CFD Simulation Of Bubble And Particle Hydrodynamics In Bubble Column Reactor

Bubble column reactors,with its extensive applications in the biochemical and petrochemical industries,have been studied for decades with theoretical and experimental endeavors as an interesting and significant subject.In this work,firstly the hydrodynamics of a continuous chain of bubbles inside a bubble column reactor were simulated with the VOF method.The checking work of grid independence was firstly conducted.The grid size of 1.0 mm was concluded to be adopted in order to minimize the computing time without compromising the accuracy of the results.The predictions were validated with the experimental studies reported in the literature.Different surface tension and adhesion models were thoroughly compared in terms of axial velocity magnitude,it can be found that all surface tension models could describe the bubble rise and bubble plume in column with slight deviations.Subsequently,the effect of gas distributor and inlet gas velocity on the bubble size distribution,bubble rise velocity and its trajectory were investigated.Secondly,a combined CFD-VOF-DPM method was used to model the bubble rising and coalescence phenomena in low hold-up particle-liquid suspension systems.The influences of grid size and time step size on simulation results were tested.Accordingly,the grid size of0.2 mm and the time step size of 5×10^-6 s were adopted for rest cases in order to minimize the computing time without compromising the accuracy of the results in this work.From the validation of bubble rising velocity profiles and bubble aspect ratio data,it can be concluding that the combined CFD-VOF-DPM method can model the fluid dynamics accurately with quite small discrepancies.Bubble hydrodynamics were investigated in the isodiametric co-axial bubble coalescence of particle-liquid suspension systems.The effects of initial distance and intersection angle between the leading and trailing bubbles and bubble diameters were systematically studied.It could be found that both bubble diameter and relative initial position were of great significance for determining bubble shape and velocity profiles.The co-axial,diagonal and co-radial bubble coalescence characteristics in liquid-particle suspension systems were systematically studied for the first time.Liquid phase hydrodynamics was mainly focused on liquid pressure distributions in different simulation time which is found to be strongly influenced by the bubble coalescence.Finally the velocity vectors and distributions as well as the particle entrainment were comprehensively investigated for particle hydrodynamics.Finally,based on the aforementioned CFD-VOF model,a two-stage internal circulation guide tube was designed as the internal component of the gas-liquid bubble column.The selection of mesh precision and time step precision was based on the results of the aforementioned mesh independence analysis.The gas volume fraction distribution,velocity magnitude and vector distribution were analyzed by CFD method.