The Experiment Study And Numerical Simulation On The Gas-Liquid Two Phase And Gas-Liquid-Solid Three Phase Flow In Bubble Column

Because of the high mass transfer efficiency, low energy consumption, simple structure and other obvious advantages, the bubble column reactor is widely used in petroleum chemical industry, biological chemical industry and so on. But so far, the understanding of the flow field in the bubble column remains very limited. The rapid development of computational fluid dynamics(CFD) provides a new way to study the flow field of the bubble column.In this paper, the gas-liquid two phase and gas-liquid-solid three phase flow in the bubble column are simulated with Euler-Euler two-fluid approach in ANSYS-Fluent software platform. In order to save the calculation time, column diameter uniform air inlet condition is used for simplification, which reduced 75%~80% of the grid number and calculation time. The single bubble size model and population balance model(PBM) are compared, and it turns out that the single bubble size model is no longer appropriate for the simplified condition, and the results by using PBM model are in good agreement with the experiment value. The Abrahamson model, which originally used for the particle aggregation, can also calculate the bubble aggregation with an appropriate Hamaker constant in the calculation of PBM model.To solve the problem of liquid escape at the outlet boundary and the eddy forms in the free area, a new boundary was used in this paper, which corrected the air and liquid velocity at the outlet boundary condition. In this way, the flow near the liquid level becomes uniform and stable, and the calculation is easier to converge.To determine the applicable drag model in the calculation of gas-liquid two phase flow, three drag models, such as Schiller-Naumann, Grace and Tomiyama models are used for calculation. After comparing the calculate value and the experiment value, the results confirm that the predicted results by Tomiyama model agree well with the experiment value.Experiments are implemented to study phase holdup distribution rule in the gas-liquid-solid three phase flow. A 1.5 m high bubble column with sampling devices are used, and the radial distribution of phase holdup at five axial heights are measured and analyzed with two superficial gas velocity of 0.01354 m/s and 0.01805 m/s.In the simulation of gas-liquid-solid three phase flow, the real experimental device is taken as the geometric model. The solid phase is added into the previously established gas-liquid two phase model, and an transient simulation has been conducted. The gas holdup distribution agrees well with the credible range of the experiment value, which verified the validity of the model used for gas-liquid phase flow again. The trend of the solid holdup distribution is the same with the experiment value, but the simulated data are larger than the experimental values overall. The possible reason is the density difference between solid and liquid phase and simple sampling method, which made the measured solid holdups smaller than the real ones.