Jung Bup Sung , Kim Sun K. , Lee Woo Il
Published: April 2009

An inverse heat conduction problem (IHCP) for nanoscale structures was studied. The conduction phenomenon is modeled using the Boltzmann transfer equation. Phonon-mediated heat conduction in one dimension is considered. One boundary, where temperature observation takes place, is subjected to a known boundary condition and the other boundary is exposed to an unknown temperature. The artificial neural network (ANN) is employed to solve the described inverse problem. Sample results are presented and discussed.
Effect of Unheated Starting Lengths on Film Cooling Experiments
Authors: Coulthard Sarah M. , Volino Ralph J. , Flack Karen A.
Published: April 2009

The effect of an unheated starting length upstream of a row of film cooling holes was studied experimentally to determine its effect on heat transfer coefficients downstream of the holes. Cases with a single row of cylindrical film cooling holes inclined at 35 degrees to the surface of a flat plate were considered at blowing ratios of 0.25, 0.5, 1.0 and 1.5. For each case experiments were conducted to determine the film cooling effectiveness and the Stanton number distributions in cases with the surface upstream of the holes heated and unheated. Measurements were made using an infrared camera, thermocouples, and hot and cold wire anemometry. Ratios were computed of the Stanton number with film cooling (Stf) to corresponding Stanton numbers in cases without film cooling (Sto) but the same surface heating conditions. Contours of these ratios were qualitatively the same regardless of the upstream heating conditions, but the ratios were larger for the cases with a heating starting length. Differences were most pronounced just downstream of the holes and for the lower blowing rate cases. Even 12 diameters downstream of the holes the Stanton number ratios were 10 to 15% higher with a heated starting length. The differences in Stanton number distributions are related to jet flow structures which vary with blowing rate.
The Flow Calculations in the High Temperature Heat Exchanger With the Manufacturing Geometrical Effects
Authors: Ponyavin Valery , Subramanian Sundaresan , De Losier Clayton Ray , Chen Yitung , Hechanova Anthony E. , Peterson Per F.
Published: April 2009

Computational simulations of a flow in the high temperature offset strip-fin heat exchanger to study the manufacturing geometrical effects (MGE) were conducted. The considered heat exchanger design is used in the cooling cycle in advanced nuclear reactors for hydrogen production by the sulfur iodine thermo-chemical cycle. The study is conducted with helium gas and molten salt as the working fluids with two different channel flow surfaces: fins with roundings on their bases (manufacturing geometrical effects (MGE)) and fins without roundings on their bases. The pre-processor GAMBIT is used to generate a computational mesh, and the CFD software package FLUENT (parallel version), that is based on the finite volume method is used to perform numerical simulations. Because the Reynolds number for the helium side is about 3000, two different models were used for the calculations: laminar model and k-ω turbulence model (for transition flow). The Reynolds number for the molten salt side is less than 100; therefore the laminar flow model was used for these calculations. The results show that manufacturing geometrical effects influence very strongly pressure drop and are negligibly small for temperature and heat transfer.
Theoretical Analysis of High Prandtl Number Heat Transfer in Non-Isothermal Pipe Flow
Authors: Chen Huajun , Chen Yitung , Hsieh Hsuan-Tsung , Tan Taide
Published: April 2009

Based on Fourier expansion, an analytical solution is developed for the high Prandtl number heat transfer in both fully developed laminar and turbulent non-isothermal pipe flow. Both of the mathematical expressions of the temperature distribution and the local Nusselt number have been obtained. A parametric study illustrates the characteristics of high Prandtl number heat transfer in non-isothermal pipe flow in detailed. The solutions obtained can be used for the numerical construction of the solution to the more general problems of heat transfer in the developed turbulent wall-bounded shear flows.
Atrium Smoke Exhaust and Technical Issues on Hot Smoke Tests
Authors: Chow W. K.
Published: April 2009

Atriums are commonly designed in big building complexes while developing big cities in the Far East. It is not clear what the fire safety provisions are; nor whether those installed systems would work as expected. Dynamic smoke exhaust systems used to be installed. Other fire protection systems such as drencher system and sprinkler systems might be required. If the design of the dynamic smoke exhaust systems does not comply with the prescriptive code, hot smoke tests are required to be carried out in site for evaluating their performance. The smoke layer interface height induced by an agreed design fire is commonly checked. Technical issues on the procedure of hot smoke tests will be discussed in this paper. Problems encountered in designing smoke exhaust systems in the Far East will be outlined. A practical case is taken as an example. Application of Computational Fluid Dynamics (CFD) in evaluating the performance of atrium smoke exhaust systems will also be discussed. CFD is now a common engineering tool for designing smoke management systems by investigating the potential fire and smoke hazard. A typical scenario of having a fire in an adjacent shopping mall is considered. Performance of the dynamic smoke exhaust system in the atrium will be simulated.
Experimental and Numerical Investigation of the Dynamics of Moving Vapor Bubbles
Authors: Christopher David M. , Wang Hao , Peng Xiaofeng
Published: April 2009

Jet flows have been observed flowing from the tops of vapor bubbles during nucleate boiling in a variety of situations. This paper analyzes the physical mechanisms that cause jet flows to emanate from the tops of bubbles moving along microwires. The flows were analyzed by numerically solving the governing differential equations for the 3-D velocity and temperature distributions around the bubble and the heated wire as the bubble moves along the wire. The results show that the flow is most likely driven by the temperature difference from the front to the back of the bubble resulting from the bubble motion which would cause Marangoni flow. The Marangoni flow provides thrust to push the bubble forward. Comparisons with experimental observations suggests that the condensation heat transfer at the bubble interface must be restricted by noncondensable gases would increase the surface temperature gradient which would in turn increase the resulting Marangoni flow.
Heat Transfer and Friction Characteristics of an Adapted Inclined Louvered Fin
Authors: T’Joen Christophe , De Paepe Michel , Steeman Hendrik-Jan , Willockx Arnout
Published: April 2009

A fin-and-tube evaporator of a commercially available air conditioning unit was studied experimentally. To this end a test rig was constructed to measure the heat transfer capacity on the air and waterside of the evaporator. A wide range of Reynolds numbers on the air airside was investigated, focusing on the low Reynolds numbers, as modern air conditioning systems mainly operate in this region (low sound levels). The resulting data was used to determine the convective heat transfer correlation (expressed using the Colburn factor) and the friction factor on the airside. This evaporator was chosen for the fin type: an adaptation of the standard inclined louvered type. The found correlation is compared to the one published for standard louvered fins. A thorough error analysis was performed to validate the results.
Experiments on Remelting and Solidification of Molten Metal Droplets Deposited in Vertical Columns
Authors: Fang M. , Chandra S. , Park C. B.
Published: April 2009

Experiments were done to determine conditions under which vertical columns could be built by metal droplets landing sequentially on top of each other. Molten tin droplets (0.6 mm diameter) were deposited using a pneumatic droplet generator on an aluminum substrate. The primary parameters varied in experiments were those found to most affect bonding between droplets: droplet temperature (250°C to 345°C), substrate temperature (60°C to 200°C) and deposition rate (1 Hz to 15 Hz). At lower deposition rates the substrate cooled down too much to induce remelting whereas at higher rates the tip of the column remained liquid and surface tension forces pulled it into a spherical mass. Assuming one-dimensional conductive heat transfer in a column a simple analytical model was developed to calculate the temperature at the tips of the column. It predicts that deposition frequency should be decreased as column height increases to hold the tip temperature constant. Droplet coalescence was best achieved when the tip temperature of a column was maintained at the melting point of the metal. Columns fabricated following the deposition frequency predicted by the model show good bonding between droplets and uniform diameter.