Dielectrically driven convection in spherical gap geometry

Dielectric heating occurs in situations where an alternating electric field is applied on an insulating dielectric material. This effect can produce thermal convection in dielectric fluid through the thermoelectric coupling by the dielectrophoretic (DEP) force. The onset and the flow properties of the convection are investigated in a spherical gap geometry. The thermoelectrohydrodynamical equations often adopted in the modeling of the DEP-force-driven thermal convection are extended by an additional source term arising from the dielectric heating in the energy equation. Three-dimensional direct numerical simulations are performed, under microgravity conditions and without any imposed temperature gradient to highlight the effects of dielectric heating. In the conduction state, dielectric heating creates a parabolic temperature profile with a maximum in the interior of the spherical gap. In the convection state, the temperature distribution is more homogeneous with a lower maximum temperature. Numerical results are compared with interferograms from the GeoFlow II experiment performed on the International Space Station to validate the model. For the comparison, a numerical interferogram is applied to temperature fields obtained in the simulation. The onset of convection and basic spatial properties of the resulting internally heated convective zone are in good agreement with the experiment. The computed velocity fields reveal strong downdrafts which lead to recognizable fringe patterns in the interferograms.