SINOPSIS

The effects of uniform rotation and porous medium on the onset of convective instability in a dielectric fluid confined between two horizontal planes under the simultaneous action of a vertical ac electric field and a vertical temperature gradient is considered. Applying linear perturbation theory and approximations analogous to the usual Boussinesq approximations, an equation of tenth order is derived. Under appropriate boundary conditions, this equation is solved exactly and the eigenvalue equations for the critical electrical Rayleigh number are obtained for both the cases of exchange of stabilities and overstability, respectively. The corresponding critical wave numbers are also obtained for both cases. It is shown that the medium permeability and Rayleigh number have destabilizing effects on the considered system, where as the porosity of porous medium, Taylor number, and Prandtl number have stabilizing effects. It is found also that, at high values of Taylor number or at any value of Prandtl number, the critical electrical Rayleigh number is independent of the Rayleigh number.