bluuebunny/crossref_metadata_2025 huggingface dataset:
Natural Convection in a Rectangular Porous Cavity With One Permeable Endwall
Authors: Haajizadeh M. , Tien C. L.
Published: October 2009

This paper describes a theoretical and experimental study of two-dimensional, buoyancy-driven flow in a rectangular porous cavity with one permeable endwall. Connected to a constant temperature tank, the permeable end allows for natural recharge and discharge of the saturating fluid. The other vertical endwall is impermeable and maintained at a constant but higher temperature, thus inducing a buoyancy-driven flow. The theoretical study includes an asymptotic analysis developed for a shallow cavity with one permeable endwall and the numerical solutions of the power-law difference representation of the full governing equations. The experimental system consists of water-saturated glass beads packed in a rectangular cavity with a length-to-height aspect ratio of 3.17, for which the Rayleigh number can vary up to 120. Measurements were made of the steady-state temperature distribution in the cavity and the heat transfer rate from the impermeable endwall. It is shown that the constant pressure and temperature assumptions at the permeable wall, as employed in the theoretical analysis, satisfactorily predict the experimental data. Results are also compared with those existing in the literature.
An Experimental Study of Laminar Heat Transfer Downstream of Backsteps
Authors: Aung W.
Published: October 2009

Results of a study of heat transfer in the vicinity of a backward-facing step of a uniform temperature are presented. Temperature distribution are measured using a Mach-Zehnder interferometer. The heat transfer upstream of the step is shown to be strongly enhanced by streamline curvature. Downstream of the step the heat transfer increases monotonically in the streamwise direction but is always less than the flat-plate value. For the largest step investigated, the average heat transfer in the reverse flow region is reduced to 56 percent of the flat-plate results, in agreement with an existing theory for laminar separated flow originally developed for a cavity. The heat transfer is systematically smaller for smaller steps. For all steps, the average heat transfer is described by the equation, St = 0.787(Res)−0.55 (s/xs)0.72.
On the Cooling of Fibers
Authors: Moutsoglou A.
Published: October 2009

The effects of the stretching of filaments on the cooling of fibers during the melt-spinning process are studied numerically. The filament is modeled as a continuous, cylindrical cone that moves steadily through an otherwise quiescent environment, with its diameter attenuating exponentially. Radiative cooling from the fiber surface is also accounted for in the analysis. The buoyancy-affected laminar and turbulent boundary layer equations are solved by a finite difference scheme, to determine the axial temperature variation of the filament. It is found that the reduction of the fiber diameter and the subsequent increase in the local speed of the filament enhances greatly the cooling from the filament surface, whereas the increase of the cooling due to radiative losses is not significant for all the flow cases considered.
Forced Convection in Non-Newtonian Flow Past A Nonisothermal Needle
Authors: Chen J. L. S. , Kearns J. W.
Published: October 2009

An analysis of the laminar steady-state forced convection heat transfer from a nonisothermal thin needle in an accelerating incompressible non-Newtonian fluid is presented. Similarity temperature profile and heat transfer characteristics are obtained for needles with axial power-law variations in surface temperature and surface heat flux. Effects of the needle size, the non-Newtonian flow behavior, and the generalized Prandtl number of the thermal characteristics of the flow are examined in detail.
Thermally Optimum Spacing of Vertical, Natural Convection Cooled, Parallel Plates
Authors: Bar-Cohen A. , Rohsenow W. M.
Published: October 2009

While component dissipation patterns and system operating modes vary widely, many electronic packaging configurations can be modeled by symmetrically or asymmetrically isothermal or isoflux plates. The idealized configurations are amenable to analytic optimization based on maximizing total heat transfer per unit volume or unit primary area. To achieve this anlaytic optimization, however, it is necessary to develop composite relations for the variation of the heat transfer coefficient along the plate surfaces. The mathematical development and verification of such composite relations as well as the formulation and solution of the optimizing equations for the various boundary conditions of interest constitute the core of this presentation.
The Effect of Vapor Velocity Profile Shape on Flow Film Boiling From Submerged Bodies
Authors: Witte L. C. , Orozco J.
Published: October 2009

An analysis of subcooled flow film boiling from submerged bodies that includes the effect of nonlinearity of the vapor film velocity profile is performed. The angle at which vapor flow reversal occurs on the back of the body is predicted by the analysis. A comparison of the predicted vapor flow reversal angle to the wake formation angle observed for flow boiling over spheres indicates that wake formation occurs a few degrees downstream of the vapor flow reversal point. A comparison of the analysis to available experimental data shows that heat transfer results based on a quadratic vapor velocity profile compare much better with experiments than do previous analyses. The heat transfer results for linear and quadratic vapor velocity profiles become virtually identical as subcooling increases.
Analysis of Two-Dimensional Melting in Rectangular Enclosures in Presence of Convection
Authors: Gadgil A. , Gobin D.
Published: October 2009

Two-dimensional melting of a solid phase change material in a rectangular enclosure heated from one side is simulated numerically. The simulations are carried out by dividing the process in a large number of quasi-static steps. In each quasi-static step, steady-state natural convection in the liquid phase is calculated by directly solving the governing equations of motion with a finite difference technique. This is used to predict the shape and motion of the solid-liquid boundary at the beginning of the next step. The predictions are found to be in good agreement with experiment. Influence of some of the governing parameters on the time development of the melting process is studied using the numerical simulation procedure.
The Effect of Entrainment Temperature on Jet Impingement Heat Transfer
Authors: Striegl S. A. , Diller T. E.
Published: October 2009

An experimental study was done to determine the effect of entrainment temperature on the local heat transfer rates to single and multiple, plane, turbulent impinging air jets. To determine the effect of entrainment of the surrounding fluid, the single jet issued into an environment at a temperature which was varied between the initial temperature of the jet and the temperature of the heated impingement plate. An analytical model was used to correlate the measured heat transfer rate to a single jet. The effect of the entrainment temperature in a single jet was then used to analyze the effect of entrainment from the recirculation region between the jets of a jet array. Using the measured temperature in the recirculation region to include the effect of entrainment, the single jet correlations were successfully applied to multiple jets.
Heat Transfer Characteristics for Jet Array Impingement With Initial Crossflow
Authors: Florschuetz L. W. , Metzger D. E. , Su C. C.
Published: October 2009

Two-dimensional arrays of circular air jets impinging on a heat transfer surface parallel to the jet orifice plate are considered. The jet flow, after impingement, is constrained to exit in a single direction along the channel formed by the jet orifice plate and the heat transfer surface. In addition to the crossflow that originates from the jets following impingement, an initial crossflow is present that approaches the array through an upstream extension of the channel. The configurations considered are intended to model the impingement cooled midchord region of gas turbine airfoils in cases where an initial crossflow is also present. A major objective is determination of the effect of initial crossflow air temperature relative to jet array air temperature on impingement surface heat fluxes. Dimensionless adiabatic wall temperatures and Nusselt numbers resolved to one streamwise jet hole spacing were experimentally determined for ratios of initial crossflow rate to total jet flow rate ranging from zero to unity. These results are presented and discussed relative to the flow and geometric parameters.
Effect of Location in an Array on Heat Transfer to a Short Cylinder in Crossflow
Authors: Simoneau R. J. , VanFossen G. J.
Published: October 2009

An experiment was conducted to measure the heat transfer from a heated cylinder, three diameters in length, in crossflow in an array of identical circular cylinders. Both in-line and staggered array patterns were studied. The cylinders were spaced on a 2.67 × 2.67 pitch. The Reynolds number range, based on cylinder diameter and average unobstructed channel velocity, was from 5000 to 125,000. Turbulence intensity profiles were measured for each case at a point one-half space upstream of the row containing the heated cylinder. The basis of comparison for all the heat transfer data was the single row with the heated cylinder. For the in-line cases, the addition of a single row of cylinders upstream of the row containing the heated cylinder increased the heat transfer by an average of 50 percent above the base case. Adding up to five more rows caused no increase or decrease in heat transfer. On the other hand, adding rows in the staggered array cases resulted in average increases in heat transfer of 21, 64, 58, 46, and 46 percent for one to five upstream rows, respectively.
The Effect of a Wall Boundary Layer on Local Mass Transfer From a Cylinder in Crossflow
Authors: Goldstein R. J. , Karni J.
Published: October 2009

A naphthalene sublimation technique is used to determine the circumferential and longitudinal variations of mass transfer from a smooth circular cylinder in a crossflow of air. The effect of the three-dimensional secondary flows near the wall-attached ends of a cylinder is discussed. For a cylinder Reynolds number of 19000, local enhancement of the mass transfer over values in the center of the tunnel are observed up to a distance of 3.5 cylinder diameters from the tunnel wall. In a narrow span extending from the tunnel wall to about 0.066 cylinder diameters above it (about 0.75 of the mainstream boundary layer displacement thickness), increases of 90 to 700 percent over the two-dimensional flow mass transfer are measured on the front portion of the cylinder. Farther from the wall, local increases of up to 38 percent over the two-dimensional values are measured. In this region, increases of mass transfer in the rear portion of the cylinder, downstream of separation, are, in general, larger and cover a greater span than the increases in the front portion of the cylinder.
The Effect of Free-Stream Turbulence on Heat Transfer From a Rectangular Prism
Authors: McCormick D. C. , Test F. L. , Lessmann R. C.
Published: October 2009

This paper discussses the effect of free-stream turbulence on the constant temperature heat transfer rate from the surface of a two-dimensional rectangular body that is subject to a strongly favorable pressure gradient. Free-stream turbulence levels of 2 to 5 percent enhanced the heat transfer by 48 to 55 percent over predicted laminar values. Free-stream turbulence levels of 10 to 35 percent produced heat transfer results that behaved in some aspects as turbulent predictions, although considerably enhanced in magnitude over the predicted values.
Heat Transfer From Rods or Fins Which Extend Radially Outward From a Rotating Shaft
Authors: Sparrow E. M. , Kadle D. S.
Published: October 2009

The heat transfer characteristics of spokelike rods that extend outward from a rotating shaft have been determined experimentally. The experiments encompassed a number of geometrical parameters, including the length and diameter of the rods, the number of rods deployed around the circumference of the shaft, and the distance between the rods and the free end of the shaft. Also varied during the experiments was the rotational Reynolds number. Per-rod Nusselt numbers were evaluated from the experimental data. By incorporating the rod dimensions in the definition of the characteristic velocity that appears in the Reynolds number, a universal Nusselt–Reynolds–Prandtl correlation was obtained which is independent of the dimension ratios of the problem. It was also found that the Nusselt number results are independent of the number of rods in the circumferential array and are very weakly dependent on the distance from the rods to the free end of the shaft. The final correlation is conveyed by equations (18) and (19), with the Reynolds number defined by equations (7) and (10).
Mixed Convective Burning of a Fuel Surface With Arbitrary Inclination
Authors: Mao C.-P. , Fernandez-Pello A. C. , Pagni P. J.
Published: October 2009

An analysis is developed for mixed, forced, and free convective combustion on a flat fuel surface of arbitrary inclination that makes use of the laminar boundary layer approximation to describe the gas flow and of the flame-sheet approximation to describe the gas-phase reactions. A mixed-convection parameter (Rexn + Grxm)1/2n that properly scales the dependent and independent variable fields and a mixed convection ratio (Grxm/Rexn)1/2 that plays the role of the downstream local similarity coordinate are introduced in the nondimensionalization of the equations. It is shown that these two parameters, rather than the standard Reynolds, Rex, and Grashof, Grx, numbers are the optimum choice of governing nondimensional groups for this problem. The values of m and n are selected to obtain a similarity solution of the governing equations in the pure free convection limit for a vertical (m = 2, n = 4) and a horizontal (m = 2, n = 5) surface, which are the cases solved in this work. With this formulation, the solution of the problem provides for both cases smooth transition of all physical variables from one convective limit to the other. Results are obtained from numerical integration of the governing equations and from application of the local similarity approximation. It is shown that the range of validity of local similarity is extended beyond that obtained with alternate formulations and that the proper limits are approached. For use in practical applications, the results suggest that explicit expressions for the mass burning rate and for the fraction of unburnt pyrolyzate can be found that will suffice over the whole range of mixed-flow intensity.
Calculated Interaction of Sprays With Large-Scale Buoyant Flows
Authors: Alpert R. L.
Published: October 2009

Turbulent, recirculating gas flows resulting from interactions of water droplet sprays with large-scale buoyancy sources are difficult to predict without the use of numerical techniques, especially when spray-induced gas motion is considered. One such flow occurs when a negatively buoyant methane cloud, generated during LNG spills in a wind, is dispersed by a line water spray. Numerical predictions of the ratio of average methane vapor concentration downwind of the line spray to the upwind value correlate as a function of the ratio of methane momentum in the vapor cloud to water momentum in the spray. Warming of the cloud, which occurs when small drops in the spray freeze, leads to the production of positive cloud buoyancy and the possibility of cloud lift off from the ground. Numerical calculations have also been used to predict how a near-ceiling, downward-directed spray interacts with an opposed, buoyant jet issuing from floor level. Recirculating gas motion induced by droplet trajectories is again an important part of the problem. This opposed spray-plume arrangement, which is important in the process of fire suppression by automatic sprinklers, allows the effectiveness of spray cooling of the near-ceiling environment to be determined as a function of droplet injection characteristics. Because of the excessive amounts of computer time required for the solution of both turbulent, buoyant flow problems, it is concluded that much more efficient numerical techniques are needed.
Asymptotically Large Area Fires
Authors: Small R. D. , Larson D. A. , Brode H. L.
Published: October 2009

The fluid dynamics of large area fires is considered. The modeling of such fires using asymptotic plume theories, rotating plume theories, and hydrocode simulations is briefly reviewed, and a new model describing the strongly buoyant flow of the burning region and its transition to a weakly buoyant, free-convection column is presented. The new model simulates combustion processes by a volume heat addition, and allows large changes in density and temperature. Jump conditions applicable at the fire periphery are used to effect model problem closure, thus permitting calculation of the induced fire winds independent of a far-field analysis. Sample results show the turning and decay of a high-velocity inflow to form a nearly vertical flow, and illustrate how the generation of high-velocity fire winds is affected by the dimensions of the burning region, heat release, and the production of buoyancy and pressure gradients.
Experimental Investigation of Natural Convection Losses From Open Cavities
Authors: Hess C. F. , Henze R. H.
Published: October 2009

Experimental results for natural convection in a cavity are reported. Both constrained and unconstrained cavity geometries were studied. Detailed velocity profiles were obtained using Laser doppler velocimetry for Rayleigh numbers between 3 × 1010 and 2 × 1011, corresponding to a constant elevated wall temperature boundary condition. Characteristics of two-dimensional and three-dimensional flows obtained with dye flow visualization are discussed, including boundary layer transition to turbulence, flow patterns in the cavity, and flow outside of the cavity. Local Nusselt number is correlated with local Rayleigh number for constrained and unconstrained cavities.
Matrix Formalism for Complex Heat Exchangers
Authors: Pignotti A.
Published: October 2009

The matrix formalism introduced by Domingos for the calculation of the effectiveness of assemblies of heat exchangers is extended to the case of complex exchangers, for which the restriction of complete mixing for each fluid in the inlet and outlet streams is relaxed. Rectangular matrices are used to relate the inlet and outlet temperatures, and their properties are discussed. The method can be used to find explicit solutions for configurations of practical interest, which are analyzed as assemblies of simpler units, coupled together in various ways. The formalism is illustrated by a model calculation of a 1–2 shell-and-tube exchanger with a finite number of baffles, for TEMA E (normal flow) and TEMA J (divided flow) types of shells.
Design Considerations for Aerodynamically Quenching Gas Sampling Probes
Authors: Chiappetta L. , Colket M. B.
Published: October 2009

An aerodynamic quench is the most rapid method for quenching temperature and pressure-dependent chemical reactions. Attempts have been made to quench gas samples aerodynamically, but many of these attempts have been unsuccessful because of a lack of understanding of the internal aerodynamics of sampling probes. A one-dimensional model developed previously by the authors has been used for the design and analysis of aerodynamically quenching probes. This paper presents in detail the important aerodynamic and heat transfer equations used in the model, a description of the method of solution, and the results of a sensitivity study. These calculations demonstrate the limitations and important trade-offs in design and operating conditions of probes using an aerodynamic quench.
Convective Filmwise Condensation of Nonazeotropic Binary Mixtures in a Vertical Tube
Authors: Mochizuki S. , Yagi Y. , Tadano R. , Yang Wen-Jei
Published: October 2009

Complete condensation of binary mixtures of R11-R114 refrigerants is experimentally and theoretically studied. The test apparatus consists of two concentric tubes, with the vapor mixture flowing downward in the inner tube and the cooling water in the annular space in countercurrent direction. The composition of the binary-component mixtures is varied. An empirical equation is derived to correlate condensation heat transfer performance. A semitheoretical model is developed to predict laminar- and turbulent-film condensation on a vertical surface. Theory compares well with experiments. The vapor-coolant temperature difference remains practically constant throughout the entire flow passage, thus reducing the exergy loss to a minimum. The device is particularly attractive in extracting the available energy from geothermal and ocean thermal energy sources.
On the Steady-State Temperature Distribution in a Rotating Cylinder Subject to Heating and Cooling Over Its Surface
Authors: Yuen W. Y. D.
Published: October 2009

A series solution for the two-dimensional, steady-state temperature distribution in a rotating cylinder, subject to surface heating flux conditions that are at most linear functions of the surface temperature, is applied to strip rolling. An examination of the influence of heat input over the heating region (roll gap) on the peak cylinder (roll) temperature is made. A strip scale layer (which is present in hot rolling) is shown to have a significant effect on roll temperatures through its modification of the heat transfer between strip and roll. The present results indicate that significant errors will arise in estimating the peak roll temperature if insufficient terms are used or if the heat distribution is taken to be uniform in the heating region.
Laminar Heat Transfer in a Channel With Two Right-Angled Bends
Authors: Amano R. S.
Published: October 2009

A numerical study is reported on the flow and heat transfer in the channel with two right-angled bends. The modified hybrid scheme was employed to solve the steady full Navier-Stokes equations with the energy equation. The computations were performed for different step heights created in a long channel. The local heat transfer rate along the channel wall predicted by employing the present numerical model showed good agreement with the experimental data. The behavior of the flow and the heat transfer were investigated for the range of Reynolds number between 200 and 2000 and for step height ratios H/W = 1, 2, and 3. Finally, the correlation of the average Nusselt number in such channels as a function of Reynolds number is postulated.
Thermal Stability of Two Fluid Layers Separated by a Solid Interlayer of Finite Thickness and Thermal Conductivity
Authors: Catton I. , Lienhard J. H.
Published: October 2009

Stability limits of two horizontal fluid layers separated by an interlayer of finite thermal conductivity are determined. The upper cooled surface and the lower heated surface are taken to be perfectly conducting. The stability limits are found to depend on the ratio of fluid layer thicknesses, the ratio of interlayer thickness to total fluid layer thickness, and the ratio of fluid thermal conductivity to interlayer thermal conductivity. Results are given for a range of values of each of the governing parameters.
Coupled Radiative and Conductive Heat Transfer in a Two-Dimensional Rectangular Enclosure With Gray Participating Media Using Finite Elements
Authors: Razzaque M. M. , Howell J. R. , Klein D. E.
Published: October 2009

A numerical solution of the exact equations of coupled radiative/conductive heat transfer and temperature distribution inside a medium, and of the heat flux distribution at all the gray walls of a two-dimensional rectangular enclosure with the medium having uniform absorbing/emitting properties, using the finite element method, is presented. The medium can also have distributed energy sources. Comparison is made to the results of the P-3 approximation method.
Performance of One- and Two-Row Tube and Plate Fin Heat Exchangers
Authors: Rosman E. C. , Carajilescov P. , Saboya F. E. M.
Published: October 2009

Heat exchangers consisting of finned tubes are commonly employed in air conditioning systems, air heaters, radiators, etc. Local measurements of mass transfer coefficients on fins, obtained by Saboya and Sparrow, are very nonuniform. In the present work, an experimental apparatus was set up to measure overall heat transfer coefficients for two-row tube and plate fin heat exchangers. The obtained results, together with Shepherd’s results for one-row exchangers, are used to transform the local mass transfer coefficients into local heat transfer coefficients. A numerical two-dimensional heat transfer analysis has been performed in order to obtain the temperature distribution and fin efficiency. The influences of the Reynolds number and fin material are also analyzed.
Dimensioning of Spiral Heat Exchangers to Give Minimum Costs
Authors: Jarze˛bski A. B.
Published: October 2009

Simple expressions are presented for calculating approximate dimensions of spiral heat exchangers to give minimum annual cost of heating surface plus energy required to pump the fluids. The case of spiral–spiral flow is considered. Equations are derived for exchangers with and without distance holders between plate strips and for two sets of input data: (i) both volumetric fluid flow rates V1, V2 and all inlet and appropriate outlet temperatures are given; (ii) the flow rate of the process fluid V1 and the effectiveness e1 are imposed, while the flow rate of the working fluid V2 is an additional variable subject to optimization. For the latter case, appropriate optimum values of V2 can readily be found from the graphs provided.
Effect of Matrix Properties on the Performance of a Counterflow Rotary Dehumidifier
Authors: Jurinak J. J. , Mitchell J. W.
Published: October 2009

A finite difference model of a counterflow rotary dehumidifier is used to determine the effect of six matrix properties of dehumidifier performance. The matrix properties considered are the sorption isotherm shape, the maximum sorbent water content, the heat of sorption, the matrix thermal capacitance, matrix moisture diffusivity, and sorption isotherm hysteresis. The isotherm shapes and the sorption parameter values are selected to be representative of available insoluble desiccants. The results of the finite difference calculations show that the shape of the isotherm has a greater effect on dehumidification than the maximum water content. Large adsorption heat effects or matrix thermal capacitance has a detrimental impact on dehumidification. Hysteresis in the adsorption isotherm significantly impairs dehumidifier performance. The anlaysis shows that commercially available solid desiccants can result in nearly optimal dehumidifier performance.
Flow Around Baffles
Authors: Berner C. , Durst F. , McEligot D. M.
Published: October 2009

Flow visualization, manometry, and laser-Doppler anemometry have been applied to approximately two-dimensional water flow around segmental baffles with baffle spacing/depth equal to 0.4, window cuts from 10 to 50 percent, and Reynolds numbers ranging from 600–10,500 in order to simulate important aspects relating to shellside flow in shell-and-tube heat exchangers. The main features of the flow (which is eventually periodic in the streamwise direction), development lengths, pressure loss coefficients, and mean and rms velocity distributions are presented.
Entrainment Effects on Impingement Heat Transfer: Part I—Measurements of Heated Jet Velocity and Temperature Distributions and Recovery Temperatures on Target Surface
Authors: Hollworth B. R. , Wilson S. I.
Published: October 2009

Experiments were conducted to characterize a heated turbulent air jet discharged from a square-edged orifice having length to diameter equal to unity. Reported are measurements of mean axial velocity and total temperature in the jet as well as recovery temperatures on a flat surface normal to the jet axis. A simple theoretical model, which predicts distributions of recovery temperature consistent with the test data, is given.
Natural Convection Heat Transfer Through Inclined Longitudinal Slots
Authors: Symons J. G. , Peck M. K.
Published: October 2009

The convective rates of heat transfer through inclined longitudinal slots is studied for the case where heat is transferred from a lower heated isothermal surface, through the slots, to an upper cooled isothermal surface. Experimental data are given for longitudinal slots having aspect ratios from 6–12, slot heights of 25–60 mm, inclinations from horizontal to vertical, and Ra < 107. Data are also given for a transverse slot of aspect ratio 6, for inclinations from horizontal to vertical, and Ra < 107. It is shown that convective heat transfer rates are essentially independent of slot orientation for inclinations up to 15 deg from the horizontal, but longitudinal slots are more effective in suppressing natural convection than transverse slots with the same aspect ratio, for inclinations from 24 to 75 deg from the horizontal. The difference in heat transfer rates for longitudinal and transverse slots inclined between 24 and 75 deg from the horizontal are shown to be due to different convective flows occurring in each slot. The heat flow measurements are supported by convective flow visualization experiments which demonstrate the modes of convective flow within slots.
Boiling Heat Transfer From a Horizontal Tube in an Upward Flowing Two-Phase Crossflow
Authors: Wege M. E. , Jensen M. K.
Published: October 2009

An experimental investigation has been performed to determine the effects of a low-quality (≤ 20 percent) upward flowing mixture on the nucleate boiling on a single horizontal lube. An electrically heated, 12.7-mm-dia tube was centered in a plane wall vertical channel, the width of which resulted in channel width-to-tube diameter ratios (w/d) of 1.16 and 1.95. The working fluid was R-113. The two-phase heat transfer data showed a variety of effects. For a fixed w/d, pressure (P), and quality (x), the average heat transfer coefficients (h) increased with increasing mass velocity (G), but the effect of G decreased as the wall superheat (ΔT) increased. For a fixed w/d, G and x, h increased as the pressure increased except at low ΔT’s where the reverse was found. For fixed w/d, P and G, h increased with increasing quality with the effect appearing to be more pronounced at the lower pressure. At a fixed P, G and x, h was at larger w/d ratios at small ΔT’s, but as the wall superheat increased an inversion occured and h became smaller at the larger w/d ratio. The behavior exhibited in this experiment can be explained in terms of the velocity of the fluid flowing past the test section. The data were successfully predicted to within an average deviation of ±11.6 percent using a Chen-type correlation. Data from the literature also were predicted well.
Entropy Production and Thermoelectric Device Performance
Authors: Thacher E. F.
Published: October 2009

Integral forms for the thermal efficiency of thermoelectric generators, the coefficient of performance of thermoelectric refrigerators, and the coefficient of performance of thermoelectric heat pumps are derived. These forms are obtained for the isotropic material, nonsteady-state, nonadiabatic leg surface case. An example of the use of these forms is given.
A Linear Time-Domain Two-Fluid Model Analysis of Dynamic Instability in Boiling Flow Systems
Authors: Dykhuizen R. C. , Roy R. P. , Kalra S. P.
Published: October 2009

A linear analysis of dynamic instability in boiling flow systems has been carried out in the time domain. An unequal velocity, unequal temperature two-fluid model description of boiling flow is used. Instability threshold results of the density-wave oscillation type obtained have been compared with experimental data from Refrigerant-113 and water systems with satisfactory agreement.
Melting and Solidification of a Pure Metal on a Vertical Wall
Authors: Gau C. , Viskanta R.
Published: October 2009

This paper reports on the role of natural convection on solid–liquid interface motion and heat transfer during melting and solidification of a pure metal (gallium) on a vertical wall. The measurements of the position of the phase-change boundary as well as of temperature distributions and temperature fluctuations were used as a qualitative indication of the natural convection flow regimes and structure in the melt during phase transformation taking place in a rectangular test cell heated or cooled from one of the vertical walls. For melting, the measured melt volume and heat transfer coefficients are correlated in terms of relevant dimensionless parameters. For solidification, the measured volume of metal solidified on the wall is compared with predictions based on a one-dimensional model.
Correlation of Mixed Layer Growth in a Double-Diffusive, Salt-Stratified System Heated From Below
Authors: Bergman T. L. , Incropera F. P. , Viskanta R.
Published: October 2009

Although many mixed layer growth correlations have been developed for stratified solutions which are eroded by mechanically driven mixed layers, little has been done to determine their applicability to solutions for which erosion is thermally driven. In this study entrainment rates have been determined from measurements of mixed layer growth in salt-stratified solutions heated from below. Entrainment data have been obtained for Richardson numbers in the range 80 < Ri < 1000, and when normalized with respect to the mixed layer convective velocity, the data are well correlated in terms of Ri−1. The correlation also agrees with published data obtained at larger and smaller Richardson numbers for both thermally and salt-stratified solutions heated from below. Predictions based on use of the correlation in a mathematical model of mixed layer development are in excellent agreement with measured mixed layer heights and temperatures.
Turbulent Flow and Heat Transfer in Bends of Circular Cross Section: I—Heat Transfer Experiments
Authors: Sparrow E. M. , Chrysler G. M.
Published: October 2009

Experiments were performed to determine the local heat transfer characteristics of bends of circular cross section to which fluid was delivered either via a sharp-edged inlet or via a hydrodynamic development tube. The naphthalene sublimation technique, a mass transfer method, was used to facilitate the experiments. Bends subtending turning angles of 30, 60, and 90 deg were investigated, and the Reynolds number was varied between 5000 and 100,000. It was found that the local heat transfer coefficients at the outside of the bend were, for the most part, larger than those at the inside of the bend, but the deviations decreased as the Reynolds number increased. The streamwise distributions of the local transfer coefficient were markedly affected by the inlet condition; those for the sharp-edged inlet exhibited a universal shape, while the shapes of those for the tube-fed inlet depended both on the Reynolds number and on whether the distribution corresponded to the inside or the outside of the bend. In addition, the distributions for the case of the sharp-edged inlet exhibited higher local maxima and approached the fully developed regime more rapidly than did those for the tube-fed inlet. The heat transfer results were supplemented by flow visualization.
Turbulent Flow Friction and Heat Transfer Characteristics of Single- and Multistart Spirally Enhanced Tubes
Authors: Sethumadhavan R. , Raja Rao M.
Published: October 2009

Investigations have been carried out on heat transfer and frictional characteristics of five spirally corrugated tubes of one to four corrugation starts, having the same helix angle, but of varying geometrical aspect ratios, for the turbulent flow of water and 50 percent glycerol. The thermal performance of these tubes was found to be superior compared to a smooth tube. Friction factors and heat transfer coefficients in these rough tubes were analysed on the basis of momentum and heat transfer analogy, and the correlation obtained was tested with the present data and also the published results of previous investigators. Performance evaluation criteria were used for the quantitative demonstration of the benefits offered by these spirally corrugated tubes for heat exchanger applications.
Hydrodynamic Stability of Inverted Annular Flow in an Adiabatic Simulation
Authors: De Jarlais G. , Ishii M. , Linehan J.
Published: October 2009

Inverted annular flow was simulated adiabatically with turbulent water jets, issuing downward from large aspect ratio nozzles, enclosed in gas annuli. Velocities, diameters, and gas species were varied, and core jet length, shape, breakup mode, and dispersed core droplet sizes were recorded at approximately 750 data points. Inverted annular flow destabilization led to inverted slug flow at low relative velocities, and to dispersed droplet flow at high relative velocities. For both of these transitions from inverted annular flow, core breakup length correlations were developed by extending work on free liquid jets to include this coaxial, jet disintegration phenomenon. The results show length dependence upon DJ, ReJ, WeJ, α, and WeG,rel. Correlations for core shape, breakup mechanisms, and dispersed core droplet size were also developed, by extending the results of free jet stability, roll wave entrainment, and churn turbulent droplet stability studies.
Free Convection in a Two-Dimensional Porous Loop
Authors: Robillard L. , Nguyen T. H. , Vasseur P.
Published: October 2009

A study is made of the natural convection in an annular porous layer having an isothermal inner boundary and its outer boundary subjected to a thermal stratification arbitrarily oriented with respect to gravity. For such conditions, no symmetry can be expected for the flow and temperature fields with respect to the vertical diameter and the whole circular region must be considered. Two-dimensional steady-state solutions are sought by perturbation and numerical approaches. Results obtained indicate that the circulating flow around the annulus attains its maximum strength when the stratification is horizontal (heating from the side). This circulating flow is responsible for an important heat exchange between the porous layer and its external surroundings. The flow field is also characterized by the presence of two convective cells near the inner boundary, giving rise to flow reversal on this surface. When the maximum temperature on the outer boundary is at the bottom of the cavity, the convective motion becomes potentially unstable; for a Rayleigh number below 80, there exists a steady-state solution symmetrical with respect to both vertical and horizontal axes; for a Rayleigh number above 80, an unsteady periodic situation develops with the circulating flow alternating its direction around the annulus.
Laminar Natural Convection in Shallow Open Cavities
Authors: Chan Y. L. , Tien C. L.
Published: October 2009

Experimental investigation on natural convection in a two-dimensional open cavity was performed using laser-Doppler velocimetry. The cavity is rectangular with one vertical heated wall facing a vertical opening, and with the two horizontal walls insulated. Studies for an open shallow cavity with an aspect ratio of 0.143 and Rayleigh numbers ranging from 106 to 107 under the steady laminar conditions were carried out using water as the working fluid. Heat transfer was found to approach that for a vertical heated flat plate. The measured velocity and temperature profiles illustrate the effect of the open boundary which can be viewed as consisting of two parts: the outgoing hot fluid flow exhibiting strong characteristics of the cavity condition, and the incoming flow influenced by outside conditions.
Heat Transfer Enhancement in Natural Convection Enclosure Flow
Authors: Anderson R. , Bohn M.
Published: October 2009

The results of an experimental investigation that examines the effects of one type of surface roughness upon heat transfer in a water-filled cubical enclosure are reported. The experiments covered the range from the beginning of transition to the point where the flow over 60 percent of the length of the heated side had undergone transition. Tests were conducted using both isothermal and constant flux boundary conditions. The largest increase in overall Nusselt number was 15 percent at Ra = 3.3 × 1010 on the isothermal heated plate. Increases of the local Nusselt number on the isothermal heated plate were as large as 40 percent. The roughness elements used in the present study were found to be ineffective on the upper portion of the heated plate where fluid detrains from the vertical boundary layer.
Laminar Heat Transfer and Pressure Drop in a Rectangular Duct Rotating About a Parallel Axis
Authors: Levy E. , Neti S. , Brown G. , Bayat F. , Kadambi V.
Published: October 2009

Experimental results were obtained on pressure drop and heat transfer in a laminar flow of air in a rotating heated rectangular duct. The duct had a 2 to 1 aspect ratio, and was parallel to, but displaced from, the rotor axis. Data presented on Nusselt number in the inlet region and dimensionless pressure drop in the inlet and fully developed regions were found to be in close agreement with numerical finite difference solutions to the laminar flow equations. Laminar heat transfer and pressure drop are strongly affected by rotation, beginning to increase for values of Grashof number in excess of 103. For a Grashof number of 106, the Nusselt number is approximately twice the value of that in a flow with zero Grashof number. The effect of rotation on dimensionless pressure drop is smaller, with increases of the order of 35 percent occurring from Gr = 0 to 106.
Local Heat Transfer From a Rotating Disk in an Impinging Round Jet
Authors: Popiel C. O. , Boguslawski L.
Published: October 2009

The results of an experimental investigation of local convective heat transfer from the surface of a rotating disk in an impinging free round air jet, issuing from a long tube, are reported. Using a transient heat transfer method applied to the ring-shaped h-calorimeter (as a single lumped capacitance element) measurements of convective heat transfer rates were made for five impingement radius (fixed) to tube diameter ratios for a range of rotational and jet Reynolds numbers. In the pure impingement-dominated regime, where the rotation of the disk does not show an effect on heat transfer, the velocity ratio is ur/uj ≤ (1 − 2 × 10−4 Re2/3) (1 − 0.18 r/d), where ur = tangential velocity of the disk at the jet impingement radius r, uj = average exit velocity of jet, and d = jet tube diameter. In this regime, the local heat transfer on the rotating disk can be strongly enhanced by jet impingement. For ur/uj ⪞ 5, the effect of the jet impingement on heat transfer can be neglected. The discussion of the heat transfer results has been supported by smoke flow visualization.
A Transient Heat Exchanger Evaluation Test for Arbitrary Fluid Inlet Temperature Variation and Longitudinal Core Conduction
Authors: Mullisen R. S. , Loehrke R. I.
Published: October 2009

An improved version of the transient technique is described which utilizes a finite-difference model of the heat exchanger for the evaluation of an average hem transfer coefficient. The model, which can accommodate arbitrary inlet fluid temperature variation as well as longitudinal conduction in the heat exchanger core, is well suited for a computer-based data reduction procedure. The finite-difference model is validated by comparison with the predictions of exact solutions for a step change in inlet temperature. Actual tests on a core of known performance indicate that the overall accuracy of the technique can be within ± 2 percent.
Effects of Ambient Pressure on the Instability of a Liquid Boiling Explosively at the Superheat Limit
Authors: Frost D. , Sturtevant B.
Published: October 2009

The effect of ambient pressure on the intrinsic instability of rapid vaporization in single droplets boiling explosively at the limit of superheat has been studied experimentally and theoretically. The instability that distorts the evaporating interface and substantially enhances the mass flux at atmospheric pressure is suppressed at high pressure. The radiated pressure field is two orders of magnitude smaller from stabilized bubbles than from unstable. At intermediate pressures bubble growth occurs in two stages, first stable, then unstable. The Landau–Darrieus instability theory predicts absolute stability at atmospheric pressure for a spherical bubble, whereas the theory for planar interfaces yields results in general agreement with observation. The sensitivity of the instability to temperature suggests that small temperature nonuniformities may be responsible for quantitative departures of the behavior from predictions.
Boiling Heat Transfer in a Narrow Eccentric Annulus: Part III—A Model of Dry Patch Extent and Temperature Distribution
Authors: Johnston B. S. , Bankoff S. G.
Published: October 2009

A previous paper, Johnston et al. (1983a), has described the phenomenon of dryout under a condition of line contact in tube support plate crevices. This paper presents the development of a model for the tube wall temperature distribution. The major effort is given to predicting the extent of the dry patch. The results show a satisfactory comparison with experimental data.
Effect of Tip-to-Shroud Clearance on Turbulent Heat Transfer From a Shrouded, Longitudinal Fin Array
Authors: Sparrow E. M. , Kadle D. S.
Published: October 2009

Experiments were performed to determine the response of the heat transfer from a longitudinal fin array to the presence of clearance between the fin tips and an adjacent shroud. During the course of the experiments, the clearance was varied parametrically, starting with the no-clearance case; parametric variations of the fin height and of the rate of fluid flow through the array were also carried out. Air was the working fluid, and the flow was turbulent. The fully developed heat transfer coefficients corresponding to the presence and to the absence of clearance were compared under the condition of equal air flowrate, and substantial clearance-related reductions were found to exist. For clearances equal to 10, 20, and 30 percent of the fin height, the heat transfer coefficients were 85, 74, and 64 percent of those for the no-clearance case. The ratio of the with-clearance and no-clearance heat transfer coefficients was a function only of the clearance-to-fin-height ratio, independent of the air flowrate, the fin height, and the fin efficiency model used to evaluate the heat transfer coefficients. The presence of clearance slowed the rate of thermal development in the entrance region.
Heat Transfer From Two Elliptic Cylinders in Tandem Arrangement
Authors: Ota T. , Nishiyama H. , Kominami J. , Sato K.
Published: October 2009

An experimental investigation has been conducted to clarify heat transfer characteristics of two elliptic cylinders having an axis ratio 1:2. They were placed in tandem arrangements and their angles of attack to the upstream uniform flow were identical. The testing fluid was air and the Reynolds number based on the major axis length c ranged from about 15,000 to 80,000. The angle of attack was varied from 0 to 90 deg at 30 deg intervals and the nondimensional cylinder spacing l/c from 1.25 to 4.0, where l denotes the streamwise distance between the cylinder centers. It has been found that the heat transfer features vary drastically with the angle of attack and also with the cylinder spacing.