辐流式二沉池中异重流的计算流体力学模型研究

Computational fluid dynamic model for density currents in activated sludge secondary clarifier

异重流的形成是影响活性污泥系统二沉池水力学性能的主要因素,形成异重流的主要原因包括沉淀池内不均匀的污泥分布和温度分布。采用多相流欧拉模型、标准k-ε湍流模型和Boussinesq假设研究了二沉池中活性污泥和表面散热引起的异重流。表面散热的计算采用经验方程,数值计算结果同实验结果作了比较,结果表明模型能较好地预测辐流式二沉池的流场、温度场和污泥分布。研究还表明,Fr2pGr/Re2表示了不均匀温度分布引起的浮升力与不均匀污泥分布引起的作用力的比值,用它可以判断两种作用力在异重流的形成当中的相对大小。

A major factor in deviation from optimal performance of the activated sludge secondary clarifier is the presence of density currents, resulting from the density difference and temperature difference. In this study, the density flow caused by the activated sludge and surface heat loss in radial clarifier is modeled with the Boussinesq approximation, the muhiphase Eulerian model and the standard k-ε turbulent model on a two-dimensional grid. The water surface heat loss is estimated with the experiential equations. The calculations are reported to estimate the flow pattern, and the temperature and sludge distribution for activated sludge secondary clarifier and the results are compared with the experimental data. It is suggested that Frp^2Gr/Re^2 can be used for analyzing the major cause of the density currents, buoyancy force resulting from the temperature difference, or the gravitational force from the density difference.