(596b) Two-Drop Model of Depth Coalescing Filter Performance

Depth coalescing filters are used to enlarge droplets in liquid aerosols and in liquid-liquid emulsions. The enlarged drops are subsequently separated from the continuous phase by interfacial mechanisms, gravity, or inertial forces. Mathematical models of coalescing filters are useful to predict performance and to guide filter design. Models using CFD are successful at predicting performance at the cost of significant computational effort. For many practical applications, simpler less computationally intensive models are desired.

In this work, a “two-drop” model is described. The drops are of two sizes. The small drop, carried by the continuous phase, is captured on fibers of the filter. Once captured, the small drops are immobilized. The small drops coalesce to form the second, larger drops. The larger drops move through the filter due to fluid drag force. The model aims to account for significant mechanisms including capture, coalescence, drag, and capillary forces.

A unique feature of the model is the mathematical description of the capillary forces as a gradient of a capillary potential function. This capillary potential function enables prediction of the effects of the capillary forces near the surfaces of the filter medium that can cause liquid accumulation at the surfaces.