0


EDITORIAL

J. Heat Transfer. 1998;120(3):537. doi:10.1115/1.2824300.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster

PHOTOGALLERY

J. Heat Transfer. 1998;120(3):538. doi:10.1115/1.2824301.
FREE TO VIEW
Abstract
Topics: Heat transfer
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):541. doi:10.1115/1.2824304.
FREE TO VIEW
Abstract
Topics: Flames
Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):542. doi:10.1115/1.2824305.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):543. doi:10.1115/1.2824306.
FREE TO VIEW
Abstract
Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):544. doi:10.1115/1.2824307.
FREE TO VIEW
Abstract
Topics: Fuels , Flames , Shells , Soot
Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):545. doi:10.1115/1.2824308.
FREE TO VIEW
Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):546. doi:10.1115/1.2824309.
FREE TO VIEW
Abstract
Topics: Visualization
Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: 1997 Max Jakob Memorial Award Lecture

J. Heat Transfer. 1998;120(3):547-560. doi:10.1115/1.2824310.

The use of the Monte Carlo method in radiative heat transfer is reviewed. The review covers surface-surface, enclosure, and participating media problems. Discussion is included of research on the fundamentals of the method and on applications to surface-surface interchange in enclosures, exchange between surfaces with roughness characteristics, determination of configuration factors, inverse design, transfer through packed beds and fiber layers, participating media, scattering, hybrid methods, spectrally dependent problems including media with line structure, effects of using parallel algorithms, practical applications, and extensions of the method. Conclusions are presented on needed future work and the place of Monte Carlo techniques in radiative heat transfer computations.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Analytical and Experimental Techniques

J. Heat Transfer. 1998;120(3):561-567. doi:10.1115/1.2824311.

A photographic measurement technique is developed to quantify the vapor volume flow rate departing from a wire during boiling. The vapor flow rate is determined by measuring the volume of bubbles after departure from the boiling surface in consecutive frames of high-speed video. The measurement technique is more accurate and easier to implement than a previously developed photographic/laser Doppler anemometry (LDA) method. Use of the high-speed camera in place of a standard video camera eliminates the requirement for LDA-acquired bubble velocity measurements. The consecutive-photo method requires relatively few video images to be analyzed to obtain steady-state vapor volume flow rates. The volumetric flow rate data are used to calculate the latent heat transfer and, indirectly, sensible heat transfer which comprise the nucleate boiling heat flux. The measurement technique is applied to a 75-μm diameter platinum wire immersed in saturated FC-72.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):568-576. doi:10.1115/1.2824312.

The frequency domain provides an interesting alternative platform for measuring thermophysical properties. The resulting measurement technique produces reasonably accurate thermophysical data from imprecise surface information. Having a periodic heat flux input at one surface, the thermal diffusivity is obtainable if temperature produces a measurable periodic effect at another location. The analysis shows that only the phase shift is necessary to produce needed information while the boundary conditions can affect the experimental results. This method was tested near room temperature using two different materials: Delrin and 304 stainless steel. The experiments yield accurate thermal diffusivity data for both materials but the data for Delrin exhibit smaller errors. Before performing the experiments, a sensitivity analysis was carried out to determine the best range of frequencies for an experimental investigation.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):577-582. doi:10.1115/1.2824314.

The transient response and frequency response of a constant-temperature platinum film gage are computationally modeled for application to heat flux measurement. The probe consists of a thin platinum film (sensor) deposited on a Pyrex substrate, and coated with aluminum oxide. The probe is exposed to a convective environment, and the power required to maintain the sensor at a constant temperature is a direct indication of the local, instantaneous heat transfer rate. In application, the probe is mounted in a heated, high thermal conductivity material, creating an isothermal heat transfer surface. A two-dimensional numerical model was developed to represent the sensor, the Pyrex substrate and the coating. Ideally, the probe would be operated with the platinum at identically the same temperature as the isothermal surface. In the present study, the effects of non-ideal operating conditions, resulting in differences between the sensor and surface temperature, are examined. Frequency response characteristics are presented in a nondimensional form. The results of this modeling effort clearly indicate the importance of precise control over the sensor temperature in employing the present method for heat flux measurement. With the sensor temperature equal to the isothermal surface temperature, the probe calibration is insensitive to the heat transfer rate over a wide range of heat transfer coefficients. However, a 0.5°C difference between the sensor and surface temperatures yields a change in the calibration of approximately 20 percent over a range of heat transfer coefficient of 500 W/m2 K. At an input frequency of 10 Hz and an average heat transfer coefficient of 175 W/m2 K, amplitude errors increase from 3 percent to 35 percent as the temperature difference changes from zero to 1°C. These results are useful guide to calibration, operation, and data reduction in active heat flux measurement.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Conduction Heat Transfer

J. Heat Transfer. 1998;120(3):583-591. doi:10.1115/1.2824315.

This paper presents a conservative finite volume scheme for computing conduction heat transfer in materials with anisotropic conductivity. Unstructured solution-adaptive meshes composed of arbitrary convex polyhedra are used. Discrete energy balances are written over these polyhedra. Temperature gradients required for the evaluation of secondary diffusion fluxes are found by linear reconstruction. A fully implicit scheme is used for unsteady problems. The resulting discrete equations are solved using an algebraic multigrid scheme. Schemes for hanging-node and conformal adaption are implemented. Computations are performed using a variety of triangular and quadrilateral meshes. The results are compared to published analytical and numerical solutions and are shown to be satisfactory.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):592-599. doi:10.1115/1.2824316.

Calculation of temperature in high-temperature materials is of current interest to engineers, e.g., the aerospace industry encounters cooling problems in aircraft skins during the flight of high-speed air vehicles and in high-Mach-number reentry of spacecraft. In general, numerical techniques are used to deal with conduction in composite materials. This study uses the exact series solution to predict the temperature distribution in a two-layer body: one orthotropic and one isotropic. Often the exact series solution contains an inherent singularity at the surface that makes the computation of the heat flux difficult. This singularity is removed by introducing a differentiable auxiliary function that satisfies the nonhomogeneous boundary conditions, Finally, an inverse heat conduction technique is used to predict surface temperature and/or heat flux.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Forced Convection

J. Heat Transfer. 1998;120(3):600-605. doi:10.1115/1.2824317.

Fully developed laminar flows in a semicircular duct with temperature-dependent viscosity variations in the flow cross section are analyzed, where the viscosity-temperature behavior is described by the Arrhenius model. Both the T and H1 boundary conditions are considered, as they represent the most fundamental heating/cooling conditions encountered in practical compact heat exchanger applications. Numerical solutions for the flow velocity and the temperature fields have been obtained by finite difference technique. The friction factor and Nusselt number results display a strong dependence on the viscosity ratio (μw /μb ), and this is correlated using the classical power-law relationship. However, results indicate that the power-law exponents are significantly different from traditional values for circular tube. They are found to be functions of the flow geometry, boundary condition, and direction of heat transfer (heating or cooling).

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):606-616. doi:10.1115/1.2824318.

This paper presents a thermal model describing heat transfer in multispan sandwich rectangular plates. The model is time-dependent and two-dimensional. Complex thermal phenomena occurring in light cores (honeycomb) and thermal contact resistance are taken into account in the model. Particular attention is paid to the boundary conditions on the faces of the plate: radiative and nonuniform convective exchange are taken into account. The global temperature solution for stationary cases is developed on trigonometric and exponential functions bases. The properties of the Laplace transform are used to solve time-dependent cases. Validation experiments are carried out in a wind tunnel ring for two-span plates submitted to convective exchanges on one face; the same configuration is reproduced for an aluminum sandwich plate in an industrial set-up bench. Experimental results agree well with the numerical simulation.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):617-623. doi:10.1115/1.2824319.

Compression-driven heat transfer is important to the performance of many reciprocating energy-conversion machines. For small pressure variations in cylinder spaces without inflow, heat transfer and power losses are well predicted using a simple heat transfer model which neglects turbulence. In actual engine cylinders, where significant turbulence levels can be generated by high-velocity inflow, a model which neglects turbulence may not be adequate. In this paper, a heat transfer model having an analytical solution is developed for turbulent cylinder spaces based on a mixing length turbulence model. The model is then used to develop expressions for heat-transfer-related power loss and heat transfer coefficient. Predicted results compare favorably with experimental data for two in-flow configurations.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):624-632. doi:10.1115/1.2824323.

Naphthalene sublimation experiments have been conducted to study the effects of channel orientation, rotational Coriolis force, and a sharp turn, on the local heat (mass) transfer distributions in a two-pass square channel with a sharp turn and smooth walls, rotating about a perpendicular axis. The test channel was oriented so that the direction of rotation was perpendicular to or at a 45 deg angle to the leading and trailing walls. The Reynolds number was kept at 5,500 and the rotation number ranged up to 0.24. For the radial outward flow in the first straight pass of the diagonally oriented channel, rotation-induced Coriolis force caused large monotonic spanwise variations of the local mass transfer on both the leading and trailing walls, with the largest mass transfer along the outer edges of both walls. Rotation did not lower the spanwise average mass transfer on the leading wall and did not increase that on the trailing wall in the diagonally oriented channel as much as in the normally oriented channel. The combined effect of the channel orientation, rotation, and the sharp turn caused large variations of the local mass transfer distributions on the walls at the sharp turn and immediately downstream of the sharp turn. The velocity fields that were obtained with a finite difference control-volume-based computer program helped explain how rotation and channel orientation affected the local mass transfer distributions in the rotating two-pass channel.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Natural and Mixed Convection

J. Heat Transfer. 1998;120(3):633-640. doi:10.1115/1.2824325.

An analytical solution for a system consisting of a pin-fin heat sink and a chimney is presented. The result is applied to problems in which the size of the overall system is constrained. For a given heat dissipation and total system size, optimal values of the pin-fin diameter and heat-sink porosity are observed. The optima occur for systems with and without chimneys. The optimization is used to show that the minimum thermal resistance from a pin-fin heat sink is about two times larger than that of an idealized model based on inviscid flow.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Boiling Condensation

J. Heat Transfer. 1998;120(3):641-653. doi:10.1115/1.2824329.

Boiling heat transfer from inclined surfaces is examined and an analytical model of bubble growth and nucleate boiling is presented. The model predicts the average heat flux during nucleate boiling by considering alternating near-wall liquid and vapor periods. It expresses the heat flux in terms of the bubble departure diameter, frequency and duration of contact with the heating surface. Experiments were conducted over a wide range of upward and downward-facing surface orientations and the results were compared to model predictions. More active microlayer agitation and mixing along the surface as well as more frequent bubble sweeps along the heating surface provide the key reasons for more effective heat transfer with downward facing surfaces as compared to upward facing cases. Additional aspects of the role of surface inclination on boiling dynamics are quantified and discussed.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Phase Change and Multiphase Heat Transfer

J. Heat Transfer. 1998;120(3):654-660. doi:10.1115/1.2824333.

The sublimation-condensation model, developed for freeze drying of unsaturated porous media in the author’s previous work, is analyzed numerically. The moisture redistribution in the sublimation-condensation region is taken into account in this model. The calculations show that the saturation of ice in the sublimation-condensation region will obviously decrease, and its effects on heat and mass transfer cannot be neglected for microwave freeze-drying of unsaturated porous media. The microwave freeze-drying tests of unsaturated beef are carried out. The experimental results show that the drying time is approximately proportional to the initial saturation of beef. Moreover the sublimation-condensation model is validated by the experimental results. These results show that the sublimation-condensation model agrees better with experimental results than the sublimation interface model.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Combustion

J. Heat Transfer. 1998;120(3):661-666. doi:10.1115/1.2824334.

A fire wall is made of a mortar wall in which water storage materials are mixed. However, the mortar fire wall is relatively heavy. A nonorganic insulator for middle and high-temperature ranges such as a calcium silicate board is expected as a good material for the fire wall because of a light weight. Usually, a nonorganic insulator such as the calcium silicate board consists of a hydrate which contains free water, physically adsorbed water, and crystalline water. Behavior of such waters should be considered for a numerical model which is used to predict thermal responses of a fire wall. A simple one-dimensional numerical model to predict thermal response of a fire wall which is made of a nonorganic hydrate insulator, is developed. The numerical computations to simulate the thermal responses for a standard fire resistance test were performed for a sand wall of five percent volume of moisture and two calcium silicate boards which contains free water, adsorbed water, and crystalline water. The experiments for the sand wall and the calcium silicate boards were also performed. The numerical results were compared with experiments. The proposed model well predicts the thermal responses of the walls.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Porous Media, Particles and Droplets

J. Heat Transfer. 1998;120(3):667-673. doi:10.1115/1.2824335.

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.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):674-681. doi:10.1115/1.2824336.

A singular perturbation analysis and Green’s second theorem are used in order to obtain a general expression for the heat transfer from a particle at low Peclet numbers, when advection and conduction are heat transfer modes of comparable magnitude. The particle may have arbitrary shape, and its motion in the fluid is not constrained to be Stokesian. In the ensuring analysis, the governing equations for the temperature fields at short and long times are derived. The expressions are combined to yield a general equation for the temperature field and for the total rate of heat transfer. The final results for the rate of heat transfer demonstrate the existence of a history integral, whose kernel decays faster than the typical history integrals of the purely conduction regime. As applications of the general results, analytical expressions for the Nusselt number are derived in the case of a sphere undergoing a step temperature change.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):682-689. doi:10.1115/1.2824337.

Heat transfer to a drop of a dielectric fluid suspended in another dielectric fluid in the presence of an electric field is investigated. We have analyzed the effect of drop deformation on the heat transport to the drop. The deformed drop shape is assumed to be a spheroid and is prescribed in terms of the ratio of drop major and minor diameter. Results are obtained for both prolate and oblate shapes with a range of diameter ratio b/a from 2.0 to 0.5. The internal problem where the bulk of the resistance to the heat transport is in the drop, as well as the external problem where the bulk of the resistance is in the continuous phase, are considered. The electrical field and the induced stresses are obtained analytically. The resulting flow field and the temperature distribution are determined numerically. Results indicate that the drop shape significantly affects the flow field and the heat transport to the drop. For the external problem, the steady-state Nusselt number increases with Peclet number for all drop deformations. For a fixed Peclet number, the Nusselt number increases with decreasing b/a. A simple correlation is proposed to evaluate the effect of drop deformation on the steady-state Nusselt number. For the internal problem, for all drop deformations, the maximum steady-state Nusselt number becomes independent of the Peclet number at high Peclet number. The maximum steady-state Nusselt numbers for an oblate drop are significantly higher than that for a prolate drop.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Heat Exchangers

J. Heat Transfer. 1998;120(3):690-698. doi:10.1115/1.2824338.

A detailed analysis of experimental and numerical results for flow and heat transfer in similar offset strip-fin geometries is presented. Surface-average heat transfer and pressure drop, local Nusselt numbers and skin friction coefficients on the fin surface, instantaneous flow structures, and local time-averaged velocity profiles are contrasted for a range of Reynolds numbers using both prior and new experimental and numerical results. This contrast verifies that a two-dimensional unsteady numerical simulation captures the important features of the flow and heat transfer for a range of conditions. However, flow three-dimensionality appears to become important for Reynolds numbers greater than about 1300, and thermal boundary conditions are important for Reynolds numbers below 1000. The results indicate that boundary layer development, flow separation and reattachment, wake formation, and vortex shedding are all important in this complex geometry.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):699-708. doi:10.1115/1.2824339.

A numerical model for coupled heat and moisture transfer with sorption, condensation, and frosting in rotary energy exchangers is presented and validated with experimental data. The model is used to study condensation and frosting in energy wheels. Condensation/frosting increases with humidity and at some humidity level, water/frost will continually accumulate in the wheel. The sensitivity of condensation and frosting to wheel speed and desiccant type are studied. The energy wheel performance is also presented during both sorption and saturation conditions for a desicant coating with a Type I sorption isotherm (e.g., molecular sieve) and a linear sorption isotherm (e.g., silica gel). Simulation results show that the desiccant with a linear sorption curve is favorable for energy recovery because it has better performance characteristics and smaller amounts of condensation/frosting for extreme operating conditions.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Heat Transfer Enhancement

J. Heat Transfer. 1998;120(3):709-716. doi:10.1115/1.2824340.

A comparison of fully developed heat transfer and friction characteristics has been made in rectangular ducts with one wall roughened by slit and solid ribs. The effects of rib void fraction and flow Reynolds number are examined. The rib height-to-duct hydraulic diameter and pitch-to-height ratios are fixed at H/De = 0.167 and Pi /H = 10, respectively. To understand the mechanisms of the heat transfer enhancement, smoke-wire flow visualization and measurements of mean velocity and turbulence intensity are conducted in the slit and solid-ribbed ducts. In addition, by separately measuring the floor and rib heat transfer, two contributive factors of heat transfer promotion, namely, the fin effect and the enhanced turbulence effect, have been isolated. Because of the greater turbulence-mixing effects the slit-ribbed geometry displays higher floor heat transfer than the solid-ribbed geometry. In addition, the fin effects for the slit rib are greater than that for the solid rib. The pressure drop across the slit ribs is lower than that across the solid ribs due to less duct blockage. Furthermore, slit ribs with larger void fractions in a lower flow Reynolds number range provide better thermal performance under a constant friction power constraint.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):717-723. doi:10.1115/1.2824341.

Direct numerical simulations of three-dimensional flow and augmented convective heat transfer in a transversely grooved channel are presented for the Reynolds number range 140 < Re < 2000. These calculations employ the spectral element technique. Multiple flow transitions are documented as the Reynolds number increases, from steady two-dimensional flow through broad-banded unsteady three-dimensional mixing. Three-dimensional simulations correctly predict the Reynolds-number-independent friction factor behavior of this flow and quantify its heat transfer to within 16 percent of measured values. Two-dimensional simulations, however, incorrectly predict laminar-like friction factor and heat transfer behaviors.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):724-734. doi:10.1115/1.2824342.

Heat transfer measurements and predictions are reported for a turbulent, separated duct flow past a wall-mounted two-dimensional rib. The computational results include predictions using the standard k–ε model, the algebraic-stress (A-S) functionalized k–ε model, and the nonlinear k–ε model of Speziale (1987). Three different prescriptions for the wall functions, WF I, WF II, and WF III given, respectively, by Launder and Spalding (1974), Chieng and Launder (1980), and Johnson and Launder (1982), are examined. The experiments include laser-Doppler flow measurements, temperature measurements, and local Nusselt number results. For WF I, the nonlinear model yielded improved predictions and displayed the most realistic predictions of the streamwise turbulence intensity and the mean streamwise velocities near the high-speed edge of the separated layer and downstream of reattachment. However, no significant improvements in the surface heat transfer predictions were obtained with the nonlinear model. With WF I and WF II, the models underpredicted the local Nusselt numbers and overpredicted the flow temperatures. With WF III, the predicted results agree with the experimental Nusselt numbers quite well up to reattachment, after which it substantially overpredicted the Nusselt numbers. The AS functionalized model using only the high Re formulation and curvature corrections in Cartesian coordinates improved the temperature predictions substantially, with the predicted flow temperatures agreeing quite well with the measured temperatures.

Commentary by Dr. Valentin Fuster

RESEARCH PAPERS: Micro-Scale Heat Transfer

J. Heat Transfer. 1998;120(3):735-742. doi:10.1115/1.2824343.

Thermal bubble formation in the microscale is of importance for both scientific research and practical applications. A bubble generation system that creates individual, spherical vapor bubbles from 2 to 500 μm in diameter is presented. Line shape, polysilicon resistors with a typical size of 50 × 2 × 0.53 μm3 are fabricated by means of micromachining. They function as resistive heaters and generate thermal microbubbles in working liquids such as Fluorinert fluids (inert, dielectric fluids available from the 3M company), water, and methanol. Important experimental phenomena are reported, including Marangoni effects in the microscale; controllability of the size of microbubbles; and bubble nucleation hysteresis. A one-dimensional electrothermal model has been developed and simulated in order to investigate the bubble nucleation phenomena. It is concluded that homogeneous nucleation occurs on the microresistors according to the electrothermal model and experimental measurements.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):743-751. doi:10.1115/1.2824344.

The capillary flow along a microgroove channel was investigated both analytically and experimentally. In order to obtain insight into the phenomena, and because the governing equation had the form of a nonlinear differential equation, an analytical solution and approximate algebraic model were developed rather than using numerical methods. Approximating the governing equation as a Bernoulli differential equation resulted in an analytical solution for the radius curvature as the cube root of an exponential function. The axial variation of the radius of curvature profile as determined by this method was very similar to the numerical result as was the algebraic solution. However, the analytical model predicted the meniscus dryout location to be somewhat shorter than either the numerical results or the results from the algebraic solution. To verify the modeling results, the predictions for the axial capillary performance were compared to the results of the experimental investigation. The results of this comparison indicated that the experimentally measured wetted length was approximately 80 percent of the value predicted by the algebraic expression. Not only did the prediction for the dryout location from the algebraic equation show good agreement with the experimental data, but more importantly, the expression did not require any experimentally correlated constants. A nondimensionalized expression was developed as a function of just one parameter which consists of the Bond number, the Capillary number, and the dimensionless groove shape geometry for use in predicting the flow characteristics in this type of flow.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):752-757. doi:10.1115/1.2824345.

A spherical dielectric droplet translating steadily in another dielectric liquid with a uniform electric field imposed in the translational direction of the droplet is studied theoretically. With the small Reynolds number and large Peclet number assumptions, analytic solutions are obtained for the stream function with a term involving the interfacial temperature distribution which is then computed numerically. The results indicate that the interfacial temperature distribution is indeed nonuniform and the thermocapillarity might exist thereby. The induced thermocapillary flows in the droplet are usually of multiple cells with which the heat transfer rate may increases or decreases depending on whether the original flow is enhanced or suppressed. For the example calculated in the present study, the heat transfer rate is decreased by the thermocapillary effect.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):758-764. doi:10.1115/1.2824346.

Steady and oscillatory thermocapillary flows of high Prandtl number fluids in the half-zone configuration are analyzed theoretically. Scaling analysis is performed to determine the velocity and length scales of the basic steady flow. The predicted scaling laws agree well with the numerically computed results. The physical mechanism of oscillations is then discussed. It is shown that the deformation of free surface plays an important role for the onset of oscillations in that it alters the main thermocapillary driving force of the flow by changing the temperature field near the hot-corner region. This phenomenon triggers oscillation cycles in which the surface flow undergoes active and slow periods. Based on that concept a surface deformation parameter is derived by scaling analysis. The deformation parameter correlates available data for the onset of oscillations well.

Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):765-771. doi:10.1115/1.2824348.

New methods of removing surface contaminants from microelectronic and microelectromechanical systems (MEMS) devices are needed since the decreasing size of their components is reducing the allowable contamination levels. By choosing the pulse duration and fluence to optimize electronic rather than thermal desorption in short-pulse laser processing, surface species can be removed without exceeding maximum temperature constraints. A two-temperature model for short-pulse laser heating of, and subsequent desorption from, metal surfaces is presented. A scaling analysis indicates the material properties and laser parameters on which the ratio of electronic to thermal desorption depends. Regimes of predominantly electronic and thermal desorption are identified, and predicted desorption yields from gold films show that electronic desorption is the primary desorption mechanism in certain short-pulse laser processes.

Commentary by Dr. Valentin Fuster

TECHNICAL BRIEFS

J. Heat Transfer. 1998;120(3):777-781. doi:10.1115/1.2824350.

In extending the range of applicability of a recently developed method, a single-step containerless flash technique for determining the thermal diffusivity of levitated oblate spheroidal oblate spheroidal samples is proposed. The flash method is modeled as an axisymmetric transient conduction heat transfer problem within the oblate spheroid. It is shown that by knowing the sample geometric parameters and recording the temperature rise history at least at two different points on the surface simultaneously, the thermal diffusivity can be determined without knowing needed for determining the thermal diffusivity of oblate spheroidal samples are provided.

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):784-787. doi:10.1115/1.2824352.

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.

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):792-795. doi:10.1115/1.2824355.
Abstract
Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):795-797. doi:10.1115/1.2824356.
Abstract
Commentary by Dr. Valentin Fuster
J. Heat Transfer. 1998;120(3):797-800. doi:10.1115/1.2824357.

Second-law analysis on the herringbone wavy plate fin-and-tube heat exchanger was conducted on the basis of correlations of Nusselt number and friction factor proposed by Kim et al. (1997), from which the entropy generation rate was evaluated. Optimum Reynolds number and minimum entropy generation rate were found over different operating conditions. At a fixed heat duty, the in-line layout with a large tube spacing along streamwise direction was recommended. Furthermore, within the valid range of Kim et al.’s correlation, effects of the fin spacing and the tube spacing along spanwise direction on the second-law performance are insignificant.

Commentary by Dr. Valentin Fuster

DISCUSSIONS

J. Heat Transfer. 1998;120(3):801-803. doi:10.1115/1.2824358.
FREE TO VIEW

Recently, a new numerical scheme for solving the equations governing matrix heat exchanger thermal performance was published in this journal. It was found that this scheme does not include the full effect of longitudinal heat transfer in the said heat exchangers. This effect is demonstrated by correcting the parameter related to longitudinal heat transfer in the approximate analytical solution for the balanced flow case and finding it to deviate considerably from the numerically calculated result.

Commentary by Dr. Valentin Fuster
Commentary by Dr. Valentin Fuster

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In