A study of the influence of buoyancy on turbulent flow in a vertical plane passage

Abstract

A fundamental experimental study of buoyancy-aided and buoyancy-opposed turbulent flow and heat transfer to air in a vertical plane passage is reported. One wall was heated uniformly and the opposite one was unheated. Although the dominant mechanism for heat removal from the heated wall was convection, there was also some radiative heat transfer to the unheated wall. The heat received by thermal radiation was mainly removed from that wall by convection to the air flowing over it within the passage. Such a configuration has received little attention in earlier work on buoyancy-influenced flow in vertical passages. Detailed measurements of temperature were made on both walls and local values of convective heat transfer coefficient were determined on the heated surface taking careful account of the thermal radiation from it to the unheated wall and heat losses to the surroundings. A range of experimental conditions was covered over which the influence of buoyancy on the flow was systematically varied by adjusting the heat input and the mass flow rate. The mode of heat transfer ranged from forced convection with negligible influence of buoyancy to mixed convection with very strong influences of buoyancy. Profiles of velocity, turbulence intensity, turbulent shear stress and turbulence production were obtained from flow measurements made using a two-component laser Doppler Anemometer system. From these results a clear picture was arrived at of the mechanism by which the effectiveness of heat transfer was modified by the distortion of the mean flow due to the influence of buoyancy and the effect that this had on turbulence production and turbulent diffusion of heat.