The onset of convective motion in a horizontal fluid layer heated from below and cooled from above with constant heat flux

A theoretical analysis of thermal instability driven by buoyancy forces in transient temperature fields is conducted in an initially quiescent, horizontal fluid layer heated from below and cooled from above with uniform heat flux. 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 concentration boundary layer thickness as a characteristic length scaling factor. The prediction compares reasonably with existing experimental result. (C) 2004 Elsevier Science Ltd.