Thermal Resistance of a Closed-Ended, Annular, Air-Filled Cavity: Inclination and Eccentricity Dependence

Abstract

The steady-state rate of heat flow from a cylinder of uniform temperature (≤ 185°C) to a surrounding, concentric, water-cooled pipe has been measured experimentally. For such a closed-ended annular-cavity configuration with 23 ≤ h ≤ 40 and 1.8 times 103 < Ra < 105, where h is the aspect ratio and Ra the Rayleigh number, the heat flux exhibited a maximum at an inclination of 17 ± 2° to the horizontal. The vertical system was the maximum insulation configuration. Eccentric displacement of one vertical cylinder relative to the other, for a fixed temperature difference between the vertical cylinders, always led to an increase in the rate of heat transfer, but for eccentricities up to 0.3 the changes were negligible. The rate of heat flow for the horizontal assembly increased as the axis of the inner cylinder was eccentrically displaced vertically downwards relative to that of the outer cylinder.