Linear stability analysis for the onset of convection during microwave heating of samples confined within horizontal plates

This work performs linear stability analysis to investigate the onset of convection due to microwave incidences in water and oil confined between two semiinfinite horizontal plates. The onset has been characterized in terms of critical Rayleigh (Rac) and wave (kc) numbers, which are determined for the entire spectrum sample thickness varying from thin to thick samples exposed to various microwave source configurations including one sided to distributed incidences. The main finding of this work is the oscillatory variations of Rac and kc with sample thickness in sinusoidal regime of microwave heating, which indicates preferential onset for specific sample thicknesses. It has also been shown that materials as well as microwave source configuration play important roles in the onset of convection in this regime. The variation patterns of Rac and kc have been correlated to the spatial patterns of absorbed microwave power within the sample. These results are useful not only for forecasting the onset but also for controlling onset of convection by selecting suitable experimental parameters. Copyright c 2011 by ASME.