Effect of the Coulomb and dielectric forces on the onset of Rayleigh-Bénard convection

In this paper, the effect of Coulomb and dielectric forces on the onset of Rayleigh-Bénard convection (RBC) in a dielectric liquid layer contained between two parallel electrode plates has been numerically investigated. Two different operating conditions have been considered in electrohydrodynamic (EHD) conduction: ohmic and saturation, and variations in the physical properties of the dielectric fluid with temperature. The electric equations and the state equations based on the Boussinesq approximation are integrated in the framework of OpenFOAM buoyantBoussinesqPimpleFoam program. The results show that in the ohmic regime, the combined effect of Coulomb and dielectric forces promotes the onset of RBC flow, while in the saturation state, the inhibition of RBC flow by Coulomb force is more significant. The value of the critical Rayleigh number Ra decreases with increasing electric Reynolds number Re^E in the ohmic regime, whereas in the saturation state, the critical Ra increases with increasing Re^E. In the saturation regime, the flow field always has a steady flow in the range of parameters considered. However, the onset of the RBC flow promoted by the dielectric force is more pronounced in the ohmic state. Due to the presence of the dielectric force, the flow field exhibits periodic oscillatory flow at low electric Reynolds numbers for the range of parameters considered.