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04. Boiling and Multi-Phase Flow

Numerical simulations of drop deformation and breakup in linear shear flows made up of shear-thinning fluids

Few studies have been reported on shear-induced drop/bubble deformation and breakup in immiscible non-Newtonian (shear-thinning) fluids compared to that in Newtonian fluids. Of special significance is the fact that the study presented here is the first study of shear-induced drop deformation (and breakup) in immiscible shear-thinning fluids. In the study presented here, simulations of shear-induced drop deformation and breakup in shear thinning fluids are reported in which the coupled level set/volume-of-fluid (CLSVOF) method is used to numerically represent the deforming drop/shear-thinning fluid interface. The initial flow conditions and boundary conditions correspond to an initially imposed simple linear shear flow generated by a driven (moving) top wall (+V) and a stationary bottom wall. It is shown that the drop deformation becomes noticeably suppressed as the Carreau (Cu) number is increased (i.e. as the shear-thinning property is strengthened). A drop in a driven shear-thinning flow will exhibit different morphology in comparison to a drop in a driven Newtonian flow. Additional driving force is needed in order to compensate for the shear-thinning (i.e. decreasing viscosity with shear) property of the continuous phase fluid in order to obtain equivalent effects on the deforming droplet in comparison to the deforming drop in Newtonian driven flow. In this study, the concept (definition) of an effective viscosity defined using an effective shear-rate is considered in order to organize the morphology of shear-induced drop deformation/breakup in shear-thinning fluids. Effective Reynolds (Re_eff) and Capillary (Ca_eff) numbers are proposed based on the effective viscosity. The introduction of the effective viscosity, taking into account the shear thinning property, enables practitioners to have a unified view of drop deformation and breakup irrespective of the continuous phase fluid ranging from purely Newtonian to Non-Newtonian with strong shear-thinning properties.

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Author Information

Asumi Kato
Ms.
Presenting author
Mitsuhiro Ohta
Prof.
Corresponding author
Edwin Jimenez
Dr.
Mark Sussman
Prof.