Motion Behavior And Interaction Of Multiple Bubbles And Their Drag Coefficient In The Shear-Thinning Fluids

The gas-liquid two-phase flow widely exists in chemical process,in which the mass transfer,heat transfer and momentum transfer are closely related to the motion,deformation and interaction of bubbles.In this work,the motion,interaction and drag coefficient of the multi-bubble system in shear-thinning fluids are investigated by numerical simulation and experiment,the main contents are as follows:The rising motion of bubbles continuously generated by one or two nozzles in shear-thinning fluids is visually analyzed by a high-speed camera,the effects of the nozzle size,nozzle distance,gas flow rate and liquid rheological property on the generation,motion and coalescence of bubbles are investigated.For the generation and rising process of bubbles formed continuously from a single nozzle,the formation size of the bubble increased with the increases of the nozzle diameter and gas flow rate,and the enhancement of the shear-thinning effect of the liquid.The enhancement of liquid shear-thinning effect could intensify the wake effect of leading bubble,and increase the acceleration and rising velocity of trailing bubble,accordingly,the height of the in-line coalescence of two bubbles would decrease.For the generation and rising process of bubbles formed continuously from two nozzles,the interaction between two side-by-side bubbles increases with the decrease of the interval between two nozzles,and the minimum coalescence height of side-by-side bubbles reduces.The motion of three equal-sized bubbles with an equilateral triangle or side-by-side arrangement in shear-thinning fluids was numerically simulated by using three-dimensional volume of fluid(3D-VOF)method.It was found that the coalescence of the bubble in horizontal direction would be enhanced with the increase of bubble diameter and generation frequency or the decrease of the initial bubble distance.The aspect ratio of the bubble declines with the increase of the bubble diameter and distance or the decrease of the generation frequency,whereas the drag coefficient of the bubble reduces with the increase of the bubble diameter and generation frequency or the decrease of the bubble distance.The shear-thinning property of the liquid becomes weakened with increasing liquid flow index,and the aspect ratio and drag coefficient of the bubble increases.According to the bubble interaction,the new models for predicting aspect ratio and drag coefficient of multi-bubble systems are proposed.Furthermore,the motion and interaction of unequal-sized multi-bubble systems in shear-thinning fluids are studied.A series of two or three unequal-sized bubbles with various arrangements are investigated and compared by 3D-VOF.The effects of the bubble diameter,initial bubble spatial arrangements and liquid property on the aspect ratio,interaction and drag coefficient of bubbles are explored.Considering the interaction between bubbles,the new prediction models of the aspect ratio and drag coefficient for unequal multi-bubble systems are proposed.