Double-duffusive natural convection within a horizontal porous layer is studied both analytically and numerically. The enclosure is heated and cooled along vertical walls by uniform heat fluxes and a solutal gradient is imposed vertically. In the formulation of the problem use is made of the Darcy model and the density variation is taken into account by the Boussinesq approximation. The governing parameters of the problem are the thermal Rayleigh number, R T , Lewis number, Le , and buoyancy ratio N . The existence of multiple steady state solutions, for a given set of the governing parameters, is demonstrated. The analytical solution, based on the parallel flow approximation, is found to be in good agreement with a numerical solution of the full governing equations.
