bluuebunny/crossref_metadata_2025 huggingface dataset:
Heat Transfer Characteristics in Partial Boiling, Fully Developed Boiling, and Significant Void Flow Regions of Subcooled Flow Boiling
Authors: Kandlikar S. G.
Published: February 2008

Subcooled flow boiling covers the region beginning from the location where the wall temperature exceeds the local liquid saturation temperature to the location where the thermodynamic quality reaches zero, corresponding to the saturated liquid state. Three locations in the subcooled flow have been identified by earlier investigators as the onset of nucleate boiling, the point of net vapor generation, and the location where x = 0 is attained from enthalpy balance equations. The heat transfer regions are identified as the single-phase heat transfer prior to ONB, partial boiling (PB), and fully developed boiling (FDB). A new region is identified here as the significant void flow (SVF) region. Available models for predicting the heat transfer coefficient in different regions are evaluated and new models are developed based on our current understanding. The results are compared with some of the experimental data available in the literature.
Freezing and Melting With Multiple Phase Fronts Along the Outside of a Tube
Authors: Vick B. , Nelson D. J. , Yu X.
Published: February 2008

This paper addresses the modeling and analysis of thermal storage systems involving phase change with multiple phase fronts. The problem involves a fluid flowing inside a long tube surrounded by a phase-change material (PCM). The fluid temperature at the tube inlet cycles above and below the freezing temperature of the PCM, causing alternating liquid and solid layers to form and propagate from the tube outside surface. The objective of this paper is to predict the dynamic performance, temperature distribution, and phase front distribution along the tube. The problem is modeled as axisymmetric and two dimensional. Axial conduction is neglected and the problem is discretized into axial segments. Each of these axial sections is modeled as a transient, one-dimensional problem involving phase change with the possibility of multiple phase boundaries. The boundary element method (BEM) is used to obtain the transient solution in each axial section. Each axial segment communicates with downstream segments through the fluid flowing inside the tube. In order to ensure numerically stable results, a fully implicit discretization is used in both the axial and time variables. Results are presented for the time and axial evolution of the phase fronts and temperatures in response to a fluid inlet temperature that periodically alternates between values above and below the freezing temperature. This BEM is tested against the thermal network method (TNM) and the negligible sensible heat approximation (NSH) by comparing the outlet temperature and the latent state of charge. Results are found to be consistent and accurate.
A Model for Solidification Under the Influence of Thermoelectric and Magnetohydrodynamic Effects: Application to Peltier Demarcation During Directional Solidification With Different Gravitational Conditions
Authors: Zheng L. L. , Zhang H. , Larson D. J. , Prasad V.
Published: February 2008

A physics-based model is developed to study the gravitational (convection), thermoelectric (Peltier, Seebeck, Joule, and Thomson) and magnetohydrodynamic (Lorentz force) effects on solidification phenomena. A scaling analysis is carried out to examine the importance and contributions of various governing parameters. Directional solidification with Peltier Interface Demarcation under varying gravitational conditions is simulated for the Bridgman–Stockbarger configuration. The predicted interface location and movement during current pulsing are studied and the microstructures corresponding to different current polarities are analyzed based on Jackson–Hunt theory.
Heat Transfer Enhancement With Porous Inserts in Recirculating Flows
Authors: Martin A. R. , Saltiel C. , Shyy W.
Published: February 2008

This investigation explores the use of porous inserts for heat transfer enhancement in recirculating flows, specifically flow over a backward-facing step. Numerical computations are performed for laminar flow with high porosity inserts, which are composed of small-diameter (150 μm) silicon carbide fibers aligned transverse to the streamwise flow. The inserts are varied in length and porosity in order to determine the most favorable combinations of maximum temperature reduction and head loss penalty. In general, the porous inserts reduce or eliminate the lower wall recirculation zone; however, in some cases the recirculation zone is lengthened if the inserts are short and extremely porous. Excellent heat transfer characteristics are shown within the inserts themselves due to the high-conductivity fiber material. Non-Darcy effects are shown to be important primarily as the porosity is increased. Deviation from local thermodynamic conditions between the inserts and the fluid is most apparent for the shortest inserts considered.
Heat Transfer Correlations for Liquid Film in the Evaporator of Enclosed, Gravity-Assisted Thermosyphons
Authors: El-Genk M. S. , Saber H. H.
Published: February 2008

Heat transfer correlations were developed for the liquid film region, in the evaporator section of closed, two-phase, gravity-assisted thermosyphons in the following regimes: (a) laminar convection, at low heat fluxes, (b) combined convection, at intermediate heat fluxes, and (c) nucleate boiling, at high heat fluxes. These correlations were based on a data set consisting of a total of 305 points for ethanol, acetone, R-11, and R-113 working fluids, wall heat fluxes of 0.99–52.62 kW/m2, working fluid filling ratios of 0.01–0.62, inner diameters of 6–37 mm, evaporator section lengths of 50–609.6 mm, and vapor temperatures of 261–352 K. The combined convention data were correlated by superimposing the correlations of laminar convention and nucleate boiling using a power law approach, to ensure smooth transition among the three heat transfer regimes. The three heat transfer correlations developed in this work are within ±15 percent of experimental data.
A Boundary/Finite Element Analysis of Magnetic Levitation Systems: Surface Deformation and Thermal Phenomena
Authors: Song S. P. , Li B. Q.
Published: February 2008

This paper describes a coupled boundary and finite element analysis of electromagnetic, free surface deformation and thermal problems in magnetic levitation systems under both normal and microgravity conditions. A computer code is developed, which involves the use of finite elements in the regions of interest and boundary elements in other regions for electromagnetic field calculations, along with an iterative and remeshing scheme for free surface deformation calculations. The code is tested against available analytical solutions and experimental measurements, and then applied to study the free surface deformation and temperature distribution in magnetically levitated droplets on earth and in microgravity. It is found that an accurate assessment of the thermal behavior of a droplet must be made along with its deformation, including the bulk movement, for magnetic levitation systems. In normal gravity, a magnetically levitated droplet assumes a conical shape with its apex pointing downward, and higher temperature occurs in the lower portion of the droplet. In microgravity, on the other hand, surface deformation is primarily attributed to the heating coils and the deformation is symmetric, with the droplet squeezed at the equator plane and bulged out along the axis of symmetry. Positioning coils give rise to a smaller deformation force and a lower Joule heating rate under normal operation conditions. The temperature profiles and free surface shapes induced by the positioning coils, though symmetric, are different from those induced by heating coils.
Frequency Response Characteristics of an Active Heat Flux Gage
Authors: Dinu C. , Beasley D. E. , Figliola R. S.
Published: February 2008

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/m2K. At an input frequency of 10 Hz and an average heat transfer coefficient of 175 W/m2K, 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.
Computation of Anisotropic Conduction Using Unstructured Meshes
Authors: Murthy J. Y. , Mathur S. R.
Published: February 2008

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.
Effects of Temperature-Dependent Viscosity Variations and Boundary Conditions on Fully Developed Laminar Forced Convection in a Semicircular Duct
Authors: Harms T. M. , Jog M. A. , Manglik R. M.
Published: February 2008

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).
Two-Dimensional Modeling of Heat Transfer Through Sandwich Plates With Inhomogeneous Boundary Conditions on the Faces
Authors: Murer Y. , Millan P.
Published: February 2008

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.
Transient Heat Transfer From a Particle With Arbitrary Shape and Motion
Authors: Feng Zhi-Gang , Michaelides E. E.
Published: February 2008

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.
Heat and Moisture Transfer in Energy Wheels During Sorption, Condensation, and Frosting Conditions
Authors: Simonson C. J. , Besant R. W.
Published: February 2008

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.
Heat Transfer-Friction Characteristic Comparison in Rectangular Ducts With Slit and Solid Ribs Mounted on One Wall
Authors: Hwang Jenn-Jiang
Published: February 2008

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.
Heat Transfer in Turbulent Flow Past a Surface-Mounted Two-Dimensional Rib
Authors: Acharya S. , Dutta S. , Myrum T. A.
Published: February 2008

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.
Thermal Bubble Formation on Polysilicon Micro Resistors
Authors: Lin Liwei , Pisano A. P. , Carey V. P.
Published: February 2008

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.
Theoretical Analysis of Thermocapillary Flow in Cylindrical Columns of High Prandtl Number Fluids
Authors: Kamotani Y. , Ostrach S.
Published: February 2008

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.
Electronic Desorption of Surface Species Using Short-Pulse Lasers
Authors: Phinney L. M. , Tien Chang-Lin
Published: February 2008

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.
Second-Law Analysis on Wavy Plate Fin-and-Tube Heat Exchangers
Authors: Lin W. W. , Lee D. J.
Published: February 2008

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.
Discussion: “Analysis of Matrix Heat Exchanger Performance” (Venkatarathnam, G., and Sarangi, S., 1991, ASME J. Heat Transfer, 113, pp. 830–836)
Authors: Ahuja V. , Green R. K.
Published: February 2008

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.
Thermal Conduction in Nonhomogeneous CVD Diamond Layers in Electronic Microstructures
Authors: Goodson K. E.
Published: February 2008

Chemical-vapor-deposited diamond layers of thickness between 0.1 and 5 μm have the potential to improve conduction cooling in electronic microstructures. However, thermal conduction in these layers is strongly impeded by phonon scattering on defects, whose concentrations can be highly nonhomogeneous, and on layer boundaries. By assuming that defects are concentrated near grain boundaries, this work relates the internal phonon scattering rate to the local characteristic grain dimension and to the dimensionless grain-boundary scattering strength, a parameter defined here that varies little within a given layer. Solutions to the Peierls–Boltzmann phonon transport equation for conduction along and normal to layers account for the nonhomogeneous internal scattering rate. Predictions for conduction along and normal to layers as thin as 0.2 μm agree well with room-temperature data. This research helps optimize diamond layer thicknesses for specific microstructures, such as silicon-on-diamond (SOD) circuits.
Conjugate Heat Transfer From a Single Surface-Mounted Block to Forced Convective Air Flow in a Channel
Authors: Nakayama W. , Park S.-H.
Published: February 2008

Conjugate heat transfer from a surface-mounted block (31 × 31 × 7 mm3) to forced convective air flow (1–7 m/s) in a parallel-plate channel was studied experimentally and analytically. Particular attention was directed to the heat flow from the block to the floor through the block support, which was eventually transferred to the air flow over the floor. The concepts of adiabatic wall temperature (Tad) and adiabatic heat transfer coefficient (had) were employed to account for the effect of thermal wake shed from the block on the heat transfer from the floor. The experimental data of Tad and had were used in setting the boundary condition for the numerical analysis of heat conduction in the floor. The accuracy of the numerical predictions of the thermal conductances for different heat flow paths was proven experimentally. The heat conduction analysis code was then used to find the heat transfer capability of various block-support/floor combinations.
Performance Indicators for Steady-State Heat Transfer Through Fin Assemblies
Authors: Wood A. S. , Tupholme G. E. , Bhatti M. I. H. , Heggs P. J.
Published: February 2008

A comparative study is presented of several models describing steady-state heat flow through an assembly consisting of a primary surface (wall) and attached extended surface (fin). Attention is focused on the validity of four performance indicators. The work shows that the augmentation factor is the only indicator capable of correctly predicting the behavioral trends of the rate of heat flow through the assembly as the influencing physical parameters are varied.
Local Convective Behavior and Fin Efficiency in Shallow Banks of In-Line and Staggered, Annularly Finned Tubes
Authors: Kearney S. P. , Jacobi A. M.
Published: February 2008

Local mass transfer data for high-profile fins in the second row of in-line and staggered, circular-finned tubes are presented for Reynolds numbers from 5000 to 28,000 based on hydraulic diameter and velocity at the minimum flow area. The data, obtained using an optical adaptation of the naphthalene sublimation technique, show that local variations in heat transfer do not cause significant fin efficiency deviations from the analytical solution of Gardner (contrary to earlier reports). Average heat transfer and pressure drop data indicate that the thermal performance of the in-line arrangement is comparable to the staggered configuration.
Effect of Film Hole Row Location on Film Effectiveness on a Gas Turbine Blade
Authors: Jiang H. Wanda , Han J.-C.
Published: February 2008

Experiments were performed to study the effect of film hole row location on local film effectiveness distribution of a turbine blade model with air or CO2 film injection. Tests were performed on a five-blade linear cascade at the chord Reynolds number of 3.0 × 105 at the cascade inlet. A combination of turbulence grid and unsteady wake was used to create a higher free-stream turbulence level. The test blade had three rows of film holes in the leading edge region and two rows each on the pressure and suction surfaces. Film hole row locations were set by leaving the film holes at that row location open and covering the remaining rows. In addition, the additive nature of film cooling on the turbine blade model was examined by comparing the measured film effectiveness with the predicted effectiveness from the superposition method. Results show that injection from a different film hole row location provides a different effectiveness distribution on pressure and suction surfaces depending on local mainstream velocity and blade curvature. In most cases, the superposition method holds downstream of the last film hole row.
Experimental and Theoretical Studies of Mist Jet Impingement Cooling
Authors: Graham K. M. , Ramadhyani S.
Published: February 2008

Experimental data and analytical predictions for air/liquid mist jet cooling of small heat sources are presented. The mist jet was created using a coaxial jet atomizer, with a liquid jet of diameter 190 μm located on the axis of an annular air jet of diameter 2 mm. The impingement surface was a square of side 6.35 mm. Experimental data were obtained with mists of both methanol and water. Surface-averaged heat fluxes as high as 60 W/cm2 could be dissipated with the methanol/air mist while maintaining the target surface below 70°C. With the water/air mist, a heat flux of 60 W/cm2 could be dissipated with the target surface at 80°C. Major trends in the data and model predictions have been explained in terms of the underlying hydrodynamic and heat transfer phenomena.
Effects of Variable Properties and Viscous Dissipation During Optical Fiber Drawing
Authors: Lee S. H.-K. , Jaluria Y.
Published: February 2008

The axisymmetric free-surface flow and thermal transport of fused silica during optical fiber drawing was considered with variable properties, prescribed heat flux, and neck shape. Experimental data from previous researchers were adapted or used as the basis for assumptions in order to enable a realistic analysis. The main objectives were to model the neck-down process in order to clarify the effects of the variable properties and the associated viscous dissipation. Due to the large changes in dimension and viscosity, this system poses severe nonlinearities, and a new solution algorithm was necessarily developed. Validation was achieved and several important results were obtained. Among these, it was shown that the viscous dissipation has considerable impact on the fiber temperature due to its localization to a small volume near the fiber section. Also, it was shown that a variable viscosity generated vorticity, which was localized to the region where the preform radius undergoes large changes.
The Temperature Rise at the Surface of a Liquid Layer Subject to a Concentrated Heat Source Placed Above the Layer
Authors: Burelbach J. P. , Epstein M. , Plys M. G.
Published: February 2008

A focused heat flux on the free surface of a liquid layer gives rise to combined thermocapillary and thermogravitational flow within the layer that dictates the magnitude of the temperature rise achieved at the surface. In the case of a high-boiling-point flammable liquid layer, this temperature rise determines the ignitability of the layer. An unconventional solution technique, which transforms the combined natural convection problem into a nonlinear conductionlike problem, is introduced to derive a convenient relationship between the heater power and size and the maximum liquid surface temperature. This expression depends on the layer thickness and fluid properties, but does not contain any adjustable (empirical) parameters. Experimental data are reported for dodecane layers between 2 and 7 mm thick for heat fluxes up to 63 kW m−2. The data are well correlated by our analytical result.
Buoyancy and Property Variation Effects in Turbulent Mixed Convection of Water in Vertical Tubes
Authors: Parlatan Y. , Todreas N. E. , Driscoll M. J.
Published: February 2008

Friction factor and heat transfer coefficient behavior are investigated experimentally under mixed convection conditions in aiding and opposing transition and turbulent flow of water (4000 < Re < 9000 and Bo < 1.3). With increasing buoyancy influence, the friction factor increases by as much as 25 percent in aiding flow, while it decreases by as much as 25 percent in opposing flow (GrΔT < 7·106). The effects of temperature-dependent viscosity variations are also included in the analysis (0.5 < μw/μb < 1.0). When they are taken into account, the increase in the friction factor due to buoyancy forces alone in upward flow becomes larger. The friction factor behavior is compared with previous studies in the literature. Our experimental data agree well with some of the previous experiments described in the literature. The heat transfer coefficient was also measured under the same experimental conditions; the heat transfer coefficient monotonically increases in opposing flow by as much as 40 percent, and first decreases by 50 percent and then recovers in aiding flow with increasing buoyancy influence.
Comparison of Experiment With Monte Carlo Simulations on a Reflective Gap Using a Detailed Surface Properties Model
Authors: Zaworski J. , Welty J. R. , Palmer B. J. , Drost M. K.
Published: February 2008

The spatial distribution of light through a rectangular gap bounded by highly reflective, diffuse surfaces was measured and compared with the results of Monte Carlo simulations. Incorporating radiant properties for real surfaces into a Monte Carlo code was seen to be a significant problem; a number of techniques for accomplishing this are discussed. Independent results are reported for measured values of the bidirectional reflectance distribution function over incident polar angles from 0 to 90 deg for a semidiffuse surface treatment (Krylon™ flat white spray paint). The inclusion of this information into a Monte Carlo simulation yielded various levels of agreement with experimental results. The poorest agreement occurred when the incident radiation was at a grazing angle with respect to the surface and the reflectance was nearly specular.
Reordering the Absorption Coefficient Within the Wide Band for Predicting Gaseous Radiant Exchange
Authors: Lee P. Y. C. , Hollands K. G. T. , Raithby G. D.
Published: February 2008

The “exact” calculation of the radiant transfer in gaseous enclosures has remained impractical for design; the highly complex nature of the absorption spectrum of the gases has meant that an inordinately large computational effort is required to effect an exact answer. In this paper we show how the complex absorption distribution for an isothermal gas can be replaced by a set of smooth curves. This procedure can be visualized as one of actually reordering the full complex absorption distribution within each vibration-rotation band, and then replacing it by a smooth curve. Such a smooth curve can then be readily approximated by a stepwise function, and radiant exchange calculations can be carried out at each step and then summed over all the steps to get the total exchange. This paper explains how the reordered curve can be obtained and gives some sample plots of the reordered absorption coefficient curve. Fitted functions for the rearranged curves have been provided, and some solutions to the radiant exchange problems are given and compared to line-by-line solutions. About 50 to 200 steps in the stepwise curve are found to be adequate in order to obtain an answer within a few percent of the exact answer.
Quartz-Fiber Thermal Insulation: Infrared Radiative Properties and Calculation of Radiative-Conductive Heat Transfer
Authors: Dombrovsky L. A.
Published: February 2008

Calculations of absorption, transport scattering, and radiation diffusion coefficients for a highly porous material of quartz fibers are performed by use of rigorous scattering theory for arbitrarily oriented cylinders. New results concerning resonance absorption in the semitransparency region and intensive “scattering by absorption” at refractive index n ≈ 1 in the opacity region are obtained. Numerical results for the radiation diffusion coefficient from a theoretical model without taking into account both dependent scattering and interference effects are in a good agreement with the experimental data for isotropic fibrous material of density 144 kg/m3. Calculations allow us to give practical proposals to simplify the determination of optical properties of poly disperse material with randomly oriented fibers. Some results on the radiative–conductive heat transfer in the material considered are presented. The radiation transfer is described in the P1 approximation. A two-band spectral model with bands corresponding to semitransparency and opacity regions is proposed. Applicability of a modified radiative conduction approximation both to transient and to steady-state calculations is discussed.
Spectral Extinction Coefficients of Soot Aggregates From Turbulent Diffusion Flames
Authors: Ko¨ylu¨ U¨. O¨. , Faeth G. M.
Published: February 2008

The spectral extinction coefficients of soot aggregates were studied in the fuel-lean (overfire) region of buoyant turbulent diffusion flames. Extinction measurements were carried out in the wavelength region of 0.2–5.2 μm for flames fueled with acetylene, propylene, ethylene, and propane, burning in air. The present measurements were combined with earlier measurements of soot morphology and light scattering at 0.514 μm in order to evaluate the spectral soot refractive indices reported by Dalzell and Sarofim (1969), Lee and Tien (1981), and Chang and Charalampopoulos (1990). The specific extinction coefficients and emissivities were predicted based on Rayleigh–Debye–Gans theory for polydisperse fractal aggregates, which has been recently found to be the best approximation to treat optical cross sections of soot aggregates. The results indicated that available refractive indices of soot do not predict the spectral trends of present measurements in the ultraviolet and infrared regions. Soot complex refractive index was inferred to be m = 1.54 + 0.48i at 0.514 μm, which is surprisingly in best agreement with the values reported by Dalzell and Sarofim (1969). Additionally, specific extinction coefficients of soot aggregates varied with wavelength as λ−0.83 from the visible to the infrared. Finally, soot refractive indices were found to be relatively independent of fuel type for the visible and infrared spectral regions over the H/C ratio range of 0.08–0.22.
Analytical Study of Critical Heat Flux in Two-Phase Thermosyphon: Relationship Between Maximum Falling Liquid Rate and Critical Heat Flux
Authors: Monde M.
Published: February 2008

An analytical study has been done on the critical heat flux of a two-phase thermosyphon, in which a liquid film and a vapor flow exist in a countercurrent annular flow. The CHF point on the thermosyphon is proved to correspond to a maximum falling liquid rate fed to the thermosyphon, which can be determined from three equations of momentum, its partial derivative with void fraction, and mass balance in the thermosyphon. This maximum point, furthermore, becomes identical to the point at which an envelope line generated from the momentum equation and its partial derivative intersects the mass balance line. The CHF calculated from the maximum liquid rate is found to be in fairly good agreement with the existing CHF data.
Heat Transfer of Air/Water Two-Phase Flow in Helicoidal Pipes
Authors: Xin R. C. , Awwad A. , Dong Z. F. , Ebadian M. A.
Published: February 2008

Heat transfer of air/water two-phase flow in helicoidal pipes is experimentally investigated in this study. Three test sections were tested in axially horizontal, vertical, and inclined orientations. It has been found that the ratio of the average heat transfer coefficient to that of the water flow is affected by the water flow rate along with the Lockhart–Martinelli parameter. For a fixed water flow rate, there is a maximum heat transfer coefficient as the air fow rate increases. The results indicate that tube diameter has a significant effect on the average heat transfer coefficient ratio. For large-tube-diameter coils, average heat transfer results vary for different orientations. For small-tube-diameter coils, orientation has an insignificant effect on the average heat transfer coefficient. Based on the experimental data, a set of correlations is proposed for the average heat transfer coefficient ratio versus the liquid superficial Reynolds number and Lockhart–Martinelli parameter.
An Experimental Study of Constant-Pressure Steam Injection and Transient Condensing Flow in an Air-Saturated Porous Medium
Authors: Brouwers H. J. H.
Published: February 2008

In this paper the unsteady process of constant pressure steam injection into an air–saturated porous medium is studied experimentally. To this end, vertical glass tubes are packed with dry quartz sand and injected with dry steam. The propagation of the steam front appears to be proportional to t. It is observed that the water saturation is homogeneously distributed and remains below the irreducible water saturation. Furthermore, the theoretical model of Brouwers and Li (1994) of the process is applied to the experiments and extended to take wall effects into account. A comparison of the predicted front penetration and amount of condensed water with the experimental results yields fairly good agreement.
A Pore-Network Study of Bubble Growth in Porous Media Driven by Heat Transfer
Authors: Satik C. , Yortsos Y. C.
Published: February 2008

We present experimental and theoretical investigations of vapor phase growth in pore-network models of porous media. Visualization experiments of boiling of ethyl alcohol in horizontal etched-glass micromodels were conducted. The vapor phase was observed to grow into a disordered pattern following a sequence of pressurization and pore-filling steps. At sufficiently small cluster sizes, growth occurred “one pore at a time,” leading to invasion percolation patterns. Single-bubble (cluster) growth was next simulated with a pore-network simulator that includes heat transfer (convection and conduction), and capillary and viscous forces, although not gravity. A boundary in the parameter space was delineated that separates patterns of growth dictated solely by capillarity (invasion percolation) from other patterns. The region of validity of invasion percolation was found to decrease as the supersaturation (heat flux), the capillary number, the thermal diffusivity, and the vapor cluster size increase. Implications to continuum models are discussed.
Mechanical Coupling of Convective Rolls in a High Prandtl Number Fluid
Authors: Cerisier P. , Jaeger M. , Medale M. , Rahal S.
Published: February 2008

Experimental and numerical studies (using the finite element method) were conducted in a rectangular vessel for a high Prandtl number fluid (Pr = 880 at 25°C). The pattern of convective rolls is perturbed by lateral heating of one of the smaller sides of the box. The wave number of the roll pattern is within a narrow range (±10 percent at R = 4.6RC where R and Rc are the Rayleigh number and its critical value of Be´nard convection). The formation of a large roll induced by the lateral heating causes a slight variation in the wave number of the rolls, accompanied by the disappearance of pairs of rolls, or single rolls, depending on the boundary conditions at the other small side of the enclosure. In all instances, this disappearance respects the mechanical coupling between the rolls. Temperature and velocity fields are assessed, as well as the heat transfer. The transient states observed during the experimentation are well reproduced by the two-dimensional numerical model developed for this study.
Mixing Structure of Plane Self-Preserving Buoyant Turbulent Plumes
Authors: Sangras R. , Dai Z. , Faeth G. M.
Published: February 2008

Measurements of the structure of plane buoyant turbulent plumes are described, emphasizing conditions in the fully developed (self-preserving) portion of the flow. Plumes were simulated using helium/air sources in a still and unstratified air environment. Mean and fluctuating mixture fractions were measured using laser-induced iodine fluorescence. Present measurements extended farther from the source (up to 155 source widths) and had more accurate specifications of plume buoyancy fluxes than past measurements and yielded narrower plume widths and different scaled mean and fluctuating mixture fractions near the plane of symmetry than previously thought. Measurements of probability density functions, temporal power spectra, and temporal integral scales of mixture fraction fluctuations are also reported.
The Heat Transport Capacity of Micro Heat Pipes
Authors: Ha J. M. , Peterson G. P.
Published: February 2008

The original analytical model for predicting the maximum heat transport capacity in micro heat pipes, as developed by Cotter, has been re-evaluated in light of the currently available experimental data. As is the case for most models, the original model assumed a fixed evaporator region and while it yields trends that are consistent with the experimental results, it significantly overpredicts the maximum heat transport capacity. In an effort to provide a more accurate predictive tool, a semi-empirical correlation has been developed. This modified model incorporates the effects of the temporal intrusion of the evaporating region into the adiabatic section of the heat pipe, which occurs as the heat pipe approaches dryout conditions. In so doing, the current model provides a more realistic picture of the actual physical situation. In addition to incorporating these effects, Cotter’s original expression for the liquid flow shape factor has been modified. These modifications are then incorporated into the original model and the results compared with the available experimental data. The results of this comparison indicate that the new semiempirical model significantly improves the correlation between the experimental and predicted results and more accurately represents the actual physical behavior of these devices.
Analysis of Unsteady Heat and Mass Transfer During the Modified Chemical Vapor Deposition Process
Authors: Park K. S. , Choi M.
Published: February 2008

An analysis of unsteady heat and mass transfer in the modified chemical vapor deposition has been carried out. It is found that the commonly used quasi-steady-state assumption could be used to predict the overall efficiency of particle deposition; however, the assumption would not be valid near the inlet region where tapered deposition occurs. The present unsteady calculations have been found to be capable of predicting the detailed deposition profile correctly even from the inlet region where further optimization is needed at a practical situation. The present results have also been compared with existing experimental data and were in good agreement. It is noted that previous quasi-steady calculation resulted in a significant difference in the deposition profile near the inlet region. The effects of time-varying torch speeds were also studied. The case of a linearly varying torch speed resulted in a much shorter tapered entry than the case of a constant torch speed.
Local and Global Simulations of Bridgman and Liquid-Encapsulated Czochralski Crystal Growth
Authors: Zhang H. , Zheng L. L. , Prasad V. , Larson D. J.
Published: February 2008

A curvilinear finite volume-based numerical methodology has been developed that can be effectively used for simulation of the Bridgman and Czochralski (Cz) crystal growth processes. New features of grid generation have been devised and added to the original formulation (Zhang et al., 1995, 1996) to make it suitable for global modeling. The numerical model can account for convection in both the melt and the gas phases, convection/radiation in the furnace, and conduction in all solid components. Results for Bridgman growth show that the flow pattern and interface shape strongly depend on thermal conductivities of the crystal, melt, and ampoule materials. Transient simulations have been performed for the growth of Bismuth crystal in a Bridgman-Stockbarger system and the growth of GaAs crystal using liquid-encapsulated Czochralski (LEC) technique. This is the first time that a global high-pressure LEC model is able to account for convective flows and heat transfer and predict the interface shape and its dynamics.