Microscopic coalescence mechanism of nanoparticle-laden droplet pairs in the coupling of electric field and flow field: A molecular dynamics study

Abstract

Electrocoalescence is a time-saving and energy-efficient technology for dehydrating crude oil. The microscopic coalescence mechanism of nanoparticle-laden water droplet pair in the coupling of electric field and flow field was studied by molecular dynamics simulations. The present numerical results agreed well with the experimental work in the literature and the theoretical predictions. The effects of electric field strength and direction, flow field strength and type, droplet intersection angle, and multiple droplets on nanoparticle-laden droplet pair coalescence in the coupling fields were systematically discussed. The results illustrate that four coalescence modes occurred in the coupling of electric field and shearing flow field (E&S coupling fields), and the coalescence efficiencies ranked as: rolling coalescence mode > temporary coalescence mode > stretching mode > slipping mode. Electric fields dominate droplet coalescence, while flow fields enhance droplet coalescence in the coupling fields. Furthermore, parallel direction of electric field and flow field generally leads to high coalescence efficiencies. As to the multiple droplet systems, in the coupling of x-axis electric field and rotating flow field (E&R coupling fields), the coalescence efficiencies ranked as structure I > structure IV > structure III > structure II, whereas, in the y-axis E&R coupling fields, the coalescence efficiencies ranked as structure I > structure III > structure IV > structure II. Finally, the coalescence efficiencies of the E&R coupling fields were always higher than those of the E&S coupling fields. The results will be potentially valuable for optimizing the design of compact and efficient crude oil dehydrators.