bluuebunny/crossref_metadata_2025 huggingface dataset:
Combined Free and Forced Convection of Water Between Horizontal Concentric Cylinders
Authors: Nguyen T. Hung , Vasseur P. , Robillard L. , Chandra Shekar B.
Published: October 2009

This paper presents a theoretical study of combined free and forced laminar convection of a mass of water confined between two horizontal concentric cylinders with constant surface temperatures and subject to an externally-imposed constant pressure gradient along the axial direction. The governing system of differential equations is solved, within the Boussinesq approximation, by perturbation and finite difference methods, and the solutions are obtained in terms of the various characteristic parameters of the problem. Essentially, it is found that the flow pattern and the wall shear stress in the axial direction are significantly affected by the Prandtl and the Rayleigh numbers. Thus, the axial flow shows a tendency to develop in two or even three jets, depending on the Rayleigh number. The occurrence of the inversion of density, for water at 4°C, was found to modify completely the convective, or secondary flow, but to have little effect on the main, or axial, flow.
Heat Transfer to a Fluid in Radial, Outward Flow Between Two Coaxial Stationary or Corotating Disks
Authors: Suryanarayana N. V. , Scofield T. , Kleiss R. E.
Published: October 2009

An experimental study of heat transfer rates to air flowing radially outward between two coaxial, corotating disks was made. Heat transfer data were obtained for five mass flow rates with stationary disks and four mass flow rates and five rotational speeds with rotating disks. Rotation of the disks slightly decreased the average Nusselt numbers compared with the average Nusselt numbers without rotation at the highest speed of rotation (600 rmp), but at lower speeds no consistent trends were observed. The average Nusselt numbers, with and without rotation, can be related as Nu = 0.0529 Re0.71 and the local Nusselt number as Nu = 0.124 Re0.608.
Mean Temperature Difference Charts for Air Coolers
Authors: Pignotti A. , Cordero G. O.
Published: October 2009

Computer generated graphs are presented for the mean temperature difference in typical air cooler configurations, covering the combinations of numbers of passes and rows per pass of industrial interest. Two sets of independent variables are included in the graphs: the conventional one (heat capacity water ratio and cold fluid effectiveness), and the one required in an optimization technique of widespread use (hot fluid effectiveness and the number of heat transfer units). Flow arrangements with side-by-side and over-and-under passes, frequently found in actual practice, are discussed through examples.
Experimental Observations of the Microlayer in Vapor Bubble Growth on a Heated Solid
Authors: Koffman L. D. , Plesset M. S.
Published: October 2009

Experimental measurements of microlayer formation and of the time history of microlayer thickness change have been obtained for nucleate boiling of water and ethanol. These detailed measurements were obtained using laser interferometry combined with high-speed cinematography. The measurement technique is discussed in detail with emphasis on the difficulties encountered in interpretation of the fringe patterns. The measurements for water can be reasonably applied to the data of Gunther and Kreith, in which case it is concluded that microlayer evaporation alone cannot account for the increased heat transfer rates observed in highly subcooled nucleate boiling. It appears that microconvection must play at least an equal role.
Measurement of Condensation Curves for Dropwise Condensation of Steam at Atmospheric Pressure
Authors: Tanasawa I. , Utaka Y.
Published: October 2009

Condensation curves for dropwise condensation of steam at atmospheric pressure were measured for the range of surface subcooling between 0.5 and 180 K using a heat transfer block having a concave spherical condensing surface. The heat transfer coefficient remained constant with the increase of surface subcooling up to about 10 K, and then it decreased. The maximum heat fluxes were found to be between 9.3 and 12.2 MW/m2. Dropwise condensation could be observed at a surface subcooling larger than the one corresponding to the peak heat flux, but shortly the mode of condensation shifted to pseudo-film or on-ice condensation.
Natural Convection Experiments in a Liquid-Saturated Porous Medium Bounded by Vertical Coaxial Cylinders
Authors: Reda D. C.
Published: October 2009

An experimental effort is presently underway to investigate natural convection in liquid-saturated porous media utilizing a geometry and hydrodynamic/thermal boundary conditions relevant to the problem of nuclear-waste isolation in geologic repositories. During the first phase of this research program, detailed measurements were made of the steady-state thermal field throughout an annular test region bounded by a vertical, constant-heat-flux, inner cylinder and a concentrically placed, constant-temperature, outer cylinder. An overlying, constant-pressure fluid layer was utilized to supply a permeable upper surface boundary condition. Results showed the heater surface temperature to increase with increasing vertical distance due to the buoyantly driven upflow. The measured temperature difference (ΔT) between the average heater surface temperature and the constant outer-surface temperature was found to be progressively below the straight-line/conduction-only solution for ΔT versus power input, as the latter was systematically increased. Comparisons between measured results and numerical predictions obtained using the finite element code MARIAH showed very good agreement, thereby contributing to the qualification of this code for repository-design applications.
Experimental Comparison of Heat Transfer Data With Flow Visualization on a Flat Surface in an Air Fluidized Bed
Authors: Rubinsky B. , Starnes G. L.
Published: October 2009

A new experimental technique is introduced which facilitates visualization of the fluid flow phenomena occurring on a small surface immersed in an air fluidized bed. The flow visualization was correlated qualitatively with heat transfer data from the surface. Heat transfer coefficients versus air velocity curves were obtained and found to be strongly dependent on the angle of inclination of the surface relative to the air flow direction. Flow visualization has facilitated the identification of three mechanisms of heat transfer to a surface as a function of the angle of inclination and the air flow velocity. These include, conduction through a stationary layer of particles, convection through a flow of solid particles, and heat transfer by sequential contact with voids and a well mixed conglomerate of solid particles.
The Response of a Turbulent Boundary Layer to a Double Step-Change in a Wall Heat Flux
Authors: Andreopoulos J.
Published: October 2009

Extensive measurements were made of the response of a turbulent boundary layer to a double step change of wall heat flux. The measurements include mean temperature and velocity as well as temperature-velocity correlations up to third order occurring in the ϑ2 and vϑ transport equations together with the skewness and flatness of temperature fluctuations. Two thermal layers start to develop within the primary boundary layer due to the change in heat flux at boundary. These layers are characterized with different growth rates which depend on the wall heat flux. Most of the changes in the downstream stations take place inside the second thermal layer.
A Numerical and Experimental Investigation of Turbulent Heat Transport Downstream From an Abrupt Pipe Expansion
Authors: Amano R. S. , Jensen M. K. , Goel P.
Published: October 2009

An experimental and numerical study is reported on heat transfer in the separated flow region created by an abrupt circular pipe expansion. Heat transfer coefficients were measured along the pipe wall downstream from an expansion for three different expansion ratios of d/D = 0.195, 0.391, and 0.586 for Reynolds numbers ranging from 104 to 1.5 × 105. The results are compared with the numerical solutions obtained with the k ∼ ε turbulence model. In this computation a new finite difference scheme is developed which shows several advantages over the ordinary hybrid scheme. The study also covers the derivation of a new wall function model. Generally good agreement between the measured and the computed results is shown.
In-Tube Heat Transfer for Skewed Inlet Flow Caused by Competition Among Tubes Fed by the Same Plenum
Authors: Molki M. , Sparrow E. M.
Published: October 2009

Measurements were made of the axial and circumferential distributions of the heat transfer coefficient in a tube in which the entering airflow is highly skewed. The skewness was caused by competition between the test section tube and a parallel tube which draws air from the same plenum chamber. For each of several fixed Reynolds numbers in the test section tube, the flow imbalance between the competing tubes was varied parametrically (up to a factor of eighteen), as was the center-to-center separation distance between the tubes (separation = 1.5, 3, and 4.5 times the tube diameter). Measurements were also made of the pressure drop, and a visualization technique was employed to examine the pattern of fluid flow. Practically significant effects of the flow imbalance on the axial distribution of the heat transfer coefficient were encountered only at the smallest of the investigated intertube spacings. Even for that case, the effects were moderate; for example, the imbalance-related changes for an imbalance ratio of two did not exceed 7 percent. The experiments involved naphthalene sublimation, and a new technique was developed for coating the inside surface of a tube with naphthalene.
Flow Field Measurements of an Unsteady Reacting Muzzle Exhaust Flow
Authors: Klingenberg G. , Mach H. , Smeets G.
Published: October 2009

The events associated with the discharge of a 20-mm caliber weapon have been examined in detail in order to identify and understand important features of the reacting gun muzzle flow field. The diagnostics applied involves shadowgraph and Schlieren photography, invasive pressure probes, spectroscopy for temperature measurements and Laser-Doppler velocimetry for velocity measurements. Emphasis has been on velocity measurements using two setups to determine both the axial and lateral velocity components throughout the muzzle flow field. The data clearly demonstrate the complexity of the processes involved in the unsteady flow expansion of the gun muzzle exhaust flow.
Enhancement of Natural Convection Heat Transfer From A Horizontal Cylinder Due to Vertical Shrouding Surfaces
Authors: Sparrow E. M. , Pfeil D. R.
Published: October 2009

A comprehensive experimental study has been performed to determine the natural convection heat transfer characteristics of a heated horizontal cylinder situated in a vertical channel in air. Fifteen different channel configurations were employed, encompassing a wide range of channel heights and of spacings between the channel walls. Shroud walls having various thermal characteristics (highly conducting, highly conducting/rear insulated, and insulating) were used to form the channel. For each configuration, the cylinder Rayleigh number ranged from 1.5 × 104 to 2 × 105. It was found that a cylinder situated in a channel experiences enhanced natural convection heat transfer compared with a cylinder situated in unbounded space. Enhancements of up to 40 percent were encountered for the parameter ranges of the experiments. The enhancement is accentuated as the interwall spacing is decreased and as the channel height is increased. There is no enhancement for interwall spacings of 10 diameters or more. It was also found that the Nusselt number was quite insensitive to the various types of shroud walls employed. Measured temperature distributions along the shroud walls displayed different degrees of uniformity depending on whether the wall was conducting or insulating.
Dryout Heat Fluxes in Particulate Beds Heated Through the Base
Authors: Jones S. W. , Epstein M. , Bankoff S. G. , Pedersen D. R.
Published: October 2009

A laboratory study of dryout heat fluxes in particulate beds heated through the base is reported. More than two hundred experimental heat flux data points were measured. Semi-empirical correlations of the dryout heat flux data for both deep and shallow particulate beds are developed, based on flooding in countercurrent flow in deep beds and a boiling crises in shallow beds. The role of capillary forces in bed dryout is discussed and an explanation for the variation of dryout heat flux with bed height in volumetrically heated particulate beds is presented.
A Nonequilibrium Vapor Generation Model for Flashing Flows
Authors: Saha P. , Abuaf N. , Wu B. J. C.
Published: October 2009

A nonequilibrium vapor generation model for flashing flows is presented. The model consists of a flashing inception point, a bubbly flow regime followed by a bubbly-slug regime, an annular or annular-mist regime, and finally a dispersed-droplet regime. Existence of superheated liquid at the inception point and beyond is recognized. The vapor generation rate is calculated from the flow-regime dependent interfacial area density and net interfacial heat flux. However, the bubble number density at the flashing inception point was varied to obtain optimum fits with the void fraction data taken in a vertical converging-diverging nozzle. The interfacial area density at the inception point, thus determined, showed a rapid increase with the decrease in the liquid superheat at that point. This trend is plausible, since in the limit of thermal equilibrium flow where the liquid superheat approaches zero, the interfacial area for heat and mass transfer should be very large.
Study of Heat and Mass Transfer in a Vertical-Tube Evaporative Cooler
Authors: Perez-Blanco H. , Bird W. A.
Published: October 2009

Evaporative coolers are three-fluid heat exchangers used to reject heat to the environment. A mixture of air and recirculating water is used as the cooling medium. In this paper, the heat and mass transfer processes taking place in a vertical-tube evaporative cooler are studied. A steady-state, one-dimensional model of cooler performance is formulated and is validated by experimental measurements, taken in a single-tube exchanger, of the controlling heat and mass transfer coefficients. These coefficients occur at the air-water interface. Heat fluxes and enhancement ratios for conditions of interest are measured and calculated, and the results are compared and discussed. The model is found to adequately predict heat exchanger performance.
Heat Convection in a Horizontal Curved Pipe
Authors: Yao L. S.
Published: October 2009

Thermally and hydrodynamically developing flow in heated horizontal curved pipes is analyzed. The perturbation solution is quantitatively valid only in a small region near the pipe inlet. The solution, however, provides information about the physical importance of centrifugal force and buoyancy on the developing flow. It also reveals the length and the velocity scales for the downstream regions where the secondary flow can not be treated as a small perturbation. The relative importance of centrifugal force and buoyancy is determined by the ratio of the Dean number and the Grashof number.
A Finite Element Model for Temperature Induced Electrohydrodynamic Pumping in Horizontal Pipes
Authors: Kuo B. S. , Chato J. C. , Crowley J. M.
Published: October 2009

The electrohydrodynamic (EHD) pumping created by an axially traveling electric wave superimposed on a dielectric fluid with a transverse temperature field has been investigated using a finite element technique. Both forward wave (cooled wall) and backward wave (heated wall) modes of operation have been considered. The secondary flow generated by buoyancy effects in the cross section were included in the calculations. The driving effects of the traveling wave were calculated by assuming that only the average electric shear stress produced movement while the sinusoidally varying transient effects cancelled out. The results show that effective pumping can be achieved without the use of a grounding electrode along the axis of the tube but the design parameters have to be carefully selected. Increasing the diameter-to-wavelength ratios increases the velocities. The flow rate is maximum at an optimum frequency, about 0.8 Hz in our typical cases, but it drops off rather quickly as the frequency is either decreased or increased. The velocities were much less sensitive to heating/cooling rates (i.e., Rayleigh numbers) or changes in the magnitude of the electrical conductivity values. Although the pumping effect increases approximately as the square of the maximum applied electric potential, in practice, the electric gradients are limited by the dielectric strength of the fluid. The results indicate the EHD heat exchanger/pumps can be feasible alternatives to mechanical pumps in certain circumstances when dielectric liquids require both heat tranfer and circulation.
Heat Transfer in Large Particle Bubbling Fluidized Beds
Authors: Adams R. L.
Published: October 2009

The potential use of fluidized bed combustion of coal as a means of meeting air quality standards with high-sulfur fuels has motivated the development of theoretical models of heat transfer in large particle gas fluidized beds. Models of the separate contributions of emulsion and bubble phase heat transfer have been developed by Adams and Welty [1] and Adams [2, 3, 4] and have been substantiated by experimental data for a horizontal tube immersed in a two-dimensional cold bed obtained by Catipovic [5, 6]. The consolidation of these models to predict local and overall time-average heat transfer to immersed surfaces requires information regarding emulsion phase residence time and bubble phase contact fraction for the particular geometry of interest. The analytical procedure to consolidate these models is outlined in the present work, then applied to the case of a horizontal tube immersed in a two-dimensional atmospheric pressure cold bed. Measurements of emulsion phase residence time and bubble phase contact fraction obtained by Catipovic [5] are used in the calculations for particle diameters ranging from 1.3 to 6 mm. The results agree favorably with experimental data and further substantiate the fundamental assumptions of the model.
The Boundary Layer Natural Convection Regime in a Rectangular Cavity With Uniform Heat Flux From the Side
Authors: Kimura S. , Bejan A.
Published: October 2009

This paper summarizes an analytical and numerical study of buoyancy-driven convection in a rectangular cavity filled with fluid. The new feature of this study, suggested by architectural applications of the convection phenomenon, is the presence of constant heat flux heating and cooling along the vertical side walls. It is shown analytically that in the boundary layer regime the boundary layer thickness must be constant (independent of altitude), that the core must be motionless and linearly stratified, and that the vertical walls temperature must vary linearly with the same gradient as the core temperature. The Nusselt number (q″/ΔT)H/k was found to be equal to 0.34 (H/L)1/9 Ra2/9, where H/L is the height/length ratio and Ra = gβq″ H4/ (kαν). The second part of the paper presents a numerical study of the same phenomenon: the numerical results agree very well with the analytical predictions made in the first part of the paper.
Observed Flow Reversals and Measured-Predicted Nusselt Numbers for Natural Convection in a One-Sided Heated Vertical Channel
Authors: Sparrow E. M. , Chrysler G. M. , Azevedo L. F.
Published: October 2009

A three-part study encompassing both experiment and analysis has been performed for natural convection in an open-ended vertical channel. One of the principal walls of the channel—the heated wall—was maintained at a uniform temperature, while the other principal wall was unheated. The experiments, which included flow visualization and Nusselt number measurements, were carried out with water in the channel and in the ambient which surrounds the channel. At Rayleigh numbers which exceeded a threshold value, the visualization revealed a pocket of recirculating flow situated adjacent to the unheated wall in the upper part of the channel. The recirculation was fed by fluid drawn into the top of the channel, adjacent to the unheated wall. Average Nusselt numbers for the heated wall were measured over a three orders of magnitude range of a single correlating parameter, which includes the Rayleigh number and the ratio of the channel length to the interwall spacing. The Nusselt numbers were found to be unaffected by the presence of the recirculation zone. Numerical solutions obtained via a parabolic finite difference scheme yielded Nusselt numbers in good agreement with those of experiment. The numerical results covered the Prandtl number range from 0.7 to 10.
A Mathematical Model of Condensation Heat and Mass Transfer to a Moving Droplet in its Own Vapor
Authors: Chung J. N. , Chang Tae-Ho
Published: October 2009

A mathematical model appropriate for predicting condensation heat and mass transfer rates along the surface of a droplet moving in pure vapor is developed. A Karman-Pohlhansen type of integral approach was adopted for the solution of vapor-phase boundary layer equations. The diffusion-dominated internal core was solved using a finite difference numerical scheme. The rate-controlling mechanism of pure vapor condensing on a droplet was found in the thermal core region of the liquid phase where the streamlines correspond to the isotherms and diffusion is the primary transport mechanism. The total rate of heat transfer is found to be inversely proportional to the droplet radius. The condensation velocity at the vapor-liquid interface reduces the boundary layer thickness and moves the separation point toward the rear stagnation point. The internal motion also helps increase the transport rates by reducing both the boundary layer thickness and thermal resistance in the liquid phase. The results predicted by this model compare favorably with available experimental values.
Two-Region Analysis of Interface Shape in Continuous Casting With Superheated Liquid
Authors: Siegel R.
Published: October 2009

A slab ingot is being formed as a continuous casting by withdrawal from a mold with parallel walls. The sides of the ingot below the mold are cooled to remove heat of fusion and energy transferred to the solidification interface by superheated liquid metal in the mold. A two-region analysis is made to determine the non-uniform heat conduction from the liquid metal to the interface, and then from the interface to the cooled ingot sides. The solidification interface shape is found that is compatible with the removal of fusion energy and nonuniform heating from the liquid. The solution is obtained by two applications of a Cauchy boundary value method.
Heat Transfer Enhancement in Laminar Slurry Pipe Flows With Power Law Thermal Conductivities
Authors: Sohn C. W. , Chen M. M.
Published: October 2009

Generalized theoretical results for heat transfer in laminar pipe flow with power law varying thermal conductivities are presented. The study is motivated by experimental observations that above a threshold shear rate the effective thermal conductivity for disperse two-phase mixtures increases with shear rate. Using a relatively general three parameter power law model for conductivity as a function of shear rate, heat transfer results for short and long pipes as well as with developing thermal profiles were obtained for both the uniform wall heat flux and uniform wall temperature conditions. The results show that significant enhancement in heat transfer coefficient could be obtained from the microconvective effects.
An Experimental Investigation of Combined Convection From a Short Vertical Cylinder in a Crossflow
Authors: Clausing A. M. , Wagner K. C. , Skarda R. J.
Published: October 2009

An experimental investigation of combined convective heat transfer from a smooth, isothermal vertical cylinder to a surrounding gas medium is described. The study was motivated by the desire to predict the convective heat loss from the 10-MWe pilot plant solar receiver in Barstow, California. Hence emphasis is placed on the supercritical (Reynolds number Re greater than 105, turbulent (Rayleigh number RaL greater than 109) regime. The influences of the Reynolds number, the Rayleigh number, the Richardson number, and Tw/T∞—the ratio of the surface temperature, Tw to the ambient air temperature T∞—are deduced. Large ranges of these dimensionless parameters are covered with a single model by using a variable ambient temperature, cryogenic wind tunnel over the temperature range 80 K ≤ T∞ ≤ 300 K. The cryogenic facility also enables the simultaneous generation of large Rayleigh numbers and large Reynolds numbers.
Transient Response of the Counterflow Heat Exchanger
Authors: Romie F. E.
Published: October 2009

The exit fluid temperature responses are presented for a unit step increase in the entrance temperature of either of the fluids of a counterflow heat exchanger. The exit temperature response histories are functions of four parameters, three of which are commonly used to define the steady-state temperature distributions in the exchanger. The responses are found using a finite difference method and are represented by simple empirical equations for a range of the four parameters believed appropriate for many technical applications.
A Stochastic Approach for Radiative Exchange in Enclosures With Nonparticipating Medium
Authors: Naraghi M. H. N. , Chung B. T. F.
Published: October 2009

A stochastic method is developed for calculating radiation interchange in enclosures with a finite number of isothermal surfaces but without a participating medium. Different types of surface properties are considered. They are diffuse and specular surfaces. In this work, a stochastic n model is proposed that is based on the Markov chain theory and leads to some explicit matrix relationships for the absorption factor from which the heat transfer characteristics of the enclosure can be determined. The present approach provides an exact solution as long as the necessary view factors can be determined. The accuracy of approximate solutions can be improved as n increases.
Two-Phase Description of Hydrodynamic Fragmentation Processes Within Thermal Detonation Waves
Authors: Bu¨rger M. , Kim D. S. , Schwalbe W. , Unger H. , Hohmann H. , Schins H.
Published: October 2009

Large-scale vapor explosions are described by thermal detonation waves, proceeding through a fuel-coolant mixture. A two-phase flow model is used for modeling the processes inside a wave. One phase is formed by the drops of melt and the other by the coolant and the fragments. For the interfacial transfer relations between the phases new descriptions are presented, which extend earlier thermal detonation models. The fragmentation behavior can be calculated from two different models, one based on deformation breakup and Taylor instability and another describing fragmentation by stripping of capillary waves induced by shear flow instabilities. In addition to the time development of the fragmented mass, the models give also the actual sizes of the fragments. Results of the fragmentation models are compared with the experiments on hydrodynamic fragmentation of single drops of gallium in water flows. For vapor explosion experiments with tin-water and salt-water systems the detonation cases are determined using the wave stripping model.
An Analysis of the Effect of Entrainment Temperature on Jet Impingement Heat Transfer
Authors: Striegl S. A. , Diller T. E.
Published: October 2009

An analytical model is developed to determine the effect of the temperature of entrained fluid (entrainment temperature) on the local heat transfer to a single, plane, turbulent impinging jet. Solutions of the momentum and energy equations for a single impinging jet are accomplished using similarity and series analyses. Solutions of the energy equation are obtained for the two limiting cases of entrainment temperatures equal to the plate temperature and the initial jet temperature. The analytical solutions are superposed to obtain the solution for all intermediate entrainment temperatures. The constants in the turbulence model are determined by comparing the analytical solutions to experimentally determined local heat transfer rates for single impinging jets issuing into an environment with a controlled entrainment temperature. When the single jet model is applied to jet arrays it predicts that the entrainment in the recirculation region between the jets can significantly affect the heat transfer. Comparison of the model to heat transfer measurements performed for jet arrays shows that the model successfully predicts the local heat transfer in jet arrays.
Onset of Thermal Convection in a Fluid Layer Subjected to Transient Heating From Below
Authors: Kaviany M.
Published: October 2009

The onset of convection in a horizontal layer of fluid subject to time-dependent heating from below is studied both experimentally and analytically. The fluid layer is confined by a rigid boundary at the bottom and a shear-free surface at the top. The fluid, which is initially quiescent, is heated by increasing the temperature of the lower surface at a constant time-rate. The experimental observation of the time of the onset of convection is made through the sudden change in variation of the temperature of the lower surface with respect to time. The onset is also observed through the sudden change in the fringe pattern created by holographic interferometry. Various layer depths are considered in order to observe the influence of this variable on the onset time. The analytical prediction is made by application of the linear amplification theory subject to boundary conditions similar to those of the experiment. Good agreement is found between the experimental and analytical results. Comparisons are also made with the experimental and analytical results available in the literature.
Condensation of Flowing Vapor on a Horizontal Tube—Numerical Analysis as a Conjugate Heat Transfer Problem
Authors: Honda H. , Fujii T.
Published: October 2009

Condensation of flowing vapor on a horizontal tube is numerically analyzed under given conditions of vapor and coolant. Besides the usual boundary layer concept, some approximations are introduced for the determination of shear stress at the vapor-liquid interface. The conjugation of the two-phase boundary layer equations and the heat conduction equation within the tube wall is achieved by using an iterative scheme at the outer surface of the tube wall. The solution thus obtained reveals the effects of vapor velocity, tube material, heat transfer of coolant side, etc., upon circumferential distributions of temperature, heat flux density, and Nusselt number at the outer tube surface. Also the solution compared well with available experimental results for the wall temperature distribution and average Nusselt number. The heat transfer characteristics of steam and refrigerant vapors resemble those of the tubes with uniform wall heat flux density and uniform wall temperature, respectively.
Interfacial Drag for Two-Phase Flow Through High Permeability Porous Beds
Authors: Tutu N. K. , Ginsberg T. , Chen J. C.
Published: October 2009

Pressure drop and void fraction measurements in two-phase (air–water) flow through porous beds of randomly packed spheres have been used to determine the interfacial gas–liquid drag and the gas–solid drag for the case of zero net liquid flux through the bed. The results, presented for beds of 3.18-, 6.35-, and 12.7-mm spheres, show that the interfacial gas–liquid drag term is of the same order as the gas-solid drag term when the particle size is greater than 6 mm.
Parameters Governing Thermal Diffusivity Measurements of Unidirectional Fiber-Reinforced Composites
Authors: Taylor R. E. , Kelsic B. H.
Published: October 2009

Limitations in applying the concept of thermal diffusivity to coarse-weave fiber-reinforced composites are examined. Using the flash technique for measuring the apparent diffusivity, the effects of fiber fraction, fiber/matrix thermal conductivity ratio fiber orientation, and specimen length are studied. The conductivity ratio was the major factor governing the thermal behavior of the composite. The fiber fraction was the next most controlling parameter. Specimen length and fiber orientation can be used to modify the behavior of composites.
Numerical and Experimental Study of Turbulent Heat Transfer and Fluid Flow in Longitudinal Fin Arrays
Authors: Kadle D. S. , Sparrow E. M.
Published: October 2009

Heat transfer from an array of parallel longitudinal fins to a turbulent air stream passing through the interfin spaces has been investigated both analytically/numerically and experimentally. The fins were integrally attached to a heated base plate, while the fin tips were shrouded to avoid leakage. In the analytical/numerical work, a conjugate problem was solved which encompassed turbulent flow and heat transfer in the air stream and heat conduction in the fins and in the base plate. The turbulence model and computational scheme were verified by comparison with experiment. It was found that the local heat transfer coefficients varied along the fins and along the surface of the base plate, with the lowest values in the corners formed by the fin/base plate intersections and the fin/shroud intersections. The numerically determined fin efficiencies did not differ appreciably from those calculated from the conventional pure-conduction fin model. Average Nusselt numbers, evaluated from the experimental data in conjunction with the numerically determined fin efficiencies (for derating the fin surface area), agreed well with those for fully developed heat transfer in a uniformly heated circular tube.
Forced-Convection Heat Transfer for Single and Two-Phase Helical Flow in a Solar Receiver
Authors: Vafaie F. N. , Dunn J. R.
Published: October 2009

The heat transfer characteristics of a single-tube, helically coiled receiver for a concentrating solar collector are presented. Heat transfer coefficients were measured for single and two-phase water-steam flow in a helical coil subjected to radiant heating for a range of flow conditions and radiant flux levels. Results are presented for both the local and average heat transfer coefficients in several flow regimes.
An Initial Value Approach to the Inverse Heat Conduction Problem
Authors: Hensel E. , Hills R. G.
Published: October 2009

The one-dimensional linear inverse problem of heat conduction is considered. An initial value technique is developed which solves the inverse problem without need for iteration. Simultaneous estimates of the surface temperature and heat flux histories are obtained from measurements taken at a subsurface location. Past and future measurement times are inherently used in the analysis. The tradeoff that exists between resolution and variance of the estimates of the surface conditions is discussed quantitatively. A stabilizing matrix is introduced to the analysis, and its effect on the resolution and variance of the estimates is quantified. The technique is applied to “exact” and “noisy” numerically simulated experimental data. Results are presented which indicate the technique is capable of handling both exact and noisy data.
Radiative Transfer in Axisymmetric, Finite Cylindrical Enclosures
Authors: Mengu¨c¸ M. P. , Viskanta R.
Published: October 2009

A solution of the radiative transfer equation for an axisymmetric cylindrical enclosure containing radiatively participating gases and particles is presented. Nonhomogeneities of the radiative properties of the medium as well as of the radiation characteristics of the boundaries are allowed for, and the boundaries are assumed to be diffusely emitting and reflecting. The scattering phase function is represented by the delta-Eddington approximation to account for highly forward scattering by particulates. The model for radiative transfer is based on the P1 and P3-spherical harmonics approximations. Numerical solutions of model equations are obtained using finite-difference as well as finite-element schemes.
Natural Convection Heat Transfer From a Horizontal Cylinder Between Vertical Confining Adiabatic Walls
Authors: Karim F. , Farouk B. , Namer I.
Published: October 2009

This paper reports an experimental study of natural convection heat transfer from a horizontal isothermal cylinder between vertical adiabatic walls. Some of the industrial applications of this problem are cooling and casing design of electronic equipment, nuclear reactor safety, and heat extraction from solar thermal storage devices. Heat transfer from 3.81 cm and 2.54 cm diameter cylinders was determined by measuring the electric power supplied to the heater, which was placed inside the cylinders, and correcting for radiation and end losses. Average Nusselt numbers were determined for a Rayleigh number range of 2 × 103 to 3 × 105 and wall spacing to cylinder diameter ratios of 1.5, 2, 3, 4, 6, 8, 10, 12, and ∞. It was found that the confinement of a heated horizontal cylinder by adiabatic walls enhances the heat transfer from the cylinder continuously. This effect is more pronounced at low Rayleigh numbers. A maximum relative enhancement of 45 percent was obtained over the range of experimental conditions studied. Schlieren and flow visualization studies were conducted at selected values of Rayleigh number and wall spacing to cylinder diameter ratios to further explain the heat transfer characteristics and the associated flow physics of the present problem.
A Study of the Flow Mechanisms Responsible for Heat Transfer Enhancement in Interrupted-Plate Heat Exchangers
Authors: Mullisen R. S. , Loehrke R. I.
Published: October 2009

Certain compact heat exchanger cores are modeled by assemblies of parallel plates. The heat transfer in these cores may be enhanced if the plate surfaces are interrupted. The results of an experimental study of the mechanisms responsible for enhancement are reported here along with quantitative measures of the magnitude of the enhancement and the pressure drop penalty incurred. The aim of this work is to identify the important parameters and provide guidelines for designers of heat transfer surfaces and to workers attempting to correlate experimental data. Arrays of parallel plates were tested in a wind tunnel. Fluid flow phenomena were identified using the Schlieren visualization technique. Three distinctly different flow regimes are found within cores composed of in-line plates. These are classified as steady, general unsteady, and periodic unsteady flows. The periodic unsteady flow is accompanied by the emission of a strong acoustic tone. The heat transfer performance of these cores was determined using a transient heating technique. The evolution of the enhancement and the associated changes in the flow regimes are documented over a range of Reynolds number as the streamwise spacing between in-line plates is increased from zero. The results of these experiments are used to interpret the measured performance of cores consisting of staggered arrays of parallel plates and of cores formed by assembling parallel-plate arrays so that alternate plates in the streamwise direction are perpendicular to each other.
Heat Transfer From a Single Cylinder, Cylinders in Tandem, and Cylinders in the Entrance Region of a Tube Bank With a Uniform Heat Flux
Authors: Baughn J. W. , Elderkin M. J. , McKillop A. A.
Published: October 2009

An experimental technique for obtaining a uniform wall heat flux has been used to determine the local heat transfer coefficients around a cylinder. Data are presented for a single cylinder, for cylinders in tandem, and cylinders located in the entrance of a tube bank. Results are compared to those of other studies with uniform wall heat flux. For the single cylinder, these are found to depend upon blockage, aspect ratio, and free-stream turbulence. For both inline and staggered tube arrangements, the heat transfer coefficient distribution depends on row location but appears to be nearly established by the third row.
Laminar Combined Convection in a Horizontal Annulus Subject to Constant Heat Flux Inner Wall and Adiabatic Outer Wall
Authors: Kaviany M.
Published: October 2009

Steady-state, fully developed velocity and temperature fields in mixed convection through a horizontal annulus (ratio of outside to inside radii of 1.25), with a prescribed constant heat flux on the inner cylinder and an adiabatic outside cylinder are analyzed using finite difference approximations. The effects of the buoyancy-driven lateral flow on the temperature of the inner surface are studied in detail. The results show that, as the buoyancy potential (Rayleigh number) increases, the lateral flow structure changes from one cell (on each side) to two cells. The consequence of these flow regimes is that as Rayleigh number increases the temperature of the upper portion of the inner cylinder first increases significantly above its value for pure forced convection and then decreases significantly as the number of cells increases. The average temperature of the inner cylinder decreases monotonically as the Rayleigh number increases.
Mean-Parameter Modeling of Oscillating Flow
Authors: Gedeon D.
Published: October 2009

After looking at the exact solution for laminar incompressible oscillating flow between parallel plates with a longitudinal temperature gradient, the momentum and energy equations are reast in terms of mean (section average) velocity and temperature. It is shown that fluid shear stress and normal temperature gradient at the wall are amplified and phase shifted compared to the steady-flow case and some practical equations for friction factor and Nusselt number are given. However, the mean-parameter solution differs from the exact solution in regard to net advected energy, thereby prompting the introduction of an apparent enhanced fluid conductivity to account for the difference.
Momentum and Heat Transfer on a Continuous Moving Surface
Authors: Jeng D. R. , Chang T. C. A. , De Witt K. J.
Published: October 2009

An analysis has been carried out to determine the momentum and heat transfer occurring in the laminar boundary layer on a continuous moving surface which has an arbitrary surface velocity and nonuniform surface temperature. Merk series types of solutions are obtained for the momentum and heat transfer for an isothermal surface. The results are expressed in terms of universal functions. For a nonisothermal surface, the procedure begins with a consideration of the solution of the energy equation for a step discontinuity in the surface temperature by the introduction of appropriate transformation variables. Equations for the temperature profile and for the local heat flux are expressed explicitly in terms of the Prandtl number and the surface velocity parameter. Numerical examples for a power law surface velocity and a linearly stretching surface velocity with nonzero slot velocity are given for the isothermal surface. The accuracy of the present solutions is also discussed.
Effects of Microstructure on the Conjugated Mixed Forced and Free Convection-Conduction Analysis of Heat Transfer in a Vertical Plate Fin
Authors: Lien Fue-Sang , Chen Cha’o-Kuang
Published: October 2009

A conjugated convection-conduction analysis has been made for a vertical plate fin which exchanges heat with its micropolar fluid environment by mixed forced and free convection. The analysis is based on a one-dimensional model for the plate fin whereby the heat conduction equation for the fin is solved simultaneously with the conservation equations for mass, momentum, angular momentum, and energy in the micropolar fluid boundary layer adjacent to the fin. The local heat transfer coefficient is not specified in advance but is one of the results of the numerical solutions. Numerical results of the overall heat transfer rate, the local heat transfer coefficient, the local heat flux, and the fin temperature distribution for Pr = 5 are presented for various values of Δ (dimensionless material parameter), Nc (conjugated convection-conduction parameter), and Ω (buoyancy parameter).
Evaporative Cutting of a Semi-infinite Body With a Moving CW Laser
Authors: Modest M. F. , Abakians H.
Published: October 2009

The formation of a deep groove by evaporation on a moving semi-infinite solid is considered. Evaporative removal of material is achieved by focusing a high-power, highly concentrated Gaussian laser beam of constant wattage (CW laser) onto the surface of the solid. Assuming thermal losses due to conduction and convection to be relatively minor, these losses are treated in an approximate fashion using a simple integral method. The relevant nonlinear partial differential equations are solved numerically, and results for groove depth and shape are presented for a variety of laser and solid parameters.
Radiative Transfer With Dependent Scattering by Particles: Part 1—Theoretical Investigation
Authors: Cartigny J. D. , Yamada Y. , Tien C. L.
Published: October 2009

Dependent radiation scattering for which the independent scattering theory fails to predict the scattering properties is important in analyzing radiative transfer in packed and fluidized beds. In this paper the dependent scattering properties have been derived assuming the Rayleigh–Debye scattering approximation for two cases: two identical spheres and a cloud of spherical particles. The two-sphere calculated results compare well with the exact solutions in the literature, giving confidence in the present analytical approach. The gas model and packed-sphere model have been employed to calculate dependent scattering properties for a cloud of particles of small and large particle volume fraction, respectively. The calculated dependent scattering efficiencies for a cloud of particles are smaller than the independent scattering efficiencies and decrease with increasing particle volume fraction. A regime map for independent and dependent scattering has been constructed and compared with existing empirical criteria.
The Formulation of Spray Combustion Models: Resolution Compared to Droplet Spacing
Authors: Sirignano W. A.
Published: October 2009

Formulations of the governing equations for burning air/fuel spray mixtures are discussed. The subsystem of equations describing liquid properties is formulated in three ways: Eulerian description, Lagrangian description, and probabilistic or distribution function description. The relationships among these approaches and the relative advantages and disadvantages are discussed. The reduction of numerical error, the ability to resolve multivalued solutions, and the ability to achieve resolution a scale smaller than droplet spacing lead to a preference of the Lagrangian method over the Eulerian method. However, when resolution is desired on a scale smaller than the average droplet spacing, the location of each droplet is known only in a statistical manner. The advantages of a probabilistic formulation in this case are evaluated.
Thermal Transport From a Heated Moving Surface
Authors: Karwe M. V. , Jaluria Y.
Published: October 2009

A numerical and analytical study of the transport process arising due to the movement of a continuous heated body has been carried out. The relevant heat transfer mechanisms are of interest in a wide variety of practical applications, such as continuous casting, extrusion, hot rolling, and crystal growing. The conjugate problem, which involves a coupling between the heat transfer in the moving material and the transport in the fluid, is considered. The thermal fields in the material and in the fluid are computed. The temperature level is found to decay gradually with distance along the moving material, as expected. Results are obtained for a wide range of governing parameters, particularly the Peclet number Pe and the parameter R, which depends on the properties of the fluid and the material. The results obtained are compared with those for the idealized cases of an assumed surface heat transfer coefficient and of a moving isothermal surface. Of particular interest were the nature of the flow generated by the moving surface and the resulting thermal transport. The results obtained are also considered in terms of the underlying physical processes in the problem.