Experimental and computational studies of water drops falling through model oil with surfactant and subjected to an electric field

TL;DR

This study combines experimental and computational methods to analyze how surfactant-covered water drops fall through oil under electric fields, emphasizing well-characterized fluid systems for industrial applications.

Contribution

It introduces a controlled water-oil system with surfactant addition, enabling precise characterization and comparison of experimental and simulation results under electric fields.

Findings

Good agreement between experiments and simulations below critical micelle concentration.

Surfactant presence significantly influences drop behavior under electric fields.

Controlled fluid characterization improves understanding of electrocoalescence processes.

Abstract

The behaviour of a single sub-millimetre-size water drop falling through a viscous oil while subjected to an electric field is of fundamental importance to industrial applications such as crude oil electrocoalescers. Detailed studies, both experimental and computational, have been performed previously, but an often challenging issue has been the characterization of the fluids. As numerous authors have noted, it is very difficult to have a perfectly clean water-oil system even for very pure model oils, and the presence of trace chemicals may significantly alter the interface behaviour. In this work, we consider a well- characterized water-oil system where controlled amounts of a surface active agent (Span 80) have been added to the oil. This addition dominates any trace contaminants in the oil, such that the interface behaviour can also be well-characterized. We present the results of experiments and corresponding two-phase- flow simulations of a falling water drop covered in surfactant and subjected to a monopolar square voltage pulse. The results are compared and good agreement is found for surfactant concentrations below the critical micelle concentration.