Effect of opposed eccentricity on free convective heat transfer through elliptical annulus enclosures in blunt and slender orientations

Abstract

This paper presents an experimental investigation for the effect of opposed lateral and vertical eccentricities on free convective heat transfer through elliptical annulus enclosures in blunt and slender orientations. Three test specimens of elliptical cylinders having an equal radius ratio and an equal length were prepared. The surface area of the inner cylinder is the same for each specimen as well as the area of the outer cylinder. Different elliptical ratios of 0.662, 0.866 and 0.968 were investigated. Experimental tests were done by maintaining constant heat flux on 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. The experimental tests monitored Rayleigh number (1.642 × 103 ≤ Ra* ≤ 3.849 × 106). The effects of both opposed vertical and lateral eccentricities for both blunt and slender orientations were investigated. The experimental results were fitted by correlations. Considerable agreement was found in the comparison among the results of present and previous works. Opposed eccentricity enhances free convective heat transfer by about 40 % from concentric. Slender orientation results in more enhancements in free convection than blunt one.