The Effect of Surface Interactions on the Coalescence of Water Droplets in Fuel*

The process of coalescence plays a crucial role in treating phase separation in emulsions, especially in industrial filtration applications. Water trapped in fuel commonly causes corrosion of fuel engine parts, which necessitates water removal in fuel applications. This is often achieved using coalescence filters. The interaction between the filter’s fibers and other droplets significantly impacts the coalescence process, but its precise effects remain under-characterized. This presentation investigates how surface interactions affect droplet coalescence using microfluidic platforms. The film drainage times of surfactant-laden water-in-fuel emulsions are measured using a “contact” device that examines the coalescence of droplets in contact with poly(dimethylsiloxane) (PDMS) traps. The results are compared to  a “contactless” Stokes trap device, which studies the coalescence of free droplets in a hydrodynamic cross-slot. It was found that droplets that have multiple contacts, either with other droplets or with the PDMS droplet traps, coalesce more readily and exhibit a lower dimensionless drainage time compared to two free droplets brought together in the Stokes trap. This work serves as a foundational understanding of coalescence, critical in various industrial applications.