bluuebunny/crossref_metadata_2025 huggingface dataset:
A Variable Heat Flux Model of Heat Transfer in Grinding With Boiling
Authors: Jen T.-C. , Lavine A. S.
Published: February 2008

In grinding processes, the grinding fluid is used to suppress the temperature rise in the grinding zone. Under some circumstances, the grinding fluid may undergo film boiling in the grinding zone, causing the workpiece temperature to rise significantly. The onsets of nucleate boiling and film boiling in the grinding zone are investigated in the present study. A model of heat transfer in grinding was previously developed (Jen and Lavine, 1995), which predicts the temperature and heat fluxes in the grinding zone. With some modification, this model is used here to predict the occurrence of film boiling of the grinding fluid. The dependence of the workpiece background temperature on the various grinding parameters is explored. The workpiece background temperature distribution along the grinding zone, and comparisons with experimental results, are presented.
Natural Convection in a Narrow Horizontal Annulus: The Effects of Thermal and Hydrodynamic Instabilities
Authors: Cadiou P. , Desrayaud G. , Lauriat G.
Published: February 2008

Multicellular natural convective flows in narrow horizontal air-filled concentric annuli are considered numerically in this paper. The results show that the multiplicity of the multicellular upper flows reported in the literature can be credited to the existence of an imperfect bifurcation with two stable branches. The emergence and extinction of the buoyancy-driven cells have been proved to be identical on both branches. The appearance of another secondary flow, the origin of which is purely hydrodynamic and located within the crescent base flow at the vertical portions of the annulus, has also been evidenced at moderate values of the Rayleigh number. As Ra is increased a reverse transition from a multicellular structure to a unicellular pattern occurs through a gradual decrease in the number of cells. In addition, it is shown that shear-driven instabilities cannot develop for radius ratios larger than a value close to R = 1.15.
Enhanced Heat Transfer Rate Measured for Natural Convection in Liquid Gallium in a Cubical Enclosure Under a Static Magnetic Field
Authors: Tagawa Toshio , Ozoe Hiroyuki
Published: February 2008

The heat transfer rate of natural convection in liquid gallium in a cubical enclosure was measured experimentally under an external magnetic field applied horizontally and parallel to the vertical heated wall and the opposing cooled wall and the opposing cooled wall of the enclosure. One vertical wall was heated with an electric heater and the opposing wall was cooled isothermally with running water. Experiments were conducted in the range of modified Rayleigh number from 1.85 × 106 to 4.76 × 106 and of Hartmann number from 0 to 573. The average Nusselt number was measured and found to increase when a moderate magnetic field was applied, but to decrease under a stronger magnetic field. This result means that the heat transfer rate has a maximum value at a certain moderate magnetic field, which supports our previous numerical analyses.
A Parametric Study of Nucleate Boiling on Structured Surfaces, Part I: Effect of Tunnel Dimensions
Authors: Chien Liang-Han , Webb R. L.
Published: February 2008

This two-part experimental work identifies the effect of geometric dimensions on the boiling performance of “tunneled” enhanced boiling surfaces. The surface is formed on an integral-fin tube having a copper foil wrapped over the fin tips. Pores of known diameter and pitch are pierced in the foil cover. Tests were performed on a 19.1-mm diameter horizontal tube using R-11 and R-123 at 26.7°C for heat fluxes from 2 to 70 kW/m2. The first part of the study defines the effect of the tunnel dimensions. The data show that greater tunnel height and smaller tunnel pitch are preferred. Sharp tunnel corners provides greater enhancement.
A Parametric Study of Nucleate Boiling on Structured Surfaces, Part II: Effect of Pore Diameter and Pore Pitch
Authors: Chien Liang-Han , Webb R. L.
Published: February 2008

This two-part experimental work identifies the effect of geometric dimensions on the boiling performance of “tunneled” enhanced boiling surfaces, which is similar to the Hitachi Thermoexcel-E surface. Tests were performed on a horizontal tube using R-11 and R-123 at 26.7°C for heat fluxes from 2 to 70 kW/m2. This second part of the study defines the effect of the pore dimensions (pore diameter and pore pitch). The pore diameters are 0.12, 0.18, 0.23, and 0.28 mm and the pore pitches are 0.75, 1.5, and 3.0 mm. The results are interpreted to explain the relationship between pore diameter and pore pitch on the boiling performance.
Numerical Simulation of Combustion and Extinction of a Solid Cylinder in Low-Speed Cross Flow
Authors: Yang Chin Tien , T’ien J. S.
Published: February 2008

The combustion and extinction behavior of a diffusion flame around a solid fuel cylinder (PMMA) in low-speed forced flow in zero gravity was studied numerically using a quasi-steady gas phase model. This model includes two-dimensional continuity, full Navier Stokes’ momentum, energy, and species equations with a one-step overall chemical reaction and second-order finite-rate Arrhenius kinetics. Surface radiation and Arrhenius pyrolysis kinetics are included on the solid fuel surface description and a parameter Φ, representing the percentage of gas-phase conductive heat flux going into the solid, is introduced into the interfacial energy balance boundary condition to complete the description for the quasi-steady gas-phase system. The model was solved numerically using a body-fitted coordinate transformation and the SIMPLE algorithm. The effects of varying freestream velocity and Φ were studied. These parameters have a significant effect on the flame structure and extinction limits. Two flame modes were identified: envelope flame and wake flame. Two kinds of flammability limits were found: quenching at low-flow speeds due to radiative loss and blow-off at high flow speeds due to insufficient gas residence time. A flammability map was constructed showing the existence of maximum Φ above which the solid is not flammable at any freestream velocity.
Thermal and Hydraulic Performance of a Rectangular Duct With Multiple V-Shaped Ribs
Authors: Olsson C.-O. , Sunden B.
Published: February 2008

Experiments have been carried out to investigate the performance of a new swirl flow duct which is suitable for compact heat exchangers such as radiators. The ducts tested have rectangular cross sections with aspect ratio 1 to 8, and multiple V-shaped ribs are attached to the wide walls in a staggered arrangement such that square secondary flow cells are established. A previous investigation has shown that multiple V-shaped ribs may provide greater heat transfer enhancement than angled straight ribs and V-shaped ribs at Reynolds numbers below 2000. The data are presented as j and f factors for Reynolds numbers from 500 to 15,000, and correlations are obtained for the influence of rib height (0.1 < e/H < 0.2), rib pitch (3 < p/H < 7), and rib angle (15 deg < Φ < 45 deg). It was found that a rib angle of 45 deg provided the highest j/f ratio, while increasing the rib height or decreasing the rib pitch lowers the j/f ratio.
Heat Transfer in Living Systems: Current Opportunities
Authors: Diller K. R. , Ryan T. P.
Published: February 2008

This paper presents an overview of the field of bioheat transfer. Topics covered include factors that distinguish heat transfer in living systems from inanimate systems, application areas in basic research and in clinical diagnosis and therapy, and our projection of where the field is headed and what are likely to be the most fertile opportunities for contributions by members of the heat transfer community.
A Review of Recent Developments in Some Practical Aspects of Air-Cooled Electronic Packages
Authors: Sathe S. , Sammakia B.
Published: February 2008

The recent emphasis on low-cost high-end servers and desktop workstations has resulted in a renewed interest in the development of high-performance air-cooled systems. A new generation of advanced heat sink designs capable of dissipating up to 105 W/m2 have been proposed and developed. Better manufacturing tolerances, lower defects, and an improved understanding of card and enclosure effects have been attained and shown to be critical to achieving the desired thermal performance. Advanced internal thermal enhancements, encompassing high thermal conductivity adhesives and greases have also been implemented. This review article covers recent developments in heat sink designs and applications intended for high-end high-power dissipation systems. A review of recent studies of card effects in the thermal enhancement of electronic packages is also presented. In certain applications the card heat-sinking effect can play a major role in the thermal management of a package, accounting for more than 50 percent of the total power dissipation of the package.
Fundamental Issues and Recent Advancements in Analysis of Aircraft Brake Natural Convective Cooling
Authors: Dyko M. P. , Vafai K.
Published: February 2008

A heightened awareness of the importance of natural convective cooling as a driving factor in design and thermal management of aircraft braking systems has emerged in recent years. As a result, increased attention is being devoted to understanding the buoyancy-driven flow and heat transfer occurring within the complex air passageways formed by the wheel and brake components, including the interaction of the internal and external flow fields. Through application of contemporary computational methods in conjunction with thorough experimentation, robust numerical simulations of these three-dimensional processes have been developed and validated. This has provided insight into the fundamental physical mechanisms underlying the flow and yielded the tools necessary for efficient optimization of the cooling process to improve overall thermal performance. In the present work, a brief overview of aircraft brake thermal considerations and formulation of the convection cooling problem are provided. This is followed by a review of studies of natural convection within closed and open-ended annuli and the closely related investigation of inboard and outboard subdomains of the braking system. Relevant studies of natural convection in open rectangular cavities are also discussed. Both experimental and numerical results obtained to date are addressed, with emphasis given to the characteristics of the flow field and the effects of changes in geometric parameters on flow and heat transfer. Findings of a concurrent numerical and experimental investigation of natural convection within the wheel and brake assembly are presented. These results provide, for the first time, a description of the three-dimensional aircraft braking system cooling flow field.
Diameter-Controlled Czochralski Growth of Silicon Crystals
Authors: Zhang H. , Zheng L. L. , Prasad V. , Larson D. J.
Published: February 2008

A thermal-capillary dynamic model for Czochralski (Cz) growth of silicon single crystal is presented that accounts for convection in the melt, conduction in the crystal, and radiation from the melt free surface and crystal. The shapes of the crystal/melt interface, moving crystal, and free surface are governed by the balance of energy and stresses. Decrease of the melt volume as the crystal is grown is also considered. A control algorithm based on the adjustment of the pull rate and/or crucible wall temperature has been developed. The diameter of the crystal can remain constant or vary with time based on the strategies implemented to control the growth process.
A Model for Radiative Cooling of a Semitransparent Molten Glass Jet
Authors: Song M. , Ball K. S. , Bergman T. L.
Published: February 2008

A mathematical model for the radiative cooling of a semitransparent molten glass jet with temperature-dependent viscosity has been developed and is implemented numerically. The axial velocity and jet diameter variations along the length of the jet, the axial bulk mean temperature distributions, and the centerline-to-surface glass temperature distributions are determined for different processing conditions. Comparisons are also made between the semitransparent predictions, which are based on a spectral discrete ordinates model, and predictions for an opaque medium.
TECHNICAL NOTE: Weakly Ionized Plasma Arc Heat Transfer Between Geometrically Dissimilar Electrodes
Authors: Sripada S. S. , Ayyaswamy P. S. , Cohen I. M.
Published: February 2008

A set of self-consistent conservation equations for the charged particle densities and the temperatures in a weakly ionized plasma between two dissimilar electrodes is numerically solved using an orthogonal body-fitted coordinate system. The electron number density and temperature variation in the discharge gap, and the results for the heat transfer to the anode are presented. Results have been developed for a configuration that commonly arises in microelectronic manufacturing—a thin cylindrical anode together with a planar cathode.
One-Dimensional Phase Field Models With Adaptive Grids
Authors: McCarthy J. F.
Published: February 2008

The phase field method has been demonstrated to hold promise for enabling the physics at the microscale to be incorporated in macroscopic models of solidification. However, for quantitatively accurate simulations to be performed, it will be necessary to develop algorithms which enable the interface width to be made very small. Adaptive grid techniques offer a means of achieving this within practical computational limits. This paper investigates the solution of one-dimensional phase field models using an adaptive grid technique. Three problems are considered: (1) the classical Stefan model, (2) the case of a solid sphere in equilibrium with its melt, and (3) a modified Stefan model with a generalized kinetic undercooling term. The numerical results are compared with those obtained using a fixed grid algorithm. In general, the adaptive grid technique is shown to be far more efficient, but it requires some care in its implementation.
A Modified Temperature-Jump Method for the Transition and Low-Pressure Regime
Authors: Beikircher T. , Benz N. , Spirkl W.
Published: February 2008

For modeling the gas heat conduction at arbitrary Knudsen numbers and for a broad range of geometries, we propose a modified temperature-jump method. Within the modified approach, we make a distinction between an inner convex surface and an outer concave surface enclosing the inner surface. For problems, where only a single geometric length is involved, i.e., for large parallel plates, long concentric cylinders and concentric spheres, the new method coincides at any Knudsen number with the interpolation formula according to Sherman, and therefore also with the known solutions of the Boltzmann equation obtained by the four momenta method. For the general case, where more than one geometric length is involved, the modified temperature method is trivially correct in the limit of high pressure and identical with Knudsen’s formula in the limit of low pressure. For intermediate pressure, where there is a lack of known solutions of the Boltzmann equation for general geometries, we present experimental data for the special two-dimensional plate-in-tube configuration and compare it with results of the modified temperature-jump method stating good agreement. The results match slightly better compared to the standard temperature method and significantly better compared to the interpolation formula according to Sherman. For arbitrary geometries and Knudsen numbers, the modified temperature method shows no principal restrictions and may be a simple approximative alternative to the solution of the Boltzmann equation, which is rather cumbersome.
Numerical Simulation on Heat Transfer and Fluid Flow Characteristics of Arrays With Nonuniform Plate Length Positioned Obliquely to the Flow Direction
Authors: Wang L. B. , Jiang G. D. , Tao W. Q. , Ozoe H.
Published: February 2008

The periodically fully developed laminar heat transfer and pressure drop of arrays with nonuniform plate length aligned at an angle (25 deg) to air direction have been investigated by numerical analysis in the Reynolds number range of 50–1700. The body-fitted coordinate system generated by the multisurface method was adopted to retain the corresponding periodic relation of the lines in physical and computational domains. The computations were carried out just in one cycle. Numerical results show that both the heat transfer and pressure drop increase with the increase in the length ratio of the long plate to the short plate, and decrease with the decrease in the ratio of transverse pitch to the longitudinal pitch. The numerical results exhibit good agreement with available experimental data.
Flat Miniature Heat Pipes With Micro Capillary Grooves
Authors: Hopkins R. , Faghri A. , Khrustalev D.
Published: February 2008

Flat miniature heat pipes (FMHP’s) are shown to be very promising in the cooling of electronic component systems. This investigation presents a detailed experimental and theoretical analysis on maximum heat transfer capabilities of two copper-water FMHP’s with diagonal trapezoidal micro capillary grooves and one copper-water FMHP with axial rectangular micro capillary grooves. Maximum heat flux on the evaporator wall of the 120-mm long axial grooved heat pipe, with a vapor channel cross-sectional area of approximately 1.5 × 12 mm2 and rectangular grooves of dimensions 0.20 mm wide by 0.42 mm deep, exceeded 90 W/cm2 in the horizontal orientation and 150 W/cm2 in the vertical orientation. Theoretical prediction of the capillary limitation in the horizontal orientation agreed reasonably well with the experimental data.
Evaporation Heat Transfer and Pressure Drop of Refrigerant R-134a in a Plate Heat Exchanger
Authors: Yan Y.-Y. , Lin T.-F.
Published: February 2008

The evaporation heat transfer coefficient and pressure drop for refrigerant R-134a flowing in a plate heat exchanger were investigated experimentally in this study. Two vertical counterflow channels were formed in the exchanger by three plates of commercial geometry with a corrugated sine shape of a chevron angle of 60 deg. Upflow boiling of refrigerant R-134a in one channel receives heat from the hot downflow of water in the other channel. The effects of the mean vapor quality, mass flux, heat flux, and pressure of R-134a on the evaporation heat transfer and pressure drop were explored. The quality change of R-134a between the inlet and outlet of the refrigerant channel ranges from 0.09 to 0.18. Even at a very low Reynolds number, the present flow visualization of evaporation in a plate heat exchanger with the transparent outer plate showed that the flow in the plate heat exchanger remains turbulent. It is found that the evaporation heat transfer coefficient of R-134a in the plates is much higher than that in circular pipes and shows a very different variation with the vapor quality from that in circular pipes, particularly in the convective evaporation dominated regime at high vapor quality. Relatively intense evaporation on the corrugated surface was seen from the flow visualization. Moreover, the present data showed that both the evaporation heat transfer coefficient and pressure drop increase with the vapor quality. At a higher mass flux the pressure drop is higher for the entire range of the vapor quality but the evaporation heat transfer is clearly better only at the high quality. Raising the imposed wall heat flux was found to slightly improve the heat transfer, while at a higher refrigerant pressure, both the heat transfer and pressure drop are slightly lower. Based on the present data, empirical correlations for the evaporation heat transfer coefficient and friction factor were proposed.
Local Flow and Heat Transfer Behavior in Convex-Louver Fin Arrays
Authors: DeJong N. C. , Jacobi A. M.
Published: February 2008

Local and surface-averaged measurements of convection coefficients and core pressure-drop data are provided for an array of convex-louver fins. For a Reynolds number range from 200 to 5400, these data are complemented with a flow visualization study and contrasted with new measurements from a similar offset-strip geometry. The results clarify the effects of boundary layer restarting, shear-layer unsteadiness, spanwise vortices, and separation, reattachment, and recirculation on heat transfer in the convex-louver geometry.
Mechanisms of Thermo-Solutal Transport and Segregation in High-Pressure Liquid-Encapsulated Czochralski Crystal Growth
Authors: Zou Y. F. , Wang G.-X. , Zhang H. , Prasad V.
Published: February 2008

The mechanism of dopant transport and segregation in high-pressure liquid-encapsulated Czochralski (HPLEC) grown III-V compound crystals (e.g., GaAs, InP) has been numerically studied using an integrated model, MASTRAPP. The model approximates the melt flow in the crucible as a quasi-steady-state, laminar, and axisymmetric flow, but the gas flow is considered as turbulent. Based on the physics of the growth process, a two-time-level scheme has been implemented where the dopant transport and growth are simulated at a smaller time scale while flow and temperature solutions are obtained from quasi-static calculations. Detailed numerical analyses are performed for the conditions of pure crystal rotation, pure thermally driven natural convection, and pure crucible rotation as well as for mixed flow with all of these forces present simultaneously. The dopant transport and segregation in these cases are well correlated to the corresponding melt flow pattern. Very weak radial segregation is predicted for pure crystal rotation because the resulting melt flow leads to a fairly flat solute boundary layer. The natural convection, on the other hand, produces a nonuniform boundary layer along the melt/crystal interface. This leads to a strong radial segregation with a high concentration along the central axis of the crystal. The crucible rotation has a similar effect. The combined effect of all of these flow mechanisms produces a strong radial segregation, whose extent depends on the relative strength of the driving forces. In all of these cases, strong melt flows lead to thin boundary layers that result in decreased longitudinal segregation. The predictions agree well with the experimental observations reported in the literature.
Thermal Conductivity of a Material Containing a Layer of Thin Strips or a Staggered Array of Thin Strips
Authors: Wang C. Y.
Published: February 2008

The effective conductivity of a composite containing layers of thin strips is found by conformal mapping and the method of eigenfunction expansions and matching.
Thermal Analysis of Solids at High Peclet Numbers Subjected to Moving Heat Sources
Authors: Manca O. , Morrone B. , Nardini S.
Published: February 2008

A three-dimensional heat transfer model has been developed to obtain the conductive thermal field inside a brick-type solid under a moving heat source with different beam profiles. The problem in quasi-steady state has been approximated by neglecting the axial diffusion component; thus, for Peclet numbers greater than 5, the elliptic differential equation becomes a parabolic one along the motion direction. The dependence of the solution on the radiative and convective heat losses has been highlighted. Thermal fields are strongly dependent on different spot shapes and on the impinging jet; this situation allows control of the parameters involved in the technological process.
Heat Flux Measurements in Homogeneous Curved Shear Flow
Authors: Holloway A. G. L. , Ebrahimi-Sabet S. A.
Published: February 2008

Turbulent heat fluxes were measured far downstream of a fine heating wire stretched spanwise across a curved, uniform shear flow. The turbulence was approximately homogeneous and the overheat small enough to be passive. Strong destabilizing and stabilizing curvature effects were produced by directing the shear toward the center of curvature and away from the center of curvature, respectively. The dimensionless turbulent shear stress was strongly affected by the flow curvature, but the dimensionless components of the turbulent heat flux were found to be relatively insensitive.
Enhanced Cooling via Boiling in Porous Layers: The Effect of Vapor Channels
Authors: Stubos A. K. , Buchlin J.-M.
Published: February 2008

Enhanced heat transfer via boiling in a porous layer covering the heated surface is considered analytically. The effect of vapor channels traversing the porous layer on the power for which a vapor film on the heated surface occurs, is examined by comparing the heat removal capability of the system with and without channels. A significant increase of the attained coolability level is obtained theoretically leading to the possibility of new design configurations for the cooling of intensely heated surfaces.
Predictions of Turbulent Heat Transfer in an Axisymmetric Jet Impinging on a Heated Pedestal
Authors: Parneix S. , Behnia M. , Durbin P. A.
Published: February 2008

Cooling or heating of a flat plate by an impinging jet, due to its many applications, has been widely studied. Recent experimental data concerning more complex geometries has become available. In this study, the cooling of a heated pedestal mounted on a flat plate, a configuration which is closer to the one met in some engineering applications (e.g., cooling of electronic components), has been numerically simulated. The normal velocity relaxation turbulence model (V2F model) in an axisymmetric geometry has been adopted. Results have been obtained for a range of jet Reynolds numbers and jet-to-pedestal distances. Comparison of the predicted heat transfer coefficient with experiments has shown a very good agreement. For comparison, results have also been obtained with the widely used κ – ε turbulence model and the agreement with the data is poor.
A Sequential Gradient Method for the Inverse Heat Conduction Problem (IHCP)
Authors: Dowding K. J. , Beck J. V.
Published: February 2008

A sequential-in-time implementation is proposed for a conjugate gradient method using an adjoint equation approach to solve the inverse heat conduction problem (IHCP). Because the IHCP is generally ill-posed, Tikhonov regularization is included to stabilize the solution and allow for the inclusion of prior information. Aspects of the sequential gradient method are discussed and examined. Simulated one and two-dimensional test cases are evaluated to study the sequential implementation. Numerical solutions are obtained using a finite difference procedure. Results indicate the sequential implementation has accuracy comparable to the standard whole-domain solution, but in certain cases requires significantly more computational time. Benefits of the on-line nature of a sequential method may outweigh the additional computational requirements. Methods to improve the computational requirements, which make the method competitive with a whole domain solution, are given.
An Experimental Study on Forced Convection Heat Transfer From Flush-Mounted Discrete Heat Sources
Authors: Tso C. P. , Xu G. P. , Tou K. W.
Published: February 2008

Experiments have been performed using water to determine the single-phase forced convection heat transfer from in-line four simulated electronic chips, which are flush-mounted to one wall of a vertical rectangular channel. The effects of the most influential geometric parameters on heat transfer including chip number, and channel height are tested. The channel height is varied over values of 0.5, 0.7, and 1.0 times the heat source length. The heat flux is set at the three values of 5 W/cm2, 10 W/cm2, and 20 W/cm2, and the Reynolds number based on the heat source length ranges from 6 × 102 to 8 × 104. Transition Reynolds numbers are deduced from the heat transfer data. The experimental results indicate that the heat transfer coefficient is affected strongly by the number of chips and the Reynolds number and weakly by the channel height. Finally, the present results from liquid-cooling are compared with other results from air-cooling, and Prandtl number scaling between air and water is investigated.
Experimental and Numerical Studies of Heat Transfer From a Liquid Bath due to an Impinging Gas Jet
Authors: Qian F. , Farouk B. , Mutharasan R. , Macken N.
Published: February 2008

There have been extensive heat transfer studies of impinging gas jets on solid surfaces, but few on impinging gas jets on a liquid bath. In this paper, air-jet-induced transport in a heated liquid bath is considered. Two different liquids having widely different Prandtl numbers (silicone oil and a molten metal alloy, Amalloy-203®) were used as bath liquids. Both numerical calculations and experimental measurements were carried out to characterize the jet-induced flow and heat transfer in the liquid bath. The numerical model developed considers the interaction of the jet flow and the liquid bath circulation. The mixing and thermal behavior of the heated bath were determined as functions of the air-jet characteristics (inlet temperature, Reynolds number) and the bath liquid properties (liquid Prandtl number and a “bath Grashof number”).
Analysis of Combined Forced and Free Flow in a Vertical Channel With Viscous Dissipation and Isothermal-Isoflux Boundary Conditions
Authors: Barletta A.
Published: February 2008

Fully developed and laminar mixed convection in a parallel-plate vertical channel is investigated in the case of non-negligible viscous heating. The channel walls are subjected to asymmetric boundary conditions: One wall experiences a constant and uniform heat flux, while the other is kept at a uniform and constant temperature. The velocity field and the temperature field are evaluated analytically by means of perturbation expansions with respect to a buoyancy parameter, i.e., the ratio between the Grashof number and the Reynolds number. The Nusselt numbers and the friction factors are obtained as functions of the buoyancy parameter.
Nucleate Pool Boiling on Ribbed Surfaces With Micro-Roughness at Low and Moderate Heat Flux
Authors: Hsieh S.-S. , Weng C.-J. , Chiou J.-J.
Published: February 2008

Nucleate pool boiling correlation was developed for five different rib-type roughened tube geometries (including plain tube) with different rib angles of 30 deg, 45 deg, 60 deg, and 90 deg for both distilled water and R-134a as the working media. A scanning electron micrograph (SEM) examination was made for these horizontal roughened tubes. Bubble departure diameter, frequency of bubble emission, and the active nucleation site density with the influence of the rib angle for this type of roughened surface were obtained. Boiling heat flux incorporating natural convection, nucleate boiling, and microlayer evaporation mechanisms following Benjamin and Balakrishnan (1996) was predicted. Heat transfer correlation was also developed in terms of the degree superheat and active nucleation site density. The dependence for these two parameters was found in favorable agreement with that of previous study for smooth surfaces.
Effect of Combined Particle-Phase Diffusivity and Viscosity on the Compressible Boundary Layer of a Particulate Suspension Over a Flat Plate
Authors: Chamkha A. J.
Published: February 2008

A mathematical dilute fluid-particle suspension model governing steady, laminar, compressible, boundary layer flow and heat transfer over a semi-infinite flat plate based on the Eulerian or continuum approach is developed. The model accounts for both particulate viscous and diffusive effects. Both the fluid and the particle phases are assumed to have general power-law viscosity-temperature relations. For the case of finite particle-phase viscosity, a general boundary condition borrowed from rarefied gas dynamics is used for the particle phase at the surface. Uniform and nonuniform particle-phase slip coefficients are investigated. Numerical solution of the governing equations is obtained by an implicit, iterative, tridiagonal finite difference method. Graphical results for the displacement thicknesses and skin-friction coefficients of both phases as well as the wall heat transfer are presented for various parametric conditions.
Mass, Momentum, and Energy Transport in a Molten Pool When Welding Dissimilar Metals
Authors: Chung F. K. , Wei P. S.
Published: February 2008

Velocity and temperature fields, and shapes of the fusion zone in welding dissimilar metals are systematically investigated. Fluid flow in the molten pool is driven by the Marangoni force in different directions and magnitudes on the flat free surface. To interpret clearly without loss of generality, the three-dimensional quasi-steady welding is simulated by an unsteady two-dimensional process. Transport process on the maximum cross section of the molten region (or a cross section of the fusion zone) therefore is predicted. Interfaces between immiscible dissimilar metals and solid and liquid are, respectively, calculated by the volume of fluid and enthalpy methods. The computed results show different flow and thermal fields and molten regions of dissimilar metals as functions of dimensionless surface tension coefficients, viscosities, melting temperatures, and thermal conductivities of dissimilar metals and distinct phases, and beam power, welding speed, and the energy distribution parameter. The predicted shapes of fusion zones in welding pure irons, and aluminum to iron, agree with the experimental results.
Heat and Mass Transfer Problems for Film Cooling
Authors: Leontiev A. I.
Published: February 2008

In the paper, a review of calculation methods and of experimental results for heat transfer under film cooling is presented. The effects of arrangement of film cooling, longitudinal pressure gradient, nonisothermality and compressibility of the gas, injection of a foreign gas, surface roughness, swirling of flow, and turbulent pulsations of the main gas flow on the effectiveness of film cooling are considered. A generalized correlation for the effectiveness of film cooling, is proposed, which makes it possible to take into account the influence of the above factors. It is shown, that in determination of the heat transfer coefficient in the region of film cooling, it is necessary to take into account the influence of injected gas on the development of the thermal boundary layer. A method of calculation for combined cooling (film, porous or transpiration and convective), which accounts for effect of longitudinal heat conductivity of the wall on the film cooling effectiveness is proposed. An estimation of profile losses on a gas turbine blade is given for the cases of film and porous or transpiration cooling.
Laminar Convective Heat Transfer of a Bingham Plastic in a Circular Pipe With Uniform Wall Heat Flux: The Graetz Problem Extended
Authors: Min T. , Yoo J. Y.
Published: February 2008

Thermally developing laminar flow of a Bingham plastic in a circular pipe with uniform wall heat flux has been studied analytically. Expressions for the fully developed temperature and Nusselt number are presented in terms of the yield stress, Peclet number, and Brinkman number. The solution to the Graetz problem has been obtained by using the method of separation of variables, where the resulting eigenvalue problem is solved approximately by using the method of weighted residuals. The effects of the yield stress, Peclet, and Brinkman numbers on the Nusselt number are discussed. In particular, it is shown that the heat transfer characteristics in the entrance region are significantly affected by the yield stress with the inclusion of viscous dissipation.
Free Jet Impingement Heat Transfer of a High Prandtl Number Fluid Under Conditions of Highly Varying Properties
Authors: Leland J. E. , Pais M. R.
Published: February 2008

An experimental investigation was performed to determine the heat transfer rates for an impinging free-surface axisymmetric jet of lubricating oil for a wide range of Prandtl numbers (48 to 445) and for conditions of highly varying properties (viscosity ratios up to 14) in the flowing film. Heat transfer coefficients were obtained for jet Reynolds numbers from 109 to 8592, nozzle orifice diameters of 0.51, 0.84 and 1.70 mm and a heated surface diameter of 12.95 mm. The effect of nozzle to surface spacing (1 to 8.5 mm), was also investigated. Viscous dissipation was found to have an effect at low heat fluxes. Distinct heat transfer regimes were identified for initially laminar and turbulent jets. The data show that existing constant property correlations underestimate the heat transfer coefficient by more than 100 percent as the wall to fluid temperature difference increases. Over 700 data points were used to generate Nusselt number correlations which satisfactorily account for the highly varying properties with a mean absolute error of less than ten percent.
Plume Dynamics in Natural Convection in a Horizontal Cylindrical Annulus
Authors: Fisher C. E. , Ball K. S.
Published: February 2008

Measurements of the unsteady temperature fluctuations in the plume region between differentially heated horizontal concentric cylinders are reported. In particular, power spectral density estimates of the temperature fluctuations within the plume show the development and breakdown of the oscillatory plume structure at high Rayleigh number, Rad, by two relatively independent processes: (1) the development of harmonic oscillations related to the dominant plume oscillation frequency, and (2) interactions between the oscillating plume and the adjacent relatively stagnant core flow (shear and entrainment). The harmonic oscillations are shown to be the dominant energy transfer mode at moderate Rad (up to Rad = 108), acting to disperse the plume energy without generating a broadband spectrum. The spectral density estimates show that while a distinct plume oscillation is still present near the inner cylinder at Rad = 109, the plume becomes increasingly turbulent as the outer cylinder is approached. A new correlation for the plume oscillation frequency, which is found to be proportional to Rad0.5, is also presented.
Experiments on Chimney-Enhanced Free Convection
Authors: Fisher T. S. , Torrance K. E.
Published: February 2008

Experimental results are presented for thermal systems consisting of a vertical, parallel-plate, isothermal heat sink and a chimney. A ridge of maximum total heat transfer is observed with respect to the plate spacing and heat-sink height. The magnitude of heat transfer and the location of optima confirm prior theoretical predictions by Fisher et al (1997) to within 11 percent. Averaged velocity measurements closely match theoretical predictions of mean velocity. Cold inflow at the chimney exit is quantified and shown to decrease overall heat transfer by approximately four percent.
Effect of Surface Radiation and Partition Resistance on Natural Convection Heat Transfer in a Partitioned Enclosure: An Experimental Study
Authors: Ramesh N. , Venkateshan S. P.
Published: February 2008

The heat transfer across an air-filled partitioned square enclosure is studied experimentally using a differential interferometer. The partition was located centrally inside the enclosure, parallel to the two isothermal differentially heated vertical walls, and extended the full height of the enclosure. The top and bottom horizontal walls of the enclosure were maintained adiabatic. A parametric study has been carried out using different partitions, focusing attention on the effect of partition thermal resistance as well as the interaction of surface radiation and natural convection, and on the total heat transfer between the vertical walls, inside the enclosure. Correlations, valid for the laminar range, are proposed.
Gibbs-Thomson Effect on Droplet Condensation
Authors: Lai Chun-Liang
Published: February 2008

The present study is primarily aimed at theoretically investigating the growth of a single spherical droplet due to condensation. The droplet is either at the center of a large spherical container or in an infinite domain. The effect on the droplet growth due, respectively, to the subcooling, the Gibbs-Thomson condition, and the density-difference-induced convection will be analyzed and discussed systematically. Dimensional analysis indicates that three different time scales exist during the droplet growth due to condensation. The first and second small time scales describe, respectively, the transient temperature distributions of the gas phase and droplet, while the largest time scale describes the droplet growth. With the aid of multiple time-scale analysis, the analytic solutions for the droplet growth and the temperature distribution are obtained. The results indicate that, with a large Stefan number, the subcooling effect is stronger and the droplet grows faster. The Gibbs-Thomson effect, on the contrary, suppresses the droplet growth. However, the effect becomes smaller as time proceeds. Moreover, if the density difference between the liquid and the gas phases becomes larger, the induced convection will be stronger, which is conducive to the droplet growth.
Forced Convection in Microstructures for Electronic Equipment Cooling
Authors: Kim S. J. , Kim D.
Published: February 2008

This paper reports analytical solutions for both velocity and temperature profiles in Microchannel heat sinks by modeling the Microchannel heat sink as a fluid-saturated porous medium. The analytical solutions are obtained based on the modified Darcy model for fluid flow and the two-equation model for heat transfer. To validate the porous medium model and the analytical solutions based on that model, the closed-form solution for the velocity distribution in the fully-developed channel flow and the numerical solutions for the conjugate heat transfer problem, comprising the solid fin and the fluid, are also obtained. The analytical solutions based on the porous medium model are shown to predict the volume-averaged velocity and temperature distributions quite well. Using the analytical solutions, the aspect ratio and the effective thermal conductivity ratio are identified as variables of engineering importance and their effects on fluid flow and heat transfer are studied. As either one of these variables increases, the fluid temperature is shown to approach the solid temperature. Finally, the expression for the total thermal resistance, derived from the analytical solutions and the geometry of the microchannel heat sink for which the thermal resistance of the heat sink is minimal, is obtained.
Variations of Buoyancy-Induced Mass Flux From Single-Phase to Two-Phase Flow in a Vertical Porous Tube With Constant Heat Flux
Authors: Zhao T. S. , Liao Q. , Cheng P.
Published: February 2008

This paper presents an experimental study of a buoyancy-induced flow of water with phase-change heat transfer in a vertical porous tube heated at a constant heat flux. Experiments were carried out from subcooled liquid flow to connective boiling by varying the imposed heat fluxes. At a prescribed heat flux the steady-state mass flux of water, as well as the temperatures along the tube wall and along the centerline of the packed tube, were measured. It is shown that for both single-phase flow and the two-phase flow with a rather low vapor fraction, the induced mass flux increased as the heat flux was increased. However, as the imposed heat flux was increased further, the induced mass flux dropped drastically, and remained relatively constant afterwards. The influences of various parameters such as the porous tube diameter, the particle sizes, and the hydrostatic head on the induced mass flux are also examined.
Effects of Perpendicular Flow Entry on Convective Heat/Mass Transfer From Pin-Fin Arrays
Authors: Chyu M. K. , Hsing Y. , Natarajan V. , Chiou J. S.
Published: February 2008

Convective heat transfer with pin-fin arrays have been studied extensively in laboratory experiments where flow is introduced to the array uniformly over the channel span. However, the flow path in actual cooling designs is often serpentine-shaped with multiple turns, and the pin-fin array section is often located immediately downstream of a turn. The present study, using an analogous mass transfer technique based on naphthalene sublimation, investigates the effects of three different, nonaxial flow entries on array heat transfer for both an inline and a staggered arrangement of pins. The measurement acquires the mass transfer rate of each individual pin in a five row by seven column array for the Reynolds number varying from 8000 to 25,000. The mass transfer and associated flow visualization results indicate that the highly nonuniform flow distribution established at the array entrance and persisting through the entire array can have significant effects on the array heat transfer characteristics. Compared to the conventional case with axial-through flow entrance, the overall array heat transfer performance can be either enhanced or degraded, depending on the actual inlet arrangements and array configurations.
Augmented Heat Transfer in a Triangular Duct by Using Multiple Swirling Jets
Authors: Hwang J.-J. , Cheng C.-S.
Published: February 2008

Measurements of detailed heat transfer coefficients on two principal walls of a triangular duct with a swirling flow are undertaken by using a transient liquid crystal technique. The vertex corners of the triangular duct are 45, 45, and 90 deg. The swirl-motioned airflow is induced by an array of tangential jets on the side entries. The effects of flow Reynolds number (8600 ≦ Re ≦ 21000) and the jet inlet angle (α = 75, 45, and 30 deg) are examined. Flow visualization by using smoke injection is conducted for better understanding the complicated flow phenomena in the swirling-flow channel. Results show that the heat transfer for α = 75 deg is enhanced mainly by the wall jets as well as the impinging jets; while the mechanisms of heat transfer enhancement for α = 45 and 30 deg could be characterized as the swirling-flow cooling. On the bottom wall, jets at α = 75 deg produce the best wall-averaged heat transfer due to the strongest wall-jet effect among the three angles (α) investigated. On the target wall, however, the heat transfer enhancements by swirling flow (α = 45 and 30 deg) are slightly higher than those by impinging jets (α = 75 deg). Correlations for wall-averaged Nusselt number for the bottom and target walls of the triangular duct are developed in terms of the flow Reynolds number for different jet inlet angles.
Improved Modeling of Turbulent Forced Convective Heat Transfer in Straight Ducts
Authors: Rokni M. , Sunden B.
Published: February 2008

This investigation concerns numerical calculation of turbulent forced convective heat transfer and fluid flow in their fully developed state at low Reynolds number. The authors have developed a low Reynolds number version of the nonlinear k-ε model combined with the heat flux models of simple eddy diffusivity (SED), low Reynolds number version of generalized gradient diffusion hypothesis (GGDH), and wealth ∝ earning × time (WET) in general three-dimensional geometries. The numerical approach is based on the finite volume technique with a nonstaggered grid arrangement and the SIMPLEC algorithm. Results have been obtained with the nonlinear k-ε model, combined with the Lam-Bremhorst and the Abe-Kondoh-Nagano damping functions for low Reynolds numbers.