Dynamic processes in a deformed drop rising through shear-thinning fluids

The motion of a Newtonian deformed drop freely rising through shear-thinning fluids characterized by the Carreau-Yasuda model was considered experimentally and computationally. By numerically evaluating the local viscosity profiles as functions of the shear-rate and the drop shape, it is clear that a numerical approach can be very useful for understanding droplet rise velocities in shear-thinning fluid systems. It was shown numerically that the state and characteristics of the local changes in viscosity around the drop depend significantly on the drop shape. A distinguishing feature of the deformed drop is the formation of a much higher viscosity area at the rear of a drop as a result of the effect of the stagnant flow field behind the drop. Also, the rise velocity of the drop based on the modified Reynolds (ReM) and Morton (MM) numbers and the representative (effective) viscosity (Cη0) was quantitatively evaluated. The variations in these values of ReM, MM and Cη0 were then used to assess the drop rise motion in shear-thinning fluid systems from a practical viewpoint.