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Athough the Grace curve is often used to select the material components and optimal flow rates in blending operations, its validity for industrial mixing practice remains to be seen. Among other reasons, the flow field in industrial mixers is not homogeneous. This causes the actual shear/ elongation rate imposed upon a (moving) droplet to be time‐dependent. To investigate the importance thereof, analytical models are used which describe the droplet stretching rate as a function of the droplet shape, viscosity ratio and time‐varying capillary number. Both experiments and model predictions show that droplet breakup can be caused by inhomogeneous flow fields, even if the average capillary number is sub‐critical. Moreover, the model predicts how the critical capillary number is influenced by a non‐spherical initial shape. At higher aspect ratios the critical capillary number can be reduced significantly, especially for higher viscosity ratio droplets.

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