Showing papers by "Richard J Goldstein published in 1990"

Effect of entrainment on the heat transfer to a heated circular air jet impinging on a flat surface

Abstract: An experimental investigation is described that characterizes the convective heat transfer of a heated circular air jet impinging on a flat surface. The radial distributions of the recovery factor, the effectiveness, and the local heat transfer coefficient are presented. The recovery factor and the effectiveness depend on the spacing from jet exit to the impingement plate, but do not depend on jet Reynolds number. The effectiveness does not depend on the temperature difference between the jet and the ambient. A correlation is obtained for the effectiveness. The heat transfer coefficient is independent of the temperature difference between the jet and the ambient if it is defined with the difference between the heated wall temperature and the adiabatic wall temperature.

High-Rayleigh-number convection in a horizontal enclosure

Abstract: A review of the literature on natural convection in a horizontal layer heated from below shows the need for reliable data at high Rayleigh number (Ra) to determine the asymptotic Nusselt number (Nu) variation with Rayleigh number. The present study expands the data base by the use of an electrochemical mass transfer technique to determine the asymptotic dependence of the Sherwood number (Sh) on Ra at high Schmidt number (Sc). The results of the present study give Sh = 0.0659 for Sc ≈ 2750, 3 × 109 < Ra < 5 × 1012. Using the heat-mass transfer analogy, this indicates the high Prandtl number variation of Nu with Ra.

The Influence of Curvature on Film Cooling Performance

Abstract: The effects of injection rate and strength of curvature on film cooling performance of gas injected through a row of holes on a convex surface is studied. Comparisons are made to film cooling of concave and flat surfaces. Three different relative strengths of curvature (ratio of radius of curvature to radius of injection hole), two density ratios (0.95 and 2.0), and a wide range of blowing rates (0.3 to 2.7) are considered. A foreign gas injection technique (mass transfer analogy) is used. The strength of curvature was controlled by varying the injection hole diameter. At low blowing rates, film cooling is more effective on the convex surface than on a flat or a concave surface. The cross stream pressure gradient present in curved flows tends to push the jet into the convex wall. As the injection rate is increased, normal and tangential jet momentum promote lift-off from the convex surface, thereby lowering performance. In contrast, previous studies show that on a concave surface, tangential jet momentum, flow instabilities, and blockage improve performance on a concave surface as blowing rate is increased.Copyright © 1990 by ASME

Visualization of longitudinal convection roll instabilities in an inclined enclosure heated from below

Abstract: Experiments have been performed on the stability of buoyancy-driven flows of a high-Prandtl-number fluid in an inclined rectangular enclosure. Visualization of the stable planform of convection for various Rayleigh numbers and inclination angles is provided by a temperature-sensitive liquid crystal and gold-coated film heater assembly which serves as the lower surface of the enclosure. This assembly produces a nearly constant heat flux surface with a thermal conductivity of the same order as that of the test fluid. The results indicate that for large angles of inclination from the horizontal a steady transverse roll(s) structure is stable. As the angle of inclination is decreased steady longitudinal rolls replace the transverse roll(s) and for low angles a steady square-cell convection planform is observed. A region of unsteady wavy longitudinal rolls is also observed at sufficiently high Rayleigh numbers for low to moderate angles of inclination. In general the wavenumber of the longitudinal rolls increases with angle of inclination from the horizontal. Two distinct types of instability mechanisms are observed which modify the wavenumber of the longitudinal rolls: a cross-roll instability, which is a disturbance perpendicular to the original roll axis; and a pinching mechanism which combines two neighbouring longitudinal roll pairs into a longer wavelength roll pair.

Effect of boundary conditions on mass transfer near the base of a cylinder in crossflow

Abstract: The mass (heat) transfer pattern near the base of a cylinder in crossflow, at Re{sub d} of 10,000-80,000, was described by Goldstein and Karni and Karni and Goldstein. Two small, intense vortices within the horseshoe vortex system produce high values and steep gradients of the transport coefficient over a narrow strip extending from the cylinder base to about 0.07d above it. The studies also indicate the effects of cylinder diameter and endwall boundary layer thickness on these phenomena. In the present study a portion of the endwall and the test cylinder placed normal to it are coated with naphthalene. Local mass transfer measurements are conducted on both surfaces and the results are compared to earlier data by Karni and Goldstein. Thus, the effect of changing the endwall boundary conditions from inactive to active on the mass (heat) transfer pattern is investigated.

Heat transfer reviews

Abstract: This book presents tools for continuous improvements in the efficiency of engineering devices, including the recent awareness of the necessity to conserve energy and to find new energy sources. It reports on recent developments in specialized research areas.