Convective instability in fluid-saturated porous layer under uniform volumetric heat sources

A theoretical analysis of thermal instability driven by buoyancy forces in transient temperature fields is conducted in an initially quiescent, fluid-saturated, horizontal porous layer. Darcy's law is used to explain characteristics of fluid motion and linear stability theory is employed to predict the onset of buoyancy-driven motion. Under the principle of exchange of stabilities, the stability analysis is performed on the basis of the propagation theory which adopts the thermal boundary layer thickness as a characteristic length scaling factor. The result predicts the critical condition of onset of buoyancy-driven convection which is governed by the Darcy-Rayleigh number. This study also shows that in the present system the propagation theory produces the stability criteria over the whole domain of time. (C) 2002 Elsevier Science Ltd.