The flow and vortex instability of horizontal natural convection in a porous medium resulting from combined heat and mass buoyancy effects

An analysis is performed to study the flow and the vortex instability of natural convection in a porous medium that results from simultaneous diffusion of heat and mass in a boundary layer adjacent to a horizontal surface. Numerical results for the Nusselt number, Sherwood number, and the neutral stability curves are presented for Lewis numbers ranging from 1 to 10 and the buoyancy ratio in the range of -0.5 to 4. For mass transfer aiding the flow, the results indicate that the Nusselt number and Sherwood number are higher than those for pure thermal convection and the flow is more susceptible to the vortex instability, while for mass transfer opposing the flow, the opposite trend is true. The critical thermal Rayleigh number is found to increase with decreasing Lewis number.