bluuebunny/crossref_metadata_2025 huggingface dataset:
Unsteady Heat Transfer From a Spherical Particle in Turbulent and Oscillating Ambient Flows
Authors: Bagchi Prosenjit , Kottam Kiritk
Published: July 2009

Direct Numerical Simulation based on pseudospectral methodology is used to study the effect of freestream turbulence and freestream oscillation on the heat transfer from a sphere. The sphere Reynolds number is in the range 63 to 400, and the ratio of sphere diameter to Kolmogorov scale ranges from 1.08 to 8. The objective is to obtain the unsteady heat transfer from the sphere at finite sphere Reynolds number Re and Prandtl number Pr in presence of a time-dependent ambient flow from the DNS, and compare that with the analytical expression valid for vanishing thermal advection. Results from three sets of simulations are presented: (1) Only turbulent velocity field is applied in the inflow, while the inflow temperature condition is held constant; (2) turbulent temperature condition is applied at the inflow, and the velocity is held constant; and (3) both turbulent velocity and temperature fields are applied in the inflow. These simulations allow us to isolate the role of freestream temperature and velocity fluctuations on Nusselt number. We show that the freestream turbulence has a very little effect on the time-averaged Nusselt number, but the instantaneous Nusselt number can vary by a factor of two over time. The unsteady thermal effects are small for small particle size, but not so when particle size is larger than the Kolmogorov scale. It is observed that the analytical expression of the thermal added-mass force significantly over-predicts the unsteady thermal effects. The thermal history effect is shown to be insignificant. The DNS result can be predicted, at best, by the quasi-steady result. The difference is maximum when both the ambient velocity and temperature are turbulent. We also examine various approximations of the ambient velocity and temperature as seen by the particle that can give a better estimate for the thermal added-mass effect. We then present results on the unsteady heat transfer in presence of an oscillating freestream velocity and temperature, considered separately. It is shown that analytical form of the thermal added-mass predicts an order of magnitude higher values than that obtained in the DNS, supporting the results on ambient turbulent condition. We further show that a pure oscillating ambient velocity also has a thermal added-mass effect.
Heat Transfer Performance During Condensation of R-134A
Authors: Al-Hajeri M. H. , Koluib A. M.
Published: July 2009

This paper reports experimental investigation of condensation heat transfer and pressure drop of an ozone friendly refrigerant, R-134a, inside a helical pipe for climatic conditioning of hot regions. This study concerns the condensation of R-134a flowing through annular helical pipes with different conditions of operating refrigerant-saturated temperatures. The average pressure drop was measured and compared with data from relevant literature. The measurements R-134a were performed on mass flow flux ranges from 50 to 680 kg/m2 s. The study provides experimental and analytical data which could be used for the design and development of more efficient condensers for refrigeration and air conditioning (A/C) systems working with the same refrigerant.
Numerical Study of Natural Convection in a Partitioned Cavity
Authors: Pirmohammadi M. , Ghassemi M. , Sheikhzadeh G. A.
Published: July 2009

The purpose of this study is to investigate the effect of insulated horizontal baffle placed at the hot wall of a differentially heated square cavity. The vertical walls are at different temperatures while the horizontal walls are adiabatic. In our formulation of governing equations, mass, momentum and the energy equations are applied to the cavity and the baffles. To solve the governing differential equations a finite volume code based on Patankar’s SIMPLER method is utilized [1]. The Results are presented for Rayleigh number from 104 up to 106 and are in form of streamlines, isotherms and Nusselt number. The baffle causes that at low Rayleigh number the horizontal isotherms are replaced by nearly vertical ones, specially around the baffle. Also it is found that thermal boundary layers are thickened, and the temperature gradients at the cold wall are reduced from their values for the case without baffle and this implies that a reduction in the heat transfer through the cavity occurs.
Artificial-Neural-Networks-Based Correlating Heat Transfer and Friction of Three Kinds of Heat Exchangers Having Large Tube-Diameter and Large Tube-Row
Authors: Xie Gongnan , Tang Linghong , Sunde´n Bengt , Wang Qiuwang
Published: July 2009

This work uses an artificial neural network (ANN) to correlate experimentally determined Nusselt numbers and friction factors for three kinds of fin-and-tube heat exchangers having plain fin, slit fin and fin with longitudinal winglet vortex generators with large tube-diameter and large tube-row. First, the relatively limited experimental data was picked up from the database of nine samples with Reynolds number being between 4,000 and 10,000. The Back Propagation (BP) algorithm was used to train the networks. Compared with correlations for prediction using conventional power-law regressions, the performance of developed ANN based prediction exhibits ANN superiority. Different network configurations were assessed to find the best architecture for correlating heat transfer and flow friction. The deviation between the predictions and experimental data was less than 4%. Then the ANN training database was expanded to include the experimental data and numerical data of some similar geometries by Computational Fluid Dynamics (CFD), which in turn indicated that the predictions agree well with the combined database. The satisfactory results suggest that the ANN model is generalized to correlate the heat transfer and fluid flow of such three kinds of heat exchangers with large tube-diameter and large tube-row. It is recommended that ANNs might be used to predict the performance of thermal systems in engineering applications.
Validation of a Thermal Spreading/Constriction Resistance Model for a Convectively Cooled Plate With an Applied Heat Flux
Authors: Lee P. Y. C. , Leong W. H.
Published: July 2009

A thermal resistance model of a two-dimensional boundary value problem (BVP) that is commonly found in engineering/experimental heat transfer is presented. The problem consists of two different convectively cooled sub-sections along one boundary, and a heat flux distribution imposed on a portion of another (opposite) boundary, coupled with adiabatic conditions (Neumann boundary conditions) along the remaining boundaries under steady-state conditions. In solving this BVP, the solution technique is highlighted. Consistent with theory, the solution to this problem depends on two Biot numbers, dimensionless heat flux and other dimensionless geometric parameters related to the problem. The present solution is an exact general solution to an existing two-dimensional problem found in literature, and as a special case, the general solution reduces exactly to the existing solution. Also, the present model is validated by comparing the present solution with measured data, and in terms of a temperature difference between two locations on the plate, the analytical solution is well within the experimental error of 0.03 K.
Numerical Investigation on Bubbly Flow and Heat Transfer Characters in a Liquid-Reactor
Authors: Yang Lixin
Published: July 2009

Gas-liquid flow and heat transfer in a nuclear reactor were investigated by the CFD simulation. The MUSIG model and the mono-disperse model are applied to model the multiphase flow and heat transfer. The comparison with experimental data indicates that the gas-liquid flow and heat transfer in the nuclear reactor could be well captured by the suggested numerical model. The temperature distribution, velocity distribution, bubble diameter distribution in the nuclear reactor and heat transfer coefficient of the cooling coils were analyzed. In addition, the effect of gas generation rate on heat transfer coefficient of the cooling coils was discussed. This research work has provided fundamental understanding of gas-liquid flow and heat transfer in the nuclear reactor as well as the design guidance of the cooling coils.
Turbulent Flow in a Composite Channel With a Wavy Interface
Authors: de Lemos Marcelo J. S.
Published: July 2009

This paper presents numerical solutions for turbulent flow in a channel containing a layer of porous material with wavy form. One unique set of transport equations, for mass and momentum, is applied to both regions, namely the clear and porous domains. Effects of interface wave number on mean and turbulence fields are investigated. Results indicate that around the peaks of the sinusoidal layer values of the turbulent kinetic energy are higher for lower values of n, where n is the wave number associated with the wavy interface shape. Also, as the surface gets rough (high n), the use of a jump condition for the diffusion flux across the interface does not affect the pressure drop along the channel.
Heat and Mass Transfer From Platinum-Coated Cylinders in Axisymmetric Hydrogen-Air Boundary Layers
Authors: Tong Timothy W. , Abou-Ellail Mohsen M. , Li Yuan
Published: July 2009

Catalytic combustion of hydrogen-air mixtures involves the adsorption of the fuel and oxidant into a platinum surface, chemical reactions of the adsorbed species and the desorption of the resulting products. Re-adsorption of some produced gases is also possible. The catalytic reactions can be beneficial in porous burners that use low equivalence ratios. In this case the porous burner flame can be stabilized at low temperatures to prevent any substantial gas emissions, such as nitric oxide. The present paper is concerned with the numerical computation of heat transfer and chemical reactions in flowing hydrogen-air mixtures axisymmetrically around a platinum-coated thin cylinder. Chemical reactions are included in the gas phase and in the solid platinum surface. In the gas phase 8 species are involved in 24 elementary reactions. On the platinum hot surface, additional surface species are included that are involved in 14 additional surface chemical reactions. The platinum surface temperature is fixed, while the properties of the reacting flow are computed. The flow configuration investigated here is the parallel boundary layer reacting flow over a cylinder. Finite-volume equations are obtained by formal integration over control volumes surrounding each grid node. Up-wind differencing is used to ensure that the influence coefficients are always positive to reflect the physical effect of neighboring nodes on a typical central node. The finite-volume equations are solved iteratively for the reacting gas flow properties. On the platinum surface, surface species balance equations, under steady-state conditions, are solved numerically by an under-relaxed linear algorithm. A non-uniform computational grid is used, concentrating most of the nodes near the catalytic surface. Surface temperatures, 1150 K and 1300 K, caused fast reactions on the catalytic surface, with very slow chemical reactions in the flowing gas. These slow reactions produce mainly intermediate hydrocarbons and unstable species. The computational results for the chemical reaction boundary layer thickness and mass transfer at the gas-surface interface are correlated by non-dimensional relations, taking the Reynolds number as the independent variable. Chemical kinetic relations for the reaction rate are obtained which are dependant on reactants concentrations and surface temperature.
Transient Pool Boiling CHF in FC-72
Authors: Sutopo P. F. , Fukuda Katsuya , Liu Qiusheng
Published: July 2009

In the current work, critical heat fluxes (CHFs) and related boiling phenomena due to transient heat inputs, Q0exp(t/τ), to horizontal finite heaters were investigated in a pool of FC-72. Investigations were made on 1.0 mm diameter horizontal cylinders and a horizontal vertically oriented ribbon (4.0 mm × 0.1 mm × 31.5 mm) under a wide range of pressures ranged from 79.5 kPa up to 1278.1 kPa and liquid subcoolings ranged from saturated up to 140 K. The CHFs obtained from each heater with their dependency on pressure and liquid subcooling, and the typical ones against exponential period, τ, were observed and compared. The transition boiling processes to film boiling including mechanisms of incipient boiling and CHF, and vapor and bubble behaviors were also derived.
Measurement of Transient Natural Convection in Non-Ventilated Aircraft Compartments
Authors: Egan V. , Confrey T. W. , Newport D. , Lacarac V.
Published: July 2009

The present study focuses on heat transfer behaviour in aircraft compartments. The objectives of the analysis were to investigate the transient effects on fluid flow structures and heat transfer mechanisms in aircraft wing boxes relative to aircraft turnaround times. Experimental methods employed were flow visualisation and thermocouple measurements. A simplified air filled aluminium rectangular enclosure of aspect ratio 0.25 was constructed to replicate an aircraft wing box. Rubber insulation was used between wall surfaces to maintain separate thermal boundary conditions at each wall. Flow visualisation was used to illustrate the transient evolution of full field flow structures and thermocouple measurements were recorded to investigate the full field transient temperature distribution. Experiments were carried out from time zero to steady state and were conducted for Rayleigh numbers of 2.87×106, 4.81×106 and 7.39×106 based on enclosure height. Fluid flow patterns revealed the presence of two counter acting flows in the cavity with a downward motion adjacent to the front and rear sides of the enclosure. The downward motions were present due to the cooling of the warm air inside the cavity by the adjacent cooler aluminium side walls. Secondary flows existed in the lower region of the cavity specifically prominent to the front and rear surfaces where the height of detachment of the flow varied with time and temperature of the adjacent side walls. Transient spatial temperature distribution plots confirmed the approach to steady state was gradual, that a vertically thermal stratified distribution existed in the cavity and the presence of the thermal boundary layers along the horizontal and vertical walls were clearly evident. It was concluded that transient effects are significant relative to aircraft turnaround times as it was observed that the flow structures change over the initial transient phase of analysis and remain similar thereafter. Wing box material thermophysical properties influenced the developed flow structures causing two secondary flows to exist along the front and rear spar walls. Vertical temperature distribution results were generalised using a power law based on dimensionless time (t*), dimensionless temperature (T*) and Rayleigh number.
Modeling and Analysis of Natural Convection Heat Transfer in Nanofluids
Authors: Congedo Pietro Marco , Collura Stefano , Congedo Paolo Maria
Published: July 2009

Nanofluids are engineered colloids made of a base fluid and nanoparticles (1–100 nm). The presence of nanoparticles causes a dramatic enhancement of thermal conductivity, an increase of convective heat transfer coefficient as well as of viscosity. These features make nanofluids suitable for the most common industrial cooling and heat transportation applications, for example in the heat exchanger whose performances can be dramatically improved. In the nanofluid literature it is not really evident the mechanism inside the unusual heat transport properties. Several studies concerning nanofluids were carried out to provide experimental data for different configurations and to find models suitable with these experiments. Unfortunately measurements available in literature seem to be affected by a significant dispersion so that some experimental data are not coherent with the others. The issue is that the properties of nanofluid are influenced by many factors such as the nature of the components, the nanoparticle size, shape and concentration, the temperature, the pH of the solution, the presence of surfactants (used to stabilize suspensions), and the charge state of the particle in suspension. Not all of these quantities are usually measured in an experimental campaign and then sometimes it is not possible to make a comparison between different experimental data available in literature. For this reason, several models proposed to validate experimental measurement work well only within a small range of validity, in terms of temperature or concentration interval or nanoparticle type. In this paper we consider always the nanofluid as a single phase and we compared different models presented in literature for the following properties: density, specific heat, viscosity and thermal conductivity. (All this properties depend, at least, on the nanoparticles concentration in the base fluid). The water-Al2O3 nanofluid is considered since several models and experimental data are available for this kind of fluid. The numerical simulations have been made by using the CFD code Fluent (release 6.3), where the models have been implemented by using external routines. The natural convection in a horizontal tube heat exchanger has been simulated in a wide region of conditions for which experimental data are available. Different models proposed in literature for viscosity and thermal conductivity have been considered, and compared to empirical models obtained by means a regression from experimental data. Aim of this work is to set suitable models which allows reproducing nanofluid behavior with a good accuracy in a wide region of different conditions.
Dryout During Flow Boiling in a Single Circular Minichannel: Experimentation and Modelling
Authors: Del Col Davide , Cavallini Alberto , Bortolin Stefano , Matkovic Marko , Rossetto Luisa
Published: July 2009

This paper presents an experimental investigation on the dryout during flow boiling of R134a and R32 inside a 0.96 mm diameter single circular minichannel. In the present tests, the test channel is not electrically heated; instead, the flow boiling is achieved by means of a secondary fluid (water). Therefore, the heat flux is not uniform in the channel since the temperature of the water varies. The onset of dryout is detected by means of the standard deviation of the temperature readings in the wall. The wall temperature in fact displays larger fluctuations in the zone where dryout occurs, which are related to the presence of a liquid film drying up at the wall with some kind of an oscillating process. These temperature fluctuations are detected by means of the standard deviation in the wall temperature. These temperature fluctuations never appear during condensation tests, neither are present during flow boiling at low vapor qualities. The fluctuations also disappear in the postdryout zone. Experimental values of dryout quality measured with the above method are reported in this paper at mass velocity ranging between 100 and 700 kg m−2s−1 for R134a and between 200 and 900 kg m−2s−1 for R32. Since the heat flux is not uniform along the channel, each dryout point is characterized by its own boiling story. Nevertheless, an average value of heat flux can be defined in the channel, with the purpose of comparing it to critical heat flux values in uniformly heated channels. Present experimental data has been compared against some models available in the literature, which provide either the critical heat flux or the dryout quality in microchannels.
Thermosolutal Convection and Solute Segregation of Hg1−xCdxTe Alloy During the Vertical Bridgman Single Crystal Growth
Authors: Lu Jun , Bai Bofeng , Wen Zhixiang
Published: July 2009

The thermosolutal convection and solute segregation of Hg1-xCdxTe alloy during the vertical Bridgman single crystal growth have been numerically analyzed. Based on the thermal properties changed with the temperature and concentration, the coupling laws between temperature and solute gradients in the melt and the effects of thermosolutal convection on the solute segregation are studied in the paper. The main results obtained are as followed. Firstly, the stabilizing solute gradient will damp the convection caused by temperature gradient in the melt. But the damping effect of solute gradient will be significant only when the absolute value of the solute Rayleigh Number increases to the thermal Rayleigh Number. Secondly, when the solute gradient is large, the upper flow in the melt will be a sideway diffusive instability flow and evolve to a twocell construction. Thirdly, the solute distribution in the melt is mainly determined by the flow intensity and construction and the solute segregation near the solidification interface will be improved as the intensity of the lower flow decreases.
Evaluating a Thermoregulatory Model for Cooling Garment Applications With Transient Metabolic Rates
Authors: Westin Johan K. , Kapat Jayanta S. , Chow Louis C.
Published: July 2009

Current state-of-the-art thermoregulatory models do not predict body temperatures with the accuracies that are required for the development of automatic cooling control in liquid cooling garment (LCG) systems. Automatic cooling control would be beneficial in a variety of space, aviation, military, and industrial environments for optimizing cooling efficiency, for making LCGs as portable and practical as possible, for alleviating the individual from manual cooling control, and for improving thermal comfort and cognitive performance. In this paper, we adopt the Fiala thermoregulatory model, which has previously demonstrated state-of-the-art predictive abilities in air environments, for use in LCG environments. We compare the model’s tissue temperature predictions with analytical solutions to the bioheat equation, and with experimental data for a 700 W rectangular type activity schedule. The thermoregulatory model predicts rectal temperature, mean skin temperature, and body heat storage (BHS) with mean absolute errors of 0.13°C, 0.95°C, and 11.9 W·hr, respectively. Even though these accuracies are within state-of-the-art variations, the model does not satisfy the target BHS accuracy of ±6.5 W·hr. We identify model deficiencies, which will be addressed in future studies in order to achieve the strict BHS accuracy that is needed for automatic cooling control development.
Thermal Transport Measurements of Nanowire-Substrate Interfaces
Authors: Mazumder Monalisa , Borca-Tasciuc Theodorian
Published: July 2009

An AFM based method for characterization of thermal transport properties of electrically conductive individual nanowires and nanowire-substrate interfaces has been developed. Nanostructures are located by topographic imaging in regular tapping mode and are then subsequently probed by an AFM cantilever tip, with a conductive coating thus establishing electrical contact at different positions on the nanowire followed by current-voltage data acquisition. This experimental approach can be implemented for a system with nanostructures in contact with the surface and, in the other case, suspended between electrodes. These configurations allow for characterization of both thermal conductivity and nano-interface thermal resistance. This work presents the technique along with the subsequent measurements of nano-interface thermal resistance of nanowire-substrate junction using the aforesaid technique.
Numerical and Experimental Study on Heat Transfer Process Under Microwave Irradiation Using Reflector to Enhance Energy Absorption Rate
Authors: Kumja M. , Choon Ng Kim , Loh Wai Soong , Yap Christopher
Published: July 2009

With the energy saving concerns, microwave heating method becomes much attention in heating process of various applications. Depending on applicator geometry design, type of work load, and position in a microwave heating system, it can save energy 20% to 40% more than the energy consumed by a conventional heating method. However, it is difficult to achieve this energy saving for low dielectric constant workload that cannot perform as a self-dielectric resonator (DR) load. This paper aspires to propose a new method of inserting reflector into the low dielectric constant load to enhance energy absorption rate under the microwave irradiation process. The spatial electromagnetic fields (E-field and H-field) patterns of this workload and applicator were simulated with the commercial HFSS software. By using the Poynting vector theorem, the dissipation power intensity can be calculated from the electromagnetic field and it is integrated to the second order heat transfer equation. The numerical temperature distribution result was resemblance with the experimental result. From both numerical and experimental results, the energy absorption rate of workload can be improved obviously by using a reflector as compared to the rate without using the reflector for low dielectric constant.
A New Bipolar Plate of PEM Electrolysis Cell With Uniform Flow and Heat Transfer Fields
Authors: Nie J. H. , Veepuri K. M. , Chen Y. T. , Wu J. F.
Published: July 2009

Optimization of electrolysis cell for producing hydrogen is dependent of a set of complex physical and chemical processes occurring simultaneously. Similar to fuel cells, it has been demonstrated that these processes are strongly dependent on the fluid dynamics inside the fuel cell. Bipolar plates are important components of PEM electrolysis cells because they are the first stage of the flow distribution system. A non-uniform flow distribution across the bipolar plate surface area will probably lead to an unbalanced use of the precious catalyst, and an overall efficiency of the device lower than expected. In the present work a new design of bipolar plate for the PEM electrolysis cell was proposed and 3-D CFD modeling was preformed. Velocity, temperature and pressure distributions within the bipolar plate were investigated. Numerical simulations showed that the flow uniformity within the designed bipolar plate is greatly improved compared with the baseline bipolar plate for water electrolysis.
CFD Analysis of Batch-Type Reheating Furnace With Regeneratve Burners
Authors: Wu Bin , Roesel Tom , Arnold Andrew M. , Xu Zhaojiang , Arnold Eugene , Downey George , Zhou Chenn Q.
Published: July 2009

A reheating furnace is a critical component in value-added steel production. These furnaces can have a significant impact on product quality and total cost. Due to the higher efficiency of regenerative burners, a growing number of reheating furnaces are using this technology. To better understand the regenerative burner operation, a Computational Fluid Dynamics (CFD) analysis has been conducted to examine the transient and three dimensional flow characteristics in the No.3 reheating furnace at ArcelorMittal Steelton. Simulation results with traditional burners and regenerative burners have been analyzed to understand the effect of retrofitting a furnace with these more modern burners. The temperature distribution on the billets has also been monitored throughout the simulated heating process providing insight into the optimization of billet residence time and improvement of the product quality control process.
Phenomenon Identification and Ranking Exercise and a Review of Large-Scale Spray Modeling Technology
Authors: Brown Alexander L. , Yoon Sam S. , Jepsen Richard A.
Published: July 2009

We are engaged in efforts to model spray phenomena. Applications of principal interest include the high-speed impact of large vessels of fuel and the subsequent fire, fire suppression, solid propellant fires, pressurized pipe or tank rupture, and fire propagation for cascading liquid fuels. To help guide research and development efforts geared towards designing an appropriate spray modeling capability, a Phenomenon Identification and Ranking exercise was conducted. The summarized results of the exercise in tabular format, a Phenomenon Identification and Ranking Table (PIRT), are presented. The table forms the context for a textual literature review of the existing state of knowledge for modeling applications of interest. This exercise highlights some of the shortcomings in existing tools and knowledge, and suggests productive research activities that can help advance the modeling capabilities for the desired applications. Notable needs exist for research in high Weber number particle-surface impacts, particle collisions, multi-physics couplings, and low void fraction multi-phase coupling.
Thermal Ablation of Mouse Skin Tissue Using Ultra-Short Pulse 1552 nm Laser
Authors: Sajjadi Amir Yousef , Onyejekwe Ogugua , Raje Shreya , Mitra Kunal , Grace Michael
Published: July 2009

Analysis of biological tissue ablation by an ultra-short pulse laser and the corresponding mathematical modeling of ablation are of fundamental importance to the understanding of laser-tissue interaction for advancing surgical application of lasers. The objective of this paper is to analyze the thermal ablated damage zones during irradiation of freshly excised mouse skin tissue samples by a novel approach of using a focused laser beam from an ultra-short pulse laser source. Experiments are performed using Raydiance Desktop Laser having a wavelength of 1552 nm and a pulse width of 1.3 ps. Mouse tissue samples are translated in a direction perpendicular to the laser beam using three-axis automated motion-controlled stages. Scanning of the tissue sample ensures a fresh region of the tissue is irradiated each time. The surface temperature distribution is measured using a thermal imaging camera. It is observed that use of focused beam results in minimal radial heat spread to the surrounding tissue regions. The ablation phenomenon is analytically modeled by the use of two-phase transient heat conduction model. After completion of tissue irradiation experiments, histological studies are performed using frozen sectioning technique to observe morphological changes in tissue samples in response to laser irradiation. The ablation depth measurements obtained using histological studies are compared with the modeling results. A parametric study of various laser parameters such as time-average power, pulse repetition rate, and pulse energy, and as well as irradiation time and scanning velocity is performed to determine the necessary ablation threshold. Analytical modeling results are in very good agreement with experimentally measured ablation depth. The goal of this research is to develop a tool for selection of appropriate laser parameters for precise clean tissue ablation.
Performance of Thermoacoustic Refrigerators: Cooling Load and Coefficient of Performance
Authors: Herman Cila , Lavin Christopher , Tra´vni´cˇek Zdeneˇk
Published: July 2009

Thermoacoustic refrigeration is an environmentally safe refrigeration technology that has evolved over the past three decades [1–5]. The influence of working fluid on the performance of the thermoacoustic refrigerator (TAR) expressed in terms of the cooling load and the coefficient of performance is discussed in the paper. The calculations rely on the short stack boundary layer approximation. A simple model of a one-dimensional half wavelength resonance tube equipped with stack plates and a pair of heat exchangers was used as the physical model. It is known that a TAR with noble gases and their mixtures as working fluids can achieve high values of the coefficient of performance (COP) because of small Prandtl number values. The present study revealed and quantified that cooling load behavior is quite different from the performance in terms of the COP: the highest cooling load is achieved with pure Helium as the working fluid. A reason is the very high sound speed in Helium. TARs with Helium as the working fluids deliver the highest cooling load of all gases and their mixtures examined here, therefore it has been suggested as a limiting case of the most powerful TAR. The influence of geometry and thermophysical parameters of the device on TAR performance was studied systematically and a performance sensitiviy analysis was presented with particular emphasis on TAR cooling load.
Investigation of Potential Benefits of Using Bricks of High Thermal Capacity and Conductivity in a Rotating Calcining Kiln
Authors: Zhao Lei , Wang Ting
Published: July 2009

Petroleum coke is processed into calcined coke in a rotary kiln, where the temperature profiles of flue gas and coke bed are highly nonuniform due to different flow and combustion mechanisms. Motivated by saving energy costs, the effect of refractory brick’s thermal properties on potential energy savings is investigated. This study focuses on investigating potential energy savings by replacing inner one third of existing bricks with higher thermal capacity (Cp) and/or higher thermal conductivity (k) bricks. This investigation is motivated by postulating that the bricks with higher thermal capacity can store more thermal energy during the period of contacting with the hot gas and release more heat to the cock bed when the bricks rotate to below and in contact with the coke bed. A rotational, transient marching conduction numerical simulation is conducted using the commercial software FLUENT. The impact of brick heat capacity and thermal conductivity on transporting thermal energy to the coke bed is analyzed. The results show: (a) Increasing the heat capacity of brick layer reduces brick temperature which helps increase the heat transfer between the hot gas and brick, in other words it does help brick store more heat from the hot gas, but, heat transfer between brick and coke is reduced, which is opposite to the original postulation. (b) Higher brick thermal conductivity decreases brick temperature thus increases heat transfer between hot gas and the brick layer. The heat transfer from brick to coke bed is also increased, but not significantly. (c) Usually a brick with a higher Cp value also has a higher k-value. Simulation of a brick layer with both four times higher Cp and k values actually show appreciable heat is transported from the brick to the coke bed for one rotation for both lower and higher Cp and k bricks. The difference is not significant.
Analytical Study of Heat and Mass Transfer in Porous Sheets During Contact Drying Process
Authors: Izadpanah Mohammad R. , Ansari Dezfooli Amir R.
Published: July 2009

Contact drying process has gained wide application in different industries including paper, ceramics and construction industries. Suitable control over temperature distribution will result in required moisture content and its distribution. In the present study, governing equations for a porous sheet are derived using Luikov equation. These equations are then converted into sturm-liouville equations and solved simultaneously. Comparison of temperature and moisture distributions with numerical data shows a close agreement.
Experimental Model to Characterize the Evaporative Cooling of Horizontal Roofs
Authors: Gil Samaniego Ramos Margarita , Campbell Rami´rez He´ctor Enrique
Published: July 2009

Heat and mass transfer models were developed experimentally to characterize the evaporative cooling of horizontal roofs, heated by thermal radiation. Surface temperatures of flat plates were evaluated at dry conditions and when humidified with water atomizers. For both conditions, heat transfer rates were calculated, and for the wet case also the mass transfer rates were predicted. Experimental data for models validation were measured at environmental and controlled conditions. Accuracies achieved were 2% for surface temperature and 13% for water evaporation rate.
Analysis of Temperature Response in Biological Tissue With Sinusoidal Temperature Oscillation on the Skin
Authors: Yuan Ping , Liu Hsueh-Erh , Chen Chih-Wei , Kou Hong-Sen
Published: July 2009

This study investigates the transient temperature response in biological tissue with sinusoidal temperature oscillation on the skin surface. Based on the Laplace transform, an exact solution of the Pennes bioheat transfer equation has been derived which includes the whole time domain from the initial transient oscillation to the final steady periodic oscillation. Furthermore, the exact solutions of special cases under no perfusion rate, constant temperature, and the combination of those two assumptions are demonstrated in this study. The primary application for this type of analysis is to assess the blood perfusion rate in the skin by imposing a periodic temperature load onto the skin surface. Through the noninvasive measurement of the maximum heat flux or minimum heat flux on the skin, equation (15) can be utilized to estimate the blood perfusion rate in living tissues. The results show that both the larger perfusion rate and greater tissue depth decrease the amplitude of the sinusoidal temperature response. A larger perfusion rate can also reduce the unstable duration for the estimation of the blood perfusion rate. Meanwhile, the shift of phase angle related to the sinusoidal temperature variation increases with tissue that is deeper and has lower perfusion rate.
Investigation on Heat Transfer and Its Effect on Titanium Hot Forging Process
Authors: Davami K. , Shaygan M. , Besharaty M. K. , Mellat A. , Serajzadeh B.
Published: July 2009

Titanium forged components have been widely used in aircraft engine industry because of their superior specific strength to weight ratio at high temperature. Turbine disk is one of the most demanding forging parts. The flow stress of titanium alloy Ti-6Al-4V is strongly dependent on temperature and strain rate during hot forging. The cooling rate can be designed to manage the temperature profile of dies by distinct spray setup. The workpiece loses heat to die by contact when getting heat up for deformation. The study aims to assess the influence of the discrete cooling rate and interfacial contact heat transfer on the optimum plastic deformation and the optimum die life for a Ti-6Al-4V hot-die forging. A two-dimensional FEM model of titanium turbine disk is employed to study the mechanical and thermal interaction between the hot dies and the workpiece. After hundreds of runs of the forging cycles thermal-steady state is built up and the thermal-steady simulation is considered to reflect the actual production situation. The development of different microstructure and phase compositions in various regions of workpiece is the result of the high sensitivity of two-phase TI-6Al-4V to strain and temperature of plastic deformation. Proper selection of these parameters allows one to control its mechanical properties and avoid deformation failure. Providing the productivity and economic demands, thermal design is a more manageable way than strain rate control for hot die forging. Microstructure control and uniformity of deformation can be achieved through the selection of optimum processing conditions with the aid of processing maps. This research focuses on the effects of forging interfacial heat transfer coefficient and discrete cooling rate along tool cavity when other processes parameters such as strain rate and cycle time given fixed. The temperature control will help achieve a good balance among strength, ductility and fracture toughness. The flow stability, load and energy, die wear, and die tempering and chilling are investigated for a turbine disk hot-die forging using a two-dimensional FEM model.
Corrosion of the Materials in Sulfuric Acid
Authors: Kim Hong Pyo , Kim Dong-Jin , Kwon Hyuk Chul , Park Ji Yeon , Kim Yong Wan
Published: July 2009

The program for hydrogen production with high temperature nuclear heat has been launched in Korea since 2004. Iodine sulfur (IS) process is one of the promising processes for a hydrogen production because it does not generate a carbon dioxide and massive hydrogen production may be possible. However, the highly corrosive environment of the process is barrier to the application in the industry. Therefore, corrosion behaviors of various materials were evaluated in sulfuric acid to select appropriate materials compatible with the IS process. The materials used in this work were Ni base alloys, Fe-Si alloys, Ta, Au, Pt, Zr, SiC and so on. The test environments were boiling 50wt% sulfuric acid without/with HI as an impurity and 98wt% sulfuric acid. The surface morphologies and cross sectional areas of the corroded materials were examined by using SEM equipped with EDS. From the results of the weight loss and potentiodynamic experiments, it was found that a Si enriched oxide is attributable to a corrosion resistance for materials including Si in boiling 98wt% sulfuric acid. Moreover the passive Si enriched film thickness increased with the immersion time leading to an enhancement of the corrosion resistance. Corrosion behaviours of the material tested are discussed in terms of the chemical composition of the materials, a corrosion morphology and the surface layer’s composition.
Development of a Continuous CVD Process for TRISO Coating of AGR Fuel
Authors: Keeley Joseph T. , Tomlin Bruce L. , Richardson W. Clay , Barnes Charles , Marshall Douglas
Published: July 2009

As part of the Department of Energy’s Advanced Gas Reactor Fuel program, Babcock & Wilcox is developing a fluidized bed chemical vapor deposition process to deposit a TRISO coating on UCO and UO2 kernels. These coated kernels will go into irradiation tests in the Advanced Test Reactor at Idaho National Laboratory. This paper reports on the development activities including the furnace design and the furnace runs made to qualify the coating process.
Improvement of Nuclear Grade Graphite Based on Isotropic and Highly Crystalline Natural Graphite by Generation of Silicon- or Zirconium-Carbide in Situ
Authors: Grosse Karl-Heinz , Hrovat Milan , Seemann Richard , Feher Robert
Published: July 2009

Following the fabrication technique originally developed for HTR-molded block fuel elements a process was introduced to fabricate nuclear graphite with the aim to attain the improved irradiation stability above 3 × 1022n/cm2, E > 0,1 MeV and to increase corrosion resistance. Nuclear highly crystalline natural graphite is used. A phenol formaldehyde resin with additives of silicon or zirconium oxide powder serves as binder. The mixture thus obtained is isostatically consolidated into spheres and spheres are crushed to granules from which the 0.3 – 3 mm fraction is obtained. The granulate is hot molded into graphite bodies. The green bodies are heated to about 800 °C to carbonise the resin and subsequently annealed at 1900°C in vacuum. The key feature of the proposed process is based on the chemical affinity of binder coke with the structure obtained by carbonisation of green bodies. Consequently it reacts selectively in situ with the added SiO2, or ZrO2to carbides in vacuum at 1900°C. Silicon carbides and zirconium carbides are characterised by high mechanical strength and very good resistance to corrosion. The properties of reactor graphite, such as density, mechanical properties and in particular stability to fast neutron irradiation are considerably improved.
Relicensing Fort St. Vrain: How the HTGR Design Basis Was Rediscovered
Authors: August J. K. , Hunter J. J.
Published: July 2009

Over its 1968–1988 life, PSCo relicensed the Fort St. Vrain (FSV) High-temperature Gas Reactor (HTGR) for light water reactor (LWR) technology requirements. Estimates of the financial losses associated with the plant range from $500 million to $2 billion in 1980 dollars. Colorado ratepayers, the shareholders of Gulf General Atomics and its corporate successors — General Atomics, GA Technologies or just GA and Public Service Company of Colorado (PSCo) bore these losses. Two critical plant issues required solution for the plant’s economic success — (1) the high-cost of 93% enriched uranium fuel and (2) low unit availability. While fuel costs were beyond utility control, low availability was controllable, yet remained unresolved. Commercially isolated for twenty years, PSCo shut the plant down in 1988. Economic success of future HTGRs depends upon avoiding similar complications. This paper examines the issues that made FSV uneconomic, including those fundamental to HTGR technology and others attributable to the utility operator and its culture. Knowing the history of FSV and HTGR design, designers should anticipate reasonable challenges. Preparations will help manage future HTGR risks, costs, and assure operating success. Regulators and industry can assure more effective, economic operations in the next round of HTGR designs.
Development of a Fuel Performance Analysis Code COPA
Authors: Kim Young Min , Cho M. S. , Lee Y. W. , Lee W. J.
Published: July 2009

A fuel performance analysis code for a very high temperature gas-cooled reactor (VHTR) COPA (Coated Particle) is being developed at the Korea Atomic Energy Research Institute (KAERI). The COPA code consists of nine modules: BURN, TEMTR, TEMPEB, TEMBL, MECH, FAIL, FPREL, ABAQ, and MPRO. The BURN determines neutron flux and fluence at a location of a reactor core, and then calculates a fuel burnup, a fission rate per volume and a fission product inventory throughout a fuel particle and a fuel element. The TEMTR, TEMPEB and TEMBL calculate the temperature distributions in a coated fuel particle, a pebble and a fuel block by using a one-dimensional finite difference method, respectively. The MECH performs mechanical calculations on a coated fuel particle by using a finite element method. The FAIL performs probabilistic calculations to estimate the failure probabilities of the coating layers during an experiment or a reactor operation. The FPREL estimates the migrations of gaseous and metallic fission products through a fuel particle and a fuel element by using a one-dimensional finite difference method. The ABAQ performs the analysis of the crack and debonding in a coated fuel particle. The MPRO calculates the material properties of the kernel, low-density pyrocarbon, high-density pyrocarbon, silicon carbide, matrix graphite, and structural graphite. Each module is used to produce input data for other modules or is inserted into other modules. The COPA code is one of the computer codes taking part in the IAEA-CRP-6 benchmarking program. The stresses and failure fractions calculated by the COPA-MECH and COPA-FAIL showed good agreements with the results by the other countries’ codes. In order to establish a good database of the related material properties, KAERI is participating in an international irradiation experiment, is planning its own irradiation and post-irradiation experiments, and will perform ab-initio calculations on the fuel materials.
Development of a Strategy for the Management of PBMR Spent Fuel in South Africa
Authors: Smith Schalk W. , Bredell P. J. , Meyer W. C. M. H.
Published: July 2009

South Africa is planning to expand its nuclear power generating capacity by deploying a number of pressurized-water reactors and pebble-bed modular reactors. It can be expected that this program will impact on the current and planned spent fuel and radioactive waste management systems in South Africa. This paper proposes an approach to develop a strategy for the management of PBMR spent fuel that would contribute to the optimization of the overall national radwaste management system. The approach is expected to provide a conceptual spent fuel management strategy and will also highlight areas that need to be further developed, thus providing guidance for basic technology development.