Effects of characteristic time on bubble dynamic in shear thinning fluids

Non-Newtonian gas-liquid two-phase flows exist widely in industrial and agricultural processes. The interaction between bubble and liquid phases is very complicated, which has the important influence on the transfer efficiency between phases. To understand hydrodynamic properties of bubbles in shear-thinning fluids, based on the continuous surface tension model and the Carreau constitutive model, the volume of fluid (VOF) method was used to numerically investigate the single bubble dynamics in the shear-thinning fluid. The present results showed that, the hydrodynamic characteristics of bubbles are closely related to the characteristic time λ of the liquid phase. The stronger the shear thinning degree of the liquid phase (the smaller rheological index n) or the smaller the surface tension (the larger Eötvös number Eo) is, the more obvious the effect of λ on bubble deformation and wake vortexes is. Under the same shear-thinning degree and the surface tension, the larger λ is, the higher the terminal velocity of the bubble is, and the size and strength of the wake vortex is, resulting in the wider ranges of the high shear rate region and the low apparent viscosity region around the bubble. In addition, for different degrees of shear thinning, at the conditions of low surface tension, there is a viscosity blind region at the tail of the bubble, and with the increase of the λ, the viscosity blind region gradually breaks away from the bubble and breaks up; the viscosity blind region reduces the region of the low apparent viscosity around the bubble, increases the friction drag during the floating process of the bubble, and also reduces the bubble terminal velocity. © 2021, Chemical Industry Press Co., Ltd. All right reserved.