bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Cell Metabolic Activities Using Fluorescence Microscopy
Authors: Sabados Dawn M. , Xu Lisa X. , Gore Jay P.
Published: December 2008

In the present study, cultured normal rat microvessel endothelial cells are first used to explore the feasibility of studying the cell metabolic activities by detecting autofluorescence intensities. A mercury lamp is used to induce autofluorescence emissions in cells. Under an excitation wavelength of 360nm, the emissions peak at 470 nm corresponds with the autofluorescence signature of NAD(P)H, the concentration of which has been linked to the metabolic rate of the cell. A relation between the emission intensity and the NAD(P)H concentration is established. Based upon the results and observations of the endothelial cells, a protocol is developed for studying the autofluorescence of other cultured cells. It has been long known that cancer cells divide much more rapidly than normal cells depending on the degree of the tumor malignancy. The differences in metabolic rates of normal and cancerous breast cells are explored as they relate to autofluorescence emissions at different wavelengths and intensities. The comparison results can be used as a guideline to determine whether cells are cancerous. At a tissue level, laser excitation is probably needed to obtain measurable autofluorescence signals. The potential of autofluorescence measurement as a breast cancer diagnostic tool is discussed.
Mixed Laminar Free Convective Flows in Enclosures With Arrays of Partial Partitions: A Numerical Study
Authors: Costa V. A. F. , Oliveira M. S. A. , Sousa A. C. M.
Published: December 2008

Laminar natural convection within a tall enclosure of aspect ratio of 5, and subdivided in five compartments by partial partitions (shutters) is studied numerically. The boundaries for the enclosure sidewalls are isothermal, while the partitions, although thin, are of finite thickness, and they participate in the overall convective heat transfer process (conjugate problem). The influence of the partitions’ angle upon the overall Nusselt number is examined for a range of 60° to −60°. The Rayleigh number was varied from 103 to 107. The results are presented in terms of a normalized Nusselt number as a function of the Rayleigh number, and of the partitions’ angle. Particular attention is given to the interaction between the flow entering the cavity and the recirculating flow within the cavity, and to the eventual linkage between adjacent compartments through their thermal and flow conditions.
Application of the Conservation Element and Solution Element Method in Numerical Modeling of Three-Dimensional Heat Conduction With Melting and/or Freezing
Authors: Ayasoufi Anahita , Keith Theo G.
Published: December 2008

The conservation element and solution element (CE/SE) method, an accurate and efficient explicit numerical method for resolving moving discontinuities in fluid mechanics problems, is used to solve three-dimensional phase change problems. Several isothermal phase change cases are studied and comparisons are made to existing analytical solutions. The CE/SE method is found to be accurate, robust and efficient for the numerical modeling of phase change problems.
Reciprocating-Mechanism Driven Heat Loops and Their Applications
Authors: Cao Yiding , Gao Mingcong
Published: December 2008

This paper introduces a novel heat transfer mechanism that facilitates two-phase heat transfer while eliminating the so-called cavitation problem commonly encountered by a conventional pump. The heat transfer device is coined as the reciprocating-mechanism driven heat loop (RMDHL), which includes a hollow loop having an interior flow passage, an amount of working fluid filled within the loop, and a reciprocating driver. The hollow loop has an evaporator section, a condenser section, and a liquid reservoir. The reciprocating driver is integrated with the liquid reservoir and facilitates a reciprocating flow of the working fluid within the loop, so that liquid is supplied from the condenser section to the evaporator section under a substantially saturated condition and the so-called cavitation problem associated with a conventional pump is avoided. The reciprocating driver could be a solenoid-operated reciprocating driver for electronics cooling applications and a bellows-type reciprocating driver for high-temperature applications. Experimental study has been undertaken for a solenoid-operated heat loop in connection with high heat flux thermal management applications. Experimental results show that the heat loop worked very effectively and a heat flux as high as 300 W/cm2 in the evaporator section could be handled. The applications of the bellows-type reciprocating heat loop for gas turbine nozzle guide vanes and the leading edges of hypersonic vehicles are also illustrated. The new heat transfer device is expected to advance the current two-phase heat transfer device and open up a new frontier for further research and development.
Experimental Description of the Convective Heat Transfer Coefficient for Pool Boiling of Binary Mixtures on Porous Heating Surfaces
Authors: Mele´ndez Elva , Reyes Rene´
Published: December 2008

This work presents the experimental results of the effect of porous heating surfaces, and the Marangoni effect on the convective heat transfer coefficient for pool boiling, h. The porous heating surfaces fabricated for these experiments, and the interfacial tension gradients in the binary mixtures reduced the bubbles’ size and their coalescence in the proximity of the heating surface. The convective heat transfer coefficient was calculated for the boiling of pure water and three aqueous mixtures with 12, 16, and 20% weight of ethanol on five different porous coverings on the heating element. Some combinations of these variables were studied in a 32 factorial design, and represented by the response surface calculated. The maximum h for boiling of pure water on the bare surface of the heating element was 50 kW/m2 °C. Using the porous coverings, the maximum h value was 180 kW/m2 °C. For boiling the binary mixtures on the smooth heating element surface the maximum h value was 65 kW/m2 °C, while on the porous coverings the values of h attained a maximum of 220 kW/m2 °C. The maximum values of h correspond to the composition of 16% ethanol, and a porous covering with the smallest porous diameter.
Plasma Torch Interaction With a Melting Substrate
Authors: Hill Stephen D. , Desai Prateen
Published: December 2008

A model of a partially ionized, high pressure plasma in stagnation flow as it melts a nonhomogeneous solid is presented. It encompasses both the analysis of the multi-fluid plasma to ascertain its bulk temperature and the heat flux profile, as well as its interaction with a receding melt interface in and around the stagnation domain. The model examined in this study couples the plasma motion, bulk energy, electron and ion densities and temperatures, with impinging jet theory to determine the amount of heat transfer into the particular substrate material — soil. “Multi-fluid” equations are derived for an axially symmetric plasma from the Boltzmann equations for Maxwellian velocity distributions. By examining the dominant effects, the equations are scaled and the roles of the driving dimensionless parameters are established. For specified values of these parameters, various numerical methods are used to couple and solve the two distinct models. The first one, to ascertain the moving boundary phase change heat transfer characteristics, is developed by adopting a form of the enthalpy method. The second model, characterizing the plasma jet is solved via and adaptation of the commercially available code, CHEMKIN, developed by the Sandia National Laboratories. A parametric study is performed, leading to evaluation of such important torch characteristics including mass flow rate of the Argon gas, temperature of the plasma bulk, and proximity of the plasma torch to the surface, as it influences the substrate melt zone. The extremely high temperatures produced by the plasma irreversilby changes the material structure of the sample. This new structure, when cooled, forms a predominantly glassy product. Such a vitrification process has been proven to improve the construction properties of the soil and to reduce a toxic sample of the soil into a leachable solid. From the calculations of solid/liquid interfacial location, radii of the melt zones, and depths of the melt zones an overall perspective of the vitrification process is assessed.
Experimental Study on Natural Convection in an Asymmetrically Heated Inclined Channel With Radiation Exchange
Authors: Lin Qin , Harrison Stephen J.
Published: December 2008

Heat transfer in an asymmetrically heated, inclined channel by natural convection and radiation exchange was experimentally investigated. Experiments were conducted on channels with small inclination angle (to horizontal) ranging from 18° to 30° and a wall surface emissivity of 0.29 to 0.95. The channel length/space ratio was between 44 and 220. In each test, a uniform heat flux was applied along the top wall of the channel, while the bottom wall was thermally insulated. Temperature profiles along both the top and bottom walls of the channel were recorded under different heat flux and channel length/space ratios. The dependency of maximum wall temperature and heat transfer on the channel spacing and surface emissivity was explored. As a result of this work, correlations of local and average Nusselt number, with modified channel Rayleigh number, were determined and proposed for channels at inclination angle of around 18° and surface emissivities of around 0.95. The proposed correlation will be valid for modified-Rayleigh number in the range of 10 < Ra” < 5.6 × 104 at asymmetric heat flux boundary conditions.
Design Optimization of Heater Grid Plates
Authors: Khalilollahi Amir , Torab Hamid
Published: December 2008

Compact electrical heating and heat dissipating units are designed for several industrial applications where durability and stability of the unit under dynamic conditions have high priority. This paper initially investigates numerically the thermal characteristics of a custom build compact heater plate which can provide a geometrically optimized electrical resistance in application to heating or eliminating unwanted currents. The electrical resistance varies with the geometry and the locations of the cutouts (holes) in the plate. This analysis will significantly contribute to overall optimization of heating units that utilize these plates. The flow and thermal regimes between two adjacent ribbed plates with cutout holes were evaluated numerically by a finite difference code. This results in estimated local heat transfer coefficients which are used in the next phase of study. The second phase relates the heat transport to the temperature distribution on the plate by using a 3D finite element model. In the F.E. model, heat is generated due to non-uniform current through properly divided plate segments. Using this model the electrical resistance was evaluated as a function of hole geometry. Finally the geometry and location of ribs and holes were determined using a simple optimization technique in order to render the uniformity of surface temperature as desired for prevention of warping or excessive stresses.
Bubble Lift-Off Size in Forced Convection Subcooled Boiling
Authors: Situ Rong , Mi Ye , Sun Xiaodong , Ishii Mamoru , Mori Michitrugu
Published: December 2008

Forced convection subcooled boiling experiments were conducted in a BWR-scaled vertical upward annular channel. Water was used as the testing fluid, and the tests were performed at atmospheric pressure. A high-speed digital video camera was applied to capture the dynamics of the bubble nucleation process. Bubble lift-off diameters were obtained from the images for a total of 91 test conditions. A force balance analysis of a growing bubble was carried out. A constitutive relation for bubble lift-off size was obtained by correlating current water data and R113 data from literature. The proposed constitutive relation and experimental data agree well with each other.
Scaling of Downward Facing Boiling and Steam Venting in a Reactor Vessel/Insulation System
Authors: Cheung F. B. , Yang J. , Dizon M. B. , Rempe J. L. , Suh K. Y. , Kim S. B.
Published: December 2008

As part of joint U.S.–Korean International Nuclear Engineering Research Initiative (INERI) investigating methods to enhance external cooling of advanced reactor vessel under severe accident conditions, a scaling analysis has been performed to study the phenomena of external cooling of an advanced reactor vessel under severe accident conditions. Five key transfer processes have been considered and the characteristic time for each of these processes has been determined and compared with the residence time for external reactor vessel cooling (ERVC) in the flow channel. To complement the scaling analysis, an ERVC upward co-current two-phase flow model has been developed to predict the total mass flow rate induced in the annular channel by the process of downward facing boiling on the vessel outer surface. The model takes into account the wall heat flux level, the geometry of the vessel/insulation system, the local variation of the cross-sectional flow area, and the pressure drops through various segments of the channel. Based on the results of the ERVC flow calculations and the scaling analysis, criteria for experimental simulation have been established to assure that the ERVC phenomena simulated in laboratory-scale experiments would have the same effects as those anticipated for the full-scale reactor system.
Effects of Surface Coating on Nucleate Boiling Heat Transfer From a Downward Facing Surface
Authors: Dizon M. B. , Yang J. , Cheung F. B. , Rempe J. L. , Suh K. Y. , Kim S.-B.
Published: December 2008

As part of a joint U.S.-Korean International Nuclear Engineering Research Initiative investigating methods to enhance external reactor vessel cooling (ERVC) under severe accident conditions, it was proposed that surface coating be used to facilitate the process of downward-facing boiling. Toward this end, metallic micro-porous layer coatings were selected and different compositions of the coating material were evaluated to obtain a mixture with desirable qualities. Durability and adhesion tests were also done to study the performance of each of the resulting coatings. Quenching of the candidate coatings were then conducted under downward facing boiling conditions using hemispherical test vessels to obtain the local boiling curves. Compared to the case of plain vessel surface under identical experimental conditions, considerable enhancement was observed in nucleate boiling heat transfer and the critical heat flux (CHF) for the case with surface coatings. Optical and SEM (Scanning Electron Microscope) photos showed that the candidate coating possessed the desired porous microstructure with interconnecting channels and pores, leading to appreciable increases in the boiling heat transfer and the local CHF limits.
Development of a Negative Thermal Expansion Capsular Object Using Phase Change Material
Authors: Yamaguchi Y. , Takanashi K.
Published: December 2008

Driving device for heat transfer enhancement in a fluid layer heated from above was developed. The device was composed of two closed vessels of which the size differs. They are flexible in axial direction, and the lager vessel is filled with air and the smaller one is filled with phase change material (PCM). By the change of the steam pressure of the PCM, the device shrinks and sinks under water when it is hot, and it expands and floats on water when it is cold. The device has a negative thermal expansion behavior, so the authors named it negative thermal expansion capsular object, NTE capsule for short. In this study, the NTE capsule using phase change material (PCM) was developed. It was composed of the large vessel enclosing the air and small vessel enclosing the PCM. Perfluorocyclobutane (RC318) was used for the PCM. The vapor pressure of the PCM changes widely according to the temperature. The motion characteristics of the NTE capsule using PCM were investigated experimentally. As a result, it was confirmed that the new NTE capsule falls downward and rises upward spontaneously in a fluid layer heated from above.
Effect of Bubble Turbulence and Submergence on Onset of Boiling in Natural Circulation Loop
Authors: Shamsuzzoha M. , Kamil M. , Alam S. S.
Published: December 2008

Analysis of incipience boiling was developed for five different types of organic liquids including water covering wide range of physical properties. Incipience in liquid films is influenced by turbulent eddies and liquid submergence. This approach utilizes physical parameters of commonly accepted incipience models and provides a means of correcting these models for the effect of turbulent eddies and submergence. The results predicted from the theoretical analysis are consistent with the experimental data, having average absolute relative error of 13.61 percent.
Condensation Heat Transfer and Pressure Drop of R-134a Flowing in Annular Helical Pipes at Different Orientations
Authors: Yu B. , Lin C. X. , Ebadian M. A. , Prattipati R. C.
Published: December 2008

This paper presents an experimental investigation of condensation heat transfer and pressure drop characteristics of refrigerant R-134a flowing through an annular helicoidal passage with the hydraulic diameter of 8.5 mm. The angles of helix axis are oriented at 0, 45, 90 degrees to gravity. The overall and refrigerant-side heat transfer coefficients and pressure drops are experimentally determined at saturation temperature 35°C, refrigerant mass flux 35–180 kg/s·m2, and cooling water temperature 27°C. The results show that orientation has significant influence on the thermal and hydraulic behaviors of the helical pipe. The results can be employed for reference in the effective design of annular helicoidal heat exchangers with R-134a as the working fluid.
Characterization of Convection Patterns During the Solidification Process Using Particle Image Velocimetry
Authors: Ghenai C. , Duggirala R. K. , Lin C. X. , Ebadian M. A.
Published: December 2008

This experimental study focused mainly on the solidification of a binary mixture of ammonium chloride and water (NH4Cl-H2O) in a differentially heated cavity. One vertical wall is cooled at temperature TC, and the opposite vertical wall is kept at constant temperature TH = +20°C. The effect on the solidification process of the initial concentration of ammonium chloride and cooling conditions is examined. Particle image velocimetry (PIV) is used for the visualization of the dynamic field during the solidification process. The temperature distribution at discrete locations in the solution and on the vertical cooling wall was monitored using thermocouples. The convection flow patterns, the ice thickness, and the temperature distribution were obtained for various initial concentrations of ammonium chloride ranging from 0wt% to 20wt% (sub-eutectic and near-eutectic growth). The convection patterns obtained for different initial concentrations showed significant differences. The results showed that the process of solidification is slower with an increase in the initial concentration levels of the binary solution. The ice growth rate was almost double at the bottom of the cavity.
Turbulent Flow and Heat Transfer in a Porous Chamber
Authors: Assato Marcelo , de Lemos Marcelo J. S.
Published: December 2008

This work presents a numerical investigation of turbulent flow past a porous structure in a channel using linear and non-linear eddy viscosity macroscopic models. Parameters such as porosity and permeability of the porous material are varied in order to analyze their effects on the flow pattern, particularly on the damping of the recirculating bubble after the entrance and exit regions. The numerical technique employed for discretizing the governing equations is the control-volume method. The SIMPLE algorithm is used to correct the pressure field. The classical wall function is utilized in order to handle flow calculation near the wall. A discussion on the use of this technique for simulating the flow in question is presented. Comparisons of results simulated with both linear and non-linear turbulence models are shown.
Effect of Permeability on Convergence Rates of Multigrid Solutions of Laminar Flows in Porous Media
Authors: Mesquita Maximilian S. , de Lemos Marcelo J. S.
Published: December 2008

The present work investigates the efficiency of the multigrid method when applied to solve laminar flow in a two-dimensional tank filled with a porous material. The numerical method includes finite volume discretization with the flux blended deferred correction scheme on structure orthogonal regular meshes. Performance of the correction storage (CS) multigrid algorithm is compared for different numbers of sweeps in each grid level. Up to four grids, for both multigrid V- and W-cycles, are considered. Effects of medium permeability on converged rates are presented. Results indicate that W-cycles perform better in reducing the required computational effort and that the lower the permeability, faster solutions are obtained.
Discrete Ordinates Method for Transient Radiation Transfer in Cylindrical Enclosures
Authors: Kim Kyunghan , Guo Zhixiong
Published: December 2008

The Discrete Ordinates Method (DOM) for solving transient radiation transfer equation in cylindrical coordinates is developed for radiation heat transfer in participating turbid media in pico-scale time domain. The application problems addressed here are laser tissue welding and soldering. The novelty of this study lies with the use of ultrashort laser pulses as the irradiation source. The characteristics of transient radiation heat transfer in ultrafast laser tissue welding and soldering are studied with the DOM developed. The temporal distribution of radiative energy inside the tissue cylinder as well as the radiative heat flux on the tissue surface is obtained. Comparisons are performed between laser welding without use of solder and laser soldering with use of solder. The use of solder is found to have highly concentrated radiation energy deposition in the solder-stained region and reduce the surface radiative heat flux accordingly. Comparisons of transient radiation heat transfer between the spatially square-variance and Gaussian-variance laser inputs and between the temporally Gaussian and skewed input profiles are also conducted.
Outside Vapor Deposition of High-Purity Silicon Dioxide
Authors: Woodmansee M. A. , McNulty T. F. , Giddings R. A.
Published: December 2008

A study of the outside vapor deposition (OVD) process for the manufacture of fiber optic sleeve tubes is presented. High purity silicon dioxide (SiO2) is deposited on the outside of a rotating substrate via flame hydrolysis of silicon tetrachloride (SiCl4). Three double-flame burners hydrolyze the precursor forming streams of nominal 50 nm particulate, which are driven to the substrate surface via thermophoresis. The partial-premix burners utilize two concentric combustion chambers to provide fine control of the hydrolyzation process and heat flux to the preform surface. The bulk average deposition rate and efficiency to create a full-size sample are 4.93 gm/min/burner and 28%, respectively. The peak surface temperatures hover around 980 deg C at the bare quartz substrate surface, but then rapidly increase to 1200 deg C as the first four layers of SiO2 are deposited. These peak surface temperatures then monotonically decrease as the circumference and surface area of the porous preform increase. Similarly, the SiO2 layer density is 0.96 gm/cm3 at the substrate surface, but then decreases to 0.28 gm/cm3 as the porous preform grows to a diameter of 174 mm.
Design Study Comparison of Plain Finned Versus Louvered Finned-Tube Condenser Heat Exchangers
Authors: Stewart Susan W. , Shelton Sam V.
Published: December 2008

Enhanced fins are widely used in residential air conditioning system finned-tube condenser designs. While this heat transfer augmentation technique increases the heat transfer coefficient in the heat exchanger, it also increases the air side frictional pressure drop. These two effects compete with each other, making it difficult to determine the relative goodness between plain fin versus enhanced fin designs with realistic constraints. In the past, this design tradeoff has been largely determined by experimental trial and error or heuristic figures of merit. No studies are available showing the effect of fin augmentation on overall system performance under consistent cost and frontal area constraints. The residential air conditioning system model calculates all component and system performance parameters. The condenser design requires the specification of approximately ten design parameters. A search method is used to vary these ten parameters and reach an optimum design based on a COP (efficiency) figure-of-merit with condenser cost and other appropriate constraints. It was found that when optimized, louvered fin designs always show better system performance than the optimum plain fin design for the cases studied. However a decrease in system efficiency can result if louvers are merely added to a plain fin optimum design.
Supercritical Heat Transfer and Pressure Drop in Refrigerant R410A
Authors: Mitra Biswajit , Garimella Srinivas
Published: December 2008

This paper presents the results of an experimental study on heat transfer and pressure drop at critical and supercritical pressures of refrigerant R410A inside a horizontal 9.4 mm I.D. tube. Knowledge of heat transfer and pressure drop in such refrigerants blends at elevated pressures is gaining increasing attention for the design of vapor-compression space-conditioning and water heating systems at high heat rejection temperatures. Local heat transfer coefficients and pressure drops were measured for the mass flux range 200 < G < 800 kg/m2-s for the temperature range from 30–110°C. A technique that simultaneously allows accurate measurement of low local heat duties and deduction of the tube-side heat transfer coefficient from the measured overall resistance was used. A primary cooling loop using water at high flow rates ensures that the refrigerant side presents the governing thermal resistance. Heat exchange with a secondary cooling water stream at a much lower flow rate amplifies the coolant temperature difference, which in turn enables accurate heat duty measurements. The results show that the heat transfer coefficient exhibits a sharp peak in the vicinity of the vapor-liquid dome. These data are compared with the most relevant correlations from the literature and possible explanations for agreement and discrepancies between the data and predictions are provided.
Instrumented Air Conditioning Bench Experimental Apparatus
Authors: Abdelmessih Amanie N. , Dye Dan , Holtcamp Greg , Doughty Chet , Heitzmannp Eric , Miller Scott , Perkins Thomas Seth , Thabet Jasim
Published: December 2008

The Senior Mechanical Engineering students at Saint Martin’s College designed and built a unique, safe air conditioning/refrigeration bench experimentation apparatus. The apparatus is currently used as laboratory equipment to support instruction in four thermal engineering courses. This system demonstrates the fundamentals of the refrigeration cycle and psychrometric properties of air, as well as some fundamental concepts in heat transfer, heat exchangers, and thermodynamics. The refrigeration cycle working fluid is R-134a. The cycle operates with pressures between 760 kPa and 210 kPa, and with temperatures between 44 °C and −7 °C with flow rate of 6.8 kg/h. The apparatus is equipped with an instrumentation package to monitor the psychrometric properties of the effected air inside the ductwork. In addition the instrumentation package contains instrumentation to monitor the working fluid properties via computerized data logging equipment. Technical details about the uniqueness of this design and operation are given in the article.
Determining the Effective Thermal Conductivity of a Nanofluid Using Brownian Dynamics Simulation
Authors: Bhattacharya P. , Saha S. K. , Yadav A. , Phelan P. E. , Prasher R. S.
Published: December 2008

A nanofluid is a fluid containing suspended solid particles, with sizes of the order of nanometers. Normally the fluid has a low thermal conductivity compared to the suspended particles. Therefore introduction of these particles into the fluid increases the effective thermal conductivity of the system. It is of interest to predict the effective thermal conductivity of such a nanofluid under different conditions like varying particle volume fraction, varying particle size, changing fluid conductivity or changing fluid viscosity, especially since only limited experimental data are available. Also, some controversy exists about the role of Brownian motion in enhancing the nanofluid’s thermal conductivity. We have developed a novel technique to compute the effective thermal conductivity of a nanofluid using Brownian dynamics simulation, which has the advantage of being computationally less expensive than molecular dynamics. We obtain the contribution of the nanoparticles towards the effective thermal conductivity using the equilibrium Green-Kubo method. Then we combine that with the thermal conductivity of the base fluid to obtain the effective thermal conductivity of the nanofluid, and thus are able to show that the Brownian motion contributes greatly to the thermal conductivity.
CFD Modeling of Flow and Heat Transfer Inside a Liquid-Cooled Exhaust Manifold
Authors: Milanovic Rade , Zhou Chenn Q. , Majdak Jim , Cantwell Robert
Published: December 2008

Liquid cooled exhaust manifolds are used in turbo charged diesel and gas engines in the marine and various industrial applications. Performance of the manifold has a significant impact on the engine efficiency. Modifying manifold design and changing operational parameters are ways to improve its performance. With the rapid advance of computer technology and numerical methods, Computational Fluid Dynamics (CFD) has become a powerful tool that can provide useful information for manifold optimization. In this study, commercial CFD software (FLUENT®) was used to analyze liquid cooled exhaust manifolds. Detailed information of flow property distribution and heat transfer were obtained in order to provide a fundamental understanding of the manifold operation. Experimental data was compared with the CFD results to validate the numerical simulation. Computations were performed to investigate the parametric effects of operating conditions (engine rotational speed, coolant flow rate, coolant inlet temperature, exhaust gas inlet temperature, surface roughness of the manifold’s material) on the performance of the manifold. Results were consistent with the experimental observations. Suggestions were made to improve the manifold design and performance.
Study on Spray Mist Cooling Between Two Adjacent Parallel Boards
Authors: Kearns Don , Du Jian-Hua , Chen Ruey-Hung , Chow Louis C.
Published: December 2008

Experiments of dielectric liquid spray mist cooling of a row of 9, 38 mm square heaters located along one side of a 400 mm channel formed by two adjacent parallel boards were carried out. The objective was to determine the heat removal capability of the approach as a function of heater downstream distance from a single atomizer for channel height (board pitch) and orientation effects. Fundamental characteristics of the spray field and heat transfer were sought and no attempt was made to optimize the system for high heat transfer rate. The fluid used was FC-72 which as delivered into the gap between the boards by a full-cone TG0.3 atomizer oriented parallel to the row of heaters. The results indicate that heat transfer in the upstream region is dominated by droplet impingement which depends on the board pitch. The heat removal at the leading heater is up to 4 W/cm2 at 60°C uniform heater temperature. The heat transfer rate in the downstream region is determined by the flow pattern of the liquid film on the boards, which in turn depends on droplet behavior between the boards. For the horizontal orientation, gravitational forces cause the droplets to fall onto the heated board and improve heat transfer in the middle region along the heaters. This effect was enhanced and heat transfer coefficient was improved with the increase of liquid temperature which is consistent with the phenomena observed in the experiments. For the vertical orientation, gravitational effects do not appear to have an effect on heat transfer. Flow pattern of liquid film in the downstream region is heavily affected by the liquid distribution in the upstream region in the vertical orientation. In this case, the liquid film pattern was preserved and shifted downstream when the power to the upstream heaters was turned off. The heat removal at the “leading” heater at a specific uniform heater temperature is shown to depend on the subcooling of liquid for both orientations.
Natural Convection in Modulated Thermal Gradients and Gravity: Numerical Simulation and Experimental Measurements
Authors: Shu Y. , Li B. Q. , Ramaprian B. R.
Published: December 2008

This paper presents an investigation on natural convection in a cavity with an imposed modulated thermal gradient or modulated gravity forces. Numerical computations are presented, which are based on the finite element solution of transient Navier-Stokes and energy balance equations, along with appropriate boundary conditions or time-varying gravity forces. To verify the numerical predictions, an experimental system is setup where wall temperatures are oscillated to produce modulated temperature gradients and the velocity fields are measured by a laser-based Particle Image Velocimetry (PIV) system. Computed results compare well with experimental measurements for various conditions. With the mathematical model, so verified by experimental measurements, extensive numerical simulations are carried out to study the effects of modulation frequency and Prandtl numbers on the fluid flow. Results show the strong nonlinear interaction in the intermediate range of modulation frequency. It is also found that with a small Prandtl number typical of molten metals and semiconductor melts, modulated gravity and thermal gradients produce almost the same flow field both in structure and in magnitude.
Reducing Convection Effects in Solidification by Applying Magnetic Fields Having Optimized Intensity Distribution
Authors: Colac¸o Marcelo J. , Dulikravich George S. , Martin Thomas J.
Published: December 2008

This paper presents a numerical procedure for achieving desired features of a melt undergoing solidification by applying an external magnetic field whose intensity and spatial distribution are obtained by the use of a hybrid optimization algorithm. The intensities of the magnets along the boundaries of the container are described as B-splines. The inverse problem is then formulated as to find the magnetic boundary conditions (the coefficients of the B-splines) in such a way that the gradients of temperature along the gravity direction are minimized. For this task, a hybrid optimization code was used that incorporates several of the most popular optimization modules; the Davidon-Fletcher-Powell (DFP) gradient method, a genetic algorithm (GA), the Nelder-Mead (NM) simplex method, quasi-Newton algorithm of Pshenichny-Danilin (LM), differential evolution (DE), and sequential quadratic programming (SQP). Transient Navier-Stokes and Maxwell equations were discretized using finite volume method in a generalized curvilinear non-orthogonal coordinate system. For the phase change problems, an enthalpy formulation was used. The code was validated against analytical and numerical benchmark results with very good agreements in both cases.
Effects of Forced Wall Vibration on the Onset of Flow Instability and Critical Heat Flux in Uniformly-Heated Microchannels
Authors: Stromberger J. H. , Abdel-Khalik S. I. , Ghiaasiaan S. M. , Jeter S. M.
Published: December 2008

Forced convection using single-phase liquid water is a common cooling mechanism utilized in high power density engineering applications. Typically, design specifications require the coolant to remain subcooled throughout the heat transfer channel to ensure adequate cooling of the heated surfaces. Despite these planned steady state parameters, accident or transient conditions can cause boiling to take place within the channels. For this reason, it is important in the design and operation of heated channels to understand and predict the onset of boiling and two-phase flow instabilities that can lead to channel dryout and potential overheating and/or burnout of the heat transfer system.
A Simple Kinetic Model for Extinction of a Diffusion Flame
Authors: Quintiere James G.
Published: December 2008

An approximate one-dimensional analytic model is presented for the propagation of a laminar pre-mixed flame, and the diffusive burning of a condensed phase. Zero-order Arrhenius kinetics is used to describe the burning rate. Extinction of the pre-mixed and the diffusion flame systems is graphically illustrated to show the critical condition in terms of heat loss and the net generation of energy. The analysis is meant to be tutorial, and to serve as an indication of the similarity of extinction in the two systems. An example, using n-heptane as the fuel is given.
Fabrication and Characterization of a Liquid-Metal Micro-Droplet Array for Use as a Thermal Switch
Authors: Christensen A. O. , Jacob J. P. , Richards C. D. , Bahr D. F. , Richards R. F.
Published: December 2008

This paper presents the development of a liquid metal micro-droplet array for use as a thermal switch. A method of producing arrays of mercury micro-droplets on a silicon substrate, which is compatible with batch manufacturing, is detailed. A technique for examining the deformation of the micro-droplets under an applied load is offered. For 30μm diameter droplets under deformation, contact diameters ranging from 0–30μm, and forces of 0–0.10mN are examined. Predicted values of thermal contact resistance as a function of applied load to the switch are given, indicating that a thermal switch whose thermal resistance changes by a factor of ten could be fabricated.
Multi-Group Full-Spectrum k-Distribution Database for Water Vapor Mixtures in Radiative Transfer Calculations
Authors: Zhang Hongmei , Modest Michael F.
Published: December 2008

A thorough investigation of the absorption coefficient dependence on temperature and pressure has been performed for water vapor and a 32-group database has been assembled for H2O mixtures at atmospheric pressure, based on the Multi-Group Full-Spectrum Correlated k-distribution model. The method is fully scalable, i.e., spectral groups from the database can be combined to obtain coarser group models (N = 1, 2, 4, …) for greater numerical efficiency (accompanied by slight loss in accuracy). The databases for CO2 and H2O, together with the random-overlap mixture model have been used to simulate a practical combustion problem.
Experimental Study of Thermal Resistance of a Liquid-Thermoelectric System
Authors: Hammoud Jihad Y.
Published: December 2008

The heat generated by microprocessors is steadily increasing as die size shrinks. The trend towards increasing microprocessor heat flux is forcing thermal engineers to consider alternative system cooling technologies. Greater thermal control is also an issue during the engineering test of microprocessors and package characterization. The thermal challenges posed during test and debug are significant as power levels are higher than system power and temperature control requirements are very tight. Thermo-electric cooling technology (TEC) integrated with liquid cooling has evolved significantly in the past few years as a thermal management technique for engineering test and debug. In this study, an experimental approach was taken to characterize a TEC-based thermal control unit (TCU). The TCU thermal resistance was calculated as a function of the water temperature and device heat outputs. Several tests evaluated the suitability of using the TCU to control a device at low and elevated package case temperatures. Test results indicated that the TEC-Liquid system can operate in a cold or hot mode and that the thermal management capability of the system is a strong function of the liquid bulk temperature on the hot side of the TEC surface. The water bulk temperature at which the TCU fails to maintain the required device temperature is also reported in this paper.
An Analytical Derivation of 2-D Conduction Shape Factors
Authors: Shrivastava Devashish , Roemer Robert
Published: December 2008

New, improved formulations to evaluate two commonly used 2-D conduction shape factors, standard and average, are presented for a single, circular vessel eccentrically imbedded in a uniformly heated circular tissue matrix in terms of three non-dimensional parameters. The standard conduction shape factor is defined based on the vessel wall temperature and the outer wall temperature. The average conduction shape factor is defined based on the average tissue temperature and the vessel wall temperature. It is shown that both types of 2-D conduction shape factors are functions of the deposited power. The need to use proper expressions to evaluate conduction shape factors to accurately estimate the heat transfer from/to a region of interest when heating is present is stressed.
A Comparison Between 2-D and 3-D Conduction Shape Factors
Authors: Shrivastava Devashish , Roemer Robert
Published: December 2008

Conduction shape factors are frequently used in a variety of heat transfer applications to evaluate heat transfer from one three-dimensional body to another three-dimensional body. Previous investigators have used conduction shape factors derived using the 2-D cross-section of the 3-D geometries for non-heating conditions as approximations to 3-D conduction shape factors with heating and no-heating present. This paper investigates the suitability of neglecting the axial conduction and power deposition in deriving expressions for conduction shape factors for the case of a single, cylindrical vessel imbedded concentrically in a cylindrical, uniformly heated tissue matrix. It is shown that 1) conduction shape factors are functions of the deposited power and the temperature distribution and 2) the magnitudes of conduction shape factors are affected significantly by axial conduction.
Skin Friction and Heat Transfer on a Continuous Moving Flat Surface in Power Fluids
Authors: Zhang Xinxin , Zheng Liancun , He Jicheng
Published: December 2008

A theoretical analysis for the laminar momentum and energy boundary layer on a moving flat surface in power law fluids is made. The results indicate that while the plate moves in the direction of the flow, the boundary layer problem has a unique solution. Both skin friction and shear stress decrease with the increase of the ratio of the surface velocity to the free stream velocity and the power law n, the thermal diffusion ratio increases with the increase of n and ξ. However, in the case of the plate moving opposite to the flow, it is shown that the boundary layer solutions do not exist when velocity ratio ξ is larger than a positive critical value ξ*. For 0 < ξ < ξ*, the boundary layer solutions are found to be non-unique. Both superior and inferior solutions are noticeable. Skin friction and shear force for the superior solution decrease with the increase of the velocity ratio ξ. This is opposite for the inferior solution. The skin friction for both superior solution and inferior solution decrease with the increase of power law n. The result reveal the relations between momentum and thermal transfer, as well as the effects of parameters Pr, n and ξ on the transport process.
Mixed Convection in Cooling of a Surface by Two-Dimensional Confined Slot Jet Impingement
Authors: Sahoo Dipankar , Sharif M. A. R.
Published: December 2008

The flow and heat transfer characteristics in the cooling of a heated surface by impinging confined jets have been investigated numerically through the steady state solution of laminar two-dimensional Navier-Stokes and energy equations. The principal objective of this study is to investigate the effect of buoyancy on the associated heat transfer process. Numerical computations are done for vertically downward directed two-dimensional confined slot jets impinging on a hot isothermal surface at the bottom. The computed flow patterns and isotherms for various domain aspect ratios and for a range of jet exit Reynolds numbers (100–500) and Richardson numbers (0–10) are analyzed to understand the heat transfer phenomena. The local and average Nusselt numbers at the hot surface for various conditions are compared. It is observed that for a given domain aspect ratio and Richardson number, the average Nusselt number at the hot surface increases with increasing jet exit Reynolds number. On the other hand, for a given aspect ratio and Reynolds number the average Nusselt number does not change significantly with Richardson number indicating that the buoyancy effects are not very significant on the overall heat transfer process for the range of jet Reynolds number considered in this study.
Investigation of Various Source Models in the Diffusion Approximation
Authors: Jones Matthew R. , Solovjov Vladimir P. , Webb Brent W.
Published: December 2008

Applications involving foams in industrial processes are widespread. Foams are encountered in enhanced oil recovery and drilling operations, in the production of cosmetics, in the production of food and in the development of new insulation and construction materials. Often the development of foam is a desired outcome. However, in applications such as glass melting or fermentation processes, foam layers act as barriers to heat and mass transfer, and the presence of foam is undesirable. Due to their widespread use and importance, techniques for characterizing foams are of interest. A technique known as diffusing-wave spectroscopy has shown promise as a method for determining the radiative properties of foam. Relationships between measurable quantities and the radiative properties of the foam are derived using the diffusion approximation to the radiative transfer equation. The objective of this paper is to investigate the use of various models for the source term in the diffusion approximation. The diffusion model is validated by comparison with a Monte Carlo simulation for one case.
Transient Analysis of Flat Heat Pipes
Authors: Vadakkan Unnikrishnan , Murthy Jayathi Y. , Garimella Suresh V.
Published: December 2008

A stable numerical procedure is developed to analyze the transient performance of flat heat pipes for large input heat fluxes and high wick conductivity. Computation of flow and heat transfer in a heat pipe is complicated by the strong coupling among the velocity, pressure and temperature fields with phase change at the interface between the vapor and wick. A structured collocated finite volume scheme is used in conjunction with the SIMPLE algorithm to solve the continuity, energy and momentum equations. In addition, system pressurization is computed using overall mass balance. The stability of the standard sequential procedure is improved by accounting for the coupling between the evaporator/condenser mass flow rate and the interface temperature and pressure as well as the system pressure. The improved numerical scheme is applied to a flat two-dimensional heat pipe and shown to perform well. Parametric studies are performed by varying the vapor core thickness of the heat pipe and the heat input at the evaporator. The model predictions are validated by comparing the heat pipe wall temperatures against experimental values.