Effect of flow type, channel height, and viscosity on drop production from micro-pores

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The formation and detachment of drops from micron-sized pores into shear flow fields is investigated using numerical simulations. The open source software OpenFOAM is used for the simulations. The numerical algorithm employs the finite volume method for solving the mass and momentum conservation equations with a volume-of-fluid approach for capturing the fluid-fluid interface. In addition, a contact model accounts for the interaction between the fluids and the walls of the channel and pore. After validating the numerical models and methods by comparison to experimental data, a parameter study is performed to investigate the effect of various geometrical, flow and fluid parameters on the characteristics of drop production, in particular, drop size. The effect of the type of imposed channel shear flow (pressure-driven or plane Couette), channel height and fluid viscosity is considered. It is found that, in one range of Reynolds and capillary numbers, the channel wall shear rate is a good indicator of drop sizes, regardless of imposed shear flow type, channel height or viscosity ratio. In this flow regime, a master drop size curve is produced for each viscosity ratio considered, with the curve being shifted lower for the higher viscous disperse phase. In another flow regime, when Reynolds numbers are very large relative to capillary numbers, the average shear rate in the channel was a better drop size indicator, although a different master curve was produced for each channel height. © 2014 Elsevier Ltd.

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Chemical Engineering Science