The onset of thermal convection in a horizontal fluid layer heated from below with time-dependent heat flux

The onset of convective motion in an initially quiescent, horizontal fluid layer heated from below is analyzed by using propagation theory. When the heat flux is changed suddenly from a constant to a linear ramp with time, cellular convection will set in due to buoyancy forces at a certain time. In this system predictions of the onset time of convective motion are compared with available experimental data and the effect of the aspect ratio is discussed. It is very interesting that propagation theory covers the whole domain of time and the results represent experimental data reasonably well.