Numerical Simulation Of Bubble Behavior In Three Phase Flow

In this paper,three-dimensional geometric model was established and initial boundary conditions were set to study and analyze bubble dynamics behavior in gas-liquid-solid three-phase flow by coupling discrete element method(DEM)and volume of fluid(VOF).The mesh size of 1-0.5mm was determined by the grid-independent verification in this paper.The settlement velocity curve of single particle was calculated in order to verify the feasibility of the DEM-VOF algorithm introduced in this paper.The calculated results were consistent with the theoretical analysis.In addition,the process of particle community entering water was simulated to verify the good volume conservation of the algorithm.Finally,the rising motion of the stationary bubble with a diameter of 10 mm was calculated in liquid-solid suspension.And the relative error was within 6% compared with the experimental data in the literature.Numerical simulations were performed to investigate the behavior of single orifice bubbles with particles lying at the bottom and settling freely,as well as the effects of bubble behavior.The results showed that the bubble growth could be divided into three processes: expansion,shrink and detachment.The first bubble was always much larger than the subsequent bubbles,and there were the bubble breaking and coalescence behavior in the bubble rising process.When particles settled freely,the detachment time was much faster,and the diameter of the first bubble was small.The particle volume fraction and particle density had little effect on bubble behavior.The detachment time of the first bubble decreased with the increase of gas velocity and orifice size.The detachment velocity and diameter increased with the increase of gas velocity and orifice size.Reducing the surface tension or increasing the liquid density can shorten the bubble detachment time.The bubble diameter increased with the increase of surface tension and slightly decreased with the increase of liquid density.Moreover,the increase of liquid density made the bubble detachment velocity increase obviously.In addition,the bubble behavior of double and three orifices had also been investigated.It was found that the multi-orifices bubbles no longer rised vertically,but moved upward in an oblique direction towards the wall.Compared with the time difference and the simultaneous air intake,it can be seen that the air intake with time difference can accelerate detachment of bubbles in double and three orifices.The in-depth and systematic study of bubble behavior in three-phase flow can not only provide basic data for optimal operation of multiphase reactor,but also promote the development and application of novel reactors.The simulation results have certain guiding significance for industrial practice.