bluuebunny/crossref_metadata_2025 huggingface dataset:
A Numerical Treatment for Attached Cavitation
Authors: Chen Yongliang , Heister Stephen D.
Published: May 2008

A new numerical treatment has been developed for the prediction of the flowfield resulting from an attached cavitation region. The cavitation model has been implemented in a viscous calculation which is an improvement over previous inviscid results. The model requires no apriori knowledge of the wall detachment point or bubble length and comparisons with experimental data indicate good predictions of these quantities for a variety of different body shapes and cavitation numbers. Furthermore, wall pressure distributions are also predicted quite accurately using this method. While the treatment has been applied to an axisymmetric calculation, the approach should be applicable to two-dimensional flows.
Intrinsic Thermal Stability of Anisotropic Thin-Film Superconductors
Authors: Flik M. I. , Tien C. L.
Published: May 2008

Intrinsic thermal stability denotes a situation where a superconductor can carry the operating current without resistance at all times after the occurrence of a localized release of thermal energy. This novel stability criterion is different from the cryogenic stability criteria for magnets and has particular relevance to thin-film superconductors. Crystals of ceramic high-temperature superconductors are likely to exhibit anisotropic thermal conductivity. The resultant anisotropy of highly oriented films of superconductors greatly influences their thermal stability. This work presents an analysis for the maximum operating current density that ensures intrinsic stability. The stability criterion depends on the amount of released energy, the Biot number, the aspect ratio, and the ratio of the thermal conductivities in the plane of the film and normal to it.
Steady-State Temperatures in an Anisotropic Strip
Authors: Xiangzhou Zhang
Published: May 2008

This article deals with the development of a rigorous solution to the steady-state temperature in an anisotropic strip. The solution is given with respect to a coordinate system (x, y), which conforms with the strip geometry but does not necessarily coincide with the principal directions of the anisotropic material. Using a partitioning–matching technique and the separation of variables method, exact expressions are obtained for temperatures in the strip under prescribed boundary temperature conditions. Numerical values of the temperatures and heat flux are provided in graphic form. Also, a discussion is presented regarding the solution method and the temperature distribution features in the heat conduction problem of an anisotropic medium.
Effect of Oxidation and Plume Formation on Low Power Nd-Yag Laser Metal Interaction
Authors: Patel R. S. , Brewster M. Q.
Published: May 2008

The effect of oxide formation and plume formation on laser energy absorption by metallic targets has been studied. The change in directional-hemispherical spectral reflectance of metallic targets during single-shot Nd-Yag laser pulse irradiation was measured using an integrating sphere under controlled environments of both oxygen and argon gas. The spectral transmittance of the plume formed over the targets was also measured using a He-Ne probe laser. The metal targets studied included A16061, Cu, 304 stainless steel, and low-carbon steel. Results obtained show that once a target is hot enough to form a vapor plume, in either argon or oxygen, absorption by the plume significantly limits the amount of laser energy available for absorption at the target surface. Prior to plume formation, the amount of laser energy absorbed by the target is determined by the target surface optical properties. Under the conditions of the present study (incident laser flux of the order of 106 W/cm2 over 0.5–1.0 ms), in the case of absorbing metals (αλ>0.3), such as stainless and low carbon steel, the intrinsic absorptivity of the metal is high enough that the effect of ambient gas (oxygen or argon) on absorptivity is insignificant. In the case of nonabsorbing metals (αλ<0.3), such as Cu and A16061, the intrinsic metal absorptivity is low enough that the ambient gas does have a significant effect on the target absorptivity. The formation of an oxide layer that occurs in an oxidizing environment generally has the effect of increasing the target absorptivity. The relative magnitude of the absorptivity enhancement due to oxide formation depends on the respective absorptivities of the oxide and metal. For metals that form oxides that are intrinsically absorbing in the solid state, such as Cu2O or CuO, the enhancement in absorptivity due to oxide formation can be as much as an order of magnitude. For metals that form oxides that are intrinsically nonabsorbing in the solid state, such as MgO or Al2O3, the enhancement in absorptivity due to oxide formation is more modest but still significant (40 percent). The enhancement in absorptivity in the latter case (MgO or Al2O3) is postulated to be associated either with a thin, absorptive, transition region composed of a mixture of metal and substoichiometric solid oxide just below target surface or with the melting of the oxide at the surface.
Dependent Absorption and Extinction of Radiation by Small Particles
Authors: Kumar S. , Tien C. L.
Published: May 2008

This study presents an analytical model to evaluate the dependent absorption and extinction characteristics of dense particulate systems. Simple expressions are obtained by considering statistical averages based on the random character of the particulate medium. Departure from the assumption of independent scattering and absorption of radiation originates from two mechanisms: perturbation of the internal field of each particle by the presence of other particles, and coherent addition (i. e., taking into account the constructive/destructive interference) of the far-field scattered radiation. Dependent scattering has been previously studied analytically by considering the second mechanism only. Dependent absorption, which is due to the former, has not been considered in the literature even though absorption is more important than scattering in the extinction of radiation by small (Rayleigh) absorbing particles.
The Effect of Heat Transfer on Coal Devolatilization
Authors: Yang J.-T. , Wang G.-G.
Published: May 2008

This study investigates the heat transfer effect on the transient behavior of preheating, ignition, and combustion of a single coal particle pyrolyzed in a hot convective environment. The theoretical model covers two aspects: (1) heat and mass transfer and pyrolysis within the particle, (2) thermal radiation, diffusion, and combustion of the reactive gases and air outside of the particle. Semenov’s criteria are adopted to define ignition and a modified model derived from droplet combustion is used to estimate the flame radius and temperature. Distributions of temperature, species concentrations, and combustion rate are solved simultaneously. The prediction is verified by a set of experimental data.
Thermal Analysis of Hydrogen Combustion in a 1/4-Scale Boiling Water Reactor Containment Building
Authors: Ural E. A. , Tamanini F.
Published: May 2008

A mathematical model has been developed for the analysis of hydrogen combustion in boiling water reactor containment buildings. The overall phenomenon is similar to that observed in enclosure fires with the major differences being: (1) The containment building is hermetically sealed, and (2) diffusion flames form above a water pool at the bottom of the containment, through which hydrogen is released. The calculated results are compared with data obtained in tests performed in a 1/4-scale model of the containment building. The zone modeling approach, which was used in these calculations, has been demonstrated to be suitable for application to the combustion dynamics produced by the hydrogen flames in containment volumes.
Experimental Study of Surfactant Effects on Pool Boiling Heat Transfer
Authors: Tzan Ying Liang , Yang Yu Min
Published: May 2008

In the first part of this work, nucleate boiling of aqueous solutions of sodium lauryl sulfate (SLS) over relatively wide ranges of concentration and heat flux was carried out in a pool boiling apparatus. The experimental results show that a small amount of surface active additive makes the nucleate boiling heat transfer coefficient h considerably higher, and that there is an optimum additive concentration for higher heat fluxes. Beyond this optimum point, further increase in additive concentration makes h lower. In the second part of this work, nucleate boiling heat transfer rate for n-propanol-water binary mixtures with various amounts of sodium lauryl sulfate were measured in the same pool boiling apparatus. The importance of the mass diffusion effect, which is caused by preferential evaporation of the more volatile component at the vapor-liquid interface on the boiling of the binary mixture, has been confirmed. However, it is shown that the effect exerted by the addition of a surfactant dominates over the mass diffusion effect in dilute binary mixtures.
Thermal Shock Waves Induced by a Moving Crack
Authors: Tzou D. Y.
Published: May 2008

The near-tip behavior of the thermal field around a moving crack is investigated analytically in this work. The thermal field is characterized by a thermal Mach number defined as the ratio between the linear speed v of the moving crack and the heat propagation speed C in the solid. Mathematically, M= v/C. In the subsonic range with M < 1, a detailed comparison with the thermal diffusion model is made. In the transonic and the supersonic ranges with M ≥ 1, thermal shock waves, which separate the heat affected zone from the thermally undisturbed zone, are shown to exist in the physical domain. A swinging phenomenon for the temperature variation as a function of the thermal Mach number is found in transition from the subsonic to the supersonic ranges. Also, the r dependency of the near-tip temperature is found to be the same as that of the near-tip heat flux vector. It transits from r1/2, r, to r2 as the thermal Mach number transits from the subsonic, transonic, to the supersonic ranges.
Film Condensation of R-11 Vapor on Single Horizontal Enhanced Condenser Tubes
Authors: Sukhatme S. P. , Jagadish B. S. , Prabhakaran P.
Published: May 2008

The heat transfer performance of R-11 vapor condensing on single horizontal trapezodially shaped integral-fin tubes has been investigated by systematically varying the fin density, the semi-vertex angle, and the fin height. For the nine copper tubes tested, the best performance has been obtained with a tube having a fin density of 1417 fpm, a semi-vertex angle of 10 deg, and a fin height of 1.22 mm. This tube has yielded a maximum value of the heat transfer coefficient of 16,500 W/m2 K at a ΔT of about 3 K, corresponding to an enhancement ratio of 10.3. The performance of the tube has been further improved by fabricating from it “specially enhanced” tubes having axial grooves of varying height. An enhancement ratio of 12.3 has been obtained with this type of tube.
Simple Pressure and Energy State Equations for Lennard-Jones (12,6) Fluid
Authors: Paynter H. M. , Fahrenthold E. P. , Masada G. Y.
Published: May 2008

A recently published (Paynter, 1985, 1988) simple veridical equation of state represents a direct extension and generalization of the classical van der Waals equation, yet at the same time remains consistent with modern nonanalytical expansions about the critical point. With the use of this particular equation of state, compact expressions are here obtained for the pressure and configurational energy of the Lennard-Jones (12, 6) fluid, together with a saturation curve and other coexistence properties.
Green’s Function Partitioning in Galerkin-Based Integral Solution of the Diffusion Equation
Authors: Haji-Sheikh A. , Beck J. V.
Published: May 2008

A procedure to obtain accurate solutions for many transient conduction problems in complex geometries using a Galerkin-based integral (GBI) method is presented. The nonhomogeneous boundary conditions are accommodated by the Green’s function solution technique. A Green’s function obtained by the GBI method exhibits excellent large-time accuracy. It is shown that the time partitioning of the Green’s function yields accurate small-time and large-time solutions. In one example, a hollow cylinder with convective inner surface and prescribed heat flux at the outer surface is considered. Only a few terms for both large-time and small-time solutions are sufficient to produce results with excellent accuracy. The methodology used for homogeneous solids is modified for application to complex heterogeneous solids.
A Comparison of Two Test Methods for Determining Transfer Function Coefficients for a Wall Using a Calibrated Hot Box
Authors: Burch D. M. , Licitra B. A. , Zarr R. R.
Published: May 2008

This paper experimentally verifies and compares two dynamic test methods for a calibrated hot box to characterize the transient thermal performance of complex walls. In these methods, a wall specimen is sandwiched between the two conditioning chambers of a calibrated hot box. The exterior surface of the wall specimen is subjected to a time-varying excitation function in air temperature. At the interior surface, the air temperature is maintained steady, and the heat transfer response is measured. Conduction transfer function coefficients that relate the measured heat transfer response to the excitation function are derived. The two dynamic test methods were applied to an insulated hollow concrete block wall that contained significant thermal bridges and lateral heat flows. Empirical transfer function coefficients derived by the test methods predicted with good agreement the heat transfer response of this wall specimen when its exterior surface was subjected to excitation functions that differed markedly from those used to derive the coefficients.
Response of Rotary Regenerators to Step Changes in Mass Rates
Authors: Romie F. E.
Published: May 2008

Rotary regenerator exit gas temperature responses to step changes in mass flow rates are presented. When the step change is the same for both gases the responses are shown to have a decaying oscillation to the final values of the exit gas temperatures. The source of the oscillations is explained. The responses are found by dividing the regenerator into pie-shaped segments and approximating the area-mean gas temperature leaving a segment as the temperature of the gas leaving a small regenerator located on the central radius of the segment.
Performance of a Heat Exchanger Based on Enhanced Heat Diffusion in Fluids by Oscillation: Analysis
Authors: Kaviany M.
Published: May 2008

Fluid flow and heat transfer in capillary tubes (Stokes’ boundary-layer thickness nearly equal to the tube radius), subject to oscillatory flow from two reservoirs maintained at different temperatures, has been analyzed. Extension of existing analysis has been made by allowing for finite wall thickness and estimating the viscous dissipation. For a bundle of tubes connected to reservoirs of finite volume, analysis is also made of the oscillatory motion in the reservoirs (assuming a piston-type displacement within the reservoirs). The effects of various fluid and tube parameters on the heat transfer in a single tube are examined. The pathlines followed by fluid particles show that the extent of interaction between the fluid exiting the bundle and the fluid in the reservoirs (or the heat transfer surfaces in the reservoirs) depends strongly on the radial position of the exiting fluid particles. In a follow-up paper, these predictions are compared with some experimental results.
Performance of a Heat Exchanger Based on Enhanced Heat Diffusion in Fluids by Oscillation: Experiment
Authors: Kaviany M. , Reckker M.
Published: May 2008

The results of a study on the performance of a heat exchanger that takes advantage of enhanced heat diffusion in oscillated fluids are presented. In this heat exchanger, the fluid occupies a bundle of capillary tubes that connects two reservoirs at different temperatures; a piston in each reservoir drives the oscillation. The experimental findings are compared with predictions based on the assumptions that (a) a capillary tube does not exchange heat with the neighboring tubes, (b) the pressure in the reservoirs undergoes an ideal sinusoidal motion, and (c) each reservoir has an infinite heat capacity such that the fluid entering the tubes is at a constant temperature. Good agreement has been found between the actual performance of the heat exchanger and the idealized analysis for low and high frequencies. However, around the frequency corresponding to optimum performance, i.e., where the thermal boundary layers occupy the entire cross section of the capillary tubes, agreement is only fair. The measurements show that there is a temperature variation across the bundle and that the fluid entering the tubes has a nonsteady temperature due to weak, nonuniform mixing within the reservoirs (therefore, a spatial/temporal average was taken). This lateral and temporal variation in the temperature distribution appears to be the leading cause of the difference between the experimental and predicted results. As with any heat pipe, the reduction in the resistance to heat flow in the pipe must be accompanied by a similar ease of heat flow to and away from the ends of the pipe. Therefore, the reservoir fluid dynamics is of paramount importance in these heat exchangers. Some numerical modeling of the fluid flow in the reservoirs, as well as some velocity measurements (using a laser-Doppler anemometer), are also presented.
Porosity and Effective Thermal Conductivity of Wire Screens
Authors: Chang Won Soon
Published: May 2008

A simple theoretical model based on combined series and parallel conduction for the effective thermal conductivity of fluid-saturated screens has been developed. The present model has been compared with the existing correlations and experimental data available in literature, and it has been found that the model is effective in predicting thermal conductivity. The study also demonstrates that it is important to include the actual thickness of the wire screen in order to calculate the porosity accurately.
Mixed Double-Diffusive Convection in Gas-Loaded Heat Pipes
Authors: Peterson P. F. , Tien C. L.
Published: May 2008

This study examines mixed double-diffusive convection in gas-loaded heat pipes and two-phase thermosyphons. The numerical simulation and experiments show that steady, laminar natural convection due to the combined effects of temperature and concentration gradients can greatly redistribute the noncondensable gas within the condenser. This change of the gas distribution, however, does not significantly alter the overall condensation heat transfer. This interesting result implies that even with natural convection present, much simpler integral models can still be applied with confidence for the design of variable-conductance heat pipes and thermosyphons.
Transient Heat Transfer in a Fluid Sphere Translating in an Electric Field
Authors: Chung J. N. , Oliver D. L. R.
Published: May 2008

The transient heat transfer in a fluid sphere translating steadily in a dielectric medium is numerically investigated. The energy equation with velocity components of combined translation-induced and electric field-induced internal motion is integrated by the Alternating Direction Implicit (ADI) method for the entire drop interior. Creeping flow is assumed and the preponderance of the thermal resistance is assumed completely in the dispersed phase. The enhancement of heat transfer due to internal motion induced by both drop translation and the electric field is given in terms of the Nusselt number. Nusselt numbers are plotted as a function of the Fourier number, the Peclet number, and a parameter E. The parameter E represents the ratio of electric field-induced flow strength to that of translation-induced flow. In general, the heat transfer rate is approximately doubled when the flow is dominated by the electric field as compared with the case where no electric field is applied. It is suggested that for large Peclet numbers, the electric field is negligible for E less than 0.5, while the translation is unimportant for E larger than 10. For small Peclet numbers, the electric field is of minor importance for E less than 2 and the translation is insignificant for E greater than 50.
Convection From a Periodically Stretching Plane Wall
Authors: Lage J. L. , Bejan A.
Published: May 2008

This paper documents the convection heat transfer enhancement effect that is associated with the periodic (timewise and spatial) longitudinal stretching of an infinite plane wall bathed by a semi-infinite fluid reservoir. It is shown that the flow field reaches a truly periodic state, and that the temperature field does not. The timedependent heat transfer rate is greater than the classical pure-diffusion limit only when the Reynolds number based on wall speed and wavelength is greater than 1. The enhancement effect becomes pronounced as Re increases above 10. The enhancement effect increases also as the Prandtl number increases, provided Re is greater than 1. The same conclusions apply in the case of convective mass transfer, when a concentration difference is maintained between the flexible wall and the ambient fluid.
A Method for Analyzing Heat Conduction With High-Frequency Periodic Boundary Conditions
Authors: Caulk D. A.
Published: May 2008

A special method is developed for calculating the steady periodic temperature solution in solid bodies with high-frequency boundary conditions. The numerical difficulty associated with steep gradients and rapid temperature variation near the boundary is addressed by confining all transient temperatures to a narrow boundary layer of constant depth. The depth of the layer is specified in advance and depends only on the period of the boundary disturbance and the thermal diffusivity of the material. The transient solution in the surface layer is represented by a polynomial in its transverse coordinate, with time-varying coefficients determined by a Galerkin method. This solution is coupled with the steady interior solution by imposing continuity of temperature and time-averaged heat flux at the interface. Although the method is sufficiently general to handle nonlinear boundary conditions, it turns out to be particularly useful in the important case of a time-varying heat transfer coefficient. In the latter case, it is possible to decouple the solution process and determine the solution in the transient surface layer separately from the solution in the steady interior. This reduces the effort of determining the complete steady periodic solution to little more than a routine steady analysis. Comparison with an exact solution shows that the polynomial representation for the transient solution in the surface layer converges very rapidly with increasing order. Moreover, the solution at the surface turns out to be relatively insensitive to the choice of the layer depth as long as it is greater than a certain minimum value. An application to permanent mold casting is given, illustrating both the utility and accuracy of the method in a practical context.
A General Method for the Comparison of Compact Heat Transfer Surfaces
Authors: Cowell T. A.
Published: May 2008

This paper presents a family of methods for comparing compact heat transfer surface configurations. It is shown how measures for the relative values of required hydraulic diameter, frontal area, total volume, pumping power, and number of transfer units for different surfaces can be derived and displayed, when any two of the above five parameters are held constant. A wide range of comparisons that are independent of the particular duty can be simply made. A further development allowing comparisons, where three of the five parameters are fixed, yields very clear and compact indications of the relative merits of different surfaces.
The Second Law Quality of Energy Transformation in a Heat Exchanger
Authors: Sekulic D. P.
Published: May 2008

This paper presents the entropy generation (irreversibility) concept as a convenient method for estimating the quality of the heat exchange process in heat exchanger analysis. The entropy generation caused by finite temperature differences, scaled by the maximum possible entropy generation that can exist in an open system with two fluids, is used as the quantitative measure of the quality of energy transformation (the heat exchange process). This measure is applied to a two-fluid heat exchanger of arbitrary flow arrangement. The influence of different parameters (inlet temperature ratio, fluid flow heat capacity rate ratio, flow arrangements) and the heat exchanger thermal size (number of heat transfer units) on the quality of energy transformation for different types of heat exchangers is discussed. In this analysis it is assumed that the contribution of fluid friction to entropy generation is negligible.
Axisymmetric Nugget Growth During Resistance Spot Welding
Authors: Wei P. S. , Ho C. Y.
Published: May 2008

Three-dimensional weld nugget growths for different welding currents, electrode tip shapes, and thickness ratios of workpieces are determined. By providing an effective model to estimate the heat generation at the faying surface between workpieces and taking into account the phase change due to melting, results show that the calculated weld nugget growth, nugget thickness, and shape of the nugget agree well with experimental data. Heat generation at the faying surface in the early stage of welding and joule heating at long weld times dominate the nugget growth. Consideration of radial heat loss is necessary at longer weld times and higher welding currents.
The Influence of a Horseshoe Vortex on Local Convective Heat Transfer
Authors: Fisher E. M. , Eibeck P. A.
Published: May 2008

The objective of this research program has been to determine experimentally the extent to which horseshoe vortices modify turbulent convective heat transfer along a flat plate downstream of an appendage. The importance of appendage shape on the heat transfer behavior was evaluated by taking Stanton-number measurements downstream of both a cylindrical body and a streamlined body. The results indicate that a region of augmented heat transfer occurs near the centerline downstream of both obstacles, with Stanton numbers 10 to 50 percent over the undisturbed values. The streamlined cylinder produces the strongest modifications in heat transfer.
Numerical Prediction of Fluid Flow and Heat Transfer in a Circular Tube With Longitudinal Fins Interrupted in the Streamwise Direction
Authors: Kelkar K. M. , Patankar S. V.
Published: May 2008

Numerical calculations have been made for the performance prediction of laminar flow through circular tubes with longitudinal fins interrupted in the streamwise direction by arranging them either in a staggered or an in-line manner. Calculations are made for three-dimensional parabolic flow. Due to the repetitive nature of the geometry in the axial direction, the flow exhibits periodically repeating behavior after some initial development length. Calculations have been made for various values of the axial length parameter and two Prandtl numbers for two different fin geometries. Results indicate that in the periodic fully developed regime, for a Prandtl number of 0.7, a tube with staggered arrangement of fins produces less heat transfer enhancement than a tube with continuous fins. A tube with in-line arrangement of fins gives about as much heat transfer augmentation as the tubes with either continuous or staggered fins but with a much less pressure drop penalty. Local quantities such as the axial velocity profiles and the variation of centerline axial velocity give a good physical understanding of the governing phenomena.
The Characteristic Behavior of Finite Length Line Sources of Heat in a Crossflow
Authors: Slawson P. R. , Hitchman G. J. , Hawker L. E.
Published: May 2008

A modified simple integral model for plume behavior from finite length line sources of heat and momentum is presented that identifies observed trends in plume trajectory data. Experiments on several finite length line sources of heat and momentum in the form of elevated (rows of stacks) and surface (slot) releases were conducted in a water tunnel. Plume behavior was documented through detailed temperature measurements of the plume cross section and by photographing the dyed plume. Results indicate the nature of any plume trajectory and growth enhancement and confirm the empirical relation for the liftoff distance for a buoyant surface plume given by Meroney (1979). In addition to the liftoff distance, the shape of the plume contact zone was measured and related to various regions of plume trajectory and cross-sectional shape. Plume trajectories from elevated line releases are adequately predicted by standard single source formulations; however, plume cross-sectional area is significantly overpredicted
Three-Dimensional Buoyant Wall Jets Released Into a Coflowing Turbulent Boundary Layer
Authors: Sinclair J. R. , Slawson P. R. , Davidson G. A.
Published: May 2008

Experiments have been conducted in a water flume to simulate finite-length line sources of heat that issue horizontally at ground level into a coflowing turbulent shear flow. The downstream development of each buoyant jet is documented by detailed mean temperature measurements, which are analyzed to determine the jet trajectory, spread rates, and distance to the point of liftoff from the surface. In addition, a three-dimensional, parabolic, numerical model based on the fundamental conservation equations is developed. Model predictions of several buoyant jets compare reasonably with the experimental data and suggest that the strength of the streamwise vorticity plays an important role in governing liftoff of a buoyant wall jet from the surface.
Effects of the Heat Transfer at the Side Walls on Natural Convection in Cavities
Authors: Le Peutrec Y. , Lauriat G.
Published: May 2008

Numerical solutions are obtained for fluid flows and heat transfer rates for three-dimensional natural convection in rectangular enclosures. The effects of heat losses at the conducting side walls are investigated. The problem is related to the design of cavities suitable for visualizing the flow field. The computations cover Rayleigh numbers from 103 to 107 and the thermal conductance of side walls ranging from adiabatic to commonly used glazed walls. The effect of the difference between the ambient temperature and the average temperature of the two isothermal walls is discussed for both air and water-filled enclosures. The results reported in the paper allow quantitative evaluations of the effects of heat losses to the surroundings, which are important considerations in the design of a test cell.
Thermal Convection With Large Viscosity Variation in an Enclosure With Localized Heating
Authors: Chu T. Y. , Hickox C. E.
Published: May 2008

The present study is undertaken in order to gain an understanding of certain aspects of convective transport in a magma chamber. We have chosen to represent the chamber by an enclosure with localized heating from below. Results of both laboratory experiments and computer modeling are reported. The experimental apparatus consists of a transparent enclosure with a square planform. An electrically heated strip, with a width equal to 1/4 of the length of a side of the enclosure, is centered on the lower inside surface of the enclosure. For the experiments reported here, the top of the fluid layer is maintained at a constant temperature and the depth of the layer is equal to the width of the heated strip. The large viscosity variation characteristic of magma convection is simulated by using corn syrup as the working fluid. Measured velocity and temperature distributions as well as overall heat transfer rates are presented. The experiment is numerically simulated through use of a finite element computer program. Numerically predicted steamlines, isotherms, and velocity distributions are presented for the transverse vertical midplane of the enclosure. Good agreement is demonstrated between predictions and measurements.
Enhanced Absorption Due to Dependent Scattering
Authors: Ma Y. , Varadan V. K. , Varadan V. V.
Published: May 2008

The role of multiple scattering on dependent scattering as well as on dependent absorption is investigated for heterogeneous media containing a high concentration of particles. The decrease of scattering and increase of absorption for lossy (with intrinsic absorption) particles in a lossless matrix is quantitatively described using a Rayleigh region solution derived from a multiple scattering formalism. For smaller wavelengths, dependent scattering and absorption can be obtained by solving the resulting dispersion equation numerically. Results are shown for lossless particles in a lossy matrix, which models an optical coating system.
Development of a Network Analogy and Evaluation of Mean Beam Lengths for Multidimensional Absorbing/Isotropically Scattering Media
Authors: Yuen W. W.
Published: May 2008

Based on Hottel’s zonal formulation, a network analogy is developed for the analysis of radiative transfer in general multidimensional absorbing/isotropically scattering media. Applying the analogy to the analysis of an isothermal medium and assuming that the incoming and outgoing flux density is homogeneous within the medium, the effect of scattering on the evaluation of mean beam lengths is illustrated. Two concepts of mean beam length, an absorption mean beam length (AMBL) and an extinction mean beam length (EMBL), are introduced and shown to be important for the analysis of radiative transfer in practical systems. Both mean beam lengths differ significantly from the conventional mean beam length in systems of moderate and large optical thickness. Relations between AMBL and EMBL and their limiting behavior are developed analytically. Numerical results for a sphere radiating to its surface and an infinite parallel slab radiating to one of its surfaces are presented to demonstrate quantitatively the mathematical behavior of the two mean beam lengths.
The Differential-Discrete-Ordinate Method for Solutions of the Equation of Radiative Transfer
Authors: Kumar S. , Majumdar A. , Tien C. L.
Published: May 2008

This paper introduces a powerful but simple methodology for solving the general equation of radiative transfer for scattering and/or absorbing one-dimensional systems. Existing methods, usually designed to handle specific boundary and energy equilibrium conditions, either provide crude estimates or involve intricate mathematical analysis coupled with numerical techniques. In contrast, the present scheme, which uses a discrete-ordinate technique to reduce the integro-differential equation to a system of ordinary differential equations, utilizes readily available software routines to solve the resulting set of coupled first-order ordinary differential equations as a two-point boundary value problem. The advantage of this approach is that the user is freed from having to understand complicated mathematical analysis and perform extensive computer programming. Additionally, the software used is state of the art, which is less prone to numerical instabilities and inaccuracies. Any degree of scattering anisotropy and albedo can be incorporated along with different conditions of energy equilibrium or specified temperature distributions and boundary conditions. Examples are presented where the radiative transfer is computed by using different quadratures such as Gaussian, Lobatto, Fiveland, Chebyshev, and Newton-Cotes. Comparison with benchmark cases shows that in a highly forward scattering medium Gaussian quadrature provides the most accurate and stable solutions.
A General Correlation for Pool Film Boiling Heat Transfer From a Horizontal Cylinder to Subcooled Liquid: Part 1—A Theoretical Pool Film Boiling Heat Transfer Model Including Radiation Contributions and Its Analytical Solution
Authors: Sakurai A. , Shiotsu M. , Hata K.
Published: May 2008

A rigorous numerical solution of a theoretical model based on laminar boundary layer theory for pool film boiling heat transfer from a horizontal cylinder including the contributions of liquid subcooling and radiation from the cylinder was obtained. The numerical solution predicted accurately the experimental results of pool film boiling heat transfer from a horizontal cylinder in water with high radiation emissivity for a wide range of liquid subcooling in the range of nondimensional cylinder diameters around 1.3, where the numerical solution was applicable to the pool film boiling heat transfer from a cylinder with negligible radiation emissivity. An approximate analytical solution for the theoretical model was also derived. It was given by the sum of the pool film boiling heat transfer coefficient if there were no radiation and the radiation heat transfer coefficient for parallel plates multiplied by a nondimensional radiation parameter similar to the expression for saturated pool film boiling given by Bromley. The approximate analytical solution agreed well with the rigorous numerical solution for various liquids of widely different physical properties under wide ranges of conditions.
A General Correlation for Pool Film Boiling Heat Transfer From a Horizontal Cylinder to Subcooled Liquid: Part 2—Experimental Data for Various Liquids and Its Correlation
Authors: Sakurai A. , Shiotsu M. , Hata K.
Published: May 2008

Experimental data of pool film boiling heat transfer from horizontal cylinders in various liquids such as water, ethanol, isopropanol, Freon-113, Freon-11, liquid nitrogen, and liquid argon for wide ranges of system pressure, liquid subcooling, surface superheat and cylinder diameter are reported. These experimental data are compared with a rigorous numerical solution and an approximate analytical solution derived from a theoretical model based on laminar boundary layer theory for pool film boiling heat transfer from horizontal cylinders including the effects of liquid subcooling and radiation from the cylinder. A new correlation was developed by slightly modifying the approximate analytical solution to agree better with the experimental data. The values calculated from the correlation agree with the authors’ data within ± 10 percent, and also with other researchers’ data for various liquids including those with large radiation effects, though these other data were obtained mainly under saturated conditions at atmospheric pressure.
EHD Enhancement of Nucleate Boiling
Authors: Cooper P.
Published: May 2008

This paper describes: (a) an experimental investigation into the effect of an electric field applied to pool boiling of Freon (R114) on a finned tube and (b) a theoretical model of electrically enhanced nucleate boiling applicable to simple surfaces only. Experimental results have shown electrohydrodynamic (EHD) enhancement of heat transfer to be manifest in two ways: (i) elimination of boiling hysteresis, (ii) augmentation of nucleate boiling heat transfer coefficients by up to an order of magnitude. These effects were also observed in electrically enhanced boiling of Freon/oil mixtures. A new analytical model is described whereby EHD nucleate boiling data from previous studies (employing simple apparatus comprising heated wires with concentric cylinder electrodes) have been correlated for the first time using the concept of an electrical influence number. This dimensionless parameter is based upon the relationship between applied electric field intensity and changes in bubble departure diameter at a heat transfer surface.
Liquid-Solid Contact During Flow Film Boiling of Subcooled Freon-11
Authors: Chang K. H. , Witte L. C.
Published: May 2008

Liquid-solid contacts were measured for flow film boiling of subcooled Freon-11 over an electrically heated cylinder equipped with a surface microthermocouple probe. No systematic variation of the extent of liquid-solid contact with wall superheat, liquid subcooling, or velocity was detected. Only random small-scale contacts that contribute negligibly to overall heat transfer were detected when the surface was above the homogeneous nucleation temperature of the Freon-11. When large-scale contacts were detected, they led to an unexpected intermediate transition from local film boiling to local transition boiling. An explanation is proposed for these unexpected transitions. A comparison of analytical results that used experimentally determined liquid-solid contact parameters to experimental heat fluxes did not show good agreement. It was concluded that the available model for heat transfer accounting for liquid-solid contact is not adequate for flow film boiling.
Practical Fin Shapes for Surface-Tension-Drained Condensation
Authors: Kedzierski M. A. , Webb R. L.
Published: May 2008

This paper introduces a new family of high-performance fin profiles for surface-tension-drained condensation. Previously described profiles for this situation have been defined in terms of the fin curvature and arc length. The existing profiles are generally not suitable for commercial manufacture. The fin profiles presented in this paper are conveniently defined by the fin tip radius, the fin height, and the fin base thickness. Consequently, the designer may easily specify a fin shape with parameters that are compatible with those used by the manufacturing industry. The heat transfer performance of the new profiles provides an improvement over existing, commercial fin shapes. An analysis is presented to show the R-11 condensation performance of the new profiles as a function of the geometric variables. A recommended design practice for fins for surface-tension-drained condensation is given also.
An Instrument for Local Radiative Heat Transfer Measurement Around a Horizontal Tube Immersed in a Fluidized Bed
Authors: Alavizadeh N. , Adams R. L. , Welty J. R. , Goshayeshi A.
Published: May 2008

An instrument for the measurement of the radiative component of total heat transfer in a high-temperature gas fluidized bed is described. The main objective of this paper is to emphasize the design, instrumentation, and calibration of this device. The results are presented and discussed elsewhere (Alavizadeh, 1985; Alavizadeh et al., 1985). The design makes use of a silicon window to transmit the radiative heat flux to a thermopile-type heat flow detector located at the base of a cavity. The window material thermal conductivity is sufficiently large to prevent conduction errors due to the convective component of total heat transfer. Also, its transmission and mechanical hardness are well suited for the fluid bed environment. The device has been calibrated using a blackbody source both before and after exposure to a fluidized bed, indicating the effect of the abrasive bed environment on performance. The instrument has been used to measure local radiative heat transfer around a horizontal tube. Typical results for a particle size of 2.14 mm and a bed temperature of 1050 K are presented and discussed to illustrate instrument performance.
1987 Max Jakob Memorial Award Lecture: Dynamics and Stability of Thin Heated Liquid Films
Authors: Bankoff S. G.
Published: May 2008

This review covers the dynamics and tendency toward rupture of thin evaporating liquid films on a heated surface. Very large heat transfer coefficients can be obtained. The applications include various boiling heat transfer and film cooling devices. A relatively new area for study is heat transfer through ultrathin films, which are less than 100 nm in thickness, and hence subject to van der Waals and other long-range molecular forces. Some recent work employing lubrication theory to obtain an evolution equation for the growth of a surface wave is described. Earlier phenomenological work is briefly discussed, as well as the connection between forced-convection subcooled nucleate boiling and thin-film heat transfer.
Model Reduction of Transfer Functions Using a Dominant Root Method
Authors: Seem J. E. , Klein S. A. , Beckman W. A. , Mitchell J. W.
Published: May 2008

Transfer function methods are more efficient for solving long-time transient heat transfer problems than Euler, Crank-Nicolson, or other classical techniques. Transfer functions relate the output of a linear, time-invariant system to a time series of current and past inputs, and past outputs. Inputs are modeled by a continuous, piecewise linear curve. The computational effort required to perform a simulation with transfer functions can be significantly decreased by using the Pade´ approximation and bilinear transformation to determine transfer functions with fewer coefficients. This paper presents a new model reduction method for reducing the number of coefficients in transfer functions that are used to solve heat transfer problems. There are two advantages of this method over the Pade´ approximation and bilinear transformation. First, if the original transfer function is stable, then the reduced transfer function will also be stable. Second, reduced multiple-input single-output transfer functions can be determined by this method.
Hyperbolic Heat Conduction Equation for Materials With a Nonhomogeneous Inner Structure
Authors: Kaminski W.
Published: May 2008

The physical meaning of the constant τ in Cattaneo and Vernotte’s equation for materials with a nonhomogeneous inner structure has been considered. An experimental determination of the constant τ has been proposed and some values for selected products have been given. The range of differences in the description of heat transfer by parabolic and hyperbolic heat conduction equations has been discussed. Penetration time, heat flux, and temperature profiles have been taken into account using data from the literature and our experimental and calculated results.
Temperature Profile in Semi-infinite Body With Exponential Source and Convective Boundary Condition
Authors: Blackwell B. F.
Published: May 2008

An analytical solution for the temperature profile in a semi-infinite body with an exponentially decaying (with position) source and convective boundary condition is obtained using Laplace transforms. The appropriate dimensionless parameters are identified and the temperature as a function of these parameters is presented in graphic form. With cooling at the exposed surface, the maximum temperature occurs in the interior of the slab instead of at the exposed surface. The location of the temperature maximum as a function of the various system parameters is presented in graphic form. Approximate relationships are presented for small values of dimensionless time.
Measurement of the Thermal Contact Conductance and Thermal Conductivity of Anodized Aluminum Coatings
Authors: Peterson G. P. , Fletcher L. S.
Published: May 2008

An experimental investigation was conducted to determine the thermal contact conductance and effective thermal conductivity of anodized coatings. One chemically polished Aluminum 6061-T6 test specimen and seven specimens with anodized coatings varying in thickness from 60.9 μm to 163.8 μm were tested while in contact with a single unanodized aluminum surface. Measurements of the overall joint conductance, composed of the thermal contact conductance between the anodized coating and the bare aluminum surface and the bulk conductance of the coating material, indicated that the overall joint conductance decreased with increasing thickness of the anodized coating and increased with increasing interfacial load. Using the experimental data, a dimensionless expression was developed that related the overall joint conductance to the coating thickness, the surface roughness, the interfacial pressure, and the properties of the aluminum substrate. By subtracting the thermal contact conductance from the measured overall joint conductance, estimations of the effective thermal conductivity of the anodized coating as a function of pressure were obtained for each of the seven anodized specimens. At an extrapolated pressure of zero, the effective thermal conductivity was found to be approximately 0.02 W/m-K. In addition to this extrapolated value, a single expression for predicting the effective thermal conductivity as a function of both the interface pressure and the anodized coating thickness was developed and shown to be within ±5 percent of the experimental data over a pressure range of 0 to 14 MPa.