Vortex instability of horizontal and inclined natural convection flows from simultaneous thermal and mass diffusion

An analysis is performed to study the heat/mass transfer and vortex instability characteristics of buoyancy-induced flows that result from simultaneous diffusion of heat and mass in laminar boundary layers adjacent to horizontal and inclined surfaces. Numerical results are obtained for a Prandtl number of 0.7 over a range of Schmidt numbers and various angles of inclination from the horizontal, phi. For a given phi, it is found that when the two buoyancy forces from thermal and mass diffusion act in the same direction, both the surface heat and mass transfer rates increase, causing the flow to become more susceptible to the vortex mode of instability. These trends are reversed when the two buoyancy forces act in the opposite directions. On the other hand, as phi is increased, the heat and mass transfer rates are enhanced, but the instability of the flow to the vortex mode of disturbances decreases and eventually vanishes at phi = 90 deg.