Study On Motion Characteristic Of Bubbles In Non-Newtonian Fluid

The bubble motion in non-Newtonian fluid is widespread in practice processes,such as chemical,environment,mineral and environmental processes.In-depth study of bubble motion in fluid will help to optimize the design of process equipment such as bioreactor and bubble column.This paper mainly study the formation behavior of single bubble in shear-thinning fluids,the numerical simulation of the interaction between bubbles and the trajectory of rising bubbles in viscoelastic fluid.The formation behavior of single bubble in power-law fluids(carboxymethy cellulose solution,CMC)and Newtonian fluids(glycerol solution)was experimentally investigated via a high-speed camera.The effects of liquid property,orifice diameter and gas flow rate on bubble volume and aspect ratio were observed.It was found that the formation time and detaching volume increased with the rising of fluid viscosity.And the increase rate of bubble aspect ratio during the bubble formation process was complex,with main emphasis on the decrease in the initial stage and an increase in the final stage along with the shear thinning property.Nevertheless,the bubble detaching volume,instantaneous volume and formation time increased following the increase of orifice diameter and gas flow rate.On the contrary,the bubble aspect ratio decreased with the orifice diameter but increases with the gas flow rate.In order to study the stability trajectory of the bubbles rising in viscoelastic fluid,the three kinds of different concentrations of viscoelastic fluid(Polyacrylamide-the PAA solution)were used to analyze the motion trajectory of bubble rise in this paper.It was found that the bubble trajectories in viscoelastic fluids are mainly divided into two types: straight path and helical path.The trajectories of the bubble are related to the shape of bubbles and the concentration of the fluid,the greater the bubble deformation,the more easily change from straight to spiral of the trajectory.The trajectory of the bubble also is related to the viscoelastic shear thinning fluid physical properties,with increasing the solution concentration,the bubble trajectory change from straight to spiral of the trajectory.Through screw diameter pitch ratio r/L represents spiral bending degree,get along with the increase of Re,pitch screw diameter ratio also more and more big,finally gradually stabilized.2-D VOF method was simulated to study in the effect of different size,distance and solution concentration on the interaction between two bubbles.It was found that the interaction between the first and the following bubble is related to the center distance between the two bubbles in the process of on-line simulation.The smaller the dimensionless distance S*,the shorter the time that the first and the following bubble gather to form a large bubble.When the dimensionless distance S* increases to a certain value,the two bubbles will not coalescence and eventually rise at different speeds.The dimensionless distance S* is related to the concentration of the solution.With concentration of the solution increases,the dimensionless variable distance S* increases and the ratio of the first bubble to the following bubble decreases,until the first and the following bubble velocity of the ratio is 1,the following bubble is not affected by the wake of the preceding bubble.In the horizontal interaction process,the interaction between the bubbles is related to the distance between the bubbles.With the distance between the bubbles increases,the interaction between the bubbles becomes mutually attraction to exclusive.The larger the two-level bubble is,the smaller the critical distance between the bubbles.At the same initial distance,the smaller bubble will easy to be interacted to a large bubble.The higher the concentration of the shear thinning fluid is,the smaller critical distance between the bubbles.