Effect of electric field strength and droplet diameter on droplet–interface coalescence mechanism

Abstract

Under high-strength electric fields, partial coalescence may occur, thus producing fine secondary droplets, which are undesirable for separating water from oil. In this study, experimental and numerical methods are employed to investigate the coalescence behavior under a DC electric field to comprehensively understand the effect of electric field strength (E) and droplet diameter (D) on coalescence. The Level-set method is employed to capture the moving interface, and the numerical data are validated through experimental tests. The results reveal the easy formation of secondary droplets with increasing E and D values. In particular, the electric field strength suppresses the expansion of the liquid bridge and hinders the vertical collapse of the droplets. The distortion of the electric field at the liquid bridge and the polarized charge both increase with E, thus resulting in stronger electric field repulsion. Moreover, the enhancement in D significantly affects the shrinkage of the liquid bridge and prevents the vertical collapse of the droplet. The pressure gradient at the liquid bridge from the outside to inside decreases as a function of D, thereby inhibiting the contraction speed. Furthermore, the number of polarized charges concentrated on the top of the droplet increases, thus resulting in an enhanced electric field tension. The results obtained herein can potentially act as guide for the design and optimization of electric dehydrators.