Investigation of the role of electrohydrodynamic forces on the heat transfer enhancement and solid extraction during melting of paraffin wax under constant temperature boundary conditions

Abstract

The melting enhancement of paraffin wax is studied experimentally under the effect of electrohydrodynamic (EHD). Paraffin wax was melted under constant temperature boundary conditions with different applied DC voltage magnitudes and polarities, and different temperature gradients. The role of EHD forces was investigated by applying DC and AC square waves with different frequencies and offset values.It was found that the melting enhancement rises nonlinearly with increasing the voltage magnitudes. The maximum effective thermal conductivity under -10 kV was found to be 0.95 W/m-K in comparison with the value of 0.2 W/m-K for the pure liquid paraffin wax, with an enhancement ratio of 4.75.The EHD solid extraction phenomenon investigation showed that the extraction was detected for all the applied DC voltages. Small dendrites were observed to be pulled out from the mushy zone melt front and rise upwards in a rotational manner. It is concluded that the Coulomb force is the primary force for extraction while the formation of electroconvection cells is the main driving mechanism for the motion of the suspended dendrites in the liquid bulk. In addition, the AC studies revealed that the dielectrophoretic force is negligible in this study.