Effect of Opposed Lateral and Vertical Eccentricity on Free Convection in an Elliptical Annulus Enclosure in Blunt and Slender Orientations

Abstract

This paper presents an investigation for the effect of opposed lateral and vertical eccentricity on free convection in anelliptical annulus enclosure in blunt and slender orientations. Three test specimens of elliptical cylinders having anequal radius ratio and an equal length were prepared for this purpose. The outer surface area of the inner ellipticalcylinder is the same for each specimen as well as the area of the inner surface of the outer elliptical cylinder for eachspecimen. Different elliptical rat ios of 0.662, 0.866 and 0.968 were investigated. The specimens were cut using thecomputed numerically controlled wire -cut machining. Experimental tests were done by maintaining constant heat fluxon the inner cylinder and the outer one was exposed to approximately constant temperature of the closed laboratory.Both annuals ends of the annular elliptical cylinders were closed by cork to form the annular enclosure space. Th eexperimental tests scanned the modified Rayleigh number (1.642×103 ≤ Ra* ≤3.849×106). The effects of the opposedvertical eccentricity, opposed lateral eccentricity on free convection for both blunt and slender orientation wereinvestigated. Empirical correlations were deduced within an acceptable uncertainty for the experimental results.Compatible and satisfactory to the conscience agreement was found in a comparison among the results of present andprevious works. In the vision of the comparison, it was found that; the convective heat transfer for the opposed verticaleccentricity is greater than the convective heat transfer for the lateral opposed eccentricity in slender orientation byabout 40% from concentric. The convective heat transfer for the opposed lateral eccentricity is greater than theconvective heat transfer for the vertical opposed eccentricity in blunt orientation by about 30% from concentric. Slenderorientation offers about 50% enhancement in free convection than the blunt situation for the same elliptical rat io.