Hydrodynamics Simulation Of Vertical Flow Sedimentation Tank

Settling tank is an important equipment in water treatment process. The performance of the settling tank can impact the removal efficiency of suspended solids in the system. But the flow pattern in settling tank is complex, and the turbulence, the density of solid particles, viscosity and particle size can impact operation of settling tank. The numerical simulation of solid-liquid two phase flow of settling tank is the important method to study the settling tank’s hydraulic and sedimentation performance, it has important reference value to optimize the design of settling tank.In this paper, the density of solid particles and solid particle size distribution are determined by the experiments, and the settling velocity model of flocs in settling tank is established. The relationship between settling velocity and concentration is conformed to the model of Vesilind. A velocity model, which can describe the materials characteristics, is obtained by numerical fitting technology.Liquid viscosity changes with the concentration of solid in the settling process, and the change of viscosity can affect the flow pattern of liquid. Meanwhile, it can also impact on the sedimentation performance and the compression performance of the solids. The paper determined the viscosity in various concentration of the solids, which can provide the correct parameters for CFD analysis of settling tank.According to the experiment, a CFD multiphase flow Euler model with k-Epsilon turbulence model is used to simulate the settling tank, and also the user defined velocity model and viscosity is obtained by numerical fitting technology, which made a connection between solids concentrations and viscosities. This paper used the ANSYS CFX software simulated the vertical flow settling tank in laboratory and studied the flow field and particle concentration distribution in the settling tank. At last, the several appropriate measured points were selected to collect the data, and make comparison with the simulation result. The simulation results were conformed to the experiment data basically. The CFD model established can described the actual operation situation of the tank, and can provide better references for further settling tank simulation and design.