bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat Transfer Characteristics of a Radial Jet Reattachment Flame
Authors: Mohr J. W. , Seyed-Yagoobi J. , Page R. H.
Published: February 2008

A Radial Jet Reattachment Combustion (RJRC) nozzle forces primary combustion air to exit radially from the combustion nozzle and to mix with gaseous fuel in a highly turbulent recirculation region generated between the combustion nozzle and impingement surface. High convective heat transfer properties and improved fuel/ air mixing characterize this external mixing combustor for use in impingement flame heating processes. To understand the heat transfer characteristics of this new innovative practical RJRC nozzle, statistical design and analysis of experiments was utilized. A regression model was developed which allowed for determination of the total heat transfer to the impingement surface as well as the NOx emission index over a wide variety of operating conditions. In addition, spatially resolved flame temperatures and impingement surface temperature and heat flux profiles enabled determination of the extent of the combustion process with regards to the impingement surface. Specifically, the relative sizes of the reaction envelope, high temperature reaction zone, and low temperature recirculation zone were all determined. At the impingement surface in the reattachment zone very high local heat flux values were measured. This study provides the first detailed local heat transfer characteristics for the RJRC nozzle.
Relative Stability Between Nucleate and Film Boiling on a Nonuniformly Heated Plate Surface
Authors: Lin W. W. , Lee D. J.
Published: February 2008

Flow boiling of methanol over a nonuniform, indirect conduction heating surface is investigated experimentally. An axial (discrete) heat flux distribution corresponding to a neutral stability region where nucleate and film boiling can coexist steadily is identified. Below such a heat flux distribution, nucleate boiling mode is more stable. Above this distribution, film boiling mode becomes more stable. We had employed an equal-area criterion for interpreting the heat flux and wall superheat relationship. Analogy between the wire boiling system is proposed. The differences between average and real transition boiling curves are discussed as well.
An Experimental Investigation of Convective Heat Transfer From Wire-On-Tube Heat Exchangers
Authors: Hoke J. L. , Clausing A. M. , Swofford T. D.
Published: February 2008

An experimental investigation of the air-side convective heat transfer from wire-on-tube heat exchangers is described. The study is motivated by the desire to predict the performance, in a forced flow, of the steel wire-on-tube condensers used in most refrigerators. Previous investigations of wire-on-tube heat exchangers in a forced flow have not been reported in the literature. The many geometrical parameters (wire diameter, tube diameter, wire pitch, tube pitch, etc.), the complex conductive paths in the heat exchanger, and the importance of buoyant forces in a portion of the velocity regime of interest make the study a formidable one. A key to the successful correlation of the experimental results is a definition of the convective heat transfer coefficient, hw, that accounts for the temperature gradients in the wires as well as the vast difference in the two key characteristic lengths—the tube and wire diameters. Although this definition results in the need to solve a transcendental equation in order to obtain hw from the experimental data, the use of the resulting empirical correlation is straightforward. The complex influence of the mixed convection regime on the heat transfer from wire-on-tube heat exchangers is shown, as well as the effects of air velocity and the angle of attack. The study covers a velocity range of 0 to 2 m/s (the Reynolds number based on wire diameter extends to 200) and angles of attack varying from 0 deg (horizontal coils) to ±90 deg. Heat transfer data from seven different wire-on-tube heat exchangers are correlated so that 95 percent of the data below a Richardson number of 0.004, based on the wire diameter, lie within ±16.7 percent of the proposed correlation.
Simple Model of Boiling Heat Transfer on Tubes in Large Pools
Authors: Parlatan Y. , Rohatgi U. S.
Published: February 2008

A simple method has been developed to model boiling heat transfer from a heat exchanger to pools using the experimental data available in the literature without modeling the flow dynamics of the pool. In this approach the heat flux outside vertical tubes is expressed as a function of outside wall temperature of the tubes and saturation temperature of the pool at or near atmospheric pressure.
Shape Optimization of Cooling Channels Using Genetic Algorithms
Authors: von Wolfersdorf Jens , Achermann E. , Weigand B.
Published: February 2008

A shape optimization method for convective cooling channels within a two-dimensional heat conduction region is presented. This method combines genetic algorithms with a point heat sink approach that is used to model the heat removal of the cooling channels during the optimization process. The method can be easily combined with the Finite Element Method (FEM) for the calculation of the optimized temperature field distribution.
Short-Time-Scale Thermal Mapping of Microdevices Using a Scanning Thermoreflectance Technique
Authors: Ju Y. S. , Goodson K. E.
Published: February 2008

The performance and reliability of microdevices can be strongly influenced by the peak temperature rise and spatial temperature distribution during brief electrical overstress (EOS) phenomena, which can occur at sub-microsecond time scales. The present study investigates short-time-scale laser reflectance thermometry of micro devices by examining the impact of passivation overlayers on the thermoreflectance signal and by demonstrating a calibration method suitable for metallization. This manuscript also describes a scanning laser thermometry facility that captures temperature fields in microdevices with 10 ns temporal resolution and 1 μm spatial resolution. The facility combines scanning laser optics with electrical stressing capability to allow simultaneous interrogation of the thermal and electrical behavior of devices. Data show the transient temperature distribution along the drift region of silicon-on-insulator (SOI) power transistors and along metal interconnects subjected to brief electrical stresses. The theory and experimental capability developed in this study are useful for studying short-time-scale thermal phenomena in microdevices and verifying models employed for their simulation.
A Data Reduction Procedure for Transient Heat Transfer Measurements in Long Internal Cooling Channels
Authors: von Wolfersdorf J. , Hoecker R. , Hirsch C.
Published: February 2008

The effect of streamwise fluid temperature variation on the local heat transfer coefficient measurements in transient heat transfer tests in long channels is addressed. Previous methods are shown to result in considerable errors. A simplified model is proposed to characterize the local fluid temperature, which drives the heat transfer. With it, analytical solutions for the local wall temperature history are derived, which involve two unknowns, the local heat transfer coefficient and a lumped upstream heat transfer parameter. Using these solutions in the data reduction, these two parameters are determined from surface temperature measurements. Numerical experiments that simulate the physical experiment show the applicability and robustness of the proposed method. The method is finally demonstrated experimentally by investigating heat transfer in a smooth, square duct.
Temperature-Dependent Absorptances of Ceramics for Nd:YAG and CO2 Laser Processing Applications
Authors: Zhang Z. , Modest M. F.
Published: February 2008

The absorptance of a material at the laser wavelength and as a function of temperature, ranging from room temperature to the removal point, significantly affects the efficiency of the laser machining process. A priori predictions of a laser machining process, using either simplistic or sophisticated models, require knowledge of the material’s absorptance behavior. An experimental apparatus for such measurements is described. The device consists of a specimen mounted inside an integrating sphere, heated rapidly by a CO2 or a Nd:YAG laser. Reflectances are measured with a small focused probe laser (Nd:YAG or CO2), while specimen surface temperatures are recorded by a high-speed pyrometer. Experimental results have been obtained for wavelengths of 1.06 μm (Nd:YAG) and 10.6 μm (CO2) for graphite, alumina, hot-pressed silicon nitride, sintered α-silicon carbide, as well as two continous-fiber ceramic matrix composites (SiC-based). Data are presented for temperatures between room temperature and the ablation/decomposition points.
Heat Transfer Enhancement in Electronic Modules Using Various Secondary Air Injection Hole Arrangements
Authors: Jubran B. A. , Al-Haroun M. S.
Published: February 2008

This paper reports an experimental investigation to study the effects of using various designs of secondary air injection hole arrangements on the heat transfer coefficient and the pressure drop characteristics of an array of rectangular modules at different values of free-stream Reynolds numbers in the range 8 × 103 to 2 × 104. The arrangement used is either one staggered row of simple holes or one row of compound injection holes. The pitch distances between the injection holes, as well as the injection angles, were varied in both the streamwise and spanwise directions. Generally, the presence of secondary air through the injection hole arrangement can give up to 54 percent heat transfer enhancement just downstream of the injection holes. The amount of heat transfer enhancement and pressure drop across the electronic modules is very much dependent on the design of the injection holes. The simple angle injection hole arrangement tends to give a better heat transfer enhancement and less pressure drop than the compound angle holes.
Heat Transfer Characteristics of a Slot Jet Reattachment Nozzle
Authors: Narayanan V. , Seyed-Yagoobi J. , Page R. H.
Published: February 2008

A two-dimensional reattachment nozzle called the Slot Jet Reattachment (SJR) nozzle was designed and built with a zero degree exit angle. The heat transfer characteristics of this submerged nozzle were investigated by varying the Reynolds number, nozzle exit opening, and nozzle to surface spacing. The pressure distribution on the impingement surface for different Reynolds numbers and exit openings were measured. Correlations for location of the maximum local Nusselt number and local Nusselt number distribution along the minor axis of the SJR nozzle were determined. A nondimensional scheme for generalized representation of heat transfer data for two-dimensional separated/reattaching flows was developed. The local and average heat transfer characteristics along the minor axis of the SJR nozzle were compared to a conventional slot jet nozzle under identical flow power condition. The comparison showed that the peak local heat transfer coefficient for the SJR nozzle was 9 percent higher than that for a standard slot jet nozzle, while its average heat transfer coefficient was lower or at best comparable to the slot jet nozzle based on the same averaged area. The net force exerted per unit width by the SJR nozzle flow was 13 times lower than the slot jet nozzle flow under this criterion. Additional experiments were conducted to compare the SJR and slot jet nozzles under matching local peak pressures exerted by the jet flow on the impingement surface. The results indicated 52 percent increase in the peak local heat transfer coefficient, and a maximum enhancement of 35 percent in average heat transfer coefficient for the SJR nozzle over the slot jet nozzle based on the same averaged area under this criterion.
Constructal Optimization of Internal Flow Geometry in Convection
Authors: Nelson R. A. , Bejan A.
Published: February 2008

In this paper “constructal theory,” is used to predict the formation of geometric shape and structure in finite-size fluid systems subjected to heating from below. Two classes of system are considered as tests: (i) single-phase fluid layers, and (ii) porous layers saturated with single-phase fluids. It is shown that the minimization of thermal resistance across the layer can be used to account for the appearance of organized macroscopic motion (streams) on the background of disorganized motion (diffusion). By optimizing the shape of the flow, it is possible to predict analytically the main structural and heat transfer characteristics of the system, e.g., the onset of convection, the relation between Nusselt number and Rayleigh number, the geometric shape of the rolls, and the decreasing exponent of RaH as RaH increases. The convective flow structure emerges as the result of a process of geometric optimization of heat flow path, in which diffusion is assigned to length scales smaller than the smallest macroscopic flow element (elemental system). The implications of this test of constructal theory are discussed in the context of the wider search for a physics law of geometric form generation in natural flow systems.
Steady-State Subcooled Nucleate Boiling on a Downward-Facing Hemispherical Surface
Authors: Haddad K. H. , Cheung F. B.
Published: February 2008

Steady-state nucleate boiling heat transfer experiments in saturated and subcooled water were conducted. The heating surface was a 0.305 m hemispherical aluminum vessel heated from the inside with water boiling on the outside. It was found that subcooling had very little effect on the nucleate boiling curve in the high heat flux regime where latent heat transport dominated. On the other hand, a relatively large effect of subcooling was observed in the low-heat-flux regime where sensible heat transport was important. Photographic records of the boiling phenomenon and the bubble dynamics indicated that in the high-heat-flux regime, boiling in the bottom center region of the vessel was cyclic in nature with a liquid heating phase, a bubble nucleation and growth phase, a bubble coalescence phase, and a large vapor mass ejection phase. At the same heat flux level, the size of the vapor masses was found to decrease from the bottom center toward the upper edge of the vessel, which was consistent with the increase observed in the critical heat flux in the flow direction along the curved heating surface.
Film Boiling Incipience at the Departure From Natural Convection on Flat, Smooth Surfaces
Authors: Chang J. Y. , You S. M. , Haji-Sheikh A.
Published: February 2008

The present research is an experimental study of pool boiling nucleation behavior using flat, smooth surfaces immersed in saturated highly wetting liquids, FC-72 and FC-87. A flush-mounted, copper surface of 10 mm × 10 mm is used as a heat transfer surface, simulating a microelectronic chip surface. At the nucleation incipient points of higher wall superheats with steady increase of heat flux, vapor film blankets the smooth surface and remains on the surface. To predict this film boiling incipience phenomenon from the smooth surface, an incipience map is developed over the boiling curve. When the incipient heat flux is higher than the minimum heat flux (MHF) and the incipient wall superheat value is higher than the transition boiling curve value at the incipient heat flux, the transition from single-phase natural convection to film boiling is observed at the incipient point. To prevent film boiling incipience, a microporous coating is applied over the smooth surface, which decreases incipient wall superheat and increases minimum heat flux. The film boiling incipience should be avoided to take advantage of highly efficient nucleate boiling heat transfer for the cooling of high-heat-flux applications.
A New Equivalent Reynolds Number Model for Condensation in Smooth Tubes
Authors: Moser K. W. , Webb R. L. , Na B.
Published: February 2008

In 1959, Akers et al. developed an in-tube condensation model, which defines the all-liquid flow rate that provides the same heat transfer coefficient as an annular condensing flow. This liquid flow rate was expressed by an “equivalent” Reynolds number and used in a single-phase, turbulent flow equation to predict the condensation coefficient. However, the assumptions on which the equivalent Reynolds number is based are shown in the present work to be faulty. This results in the underprediction of many researchers’ data. A new equivalent Reynolds number model, based on the heat-momentum analogy, is developed in this study. This model is then shown to predict the experimental Nusselt number of 1197 data points from 18 sources with an average deviation of 13.64 percent. The data are for tube internal diameters between 3.14 and 20 mm.
Convective Condensation of Superheated Vapor
Authors: Webb R. L.
Published: February 2008

This paper provides a rationally based method to calculate the condensation coefficient of superheated vapor for condensation inside tubes. The method is theoretically based, and is applicable to any pure vapor. The method may be easily extended to condensation inside enhanced tubes, or to shell-side condensation. This work is an extension of a theory previously presented by Lee et al. (1991).
Effects of Heat Exchanger Tube Parameters on Nucleate Pool Boiling Heat Transfer
Authors: Chun Moon-Hyun , Kang Myeong-Gie
Published: February 2008

In an effort to determine the combined effects of major parameters of heat exchanger tubes on the nucleate pool boiling heat transfer in the scaled in-containment refueling water storage tank (IRWST) of advanced light water reactors (ALWRs), a total of 1966 data points for q″ versus ΔT have been obtained using various combinations of tube diameters, surface roughness, and tube orientations. The experimental results show that: (1) increased surface roughness increases the heat transfer coefficient for both horizontal and vertical tubes, and the effect of surface roughness is more pronounced for the vertical tubes compared to the horizontal tubes, (2) the two heat transfer mechanisms, i.e., increased heat transfer due to liquid agitation by bubbles generated and reduced heat transfer by the formation of large vapor slugs and bubble coalescence, are different in two regions of low heat flux (q″ ≤ 50 kW/m2) and high heat flux (q″ > 50 kW/m2) depending on the orientation of tubes and the degree of surface roughness, and (3) the heat transfer rate decreases as the tube diameter is increased for both horizontal and vertical tubes, but the effect of tube diameter on the nucleate pool boiling heat transfer for vertical tubes is greater than that for horizontal tubes. Two empirical heat transfer correlations for q″, one for horizontal tubes and the other for vertical tubes, are obtained in terms of surface roughness (ε) and tube diameter (D). In addition, a simple empirical correlation for nucleate pool boiling heat transfer coefficient (hb) is obtained as a function of heat flux (q″) only.
Effect of Fouling on Temperature Measurement Error and a Solution
Authors: Cho Y. I. , Choi B.-G.
Published: February 2008

The objective of the present study was to investigate the effect of fouling on the accuracy of temperature measurement. When a thin scale layer is deposited on a temperature-measuring probe, the temperature reading can be in error by several degrees in spite of ± 0.1 K resolution of the probe. This erroneous temperature reading can pose a serious problem in the evaluation of heat exchanger performance and in the operation of an automated process control system.
Simplified and Accurate Mathematical Model for the Analysis of Heat and Moisture Transfer From Food Commodities
Authors: Ansari F. A.
Published: February 2008

The present paper deals with a simple and accurate mathematical model for making reliable heat and mass transfer analyses from high-water–content solids when exposed to a cold air stream. Such physical situations are encountered in the refrigeration industry during air blast cooling of food commodities. The concept of enthalpy potential has been used to develop a simple linear surface boundary condition equation. This equation accounts for the cooling effect due to sensible convective heat transfer as well as the latent cooling effect due to produce desiccation. Investigations on ten fresh samples each of ripe tomato and cucumber established that there is a good agreement between the computed temperatures from the proposed model and the experimentally measured values.
The Monte Carlo Method in Radiative Heat Transfer
Authors: Howell J. R.
Published: February 2008

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.
Consecutive-Photo Method to Measure Vapor Volume Flow Rate During Boiling From a Wire Immersed in Saturated Liquid
Authors: Ammerman C. N. , You S. M.
Published: February 2008

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.
Sensitivity Analysis for Thermophysical Property Measurements Using the Periodic Method
Authors: Haji-Sheikh A. , Hong Y. S. , You S. M. , Beck J. V.
Published: February 2008

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.
Exact Solution of Heat Conduction in Composite Materials and Application to Inverse Problems
Authors: Aviles-Ramos C. , Haji-Sheikh A. , Beck J. V.
Published: February 2008

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.
An Analytical Model for Turbulent Compression-Driven Heat Transfer
Authors: Cantelmi F. J. , Gedeon D. , Kornhauser A. A.
Published: February 2008

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.
Effect of Channel Orientation of Local Heat (Mass) Transfer Distributions in a Rotating Two-Pass Square Channel With Smooth Walls
Authors: Park C. W. , Lau S. C.
Published: February 2008

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.
Free Convection Limits for Pin-Fin Cooling
Authors: Fisher T. S. , Torrance K. E.
Published: February 2008

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.
Near-Wall Microlayer Evaporation Analysis and Experimental Study of Nucleate Pool Boiling on Inclined Surfaces
Authors: Naterer G. F. , Hendradjit W. , Ahn K. J. , Venart J. E. S.
Published: February 2008

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.
The Effects of Sublimation-Condensation Region on Heat and Mass Transfer During Microwave Freeze Drying
Authors: Wang Zhao Hui , Shi Ming Heng
Published: February 2008

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.
Numerical Modeling of Fire Walls to Simulate Fire Resistance Test
Authors: Jin Zhao-Fen , Asako Yutaka , Yamaguchi Yoshiyuki , Harada Minoru
Published: February 2008

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.
Effect of Drop Deformation on Heat Transfer to a Drop Suspended in an Electrical Field
Authors: Hader M. A. , Jog M. A.
Published: February 2008

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.
A Complementary Experimental and Numerical Study of the Flow and Heat Transfer in Offset Strip-Fin Heat Exchangers
Authors: DeJong N. C. , Zhang L. W. , Jacobi A. M. , Balachandar S. , Tafti D. K.
Published: February 2008

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.
Direct Numerical Simulation of Three-Dimensional Flow and Augmented Heat Transfer in a Grooved Channel
Authors: Greiner M. , Spencer G. J. , Fischer P. F.
Published: February 2008

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.
Capillary Performance of Evaporating Flow in Micro Grooves: An Approximate Analytical Approach and Experimental Investigation
Authors: Peterson G. P. , Ha J. M.
Published: February 2008

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.
Transient Thermocapillary Flows Induced by a Droplet Translating in an Electric Field
Authors: Lai Chun-Liang , Tang Wen-Lang
Published: February 2008

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.
Thermal Diffusivity Determination of High-Temperature Levitated Oblate Spheroidal Specimen by a Flash Method
Authors: Shen F. , Khodadadi J. M.
Published: February 2008

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.
Elements of a General Correlation for Turbulent Heat Transfer
Authors: Maciejewski P. K. , Anderson A. M.
Published: February 2008

Typically, heat transfer researchers present results in the form of an empirically based relationship between a length-based Nusselt number, a length-based Reynolds number, and a fluid Prandtl number. This approach has resulted in a multitude of heat transfer correlations, each tied to a specific geometry type. Two recent studies have contributed key ideas that support the development of a more general correlation for turbulent heat transfer that is based on local parameters. Maciejewski and Moffat (1992a, b) found that wall heat transfer rates scale with streamwise turbulent velocity fluctuations and Anderson and Moffat (1992a, b) found that the adiabatic temperature rise is the driving potential for heat transfer. Using these two concepts and a novel approach to dimensional analysis, the present authors have formulated a general correlation for turbulent heat transfer. This correlation predicts wall heat flux as a function of the turbulent velocity fluctuations, the adiabatic temperature rise, and the fluid properties (density, specific heat, thermal conductivity, and viscosity). The correlation applies to both internal and external flows and is tested in air, water, and FC77. The correlation predicts local values of surface heat flux to within ± 12.0 percent at 95 percent confidence.
The Effect of Placing Vortex Generators Above Ribs in Ribbed Ducts on the Flow, Flow Temperature, and Heat Transfer Behavior
Authors: Myrum T. A. , Acharya S. , Sinha S. , Qui X.
Published: February 2008

Flow temperature and laser-Doppler velocity measurements are presented to understand better the flow and heat transfer behavior resulting from the placement of vortex generators above the first and fifth ribs in a ribbed duct air flow (Re = 3450) and as a benchmark for comparing model predictions. Because the generator–rib spacing, at the smallest spacing (s/h = 0.25), was too small for the flow to pass through it, the generator–rib pair functioned as a single element with an increased effective height, comprising the rib height, the generator–rib space, and the generator proper, which resulted in a downstream shift in the flow reattachment and peak Nusselt number locations. At s/h = 0.75, the flow expanded as it passed through the generator–rib space. Dictated by the upstream flow conditions, the expansion resulted in a vertical downward flow behind the first generator–rib configuration and no vertical downward flow behind the fifth. The vertical downward flow compensated for generator-induced reductions in the near-wall streamwise velocities behind the first generator–rib configuration, resulting in increased local Nusselt numbers, whereas the generator-induced reductions in the streamwise velocities in the absence of the vertical downward flow gave way to reduced Nusselt numbers behind the fifth generator–rib configuration.
Local, Instantaneous Heat Transfer Coefficients for Jet Impingement on a Phase Change Surface
Authors: Bhansali A. P. , Black W. Z.
Published: February 2008

The local variation in the heat transfer coefficient for an axisymmetric, turbulent, submerged liquid jet impinging on a nonuniform boundary of a phase-change material is measured with an ultrasonic measurement technique. The time required for an acoustic wave to traverse the phase-change material is measured with an ultrasonic transducer and the time data are converted into local thickness profiles of the phase-change material via knowledge of the longitudinal acoustic velocity in the material. An energy balance at the melt interface between the impinging jet and the phase-change material is used in conjunction with the local thickness profile data to determine the local variation in the heat transfer coefficient. The phase-change material is originally flat, but its shape changes with time as the heated jet melts a complex shape into its surface. The heat transfer rate over the surface of the melting interface is shown to vary with time as a result of the changing shape of the phase change material. A deep cavity is melted into the solid at the stagnation point and secondary cavities are melted into the interface for certain jet flow rates and surface spacings between the jet nozzle and the melt interface. When secondary cavities are produced, secondary peaks in the local heat transfer coefficient are observed. The heat transfer data are formulated into two Nusselt number correlations that are functions of the dimensionless time, dimensionless radius, dimensionless jet-to-surface spacing, and jet Reynolds number. One correlation is formulated for all locations along the surface of the phase-change material except the stagnation point, and a second correlation is valid at the stagnation point.
Instability of Convection and Heat Transfer of High Prandtl Number Fluids in a Vertical Slot
Authors: Jin Y. Y. , Chen C. F.
Published: February 2008

The stability of convective motion of high-Prandtl-number fluids, generated by a lateral temperature difference across a vertical slot with aspect ratio 15, is studied numerically. The Prandtl number range studied is from 50 to 2000. The nonlinear governing equations are solved by a finite difference method. The predicted flow patterns and critical values are in good agreement with the recent experimental results of Wakitani (1994). It is found that the vorticity distribution along the vertical centerline of the slot is a very sensitive indicator of the onset of multicellular flow. The critical Grashof number varies almost inversely with the Prandtl number; consequently, the critical Rayleigh number is essentially independent of the Prandtl number. Heat transfer results show good agreement with the experimentally correlated values, and they are independent of the Prandtl numbers and the flow patterns.
Steady Rayleigh–Be´nard Convection in a Two-Layer System of Immiscible Liquids
Authors: Prakash A. , Koster J. N.
Published: February 2008

Two-dimensional thermal convection in a system of two immiscible liquids heated from below is studied experimentally and numerically. Convection in the two-layer system is characterized by two distinct coupling modes between the layers. They are mechanical coupling and thermal coupling. These two coupling modes are visualized experimentally and found to be in reasonable agreement with numerical simulations. When buoyancy forces in both layers are of similar strength, thermal coupling is preferred. The mechanical coupling mode dominates when the buoyancy forces are very different in both layers.
Determination of the Boiling Enhancement Mechanism Caused by Surfactant Addition to Water
Authors: Ammerman C. N. , You S. M.
Published: February 2008

In the present investigation, boiling heat transfer coefficients are measured for an electrically heated 390-μm-dia, platinum wire immersed in saturated water, and in water mixed with three different concentrations of sodium dodecyl sulfate (an anionic surfactant). The addition of a surfactant to water is known to enhance boiling heat transfer. A recently developed photographic/laser-Doppler anemometry measurement technique is used to quantify the vapor volumetric flow rate departing from the wire during the boiling process. The volumetric flow rate data are used to calculate the latent heat and, indirectly, the convection heat transfer mechanisms that constitute the nucleate boiling heat flux. Comparisons are made to determine how the heat transfer mechanisms are affected by the surfactant addition, and thus, which mechanism promotes boiling enhancement. The present data are also compared with similar data taken for a 75-μm-dia wire immersed in saturated FC-72 (a highly wetting liquid) to provide increased insight into the nature of the boiling heat transfer mechanisms.
An Experimental Investigation of the Effects of Subcooling and Velocity on Boiling of Freon-113
Authors: Huang L. , Witte L. C.
Published: February 2008

Boiling heat transfer correlations were obtained for the maximum and minimum heat fluxes. Relationships among qmin/qmax, Weber number, and liquid Jakob number were obtained. Compelling evidence was found to indicate that significant cooling of the wake and/or the forward stagnation line can be caused by large-scale liquid–solid contacts while other parts of the surface experienced film boiling with little or no contact in the transition-film boiling regime. A criterion for large-scale liquid-solid contacts was developed. Another purpose of this study was to investigate whether a stable transition of boiling exists, i.e., if the ratio of the minimum and maximum heat fluxes approaches unity as liquid subcooling and velocity are increased. Extensive data using Freon-113 were taken, covering a wide range of fluid velocities (1.5 to 6.9 m/s) and liquid subcooling (29 to 100°C) at pressures ranging from 122 to 509 kPa. Cylindrical electric resistance heaters of two diameters, 6.35 mm and 4.29 mm, and made of Hastelloy-C and titanium, respectively, were used. The maximum qmin/qmax achievable with the apparatus was 0.9.