Transient free convection from a horizontal surface in a porous medium subjected to a sudden change in surface heat flux

This paper presents an analytical and numerical study of transient free con vection from a horizontal surface that is embedded in a fluid-saturated por ous medium. It is assumed that for time <(tau)over bar> < 0 steady state ve locity and temperature fields are obtained in the boundary-layer which occu rs due to a uniform flux dissipation rate q(1)" on the surface. Then, at <( tau)over bar> = 0 the heat flux on the surface is suddenly changed to q(2)" and maintained at this value for <(tau)over bar> > 0. Firstly, solutions w hich are valid for small and large <(tau)over bar> are obtained. The full b oundary-layer equations are then integrated step-by-step for the transient regime from the initial unsteady state (<(tau)over bar> = 0) until such tim es at which this forward marching approach is no longer well posed. Beyond this time no valid solutions could be obtained which matched the final solu tion from the forward integration to the steady state profiles at large tim es <(tau)over bar> --> infinity.