Numerical simulations are used to investigate the breakup of emulsion drops within a spraying nozzle. The simulations are performed by solving a two-phase flow problem in the nozzle in which individual drops are tracked through the flow field. A modified version of an OpenFOAM® solver is used as a basis for the simulations. The numerical algorithm employs the finite volume method for solving the mass and momentum conservation equations and a volume-of-fluid approach for capturing the fluid-fluid interface. Dynamic meshing is used to maintain a sufficiently refined mesh around a drop as it moves through the flow field. The dispersed phase is Newtonian, while a Newtonian and a shear-thinning non-Newtonian continuous phase are used. The simulations show two types of breakup behavior. Larger drops break up via tipstreaming in which small drops are detached from the tail of the mother drop, while smaller drops break up via filament fracturing in which the daughter drops were formed via pinching at several locations along the stretched drop. The critical drop sizes and critical capillary numbers are determined for each continuous phase fluid along various streamlines. It is found that for both continuous phase fluids, there is an initial rapid decrease in these quantities as the distance from the centerline of the nozzle increases, i.e., as strain rates and stress increase, before leveling off. Moreover, closer to the centerline, these quantities are larger for the Newtonian continuous phase than for the non-Newtonian one, even though the strain rates and stresses are larger for the Newtonian fluid. This is explained in terms of the viscosity ratios reached within the die. Finally, proper scaling of the stresses produces a master critical drop size and critical capillary number curve for the two continuous phase fluids.

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