Distribution Regularity of Dynamic Viscosity Blind Region behind the Bubble in Shear-Thinning Fluids under Different Gravity Levels

Abstract

The gas-liquid two-phase flow has been widely applied to the field of space technology, such as thermal energy and power generation, long duration life support systems, transportation for propulsion, etc. (Microgravity Sci. Technol. 21, 175-183 (2009); Microgravity Sci. Technol. 22, 87-96 (2010); etc.). Through reviewing previous researches, it can be found that a dynamic viscosity blind region (almost not influenced by the shear-thinning effect) appears behind it when one bubble rises in the shear-thinning fluid (J. Non-Newton Fluid. Mech. 165, 555-567 (2010); Phys. Fluids. 29, 033103 (2017), J. Non-Newton. Fluid. Mech. 239, 53 -61 (2017); etc.). As a matter of fact, the occurrence of the viscosity blind region has the important effect on heat and mass transfer between bubble and liquid phases. Therefore, volume of fluid method is implemented to study the formation and evolution mechanisms of the viscosity blind region in the shear-thinning fluid. The results show that the viscosity blind region can be split into two regions, namely the first and the second viscosity blind region. The stronger the gravity level and the shear-thinning effect are, or the smaller the surface tension is, the more easily the viscosity blind region appears in the bubble wake. The viscosity blind region appears much easily in the wake of a skirt bubble under the same conditions. And in the rising process of the bubble, there is a stagnant flow region in the bubble wake, where the shear rate is very small, so the viscosity blind region appears in that region. In addition, the appearance of double wake vortices can split the stagnant flow region into two parts, which leads to the formation of the second viscosity blind region.