Simultaneous Determination of Reference Free-Stream Temperature and Convective Heat Transfer Coefficient
This paper deals with the development of a new method that can obtain heat transfer coefficient and reference free stream temperature simultaneously, The method is based on transient heat transfer experiments using two narrow-band TLCs. The method is validated through error analysis in terms of the random uncertainties in the measured temperatures. It is found that the errors could be reduced more than 2 times less. The general method described in this paper is applicable to many heat transfer models with unknown free stream temperature.
A New Hue Capturing Technique for the Quantitative Interpretation of Liquid Crystal Images Used in Convective Heat Transfer Studies
This study focuses on a new image processing based color capturing technique for the quantitative interpretation of liquid crystal images used in convective heat transfer studies. The present method is highly applicable to the surfaces exposed to convective heating in gas turbine engines. The study shows that, in single crystal mode, many of the colors appearing on the heat transfer surface strongly correlate with the local temperature. A very accurate quantitative approach using an experimentally determined linear hue versus temperature relation is possible. The new hue capturing process is discussed in detail, in terms of the strength of the light source illuminating the heat transfer surface, effect of the orientation of the illuminating source with respect to the surface, crystal layer uniformity and the repeatability of the process. The method uses a 24 bit color image processing system operating in hue-saturation-intensity domain which is an alternative to conventional systems using red-green-blue color definition. The present method is more advantageous than the multiple filter method because of its ability to generate many isotherms simultaneously from a single crystal image at a high resolution, in a very time efficient manner. The current approach is valuable in terms of its direct application to both steady state and transient heat transfer techniques currently used for the hot section heat transfer research in air breathing propulsion systems.Copyright © 1991 by ASME
Impingement cooling from a circular jet in a cross flow
Abstract Local impingement cooling effectiveness and heat-transfer coefficients are measured over the interaction area of an air jet impinging on a wall and subjected to a cross flow of air. Impingement cooling effectiveness decreases with the blowing rate and at low blowing rates, there is, near the stagnation point, a definite influence of the density ratio. Effectiveness values as high as 60 per cent are obtained at the stagnation point with blowing rate of 12 and nozzle to plate distance of six diameters. The heat-transfer coefficient can be as high as 700W/(m2 K) for a blowing rate of twelve with the jet only six diameters above the surface on which it impinges.