In order to study the gas dispersion and backmixing′s effect on its function in a gasliquid mixing reactor, on the basis of the computational fluid dynamics (CFD) software package Fluent 6.2, with a Euler model of liquid phase, and a discrete phase mode (DPM) of gas, discrete gas phase gasliquid flow in a dual sixbladediscturbine (6-DT) impeller mixing tank was numerically simulated. The macro flow field and gas residence distribution in the mixing tank was obtained. By counting bubbles escaped from the vessel at different times, gas residence time distribution in the tank was analyzed. The simulation results show that typical double circulation pattern is formed for every disc turbine and there are four circulation loops in the mixing tank. Gas easily gathers together at the center of the circulation loops, which leads to high local gas holdup there and relatively low gas holdup in the bottom region and regions between two impellers. The curve of gas residence time distribution displays as a singlepeak and a long tail, which is mainly affected by flow patterns, bubble sizes and operating circumstances. To increase impeller speed or decrease gas flow will be helpful for backmixing and gas dispersion in the mixing tank.
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