Showing papers in "Journal of Heat Transfer-transactions of The Asme in 1995"
TL;DR: In this article, a universal constitutive equation between the heat flux vector and the temperature gradient is proposed to cover the fundamental behaviors of diffusion, wave, phonon-electron interactions, and pure phonon scattering.
Abstract: A universal constitutive equation between the heat flux vector and the temperature gradient is proposed to cover the fundamental behaviors of diffusion (macroscopic in both space and time), wave (macroscopic in space but microscopic in time), phonon-electron interactions (microscopic in both space and time), and pure phonon scattering The model is generalized from the dual-phase-lag concept accounting for the laging behavior in the high-rate response While the phase lag of the heat flux captures the small-scale response in time, the phase lag of the temperature gradient captures the small-scale response in space The universal form of the energy equation facilitates identifications of the physical parameters governing the transition from one mechanism (such as diffusion or wave) to another (the phonon-electron interaction)
1,435 citations
TL;DR: In this article, the authors present experimental evidence of the wave nature of heat propagation in processed bologna meat and demonstrate that the hyperbolic heat conduction model is an accurate representation, on a macroscopic level, of the Heat conduction process in such biological material.
Abstract: The objective of this paper is to present experimental evidence of the wave nature of heat propagation in processed meat and to demonstrate that the hyperbolic heat conduction model is an accurate representation, on a macroscopic level, of the heat conduction process in such biological material. The value of the characteristic thermal time of a specific material, processed bologna meat, is determined experimentally. As a part of the work different thermophysical properties are also measured. The measured temperature distributions in the samples are compared with the Fourier results and significant deviation between the two is observed, especially during the initial stages of the transient conduction process. The measured values are found to match the theoretical non-Fourier hyperbolic predictions very well. The superposition of waves occurring inside the meat sample due to the hyperbolic nature of heat conduction is also proved experimentally. 14 refs., 7 figs., 2 tabs.
581 citations
TL;DR: In this article, the local heat transfer from a small heat source to a normally impinging, axisymmetric, and submerged liquid jet, in confined and unconfined configurations, was experimentally investigated.
Abstract: The local heat transfer from a small heat source to a normally impinging, axisymmetric, and submerged liquid jet, in confined and unconfined configurations, was experimentally investigated. A single jet of FC-77 issuing from a round nozzle impinged onto a square foil heater, which dissipated a constant heat flux. The nozzle and the heat source were both mounted in large round plates to ensure axisymmetric radial outflow of the spent fluid. The local surface temperature of the heat source was measured at different radial locations (r/d) from the center of the jet in fine increments. Results for the local heat transfer coefficient distribution at the heat source are presented as functions of nozzle diameter (0.79 ≤ d ≤ 6.35 mm), Reynolds number (4000 to 23,000), and nozzle-to-heat source spacing (1 ≤ Z/d ≤ 14). Secondary peaks in the local heat transfer observed at r/d 2 were more pronounced at the smaller (confined) spacings and larger nozzle diameters for a given Reynolds number, and shifted radially outward from the stagnation point as the spacing increased. The secondary-peak magnitude increased with Reynolds number, and was higher than the stagnation value in some instances.
245 citations
TL;DR: In this paper, a spectral-line weighted-sum-of-gray-gases (SLW) model was extended to nonisothermal, nonhomogeneous media and a spatial dependence of the gray gas absorption cross sections on local temperature, pressure, and mole fraction was introduced through the absorption-line blackbody distribution function.
Abstract: An approach is developed to extend the previously developed spectral-line weighted-sum-of-gray-gases (SLW) model to nonisothermal, nonhomogeneous media. The distinguishing feature of the SLW gas property model is that it has been developed for use in arbitrary solution methods of the radiative transfer equation (RTE). A spatial dependence of the gray gas absorption cross sections on local temperature, pressure, and mole fraction is introduced through the absorption-line blackbody distribution function. Incorporating this spatial dependence results in significant improvement over the use of spatially uniform gray gas absorption cross sections in comparisons with line-by-line benchmarks. 16 refs., 7 figs.
219 citations
TL;DR: In this article, algebraic expressions for the thermal conductivity of two-dimensional and three-dimensional spatially periodic media are obtained based on a lumped-parameter method.
Abstract: Based on a lumped-parameter method, algebraic expressions for the stagnant thermal conductivity of some two-dimensional and three-dimensional spatially periodic media are obtained. The geometries under consideration include arrays of touching and non-touching in-line square and circular cylinders (two-dimensional), as well as touching and nontouching in-line cubes (three-dimensional). A comparison of results based on these algebraic expressions with existing numerical solutions and experimental data shows that they are in excellent agreement.
169 citations
TL;DR: In this paper, three periodic structures are used to derive the apparent conductivity of a porous medium and a specific application is made to aerogel, using results for the porosity and specific surface area obtained from nitrogen adsorption-desorption measurement.
Abstract: In this paper, three periodic structures are used to derive the apparent conductivity of a porous medium and a specific application is made to aerogel. The characteristics of the structure are determined using results for the porosity and specific surface area obtained from nitrogen adsorption-desorption measurement. 10 refs., 2 figs., 2 tabs.
154 citations
150 citations
TL;DR: In this article, a spectral line-based weighted-sum-of-gray-gases (SLW) model was introduced for expressing total gas emissivities and in the context of the zone method.
Abstract: The weighted-sum-of-gray-gases model, first introduced by Hottel and Sarofim for expressing total gas emissivities and in the context of the zone method, has recently been extended to the general form of the radiative transfer equation (RTE). The fundamental radiative property of the model is the locally defined absorption coefficient, which permits the use of arbitrary solution methods of the RTE. Denison and Webb developed a spectral line-based weighted-sum-of-gray-gases (SLW) model by constructing a histogram representation of the high-resolution spectra of H{sub 2}O. Subsequently, a novel absorption-line black body distribution function was developed that easily allows the black body weights a{sub j} of any desired number of gray gases to be determined by simple differencing rather than accessing detailed spectral line information. The distribution function also provides the means of incorporating a spatial dependence of the gray gas absorption cross sections on temperature, pressure, and species mole in nonisothermal, nonhomogeneous problems. 15 refs., 3 figs.
131 citations
TL;DR: In this paper, a modified hyperbolic type heat conduction equation, which is consistent with the second law of thermodynamics, is investigated in the context of nonequilibrium rational thermodynamics.
Abstract: For situations in which the speed of thermal propagation cannot be considered infinite, a hyperbolic heat conduction equation is typically used to analyze the heat transfer. The conventional hyperbolic heat conduction equation is not consistent with the second law of thermodynamics, in the context of nonequilibrium rational thermodynamics. A modified hyperbolic type heat conduction equation, which is consistent with the second law of thermodynamics, is investigated in this paper. To solve this equation, we introduce a numerical scheme from the field of computational compressible flow. This scheme uses the characteristic properties of a hyperbolic equation and has no oscillation. By solving a model problem, we show that the conventional hyperbolic heat conduction equation can give physically wrong solutions (temperature less than absolute zero) under some conditions. The modified equation does not display these erroneous results. However, the difference between results of these two models is negligible except under extreme conditions.
128 citations
TL;DR: In this article, the shape of a two-dimensional vapor stem formed during saturated nucleate boiling on a heated surface is modeled and analyzed numerically using the extended Clausius-Clapeyron equation.
Abstract: The transport processes occurring in an evaporating two-dimensional vapor stem formed during saturated nucleate boiling on a heated surface are modeled and analyzed numerically. From the heater surface heat is conducted into the liquid macro/microthermal layer surrounding the vapor stems and is utilized in evaporation at the stationary liquid-vapor interface. A balance between forces due to curvature of the interface, disjoining pressure, hydrostatic head, and liquid drag determines the shape of the interface. The kinetic theory and the extended Clausius-Clapeyron equation are used to calculate the evaporative heat flux across the liquid-vapor interface. The vapor stem shape calculated by solving a fourth-order nonlinear ordinary differential equation resembles a cup with a flat bottom. For a given wall superheat, several metastable states of the vapor stem between a minimum and maximum diameter are found to be possible. The effect of wall superheat on the shape of the vapor stem is parametrically analyzed and compared with limited data reported in the literature.
128 citations
TL;DR: In this paper, a benign method of generating a surface microstructure that provides pool boiling heat transfer enhancement is introduced, which results in up to an 85 percent decrease in incipient superheat, a 70 to 80 percent reduction in nucleate boiling superheats, and a ∼109 percent increase in critical heat flux (CHF = 30 W/cm 2 ), beyond that of the nonpainted reference surface.
Abstract: A benign method of generating a surface microstructure that provides pool boiling heat transfer enhancement is introduced. Pool boiling heat transfer results from an enhanced, horizontally oriented, rectangular surface immersed in saturated FC-72, indicate up to an 85 percent decrease in incipient superheat, a 70 to 80 percent reduction in nucleate boiling superheats, and a ∼109 percent increase in the critical heat flux ( CHF = 30 W/cm 2 ), beyond that of the nonpainted reference surface. For higher heat flux conditions (19 to 30 W/cm 2 ), localized dryout results in increased wall superheats (8 to 48°C). The enhanced surface heat transfer coefficients are four times higher than those from the reference surface and similar to those from the Union Carbide High Flux surface. Photographs that identify differences in bubble size and departure characteristics between the painted and reference surfaces are presented.
TL;DR: In this article, the effect of a transverse magnetic field on buoyancy-driven convection in a shallow rectangular cavity is numerically investigated (horizontal Bridgman configuration), where the enclosure is insulated on top and bottom walls while it is heated from one side and cooled from the other.
Abstract: The effect of a transverse magnetic field on buoyancy-driven convection in a shallow rectangular cavity is numerically investigated (horizontal Bridgman configuration). The enclosure is insulated on the top and bottom walls while it is heated from one side and cooled from the other. Both cases of a cavity with all rigid boundaries and a cavity with a free upper surface are considered. The study covers the range of the Rayleigh number, Ra, from 10 2 to 10 5 , the Hartmann number, Ha, from 0 to 10 2 , the Prandtl number, Pr, from 0.005 to 1 and aspect ratio of the cavity, A, from 1 to 6. Comparison is made with an existing analytical solution (Garandet et al.), based on a parallel flow approximation, and its range of validity is delineated. Results are presented for the velocity and temperature profiles and heat transfer in terms of Ha number. At high Hartmann numbers, both analytical and numerical analyses reveal that the velocity gradient in the core is constant outside the two Hartmann layers at the vicinity of the walls normal to the magnetic field.
TL;DR: In this article, a detailed mathematical model was developed that describes heat transfer through this liquid films in the evaporator of heat pipes with capillary grooves, which accounts for the effects of interfacial thermal resistance, disjoining pressure, and surface roughness for a given meniscus contact angle.
Abstract: A detailed mathematical model is developed that describes heat transfer through this liquid films in the evaporator of heat pipes with capillary grooves. The model accounts for the effects of interfacial thermal resistance, disjoining pressure, and surface roughness for a given meniscus contact angle. The free surface temperature of the liquid film is determined using the extended Kelvin equation and the expression for interfacial resistance given by the kinetic theory. The numerical results obtained are compared to existing experimental data. The importance of the surface roughness and interfacial thermal resistance in predicting the heat transfer coefficient in the grooved evaporator is demonstrated. 17 refs., 5 figs., 2 tabs.
TL;DR: In this article, a study of non-Darcian forced convection in an asymmetric heating sintered porous channel is carried out to investigate the feasibility of using this channel as a heat sink for high-performance forced air cooling in microelectronics.
Abstract: A study of non-Darcian forced convection in an asymmetric heating sintered porous channel is carried out to investigate the feasibility of using this channel as a heat sink for high-performance forced air cooling in microelectronics. A volume-averaging technique is applied to obtain the macroscopic equations with the non-Darcian effects of no-slip boundary, flow inertia, and thermal dispersion. Local non-thermal-equilibrium is assumed between the solid and the fluid phases. The analysis reveals that the particle Reynolds number significantly affects the solid-to-fluid heat transfer coefficients. A wall function is introduced to model the transverse thermal dispersion process for the wall effect on the lateral mixing of fluid. The local heat transfer coefficient at the inlet is modeled by a modified impinging jet result, and the noninsulated thermal condition is considered at exit. The numerical results are found to be in good agreement with the experimental results in the ranges of 32 ≤ Red ≤ 428 and q = 0.8 ~ 3.2 W/cm2 for Pr = 0.71.
TL;DR: In this article, the authors consider a system consisting of two parallel plates at different temperatures and place a solid network, e.g., a matrix or lattice, in the system, which partitions the space into very fine open pores.
Abstract: Consider a system consisting of two parallel plates at different temperatures. To reduce the heat transfer, one can place a solid network; e.g., a matrix or lattice, in the system. The matrix Partitions the space into very fine open pores. As a result, the motion of the gas molecules is restrict d and the heat transfer is reduced. Silica aerogel is a porous medium, which has pore sizes of about 10 nm, which is smaller than the mean free path of gas molecules at atmospheric pressure (about 80 nm) in a free space. Hence, even at atmospheric pressure the matrix restricts the motion of the gas molecules; the effect is more pronounced at lower pressures. 5 refs., 2 figs.
TL;DR: In this paper, an approximate theory for the optical properties of soot is described, emphasizing the small-angle (Guinier) regime, based on the Rayleigh-Debye-Gans scattering approximation while treating soot as mass-fractal aggregates of spherical primary particles.
Abstract: A computational evaluation of an approximate theory for the optical properties of soot is described, emphasizing the small-angle (Guinier) regime. The approximate theory (denote RDG-FA theory) is based on the Rayleigh-Debye-Gans scattering approximation while treating soot as mass-fractal aggregates of spherical primary particles that have constant diameters and refractive indices. The approximate theory was evaluated by more exact predictions from the solution of the volume integral equation formulation of the governing equations, using the method of moments, and based on the ICP algorithms of Iskander et al. (1989). Numerical simulations were used to constructs statistically significant populations of soot aggregates having appropriate fractal properties and prescribed numbers of primary particles per aggregate. Optical properties considered included absorption, differential scattering, and total scattering cross sections for conditions typical of soot within flame environments at wavelengths in the visible and the infrared. Specific ranges of aggregate properties were as follows: primary particle optical size parameters up to 0.4, numbers of primary particles per aggregate up to 512, mean fractal dimensions of 1.75, mean fractral prefactors of 8.0, and refractive indices typical of soot. Over the range of the evaluation, ICP and RDG-FA predictions generally agreed within numerical uncertainties (ca. 10 percent) within the Guinier regime, complementing similar performance of RDG-FA theory in the power-law regime based on recent experiments. Thus, the use of approximate RDG-FA theory to estimate the optical properties of soot appears to be acceptable-particularly in view of the significant uncertainties about soot optical properties due to current uncertainties about soot refractive indices
TL;DR: In this article, high voltage was applied to a needle suspended above a heated plate, and heat transfer coefficients were computed by measuring the plate surface temperature distribution with an infrared camera, an enhancement of more than 25 : 1 over natural convection.
Abstract: Corona wind enhancement of free convection was investigated with the needle-plate geometry in air. High voltage was applied to a needle suspended above a heated plate, and heat transfer coefficients were computed by measuring the plate surface temperature distribution with an infrared camera. Local heat transfer coefficients greater than 65 W/m 2 K were measured, an enhancement of more than 25 :1 over natural convection. The enhancement extended over a significant area, often reaching beyond the 30 cm measurement radius. At high power levels, Joule heating significantly reduced the effective impingement point heat transfer coefficient. The corona wind was found to be more efficient with positive potential than with negative. The heat transfer efficiency was optimized with respect to electrode height and applied voltage. The needle-plate heat transfer effectiveness improved rapidly with increasing height, and became relatively insensitive to height above a threshold value of about 5 cm.
TL;DR: In this paper, a series of pool boiling experiments have been conducted under reduced gravity condition (the order of 10 -2 times the terrestrial gravity) available in an aircraft taking parabolic flight.
Abstract: A series of pool boiling experiments have been conducted under reduced gravity condition (the order of 10 -2 times the terrestrial gravity) available in an aircraft taking parabolic flight. A transparent resistant heater, a transparent indium oxide film plated on a glass plate, was employed so that the vapor/liquid behavior interacting with the heater surface could be observed from the rear side of the heater simultaneously with the side view of vapor bubbles above the heater surface. The experiments were performed for three different fluids-n-pentane, CFC-113, and water-under subcooled conditions. The critical heat fluxes for both n-pentane and CFC-113 under the reduced gravity were lowered to about 40 percent of the corresponding terrestrial values. Although the heat transfer characteristics in a low heat flux nucleate boiling regime for both n-pentane and CFC-113 showed no more than a slight change with the reduction in gravity, a significant heat transfer deterioration was noted with water in the reduced gravity boiling. The observation from the rear side of the heater suggested that this particular difference in the gravity dependency of heat transfer was ascribed to a considerable difference, between the organic fluids and water, in the behavior of attachment to the heater surface of the bubbles grown up, while the behavior of attachment must depend on the surface tension of each fluid and the wettability of the heater surface with the fluid.
TL;DR: In this paper, the authors measured local heat transfer under arrays of free-surface liquid jets with a two-dimensional infrared radiometer and found that the stagnation Nusselt number under the central jet is independent of array configuration and jet-to-jet spacing.
Abstract: In this study, local heat transfer data under arrays of free-surface liquid jets are measured with a two-dimensional infrared radiometer. Experimental measurements were made for three nozzle diameters using a seven-jet staggered and a nine-jet inline geometric array configuration. Nozzle-to-plate spacings of two and five nozzle diameters were investigated for four jet center-to-center spacings ranging from two to eight diameters in the jet Reynolds number range of 5000 to 20,000. Results show that the stagnation Nusselt number under the central jet is independent of array configuration and jet-to-jet spacing. The different inter jet flow interaction, as represented by different jet array configurations (the in-line array and the staggered array with different nozzle-to-nozzle spacings), shows negligible influence on local heat transfer under the central jet. Differences in the heat transfer characteristics for the two nozzle-to-plate spacings investigated were the result of an observed transition from confined submerged central jet flow to free-surface jet flow as the nozzle-to-plate spacing was increased. Secondary maxima in the Nusselt number were observed between the adjacent jets, being a direct consequence of the radial flow interaction between jets. A correlation for average heat transfer is presented.
TL;DR: In this paper, the authors investigated the effect of velocity gradient on stagnation-region heat transfer augmentation by free-stream turbulence and developed a prediction tool for stagnation heat transfer in the presence of free stream turbulence.
Abstract: The purpose of the present work was threefold: (1) to determine if a free-stream turbulence length scale existed that would cause the greatest augmentation in stagnation-region heat transfer over laminar levels; (2) to investigate the effect of velocity gradient on stagnation-region heat transfer augmentation by free-stream turbulence; and (3) to develop a prediction tool for stagnation heat transfer in the presence of free-stream turbulence. Heat transfer was measured in the stagnation region of four models with elliptical leading edges that had ratios of major to minor axes of 1:1, 1.5:1, 2.25:1, and 3:1. Five turbulence-generating grids were fabricated; four were square mesh, biplane grids made from square bars. The fifth grid was an array of fine parallel wires that were perpendicular to the model spanwise direction. Heat transfer data were taken at Reynolds numbers ranging from 37 000 to 228 000. Turbulence intensities were in the range of 1.1 to 15.9% while the ratio of integral length scale to leading-edge diameter ranged from 0.05 to 0.30. Stagnation-point velocity gradient was varied by nearly 50%. Stagnation-region heat transfer augmentation was found to increase with decreasing length scale but no optimum length scale was found. Heat transfer augmentation due to turbulence was found to be unaffected by the velocity gradient near the leading edge. A correlation was developed that fit heat transfer data for the square-bar grids to within +/- 4%.
TL;DR: In this paper, a detailed mathematical model of low-temperature axially grooved heat pipes (AGHP) is developed in which fluid circulation is considered along with the heat and mass transfer processes during evaporation and condensation.
Abstract: A detailed mathematical model of low-temperature axially grooved heat pipes (AGHP) is developed in which the fluid circulation is considered along with the heat and mass transfer processes during evaporation and condensation. The results obtained are compared to existing experimental data. Both capillary and boiling limitations are found to be important for the flat miniature copper-water heat pipe, which is capable of withstanding heat fluxes on the order of 40 W/cm 2 applied to the evaporator wall in the vertical position. The influence of the geometry of the grooved surface on the maximum heat transfer capacity of the miniature AGHP is demonstrated.
TL;DR: In this article, a microthermocouple probe was developed capable of detecting transient surface temperatures with a response time better than 1 ms. The transient temperature data were utilized to determine the time-varying heat flux under liquid contacts.
Abstract: Several boiling regimes are characterized by intermittent contacts of vapor and liquid at the superheated wall surface. A microthermocouple probe was developed capable of detecting transient surface temperatures with a response time better than 1 ms. The transient temperature data were utilized to determine the time-varying heat flux under liquid contacts. The instantaneous surface heat flux was found to vary by orders of magnitude during the milliseconds of liquid residence at the hot surface. The average heat flux during liquid contact was found to range from 10{sup 5} to 10{sup 7} W/m{sup 2} for water at atmospheric pressure, as wall superheat was varied from 50 to 450{degrees}C. 12 refs., 8 figs.
TL;DR: In this paper, the authors proposed two methods to optimize sensor locations: one to account for signal error, the other to consider interacting parameters, based upon variants of the normalized Fisher information matrix.
Abstract: Accurate modeling of thermal systems depends upon the determination of the material properties and the surface heat transfer coefficients. These parameters are frequently estimated from temperatures measured within the system or on the surface or from measured surface heat fluxes. Because of sensor errors or lack of sensitivity, the measurements may lead to erroneous estimates of the parameters. These errors can be ameliorated if the sensors are placed at points of maximum sensitivity. This paper describes two methods to optimize sensor locations : one to account for signal error, the other to consider interacting parameters. The methods are based upon variants of the normalized Fisher information matrix and are shown to be equivalent in some cases, but to predict differing sensor locations under other conditions, usually transient.
TL;DR: In this article, the authors considered the effect of magnetic induction on convection during the solidification of a Pb -19 wt pct Sn alloy and found that turbulence decrease the propensity for channel development and macrosegregation by enhancing mixing and reducing the effective Lewis number from 8600 to near unity.
Abstract: Electromagnetic induction is considered as a means of altering convection during the solidification of a Pb - 19 wt pct Sn alloy. Application of a time-varying magnet field induces Lorentz forces, which augment thermal buoyancy forces in the melt and oppose solutal buoyancy forces in the mushy zone. A continuum model for binary solid-liquid phase change is extended to account for turbulence, and laminar are turbulent flow predictions are contrasted. Results indicate that turbulence decrease the propensity for channel development and macrosegregation by enhancing mixing and reducing the effective Lewis number from 8600 to near unity. 17 refs., 8 figs.
TL;DR: A reaction scheme including detailed rate expressions for O and N atom recombination on the surface of re-entry vehicles is established, consisting of elementary reaction steps, and a quantitative agreement is achieved between recombination coefficients resulting from the numerical computations and those calculated from experiments.
Abstract: In connection with recombination coefficients derived from experimental data described in the literature, a reaction scheme including detailed rate expressions for O and N atom recombination on the surface of re-entry vehicles is established, consisting of elementary reaction steps. To validate the reaction mechanism derived, surface chemistry and fluid mechanical processes are coupled assuming a one-dimensional stagnation flow field. A quantitative agreement is achieved between recombination coefficients resulting from the numerical computations and those calculated from experiments. The temperature dependence of the recombination coefficient is explained by elementary reaction steps. Furthermore, the reaction scheme established is implemented in a two-dimensional Navier-Stokes code computing the re-entry flow around a simple geometry to show the importance ofa detailed modeling of surface reactions.
TL;DR: In this article, the effects on the boiling curve of having air dissolved in the fluid are documented, showing that fluid in the vicinity of the heating element is apparently liberated of dissolved gas during boiling.
Abstract: Experimental results on pool boiling heat transfer from a horizontal cylinder in an electronic cooling fluid (FC-72) are presented. The effects on the boiling curve of having air dissolved in the fluid are documented, showing that fluid in the vicinity of the heating element is apparently liberated of dissolved gas during boiling. Dissolved gas was found to influence boiling incipience only with high gas concentrations (>0.005 moles/mole). For low-to-moderate concentrations, a larger superheat is required to initiate boiling and a hysteresis is observed between boiling curves taken with increasing and decreasing heat flux steps. Boiling, a very effective mode of heat transfer, is attractive for electronics cooling. The present experiment provides further documentation of the role of dissolved gas on the incipience process and shows similarities with subcooled boiling of a gas-free fluid. 20 refs., 8 figs., 1 tab.
TL;DR: In this paper, bubble condensation in sub-cooled water-steam flow in a vertical annulus at low flow rate and low pressure is investigated experimentally, and a high-speed video system (up to 1000 frame/s) was used to visualize two orthogonal views of the flow simultaneously.
Abstract: In two-fluid modeling, accurate prediction of the interfacial transport of mass, momentum, and energy is required. Experiments were carried out to obtain a data base for the development of interfacial transport models, or correlations, for subcooled water-steam bubbly flow in vertical conduits. The experimental data of interest included the interfacial area concentration, interfacial condensation heat transfer, and bubble relative velocity. In the present investigation, bubble condensation in subcooled water-steam flow in a vertical annulus at low flow rate and low pressure is investigated experimentally. A high-speed video system (up to 1000 frame/s) was used to visualize two orthogonal views of the flow simultaneously. A digital image processing technique was used to track and measure the velocity and size of the collapsing bubbles. The axial void fraction distribution was also measured by a single beam gamma densitometer.
TL;DR: In this paper, the effects of clearance ratio (C/H) and Reynolds number (Re) on the turbulent heat transfer and friction in a rectangular duct with ribs detached from one wall were characterized quantitatively using laser holographic interferometry and pressure measurements.
Abstract: The effects of clearance ratio (C/H) and Reynolds number (Re) on the turbulent heat transfer and friction in a rectangular duct with ribs detached from one wall were characterized quantitatively using laser holographic interferometry and pressure measurements. The investigated flow was periodic in space both hydrodynamically and thermally. C/H and Re were varied from 0.25 to 1.5 and 5 × 103 to 5 × 104 , respectively. The obtained interferograms, local (Nu) and average (Nu ) Nusselt number, and thermal performance (Nu p /Nus * ) allowed the critical C/H characterizing different mechanisms of heat transfer augmentation to be identified and allowed a comparison of Nu, Nu , and Nu p /Nus * among the detached ribbed duct, the attached ribbed duct, and the smooth duct to be made. It was found that the detached ribbed geometry has the advantage of eliminating the hot spots behind the attached ribs. Optimal clearance ratios for heat transfer enhancement between the present periodic detached ribs and previous single detached cylinder were also compared. Furthermore, compact heat transfer and friction correlations were developed for a detached ribbed duct for the first time.