LAMINAR THERMAL-CONVECTION IN A VERTICAL SLOT

The validity of the conduction regime approximation is studied in a vertical slot of height to width aspect ratio equal to 28. Velocity profiles are determined by laser-Doppler velocimetry (LDV) in water and hexane near room temperature, but also in water at mean temperatures close to its density maximum. Finally a glycerol-water mixture is experimentally studied in order to check the theoretical prediction taking into account the temperature dependence of the viscosity (non-Boussinesq effects). The measured velocity profiles and the computed ones, both analytically for an infinite layer or by 2D numerical simulations, are in excellent agreement for all Grashof numbers. When the density is a quadratic function of temperature, a criterion is derived for the existence of a bicellular convective regime. The validity of this criterion is also experimentally verified. Finally, for a highly viscous fluid, the conduction regime approximation is found to be valid for an aspect ratio greater than 4.