Droplet impact on hot substrates under a uniform electric field

Abstract

Droplet impact on a hot substrate under an electric field is fundamental and crucial for electrospray cooling. However, the involved thermal-electric coupling impact electrohydrodynamic has not been well understood. In this study, the effects of an electric field on the droplet impact behavior in different thermal regimes and the subsequent dynamic mechanisms were experimentally investigated. The results showed that the vertical electric field would result in an upward liquid ejection in the film evaporation regime. In the nucleate boiling regime, the liquid pinch-off phenomenon was observed. In addition, the droplet evaporation rate was increased by approximately 23% with an electric field of 6 kV/cm. In the film boiling regime, both the residence time and bounce-off droplet height were significantly increased. The various impact phenomena were mainly explained by the competition between electrostatic and capillary pressures. The comprehensive effects of surface free charges and temperature variation on the droplet surface tension coefficient were discussed. Moreover, according to the thermal analysis, the heat transfer in the film boiling regime with an electric field was enhanced by approximately 137%. This work contributed to the development of the droplet impact dynamics under the coupling temperature and electric fields and demonstrated great promise for the electric field for thermal-fluid manipulation.