Multiple nanodroplets coalescence in the coupling of electric field and swirl centrifugal field: A molecular dynamics study

The study of nanodroplets coalescence is crucial for the development of nanofluid technology and crude oil dehydration. The coalescence behavior of multiple nanodroplets in single electric field, single swirl centrifugal field, and the coupling of electric field and swirl centrifugal field (E&SC coupling fields) was investigated using the molecular dynamics (MD) method. The validation work verified the feasibility of the present MD models. The effects of electric field frequency (f) and strength (E), angular velocity (ω), water content (wt), and component types on the coalescence behavior of multiple nanodroplets were comprehensively investigated. The results show that direct current (DC) field was more suitable for dealing with low wt emulsions, while alternating current (AC) field was more suitable for dealing with high wt emulsions. The swirl centrifugal field with low (high) ω was correspondingly suitable for dealing with low (high) wt emulsions. The coalescence efficiency increased with increasing Re (20–160) and f (0–40 GHz). In addition, not only the large-sized droplets were easy to be formed, but also the small-sized droplets were easy to be removed in the E&SC coupling fields, which can enhance the coalescence efficiency between multiple nanodroplets. The critical CaE of AC&SC coupling fields was improved 18% than DC&SC coupling fields. Finally, the presence of Span-80 (SPAN) molecules increased the coalescence efficiency of multiple nanodroplets and raised the critical CaE to 0.11. The results of this paper can be potentially helpful for the development of high-efficiency electric dehydration technology at microscale.