Heat transfer enhancement in a dielectric coolant by electroconvection in point-plane geometry

In this paper, an experimental campaign is illustrated, showing the heat transfer enhancing effect of an ionic jet that impinges on the upper surface of a heated plate. Ion injection is obtained by a sharp high-voltage electrode. The employed liquid is the space-qualified coolant H-Galden ZT S5. Several tests are conducted, with different compositions, shapes and polarities of the electrode, changing the high voltage, the electrode-to-plane distance, and the applied heat flow. The electrohydrodynamic technique produces heat transfer augmentation up to 230 % with respect to thermogravitational convection and heat transfer coefficients in the order of one kW/(m2.K). The electrohydrodynamic enhancing effect is obtained with very low power input. The ionic flow has remained active for 750 hours of continuous monitored operation. H-Galden ZT S5 performs better than other dielectric liquids, such as FC-72, HFE-7100, and Vertrel XF tested in previous campaigns reported in literature, dedicated to improving heat transfer by the application of electric fields.