A NEW PROCESS FOR SPECIES SEPARATION IN A BINARY MIXTURE USING MIXED CONVECTION

摘要

In this paper, a numerical and analytical analysis is performed in order to improve the species separation process in a binary fluid mixture by decoupling the thermal gradient from the convective velocity. The configuration considered is a horizontal rectangular cavity, of large aspect ratio, filled with a binary fluid. A constant tangential velocity is applied to the upper horizontal wall. The two horizontal impermeable walls are maintained at different and uniform temperatures T_1 and T_2 with ΔT=T_1-T_2. Species separation is governed by two control parameters, the temperature difference ΔT and the velocity of the upper plate (Ue_x){top}→. The intensity of the thermo-diffusion is controlled by the temperature, while the velocity (Ue_x){top}→ controls the convective flow. This problem depends on six dimensionless parameters, namely, the separation ratio, Ψ, the Lewis number, Le, the Prandlt number Pr, the aspect ratio of the cell, A and two control parameters: the thermal Rayleigh number, Ra and the Peclet number Pe. In this study, the formulation of the separation (mass fraction difference between the two ends of the cell) as a function of the Peclet number and the Rayleigh number is obtained analytically. For a cell heated from below, the optimal separation m=42~(1/2)/15 is obtained for Pe=42~(1/2)/Le and Ra=540/LeΨ. 2D numerical results, obtained by solving the full governing equations, are in good agreement with the analytical results based on a parallel flow approach.