鼓泡塔气液两相流不同曳力模型的数值模拟

采用欧拉-欧拉双流体模型对圆柱形鼓泡塔内气液两相流动进行了三维数值模拟. 通过UDF自定义程序对气相出口边界进行了速度修正，解决了模拟中自由区域内有漩涡的问题；分别使用单一气泡尺寸模型和群体平衡模型(PBM)计算气泡尺寸，并比较其对气含率分布的预测结果，分别采用Schiller-Naumann, Grace和Tomiyama曳力系数模型进行模拟. 结果表明，在全塔径均匀进气的简化条件下，单一气泡尺寸模型不适用，在合适的Hamaker数下，PBM模型中原用于颗粒计算的Abrahamson模型可计算气泡聚并速率；Tomiyama曳力模型耦合PBM模型可更好地描述塔内流动情况，并与文献值吻合良好. Schiller-Naumann模型所得平均气含率与实验值相差约40%，而Grace模型所得湍动耗散比Tomiyama的结果高14.5%，气含率分布与文献值相差16.3%.

Numerical Simulation of Gas-Liquid Two-phase Flow in a Bubble Column with Various Drag Models

A 3D numerical simulation of gas-liquid two phases flow in a cylindrical bubble column was conducted with Euler-Euler two-fluid approach. The gas velocity on outlet boundary condition was corrected by user-defined function (UDF) custom programs, which could prevent the flows above the liquid level from forming eddy. The single bubble size model and population balance model (PBM) were used to calculate the bubble size separately, and the results by using the two models were compared. Three drag models (i.e. Schiller-Naumann, Grace and Tomiyama models) coupling with PBM were used and analyzed. The results show that the single bubble size model is no longer appropriate for the uniform air inlet boundary condition; The Abrahamson model in PBM, which is used for particle aggregation, can calculate the bubble aggregation if an appropriate Hamaker constant is set. The predicted results by using Tomiyama model coupling with PBM model are in good agreement with the existing results reported in the literature. The average gas holdup by using Schiller-Naumann model is about 40% different from the experiment value. The turbulent kinetic energy dissipation by using Grace model is 14.5% higher than the result of Tomiyama model, the errors of the predicted gas holdup distribution caused by using Grace model is 16.3%.