Effect of the nonmonotonic temperature dependence of water density on convection under uniform heating

This paper presents the results of an experimental study of free convection in a closed rectangular tank with fresh water whose initial temperature is lower than the constant temperature of air outside the tank. Convective instability is shown to play a significant role in the process of heat transfer from the boundary layers on the walls to the bulk of water. In the case where the initial water temperature is higher than the temperature at which the density is maximal (about 4°C), convective instability occurs only in the boundary layer at the bottom of the tank. At a water temperature below 4°C convective instability also exists for some time in the boundary layer on the cover. Quantitative information is given on the variations in temperature and water density in time and on the vertical coordinate.