Dielectrophoretic influence on free convection in a differentially heated cavity

Abstract

The modification of the natural convective flow in a differentially heated cavity by means of a steady dielectrophoretic torque is investigated experimentally and numerically. This torque is produced within a dielectric liquid by imposing a high frequency alternating voltage between two opposite asymmetric electrodes located at the side walls of the cavity. The electrodes are also submitted to a temperature difference. A specific staggered configuration of the electrodes creates non homogeneous electric and temperature fields. Increasing velocities are observed with increasing voltage in the regions of intense electric fields. Subsequent modifications of the flow pattern are noted with a loss of symmetry and the reinforcement of secondary vortices. Although the magnitude of the dielectrophoretic torque is modest compared to the thermal buoyancy torque, up to 8% increase in convective heat transfer is calculated for the highest Rayleigh and Roberts numbers. This steady contribution of dielectrophoretic forces to internal free convective flows open the door to an electrode geometry optimization so as to achieve a better heat transfer enhancement and to the generation of convective flows in microgravity conditions.