Electrospray characteristics and cooling performance of dielectric fluid HFE-7100

Electrospray (ES) cooling is a promising route of efficient heat removal for electronic components with powerful cooling capacity, a small liquid supply, and precise temperature control. In this study, we experimentally investigated the electrohydrodynamic (EHD) disintegration and ES cooling performance of the dielectric fluid HFE-7100. The stainless-steel capillary nozzle was connected to a high voltage direct current (DC) power supply, whereas the hot copper surface was grounded. A high-speed camera was used to capture the spray morphology of the coolant. The results indicated that a small amount of ethanol significantly improved the charging performance of HFE-7100 by increasing the liquid electrical conductivity. An uncharged column liquid jet was stretched into a thin liquid film by the EHD forces, generating numerous ultrafine droplets along the lower edge. The ES cooling heat flux was increased by about 2.2 times compared with the neutral condition. In addition, the influences of the applied voltage, flow rate, spray height, liquid subcooling, and ethanol concentration on the ES cooling capacity were discussed. Finally, correlations of the ES cooling heat transfer based on the Reynolds number, Weber number, Prandtl number, electric Weber number, Jacob number, and normalized surface temperature were established.