Electrowetting-based control of water adhesion to surfaces
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This thesis lays the foundations for the electrical control of adhesion of water drops and films to surfaces. Electrowetting (EW) is the increase in wettability of conducting liquids via the application of a concentrated interfacial electric field. EW can be exploited to keep a surface water-wet and displace non-conducting liquids away from the surface. This concept has various applications in the field of oil-gas flow assurance, such as hydrocarbon fouling mitigation, and heavy oil pumping via core annular flows. This dissertation presents experimental results that are the first step towards experimental validation of the concept of keeping surfaces water-wet under hydrocarbon flow conditions. The first experiments involve measurements of the electrically tunable water drop-surface adhesion. Adhesion is measured in terms of the tilt angle needed to roll off an electrowetted drop from the surface. Measurements show a 67 % increase in drop-surface adhesion at a 20 V/µm electric field. The second set of experiments show that electrowetting forces are strong enough to displace very viscous oil from a surface and wet the surface with water. The influence of the magnitude and frequency of the AC voltage on oil displacement with water is experimentally quantified. Along with the experimental efforts, first order modeling results to predict the retention of electrowetted water films under hydrocarbon shear conditions are presented. These efforts map the technical feasibility of the proposed concept for field conditions. It is seen that EW is a powerful tool to enforce water wetting under relevant field conditions; furthermore the benefits of using this concept will be transformative.