bluuebunny/crossref_metadata_2025 huggingface dataset:
Theoretical Analysis of the Maximum Heat Transport in Triangular Grooves: A Study of Idealized Micro Heat Pipes
Authors: Peterson G. P. , Ma H. B.
Published: February 2008

A mathematical model for predicting the minimum meniscus radius and the maximum heat transport in triangular grooves is presented. In this model, a method for determining the theoretical minimum meniscus radius was developed and used to calculate the capillary heat transport limit based on the physical characteristics and geometry of the capillary grooves. A control volume technique was employed to determine the flow characteristics of the micro heat pipe, in an effort to incorporate the size and shape of the grooves and the effects of the frictional liquid–vapor interaction. In order to compare the heat transport and flow characteristics, a hydraulic diameter, which incorporated these effects, was defined and the resulting model was solved numerically. The results indicate that the heat transport capacity of micro heat pipes is strongly dependent on the apex channel angle of the liquid arteries, the contact angle of the liquid flow, the length of the heat pipe, the vapor flow velocity and characteristics, and the tilt angle. The analysis presented here provides a mechanism whereby the groove geometry can be optimized with respect to these parameters in order to obtain the maximum heat transport capacity for micro heat pipes utilizing axial grooves as the capillary structure.
Experimental Investigation of the Maximum Heat Transport in Triangular Grooves
Authors: Ma H. B. , Peterson G. P.
Published: February 2008

An experimental investigation was conducted and a test facility constructed to measure the capillary heat transport limit in small triangular grooves, similar to those used in micro heat pipes. Using methanol as the working fluid, the maximum heat transport and unit effective area heat transport were experimentally determined for ten grooved plates with varying groove widths, but identical apex angles. The experimental results indicate that there exists an optimum groove configuration, which maximizes the capillary pumping capacity while minimizing the combined effects of the capillary pumping pressure and the liquid viscous pressure losses. When compared with a previously developed analytical model, the experimental results indicate that the model can be used accurately to predict the heat transport capacity and maximum unit area heat transport when given the physical characteristics of the working fluid and the groove geometry, provided the proper heat flux distribution is known. The results of this investigation will assist in the development of micro heat pipes capable of operating at increased power levels with greater reliability.
The Interline Heat Transfer of Evaporating Thin Films Along a Micro Grooved Surface
Authors: Ha J. M. , Peterson G. P.
Published: February 2008

An analytical investigation of the heat transfer characteristics for evaporating thin liquid films in V-shaped microgrooves with nonuniform input heat flux was conducted. This investigation assumed that the capillary pressure difference caused by the receding of the meniscus is responsible for the axial liquid flow along the groove, and that the disjoining pressure difference along the groove side wall provided the driving force for the flow up the groove wall. The combined heat transfer mechanisms of both liquid conduction and interfacial vaporization were used to describe the local interracial mass flux in the interline region. Based on this approach, a local heat transfer coefficient was defined. The local and average heat transfer coefficients were both found to be sensitive to the characteristic thermal resistance ratio. In addition, when the film superheat was constant, the primary factor affecting the length of the evaporating interline region was found to be the heat flux supplied to the bottom plate, and for high heat flux conditions, the highest heat transfer coefficient did not necessarily exist at the axial dryout point. The expression developed for the evaporating film profile was shown to assume an exponential form if the heat flux distributed on the active interline region was assumed to be uniform.
The Stress-State in a Torsion Shear Cell Filled With a Newtonian Fluid
Authors: Koenders M. A. , Gaspar N. , Liebhart E.
Published: February 2008

The flow in a torsional shear cell is investigated with the purpose of finding a measure for the wall effect due to strongly nonuniform flow in the vicinity of the edge of the top platen. Various laminar flow problems are analysed that are relevant to this set-up. These include pure shearing flow of a single fluid in a both an infinite and finite cell, as well as pure shear of a two-fluid system in a finite cell. For pure shearing flow it is found that the extent of the wall effect is of the order of magnitude of the depth of the fluid layer. For piston flow the wall effect is entirely determined by boundary conditions at the bottom of the cell.
The Unsteady Pressure Field in a High Specific Speed Centrifugal Pump Impeller—Part I: Influence of the Volute
Authors: Kaupert Kevin A. , Staubli Thomas
Published: February 2008

An experimental investigation is presented regarding the unsteady pressure field within a high specific speed centrifugal pump impeller (ωs = 1.7) which operated in a double spiral volute. For this, twenty-five piezoresistive pressure transducers were mounted within a single blade passage and sampled in the rotating impeller frame with a telemetry system. The influence of varying volume flux on the pressure transducers was evaluated in terms of pressure fluctuation magnitudes and phase differences. The magnitude information reveals that the pressure fluctuations from the impeller-volute interaction grew as the volume flux became further removed from the best efficiency point and as the trailing edge of the impeller blade was approached. These fluctuations reached 35% of the pump head in deep part load. The upstream influence of the volute steady pressure field dominates the unsteady pressure field within the impeller at all off design load points. Acquired signal phase information permits the identification of the pressure field unsteadiness within the impeller passage as fundamentally synchronized simultaneously with the volute tongue passing frequency. Special emphasis was placed on the volume flux regime where the pump and impeller pressure discharge characteristic undergo hysteresis, as impeller inlet and outlet recirculation commence and cease. A synthesis of the rotating transducers was performed to obtain unsteady blade loading parameters. The value of the unsteady lift coefficient varies on the order of 200% for a single blade in part load operation (at 45% bep), an abrupt fluctuation occurring as the fore running blade suction side passes a volute tongue. The unsteady moment coefficient and center of pressure are also shown to vary significantly during the impeller-volute tongue interaction.
Comparison and Scaling of the Bursting Period in Rough and Smooth Walls Channel Flows
Authors: Demare S. , Labraga L. , Tournier C.
Published: February 2008

The Structure of Smooth and k-type rough wall turbulent channel flows was examined over a Reynolds number range of 12,700–55,000 using a few of the most common detection techniques (Modified U_Level (MODUL), TERA, Quadrant analysis) and conditional averages. When grouping time is used and a threshold-independent range could be found, all of the above techniques yield approximately the same time between bursts in the major part of the turbulent flow. In the range of Reynolds numbers studied, the bursting frequency is best scaled on mixed variables. The conditional averaged patterns give a representation of the bursting process and show some differences between turbulent flows which develop on smooth and rough walls, in both inner and outer regions.
Effect of Injected Longitudinal Vorticity on Particle Dispersion in a Swirling, Coaxial Jet
Authors: Wicker Ryan B. , Eaton John K.
Published: February 2008

A Passive particle dispersion control technique was investigated in which longitudinal vortices were injected into a developing coaxial swirling jet with sufficient annular swirl for flow recirculation to occur. Four vortex generators, separated by 90 degrees and placed along the outside of the annular nozzle, injected vorticity opposite in sign to the mean swirl, significantly altering the structure of the swirling jet. The injected vorticity competed with the mean swirl to reduce azimuthal particle flinging and to disrupt the development of the vortex rings in the outer shear layer. Axial flow visualization showed the formation of axial structures at the forcing frequency but considerable azimuthal asymmetry. Horizontal cross sections showed a four-lobed structure which persisted in the natural jet for at least eight inner jet diameters. The particle concentration field was measured using digital processing of pulsed laser sheet images. Outward radial particle dispersion reduced while inward dispersion toward the jet centerline increased indicating that the injected vorticity sufficiently reduced particle flinging by large-scale vortices.
Experimental Investigation of Blade Loading Effects at Design Flow in Rotating Passages of Centrifugal Impellers
Authors: Hesse Nicholas H. , Howard J. H. G.
Published: February 2008

Laser-Doppler Anemometry (LDA) was used to study the effect of blade loading on the relative velocity field in a rotating passage of a centrifugal-pump impeller. Two variations of the impeller, 8-bladed and 16-bladed, were investigated. The measured primary and secondary velocities and turbulence show that the effect of blade loading is not that previously predicted. The 16-blade impeller with high blade loading has a rapidly thickening suction side boundary layer, suggesting the onset of transient separation near the exit. However, for the 8-blade impeller with even higher blade loading, the onset of separation is not indicated at any measured location in the impeller. At the design flow, it is concluded that the stronger potential eddy and lower solidity associated with the very high blade loading caused a change in the secondary flow pattern, retarding the growth and the likelihood of transitory separation of the suction side boundary layer.
Effects of Nuclei Size Distribution on the Dynamics of a Spherical Cloud of Cavitation Bubbles
Authors: Wang Yi-Chun
Published: February 2008

The nonlinear dynamics of a spherical bubble cloud with nuclei size distribution are studied numerically. The spectrum of nuclei is assumed uniform initially. The simulations employ a nonlinear continuum bubbly mixture model with consideration of the presence of bubbles of different sizes. This model is then coupled with the Rayleigh-Plesset equation for the dynamics of bubbles. A numerical method based on the integral representation of the mixture continuity and momentum equations in the Lagrangian coordinates is developed to solve this set of integro-differential equations. Computational results show that the nuclei size distribution has significant effects on the cloud dynamics in comparison to the results for a single bubble size. One important effect is that the bubble collapse is always initiated near the surface of the cloud, even if the cloud has a very small initial void fraction. This effect has an important consequence, namely that the geometric focusing of the bubbly shock wave is always a part of the nonlinear dynamics associated with the collapse of a spherical cloud with nuclei size distribution. The strength of the shock and the oscillation structure behind the shock front are suppressed due to the effects of multiple bubble sizes. Far-field acoustic pressures radiated by two bubble clouds, one of equal-size bubbles and the other with bubble size distribution, are also compared. It is found that the cloud containing bubbles of different sizes emits a larger noise than the cloud of identical bubbles. Explanations for this effect are also presented.
Aerodynamic Torque Acting on a Butterfly Valve. Comparison and Choice of a Torque Coefficient
Authors: Solliec C. , Danbon F.
Published: February 2008

Most technological devices use butterfly valves to check the flow rate and speed, through piping. Their main advantages are their low cost, their mechanical suitability for fast operation, and their small pressure drops when they are fully open. The fluid dynamic torque about the axis of large valves has to be considered as the actuator could be overstrained. This torque is generally defined using a nondimensional coefficient KT, in which the static pressure drop created by the valve is used for normalization. When the valve is closed downstream of an elbow, the valve pressure drop is not well defined. Thus, the classic normalization method gives many ambiguities. To avoid the use of the pressure drop, we define another torque coefficient CT in which the dynamic pressure of the flow is the normalization factor instead of the pressure drop. Advantages and drawbacks of each normalization method are described in the following.
Transport Phenomena in Picoliter Size Solder Droplet Dispension
Authors: Waldvogel J. M. , Poulikakos D. , Wallace D. B. , Marusak R.
Published: February 2008

This paper presents a study of the fluid dynamics and heat transfer phenomena occurring during the impingement of a picoliter size liquid solder droplet upon a multilayer, composite substrate. The theoretical model, based on the Lagrangian formulation, is solved numerically with the finite element method. A deforming mesh is utilized to accurately simulate the large deformations, as well as the domain nonuniformities characteristic of the spreading process. The occurrences of droplet recoiling and mass accumulation around the deposit periphery are features of the numerical simulations and yield a nonmonotonic dependence of the maximum radius on time. The results also document the transient temperature fields developing in both the solder droplet and the substrate during the impingement process. Convection effects on the temperature field development in a deforming droplet are found to be important for the entire history of spreading. The work is directly applicable to the miniature solder droplet dispension technology for the mounting of microscopic electronic components on various substrates under development at MicroFab Inc. The results of the numerical simulations are used to explain the shape of solidified microscopic solder bumps.
A Conservative Formulation of the Discrete Transfer Method
Authors: Coelho P. J. , Carvalho M. G.
Published: February 2008

The discrete transfer method, often employed to calculate radiative heat transfer in combustion chambers, is not conservative. The reason for this behavior is examined and a conservative formulation is proposed and evaluated. A simple treatment of isotropic scattering media is also presented. The original and the conservative formulation of the method are applied to two-dimensional and three-dimensional enclosures containing a participating medium. It is shown that the accuracy of the original and the conservative formulation is very similar, but the proposed formulation has the advantage of ensuring energy conservation.
Point Measurements of Noncondensable Gas Concentration in Condensing Systems
Authors: Obonai A. , Peterson Per F. , Schrock V. E.
Published: February 2008

Condensation in the presence of noncondensable gases continues to receive considerable attention, most recently in the application to containment performance for advanced passive nuclear reactors. In experiments, it is often desired to make point measurements of noncondensable gas concentrations under conditions where the gas concentration can be small and superheat can be significant. This paper presents test results for a novel miniature psychrometer. The tests and analysis presented here show that a wetted cylindrical body will approach closely the local saturation temperature of an air-steam mixture, under a wide range of flow velocities and superheat levels, even when the bulb is allowed to drip water. This permits local gas concentrations to be measured with high accuracy, particularly when the thermopile method introduced here is used to measure the wet-bulb temperature relative to a reference pure steam temperature generated in a small boiler.
Numerical Solution of the General Two-Dimensional Inverse Heat Conduction Problem (IHCP)
Authors: Osman A. M. , Dowding K. J. , Beck J. V.
Published: February 2008

This paper presents a method for calculating the heat flux at the surface of a body from experimentally measured transient temperature data, which has been called the inverse heat conduction problem (IHCP). The analysis allows for two-dimensional heat flow in an arbitrarily shaped body and orthotropic temperature dependent thermal properties. A combined function specification and regularization method is used to solve the IHCP with a sequential-in-time concept used to improve the computational efficiency. To enhance the accuracy, the future information used in the sequential-in-time method and the regularization parameter are variable during the analysis. An example using numerically simulated data is presented to demonstrate the application of the method. Finally, a case using actual experimental data is presented. For this case, the boundary condition was experimentally measured and hence, it was known. A good comparison is demonstrated between the known and estimated boundary conditions for the analysis of the numerical, as well as the experimental data.
Experimental Studies and Correlations of Convective Heat Transfer in a Radially Rotating Serpentine Passage
Authors: Hwang G. J. , Kuo C. R.
Published: February 2008

The present paper investigates experimentally the effects of rotation on the convective heat transfer of air flow in a radially rotating three-passage serpentine square channel. Due to rotation, the cross-stream and radial secondary flows are induced by the Coriolis force and the centrifugal-buoyancy force, respectively. The channel walls were made of low thermal conductivity material for suppressing wall heat conduction. The wall surfaces were heated individually by four separate stainless-steel film heaters to distinguish the local heat transfer rates. The hydraulic diameter and the mean rotational radius of the flow passages were 4 and 180 mm, respectively. The governing parameters are the through-flow Reynolds number Re, the rotation number Ro, the buoyancy parameter Gr* and the main flow direction. The results show that the local heat transfer rate was enhanced by rotation on the trailing side for outward flow and on the leading side for inward flow. In the first and third passages, the effect of rotation on heat transfer is relatively prominent. The buoyancy effect is favorable to the heat transfer enhancement on four sides of these passages. The data of NuΩ/Nu0 are correlated on the leading and trailing sides of these passages.
ADE Type of Algorithms for Solving Diffusion Equations in Non-Cartesian Coordinates
Authors: Wang X. , Crawford R. J.
Published: February 2008

This paper studies the use of ADE methods for solving diffusion equations in non-Cartesian coordinates. To retain unconditional stability and greater accuracy of computation when solving diffusion equations in non-Cartesian coordinates, a new explicit algorithm is developed by combining the advantages of those originally proposed by Saul’ev, Larkin, Barakat and Clark. Analysis of accuracy shows that the new algorithm can be as accurate as either that of Larkin or that of Barakat and Clark. Stability analysis is also carried out “locally” based on the spectral stability, and this shows unconditional stability of the generalised algorithm. Numerical examples on transient heat conduction are used to support the conclusions from the analysis.
An Experimental Investigation of the Capillary Performance of Triangular Versus Sinusoidal Channels
Authors: Stroes G. R. , Catton I.
Published: February 2008

This paper discusses an experimental investigation of the performance of capillary channels with sinusoidal versus triangular geometry. Results indicate that for equivalent cross-sectional area, angle of inclination, and heat input from below, a triangular groove geometry sustains a larger wetted area while a sinusoidal groove geometry supports a greater average heat flux.
Size and Interface Effects on Thermal Conductivity of Superlattices and Periodic Thin-Film Structures
Authors: Chen G.
Published: February 2008

Superlattices consisting of alternating layers of extremely thin films often demonstrate strong quantum size effects that have been utilized to improve conventional devices and develop new ones. The interfaces in these structures also affect their thermophysical properties through reflection and transmission of heat carriers. This work develops models on the effective thermal conductivity of periodic thin-film structures in the parallel direction based on the Boltzmann transport equation. Different interface conditions including specular, diffuse, and partially specular and partially diffuse interfaces, are considered. Results obtained from the partially specular and partially diffuse interface scattering model are in good agreement with experimental data on GaAs/AlAs superlattices. The study shows that the atomic scale interface roughness is the major cause for the measured reduction in the superlattice thermal conductivity. This work also suggests that by controlling interface roughness, the effective thermal conductivity of superlattices made of bulk materials with high thermal conductivities can be reduced to a level comparable to those of amorphous materials, while maintaining high electrical conductivities. This suggestion opens new possibilities in the search of high efficiency thermoelectric materials.
Boiling Characteristics of Cylindrical Heaters in Saturated, Gas Saturated, and Pure-Subcooled FC-72
Authors: Hong Y. S. , Ammerman C. N. , You S. M.
Published: February 2008

A series of pool boiling experiments are performed in thermodynamically saturated, gas saturated, and pure-subcooled FC-72 using 25-, 50-, 75-, and 390-μm-diameter platinum wires. Comparisons of nucleate boiling characteristics are made between the various fluid-state/wire-size combinations. The effects of dissolved gas concentration on heat transfer are significant and are found to depend on length scale and heat flux. This discovery of a heater size and heat flux impact on dissolved-gas boiling enhancement provides insight into experimental results from previous investigations.
Enhanced Boiling Heat Transfer From Micro-Porous Cylindrical Surfaces in Saturated FC-87 and R-123
Authors: Chang J. Y. , You S. M.
Published: February 2008

The present research is an experimental study of pool boiling heat transfer from cylindrical heater surfaces immersed in saturated FC-87 and R-123. The baseline heater surfaces tested are plain, integral-fin with 709 fins/m, and commercial enhanced (High-Flux and Turbo-B). In addition, a highly effective micro-scale enhancement coating is applied to the plain and integral-fin surfaces to augment nucleate boiling heat transfer. Experiments are performed to understand the effects of surface micro- and macro-geometries on boiling heat transfer. The boiling performance of the micro-porous enhanced plain and integral-fin surfaces are compared with the High-Flux and the Turbo-B surfaces. At high heat flux conditions, the break down of the bulk liquid feed mechanism reduces boiling enhancement from the cylindrical surfaces.
Impact of Manifold Design on Heat Exchanger Efficiency
Authors: Harris D. K. , Warren D. G. , Goldschmidt V. W.
Published: February 2008

The impact of manifold design on single-phase heat exchanger effectiveness is studied using the NTU-Effectiveness method. Manifolds are devices that redistribute the internal flow stream of a heat exchanger from one to several passages. Two manifold types are identified: collector box and direct split designs. The particular application considered is that of a gas fired forced air heating system. A general enhancement analysis is performed which covers four different combinations of performance and objective criteria. Three cases involve increasing the heat exchanger effectiveness while constraining either the internal flow head loss, the internal mass flow rate, or their product. The other case involves reducing the required heat exchanger flow length while constraining the heat transfer rate. Familiar convection correlations are then incorporated into the enhancement analysis to predict general trends and behavior when the main tube is split into several smaller tubes. Analytical estimates of improved effectiveness are presented for three operating conditions of an actual heat exchanger which possesses a manifold. Experimental data acquired from the gas-to-gas heat exchanger are compared to numerical predictions of its performance without a manifold (baseline design). The analytical equations developed closely predict the improvement in heat exchanger effectiveness.
Boiling Heat Transfer With Binary Mixtures: Part II—Flow Boiling in Plain Tubes
Authors: Kandlikar S. G.
Published: February 2008

Flow boiling heat transfer with pure fluids comprises convective and nucleate boiling components. In flow boiling of binary mixtures, in addition to the suppression effects present in pool boiling, the presence of flow further modifies the nucleate boiling characteristics. In the present work, the flow boiling correlation by Kandlikar (1990, 1991b) for pure fluids is used as the starting point, and the mixture effects derived in Part I (Kandlikar, 1998) of this paper are incorporated. Three regions are defined on the basis of a volatility parameter, V1 = (cp/ΔhLG)(k/D12)1/2|(y1 − x1)dT/dx1|. They are: region I—near azeotropic, region II—moderate diffusion-induced suppression, and region III—severe diffusion-induced suppression. The resulting correlation is able to correlate over 2500 data points within 8.3 to 13.3 percent mean deviation for each data set. Furthermore, the α–x trend is represented well for R-12/R-22, R-22/R-114, R-22/R-152a, R-500, and R-132a/R-123 systems. Electrically heated stainless steel test sections as well as fluid-heated copper test sections are both covered under this correlation.
The Effects of Transverse Acceleration-Induced Body Forces on the Capillary Limit of Helically Grooved Heat Pipes
Authors: Thomas S. K. , Klasing K. S. , Yerkes K. L.
Published: February 2008

A helically grooved copper heat pipe with ethanol as the working fluid has been fabricated and tested on a centrifuge table. The heat pipe was bent to match the radius of curvature of the table so that uniform transverse (perpendicular to the axis of the heat pipe) body force fields could be applied along the entire length of the pipe. By varying the heat input (Qin = 25 to 250 W) and centrifuge table velocity (radial acceleration |a⃗r| = 0 to 10g), information on dry out phenomena, circumferential temperature uniformity, heat lost to the environment, thermal resistance, and the capillary limit to heat transport was obtained. Due to the geometry of the helical grooves, the capillary limit increased by a factor of five when the radial acceleration increased from |a⃗r| = 0 to 6.0g. This important result was verified by a mathematical model of the heat pipe system, wherein the capillary limit to heat transport of each groove was calculated in terms of centrifuge table angular velocity, the geometry of the heat pipe and the grooves (including helix pitch), and temperature-dependent working fluid properties. In addition, a qualitative study was executed with a copper-ethanol heat pipe with straight axial grooves. This experimental study showed that the performance of the heat pipe with straight grooves was not improved when the radial acceleration was increased from |a⃗r| = 0 to 10.0g.
Capillary Performance of Evaporating Flow in Micro Grooves: An Analytical Approach for Very Small Tilt Angles
Authors: Ha J. M. , Peterson G. P.
Published: February 2008

The axial flow of an evaporating thin film through a V-shaped micro channel was investigated for the case of a grooved plate inclined with a very small tilt angle. For this problem, the addition of the gravity term caused by the tilt angle alters the form of the governing equation from linear to nonlinear. Because the effect of the tilt angle is very small, a perturbation method was applied to obtain a first order perturbation solution of R = R0 + εR1, where R0 is the undisturbed solution caused by the tilt angle. A generalized graph of the nondimensional radius of curvature as a function of the nondimensionalized axial length was obtained. The perturbation parameter, ε, was expressed as a function of five nondimensional parameters. The results indicate that when the geometry is fixed, the effects of the Bond number and Capillary number are dominant. In addition, it was found that ε is inversely proportional to the square root of the Capillary number. This indicates that the perturbation method is applicable and accurate, even for the case of somewhat larger tilt angles (where the initial applicability of perturbation appears to be violated), is a sufficiently large heat flux is applied.
Impact of Channel Geometry on Two-Phase Flow Heat Transfer Characteristics of Refrigerants in Microchannel Heat Exchangers
Authors: Ravigururajan T. S.
Published: February 2008

Microchannel surfaces, often machined to 20 to 1000 μm in width and depth, are employed in high-heat-flux applications. However, a large number of variables, control the two-phase flow heat transfer coefficient. The pressure, the surface heat flux, and the mass flux significantly affect the thermal transport. Experiments were conducted on a setup that was built for testing microchannel heat exchanges. The parameters considered in the study are power input: 20 to 300 W, volume flow rate: 35 to 300 ml/min, quality: 0 to 0.5, inlet subcooling: 5 to 15°C. The results indicate that the heat transfer coefficient and pressure drop are functions of the flow quality, the mass flux, and, of course, the heat flux and the related surface superheat. The heat transfer coefficient decreases from a value of 12,000 W/m2-K to 9000, W/m2-K at 80°C, when the wall superheat is increased from 10 to 80°C. The coefficient decreases by 30 percent when the exit vapor quality is increased from 0.01 to 0.65.
Flow and Heat Transfer Characteristics Inside Packed and Fluidized Beds
Authors: Wu C. C. , Hwang G. J.
Published: February 2008

This paper investigates experimentally and theoretically the flow and heat transfer characteristics inside packed and fluidized beds. A single-blow transient technique combined with a thermal nonequilibrium two-equation model determined the heat transfer performances. Spherical particles were randomly packed in the test section for simulating the packed beds with porosity ε=0.38 and 0.39. Particles were strung with different spaces for fluidized beds with ε = 0.48 ~ 0.97. The ranges of dominant parameters are the Prandtl number Pr = 0.71, the particle Reynolds number Red = 200 ~ 7000, and ε = 0.38 ~ 0.97. The results show that the heat transfer coefficient increases with the decrease in the porosity and the increase in the particle Reynolds number. The friction coefficients of the fluidized beds with ε = 0.48 and 0.53 have significant deviations from that of the packed bed with ε = 0.38 and 0.39. Due to fewer interactions among particles for ε = 0.97, the friction coefficient approaches the value of a single particle.
Thermal Transport Phenomena in Turbulent Gas Flow Through a Tube at High Temperature Difference and Uniform Wall Temperature
Authors: Torii Shuichi , Yang Wen-Jei
Published: February 2008

A numerical study is performed to investigate thermal transport phenomena in turbulent gas flow through a tube heated at high temperature difference and uniform wall temperature. A k-ε turbulence model is employed to determine the turbulent viscosity and the turbulent kinetic energy. The turbulent heat flux is expressed by a Boussinesq approximation in which the eddy diffusivity of the heat is determined by a t2-ε, heat transfer model. The governing boundary layer equations are discretized by means of a control-volume finite difference technique and are numerically solved using a marching procedure. It is disclosed from the study that (i) laminarization takes place in a turbulent gas flow through a pipe with high uniform wall temperature just as it does in a pipe with high unform wall heat flux, and (ii) the flow in a tube heated to high temperature difference and uniform wall temperature is laminarized at a lower heat than that under the uniform heat flux condirion.
Monte Carlo Simulation of Radiation in Gases With a Narrow-Band Model and a Net-Exchange Formulation
Authors: Cherkaoui M. , Dufresne J.-L. , Fournier R. , Grandpeix J.-Y. , Lahellec A.
Published: February 2008

The Monte Carlo method is used for simulation of radiative heat transfers in nongray gases. The proposed procedure is based on a Net-Exchange Formulation (NEF). Such a formulation provides an efficient way of systematically fulfilling the reciprocity principle, which avoids some of the major problems usually associated with the Monte Carlo method: Numerical efficiency becomes independent of optical thickness, strongly nonuniform grid sizes can be used with no increase in computation time, and configurations with small temperature differences can be addressed with very good accuracy. The Exchange Monte Carlo Method (EMCM) is detailed for a one-dimensional slab with diffusely or specularly reflecting surfaces.
Transient Heating and Melting of Particles in Plasma Spray Coating Process
Authors: Jog M. A. , Huang L.
Published: February 2008

In the plasma spray coating process, solid particles are injected into a plasma jet. The heat transfer from the plasma to the particles results in heating and melting of the particles. The molten particles impact on a surface forming a thin coat. In this paper, we investigate the heating and melting of a spherical particle injected into a thermal plasma. The transient temperature distribution in the particle interior is obtained simultaneously with the temperature and number density variations of the ions, electrons, and the neutrals as well as the electric potential variation in the plasma. Our analysis incorporates a model for the production and recombination of electrons and ions. The transport in the plasma is modeled by considering the main body of the plasma as charge neutral and a charge sheath in the vicinity of the particle surface. The heat flux to the particle is evaluated by taking into account all modes of heat transfer to the surface. The temporal variations of the particle temperature distribution are calculated. Results are compared with the available predictions made without taking into account the gas ionization to assess the importance of ionization and particle charging on the heat transport to the particle. For argon, for the particle materials considered in this study, the effect of gas ionization on the heat transport was found to be negligible for plasma temperatures below 6500 K.
Melting and Resolidification of a Subcooled Mixed Powder Bed With Moving Gaussian Heat Source
Authors: Zhang Yuwen , Faghri A.
Published: February 2008

Melting of a subcooled powder bed that contains a mixture of two powders with significantly different melting points under a moving Gaussian heat source was investigated numerically. Shrinkage induced by the density change on the melting process was taken into account in the physical model. The problem is formulated using a temperature transforming model and solved by the finite difference method. The results show that the effect of surface heat loss due to convection and radiation is not negligible regardless of whether the shrinkage phenomena is considered. The decrease of moving heat source intensity will result in decrease of the sintering depth and the volume of the liquid pool. The increase of the scanning velocity will decrease the sintering depth and the location and shape of the liquid pool is affected significantly.
Heat Transfer Through an Extended Surface Containing He II
Authors: Van Sciver S. W.
Published: February 2008

A semi-analytic solution for the heat transfer process between a He II pressurized bath and a saturated tube-type heat exchanger is presented. The problem is modeled with an extended surface heat transfer formulation analogous to that in conventional conduction. The process is governed by Kapitza conductance and counterflow within the bulk fluid in the tube. The resulting nonlinear differential equation may be integrated for the special case of constant properties, yielding a simple solution applicable to design and analysis of practical heat exchangers.
The Effect of Periodic Unsteady Flow on Aerodynamics and Heat Transfer on a Curved Surface
Authors: Wright L. , Schobeiri M. T.
Published: February 2008

Aerodynamic and heat transfer investigations were performed on a constant curvature curved plate in a subsonic wind tunnel facility for various wake passing frequencies under zero pressure gradient conditions. Steady and unsteady boundary layer transition measurements were taken on the concave surface at different wake passing frequencies in which a rotating squirrel cage was used to generate the unsteady wake flow. The data were analyzed using time-averaged and ensemble averaged techniques to provide insight into the growth of the boundary layer and transition. Ensemble averaged turbulence intensity contours in the temporal spatial domain showed that transition was induced for increasing wake passing frequency and structure. The local heat transfer coefficient distributions for the concave and convex surfaces were determined for each wake passing frequency using a liquid crystal heat transfer measurement technique. Aerodynamic and heat transfer investigations showed that higher wake passing frequencies caused earlier transition on the concave surface. Local Stanton numbers were calculated on the concave surface and compared to Stanton numbers predicted using a boundary layer and heat transfer calculation method. On the convex side, no effect of wake passing on heat transfer was observed, due to a separation bubble that induced transition.
The Influence of Vapor Bubble Sliding on Forced Convection Boiling Heat Transfer
Authors: Thorncroft G. E. , Klausner J. F.
Published: February 2008

This paper describes experimental efforts aimed at examining the effect of vapor bubble sliding on forced convection boiling heat transfer. Flow boiling experiments using FC-87 were conducted for vertical upflow and downflow configurations. Both slightly subcooled single-phase and saturated annular flow boiling were considered. Significantly higher heat transfer rates were measured for vertical upflow than for downflow with the same wall superheat and slightly subcooled single-phase inlet conditions. This increase in heat transfer is directly attributable to sliding vapor bubbles, which remain attached to the wall during upflow and lift off the wall during downflow. Differences in the measured upflow and downflow heat transfer rates are not as significant for annular flow boiling, which is due in part to the similar vapor bubble dynamics which have been observed for upflow and downflow. Heat transfer experiments in single-phase subcooled upflow with air bubble injection at the heating surface suggest that sliding bubbles enhance the bulk liquid turbulence at the wall, which contributes significantly to the macroscale heat transfer. It is concluded from this work that vapor bubble sliding heat transport can be a significant heat transfer mechanism, and should be considered in the development of mechanistic flow boiling heat transfer models.
Evaporation of Ammonia in a Smooth Horizontal Tube: Heat Transfer Measurements and Predictions
Authors: Zu¨rcher O. , Thome J. R. , Favrat D.
Published: February 2008

Experimental test results for flow boiling of pure ammonia inside horizontal tubes were obtained for a plain stainless steel tube. Tests were run at a nominal saturation temperature of 4°C, nine mass velocities from 20–140 kg/m2 s, vapor qualities from 1–99 percent and heat fluxes from 5–58 kW/m2. Two-phase flow observations showed that the current test data covered the following regimes: fully stratified, stratified-wavy, intermittent, annular, and annular with partial dryout. The Kattan-Thome-Favrat flow boiling model accurately predicted the local heat transfer coefficients measured in all these flow regimes with only two small modifications to their flow map (to extend its application to G < 100 kg/m2 s). Their flow boiling model was also successfully compared to the earlier ammonia flow boiling data of Chaddock and Buzzard (1986). The Gungor-Winterton (1987) correlation instead gave very poor accuracy for ammonia.
Condensation of Downward-Flowing Zeotropic Mixture HCFC-123/HFC-134a on a Staggered Bundle of Horizontal Low-Finned Tubes
Authors: Honda H. , Takamatsu H. , Takata N.
Published: February 2008

Experiments were conducted to obtain row-by-row heat transfer data during condensation of downward-flowing zeotropic refrigerant mixture HCFC-123/HFC-134a on a 3 × 75 (columns × rows) staggered bundle of horizontal low-finned tubes. The vapor temperature and the HFC-134a mass fraction at the tube bundle inlet were maintained at about 50°C and nine percent, respectively. The refrigerant mass velocity ranged from 9 to 34 kg/m2 s, and the condensation temperature difference from 3 to 12 K. The measured distribution of the vapor mass fraction in the tube bundle agreed fairly well with that of the equilibrium vapor mass fraction. The vapor phase mass transfer coefficient was obtained from the heat transfer data by subtracting the thermal resistance of the condensate film. The heat transfer coefficient and the mass transfer coefficient decreased significantly with decreasing mass velocity. These values first increased with the row number up to the third (or second) row, then decreased monotonically with further increasing row number, and then increased again at the last row. The mass transfer coefficient increased with condensation temperature difference, which was due to the effect of suction associated with condensation. On the basis of the analogy between heat and mass transfer, a dimensionless correlation of the mass transfer coefficient for the 4th to 14th rows was developed.
Inverse Analysis of Radiative Heat Transfer Systems
Authors: Jones M. R.
Published: February 2008

The design of heat transfer systems in which radiation is the dominant heat transfer mode is an important industrial problem. Compared to the conventional forward approach, the inverse approach allows a more thorough analysis of a potential design. This note demonstrates that inverse methods can be powerful tools in the analysis of radiative heat transfer systems.
Experimental Study of the Local Convection Heat Transfer From a Wall-Mounted Cube in Turbulent Channel Flow
Authors: Meinders E. R. , Hanjalic K. , Martinuzzi R. J.
Published: February 2008

This paper presents some results of the experimental investigation of the local convective heat transfer on a wall-mounted cube placed in a developing turbulent channel flow for Reynolds numbers between 2750 < ReH < 4970. Experiments were conducted using a specially designed cubic assembly made of heated copper core and a thin epoxy layer on its surface. The distribution of the local heat transfer coefficient was obtained from the surface heat flux evaluated from the heat input and computed temperature field in the epoxy layer, and from the surface temperature distribution acquired by infrared thermography. In parallel, the flow field was studied using laser doppler anemometer and flow visualizations, aimed at correlating the local heat transfer with the flow pattern and turbulence field. The complex vortex structure around the cube, in particular at the top and the side faces, caused large variation in the local convective heat transfer. The largest gradients in the distributions of the surface heat transfer were found at locations of flow separation and reattachment. Areas of flow recirculation are typically accompanied by a minimum in the heat transfer coefficient. It is argued that the local temperature rise of the air in the recirculation zone is caused by the trapped vortex, which acts as an insulation layer preventing the removal of heat from the surface of the cubes. In contrast, the intermittent reattachment of the low-temperature shear flow was found to produce large heat transfer coefficients.
Mixed Convection in a Horizontal Porous Duct With a Sudden Expansion and Local Heating From Below
Authors: Yokoyama Y. , Kulacki F. A. , Mahajan R. L.
Published: February 2008

Results are reported for an experimental and numerical study of forced and mixed convective heat transfer in a liquid-saturated horizontal porous duct. The cross section of the duct has a sudden expansion with a heated region on the lower surface downstream and adjacent to the expansion. Within the framework of Darcy’s formulation, the calculated and measured Nusselt numbers for 0.1 < Pe < 100 and 50 < Ra < 500 are in excellent agreement. Further, the calculated Nusselt numbers are very close to those for the bottom-heated flat duct. This finding has important implications for convective heat and mass transfer in geophysical systems and porous matrix heat exchangers. The calculations were also carried out for glass bead-packed beds saturated with water using non-Darcy’s formula. The streamlines in the forced convection indicate that, even with non-Darcy effects included, recirculation is not observed downstream of an expansion and the heat transfer rate is decreased but only marginally.
Measurement of the Transient Glass Surface Deformation During Laser Heating
Authors: Shiu T.-R. , Grigoropoulos C. P. , Greif R.
Published: February 2008

The distinct transient geometry and material response of a deforming glass surface during CO2 laser heating are related to the temperature history and the thermal regimes resulting from different energy deposition and heating rates. The transient deformation is measured using a probing system based on the photo thermal deflection technique. The variation with temperature of the optical constants yields a variable reflection signal which ultimately decreases, corresponding to a permanent volume expansion. The transient deflection signal associated with the variable deformation results from the distinct physical mechanisms in three thermal regimes, i.e., the elastic behavior, the glass transition, and the viscous flow regimes.