Electrohydrodynamic disintegration of dielectric fluid blended with ethanol

Engineered fluid HFE-7100 is an outstanding detergent and coolant with excellent thermal and chemical stability. Electrohydrodynamic jet disintegration and subsequent droplet formation of HFE-7100 dielectric liquid mixed with ethanol were experimentally investigated in this study. Contact-type charging was employed with the capillary nozzle directly connected to a negative high-voltage power supply, while the counter electrode was grounded. High-speed photography was utilized to capture the liquid breakup and droplet formation behaviors. The results showed that an ethanol content of 8% by volume visibly improved the charging performance of HFE-7100 due to the increase in the liquid electrical conductivity. In addition, with the increase in the applied voltage, the jet breakup was found to transform from the dripping/jetting mode to the ramified mode, which is characterized by a steady liquid sheet with fine droplets forming at the edge. Two distinct ramified breakup configurations, called the pudgy-ramified and lanky-ramified modes, are proposed, and their detailed structural parameters and droplet size distributions are discussed. The diameters of the droplets produced under the permanent ramified configuration could be as small as a few micrometers. Finally, a jet breakup regime map based on the Reynolds number Re and electric bond number Bo(E) was established. Overall, the electrospray technique has shown promise for spray cooling enhancement, and the main results of this paper may be useful for the development of electrospray cooling with a dielectric coolant.