Modeling industrial coalescers : droplet dynamics

Filtration and separation of a mixture of different fluid components are fundamental in a wide variety of applications. These processes are used in the purification of water, for example, along with the development of chemical reactors for food processing and other biological applications. Intrinsic in these systems is the goal to remove contaminants or other fluid components from one fluid, or to harness a component in a mixture for later use. The physical mechanisms of advection and diffusion of a fluid mixture act to prevent segregation of components in general, so other physical phenomena need to be utilized to counter mixing. However, when the fluid components of the mixture are immiscible, diffusion of one species into the second is slow compared to the advective time scale of the fluid mixture. In this situation, fluid drops of one species deform and migrate, and the dynamics of the drop within the base flow can act toward coalescence, where smaller drops merge to form fewer, larger drops, or disperse and become finer. The drop dynamics depends on the surface tension between the two fluids, assuming evaporation and condensation effects are negligible. Further, as capillary effects become more significant, changes pressure fluctuations along the flow path can become sharp, leading to reduced performance in the condensers, or even equipment damage. The fundamental study of liquid drop dynamics in a gas has been of interest for many years. A phenomenological mapping of the different outcomes of the collision of two liquid drops was perfomed by Qian and Law [21]. In these experiments, using water drops initially and comparing the results for hydrocarbon liquids, they found that several outcomes are possible. The drops can coalesce and form a larger, single drop. The drops can bounce off of each other, or the drops