Penetration of free convection into a lateral cavity

The paper presents a theoretical and experimental study of natural convection in a horizontal cavity which communicates laterally with a large reservoir. The cavity walls and the reservoir are at different temperatures. It is shown theoretically that the flow consists of a horizontal counterflow which penetrates the cavity over a distinct length. The penetration length is shown to be proportional to the cavity height and to the square root of the Rayleigh number based on cavity height and cavity-reservoir temperature difference. The validity of the theory is demonstrated on the basis of a flow visualization experiment. It is shown also that the Nusselt number for cavity-reservoir heat exchange is proportional to the square root of the Rayleigh number, and is relatively insensitive to the Prandtl number in the Pr range 0·7 to ∞. The energy-engineering applications of the lateral penetration flow are discussed.