THE EFFECT OF STABLE STRATIFICATION ON THE NATURAL CONVECTION IN A SQUARE CAVITY CAUSED BY A HORIZONTAL TEMPERATURE DIFFERENCE

Abstract

The effect of stable stratification on the natural convection heat transfer characteristics in an air-filled square cavity with a horizontal temperature difference was investigated experimentally. The temperature distribution at different positions along the hot vertical wall was measured using a thermocouple, and these temperature profiles were used to compute the heat transfer. It was found that varying the thermal boundary conditions of the top and bottom walls of the cavity changed the stratification, and in turn the natural convection heat transfer characteristics in the square cavity. The measurements indicated that when the top wall temperature increased, it caused a local recirculation region near the top wall, and this secondary circulation approached the hot vertical wall. The non-uniformity in the temperature profiles near the top wall is relatively independent of the temperature of the bottom wall indicating the recirculatory region is independent of the bottom wall temperature. In all cases, it was found that the local heat transfer along the hot vertical wall could be expressed by the correlation Nu = CRa0.315. The constant C increased when the top wall temperature was increased, and decreased slightly when the bottom wall temperature was decreased. The constant C was found to correlate with the stratification rate, defined as the non-dimensionalized temperature gradient of the ambient air in the vertical direction in the core region of the cavity, and the non-dimensionalized mean temperature in the vertical direction of the cavity. The average Nusselt number for the hot vertical wall NuH increased with an increase in the vertical Grashof number Grv.