Numerical study on the influence of liquid viscosity ratio on the hydrodynamics of a single bubble in shear-thinning liquid

Abstract

The volume of fluid method combined with the adaptive grid method is used to study the influence of shear-thinning liquid viscosity ratio (ε) for various values of rheological index (n) and characteristic time (λ) on bubble shape, rise velocity, and apparent viscosity around a bubble; where 1/λ represents the shear rate at which the change in the viscosity curve occurs from the low shear rate to the power-law region. The results show that, depending on the magnitudes of n and λ, the bubble shape and deformation parameter are strongly related to ε, and bubble shape can exhibit both stable and unstable states. There are two types of deformation phenomena for the unsteady deformation of bubbles. First, the aspect ratio changes with time, whereas the shape remains similar throughout. Second, the shape changes periodically with time. For the given values of n and λ, the bubble rise velocity at large time shows a nonlinear increase as ε increases from 10 to ∞. Under the conditions of n ≤ 0.3, λ* ≥ 68.6, and ε ≥ 100 (λ* is the dimensionless characteristic time), a viscosity blind region (a region of high viscosity, where ε is close to 1) appears behind the bubble. The tendency for the viscosity blind region is to reduce the bubble rise velocity at large time.