Electroconvection and its effect on heat transfer

The basic properties of electroconvection resulting from unipolar injection into an insulating liquid are examined. It is shown that for very weak injection the induced motion of the liquid has only a negligible influence on the total current across the layer. The agitation of the liquid can nevertheless be very intense and orders of magnitude have been derived for the typical liquid velocity in both viscous dominated and fully turbulent regimes. This electroconvection can be used to enhance heat transfer. The experiment performed in plane-parallel electrode geometry proves that the heat transfer can be substantially augmented. Moreover it appears clear that the convection state is determined by the Coulomb force, buoyancy effects being insignificant. The experimental results can be qualitatively summarized by a power law dependence for the Nusselt number of the form Nu approximately (jd³)ⁿ. A more precise expression and, in particular, the estimation of the exponent n require a detailed analysis of the convective flow induced by a unipolar injection.