Coalescence behaviour of two large water-drops in viscous oil under a DC electric field

• The electric field favourite the drops to coalesce instantly or temperately.
• The electric force drags the drops to separate after contact.
• The coalescence is depended on the pressure difference.
• Lower electric field strength and smaller size facilitate the coalescence of drops.

Electrically driven coalescence is one of the important methods to separate water from crude oils. In this paper, the coalescence behaviour of two water drops was studied experimentally using a high-speed imaging. The results show that the electric force induces the drops migrating towards each other before their contact. However the electric force drags the drops to separate after contact. There is a critical electric field strength above which the two drops would be separated again after they have been coalesced together. The understanding of the electric coalescence could be helpful to advance the design of the electrocoalescencers.

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