Using computational fluid dynamics to study the effect of contact angle on microdroplet deformation

Computational fluid dynamics (CFD) is used to study the effect of contact angle on droplet shape as it moves through a contraction. A new non-dimensional number is proposed in order to predict situations where the deformed droplet will form a slug in the contraction and thus interact with the channel wall. We argue that droplet flow into a contraction is a useful method to ensure that a droplet will wet a channel surface without a trapped lubrication film. We demonstrate that when a droplet is larger than a contraction, capillary and Reynolds numbers, and fluid properties may not be sufficient to fully describe the droplet dynamics through a contraction. We show that with everything else constant droplet shape and breakup can be controlled simply by changing the wetting properties of the channel wall. CFD simulations with contact angles ranging from 30 to 150 shows that lower contact angles can induce droplet breakup while higher contact angles form contact-angle dependent shape slugs.