Slug bubble deformation and its influence on bubble breakup dynamics in microchannel

The deformation of moving slug bubbles and its influence on the bubble breakup dynamics in microchannel were studied.Three bubble morphologies were found in the experiment:slug,dumbbell and grenade shapes.The viscosity effect of continuous phase aggravates the velocity difference between the fluid near the wall and the bubble,resulting in that the continuous phase near the bubble head flows towards and squeezes the bubble tail,which causes the deformation of bubbles.Moreover,the experimental results show that the deformation of bubbles could significa ntly prolo ng the bubble breakup period at the downstream Y-junction.There exists the critical capillary number Ca_(Cr )for the asymmetric breakup of grenade bubbles,Ca_(Cr )increases with the rise of flow rate and viscosity of the continuous phase.

CFD-PBM simulation of bubble coalescence and breakup in top blown-rotary agitated reactor

Gas–liquid flow and bubble coalescence and breakup behavior were studied in a top blown-rotary agitated reactor for steelmaking.Several important models of bubble coalescence and breakup mechanisms were considered and compared,and water model experiment was carried out to verify and optimize the mathematical models.The influence of different operating parameters including paddle arrangement,stirring speed and top blowing flow rate on the bubble size and distribution was revealed.The results show that the predicted bubble size and distribution present a good agreement with the experimental results using the improved Luo–Laakkonen combination model.As the position of the stirring paddle moves from the center to the side wall,the bubble distribution in the reactor becomes more uniform,and the bubble size gradually decreases.With the increase in the paddle rotation speed,the bubble size decreases.However,this effect begins to weaken when the paddle rotation speed exceeds 150 r/min.Increasing the top blowing flow rate will increase the bubble size in the reactor,but it has a weak effect on bubble dispersion.When the top blowing rate exceeds 2.0 m^(3)/h,the bubble size in the bath is basically not less than 5 mm.

Simulation of bubble column reactors using CFD coupled with a population balance model

Bubble columns are widely used in chemical and biochemical processes due to their excellent mass and heat transfer characteristics and simple construction.However,their fundamental hydrodynamic behaviors,which are essential for reactor scale-up and design,are still not fully understood.To develop design tools for engineering purposes,much research has been carried out in the area of computationalfluid dynamics(CFD)modeling and simulation of gas-liquidflows.Due to the importance of the bubble behavior,the bubble size distribution must be considered in the CFD models.The population balance model(PBM)is an effective approach to predict the bubble size distribution,and great efforts have been made in recent years to couple the PBM into CFD simulations.This article gives a selective review of the modeling and simulation of bubble column reactors using CFD coupled with PBM.Bubble breakup and coalescence models due to different mechanisms are discussed.It is shown that the CFD-PBM coupled model with proper bubble breakup and coalescence models and interphase force formulations has the ability of predicting the complex hydrodynamics in differentflow regimes and,thus,provides a unified description of both the homo-geneous and heterogeneous regimes.Further study is needed to improve the models of bubble coalescence and breakup,turbulence modification in high gas holdup,and interphase forces of bubble swarms.