Flow Characteristics and Heat Transfer Enhancement of Electro-Thermo-Convection in Dielectric Liquids With Residual Conductivity

The flow features and heat transfer enhancement of electro-thermo-convection (ETC) in dielectric liquids with residual conductivity between concentric electrodes are numerically studied based on an injection–conduction model. The strongly coupled flow field, electric field, and positive/negative charge density of the ETC system are solved numerically based on the finite volume framework of OpenFOAM^®. The total variation-diminishing algorithm is adopted to handle the complex nonlinearity of the positive/negative charge transport equations. The bifurcation of plentiful flow states that are characterized by variable plumes and vortex pairs in the ETC system is investigated. It is discovered that the residual conductivity postpones the beginning of ETC flow, inhibits the convection intensity, and also diminishes heat transfer of the ETC system. In addition, the transition sequences of ETC flow are also influenced by residual conductivity. A higher residual conductivity suppresses the occurrence of different intermediate steady-states. Three different transition sequences of steady ETC states at different Rayleigh numbers (Ra) are identified. The critical point where the ETC flow bifurcates to S8 is postponed at higher Ra. And the ETC system is more prone to chaos in a system of higher Ra. The periodicity of the ETC system is analyzed and found that Ra has little influence on the periodicity.