Study On The Formation And Rising Characteristics Of Single Bubble In Yield Stress Fluid

Yield stress fluid,as a special kind of non-Newtonian fluid,has a widespread application prospect in the industrial field because of its complex rheological properties.Now,the investigations on the bubble behavior are concentrated principally on the non-Newtonian fluids,such as shear thinning fluid and viscoelastic fluid.However,the researches on the movement characteristics of single bubble in yield stress fluid are relatively lacking.It is difficult for Newtonian fluids and other non-Newtonian fluids to be applied to yield stress fluid.Therefore,the influences of nozzle inner diameter d,consistency coefficient k,flow index n and yield stress ?0 on the formation and rising process of moving single bubble in yield stress fluid are investigated via using H-B model.The main research contents are as follows:The bubble formation in yield stress fluid system is studied.Combined with Volume of Fluid method and Level Set method,a novel CLSVOF method is used to numerically study the single bubble formation process of yield stress fluid.Compared with a single numerical simulation method,the CLSVOF method can not only accurately track the gas-liquid interface,but also accurately calculate the relevant parameters.In addition,the effects of nozzle inner diameter d and rheological properties on the bubble formation time,separation volume and aspect ratio E are investigated and verified by experiments.The characteristics of bubble movement in yield stress fluid system are studied.The change of bubbles in the process of rising is investigated through experimental method.The effects of nozzle inner diameter d and solution concentration on the terminal velocity and aspect ratio E during rising bubble are investigated.It is found that with the increase of equivalent diameter,the bubble rises from steady rise to roll rise.The bubble rising characteristics in yield stress system are studied.The effects of the rheological properties in yield stress fluid on the terminal velocity and aspect ratio E of the rising bubble are investigated by the CLSVOF method.Additionally,according to the bubble deformation law of the yield stress fluid system,the bubble flow pattern diagram of the yield stress fluid system is established,and the criterion correlation formulas of drag coefficient CD and aspect rario E are fitted according to the We number and Bn number.