Numerical Simulation On Agitated Flow Field Of Submersible Mixer And Study On Impeller Optimization Design

With the development of China’s urbanization and industrialization, sewage emissions increase sharply, the submersible agitator as major sewage treatment equipment, has been widely used in the city life sewage treatment plant aeration tank and anaerobic tank to treat wastewater and the mixing effect of the sewage treatment has important implications. Impeller is the important device, in the mixing process, it transformed the rotating mechanical energy into kinetic energy of fluid. The impeller structure and running situation are the important factors that affect the flow field distribution. Although we have done many of the experimental and theoretical studies to research submersible agitator, but the relevant theory and design methods is still not perfect. With the development of computer technology, using computational fluid dynamics (CFD) method to study the flow of fluid mixing in submersible agitator is gradually developed. The study on the flow and mixing characteristics using computational fluid dynamics (CFD) research methods gradually developed. In order to save investment, improve mixing effect effectively, using CFD technology to research the mixing flow field in submersible agitator, will have reference value to the research, development and design of agitator.In this paper, in order to facilitate calculation, sewage mixing tank is simplified to a mixing tank, It will not cause bigger effect to the stir simulation, but can greatly reduce the cost and time, and reduce the requirements for computer hardware.We established the agitator model based on the Euler-Euler view, adopt standard turbulence model to describe the turbulence properties of fluid phase, then by using the method of multiple reference acquire a three-dimensional numerical simulation of fluid within the agitator, observe and analyze the mixing flow field, and focus on the analysis of the change of the structure size and geometry parameters of the agitator on the mixing flow field distribution, and thus to optimize the mixing container structure size and geometry parameters.Through the comparative study of different blade forms found that the flow velocity distribution is formed by axial-flow blades is better than radial-flow blades. The off-bottom distance of the blades will have a major impact to the flow field,this distance is too large or too small will affect the mixing effect. When the distance is too large will result in the mixture deposition within stir region, when the distance is too small is not easy to control the fluid velocity of the impeller, resulting in uneven mixing. In a certain volume of a stirred tank, the size of the impeller has a direct impact on the stirring effect. Blade diameter is too small, there will be a flow blind spot, the mixing is less effective, the smaller the diameter blades, and this situation is more obvious. But when the blade diameter is too large, there will be two recirculation zones, which is not conducive to control the mixing speed, making the mixing liquid particle concentration is uneven. For stirring speed on the mixing effect, through the simulation analysis, we can find that the change of stirring speed would have a great influence for the stir mixing flow field, but considering the impeller strength, durability, mixing power and other factors, the stirring speed is not the faster the better to it is need to determine a reasonable speed in the comprehensive factors.After the comparison and analysis, found that when we choose eight pieces of axial flow type blades, the blades size is500mm, the distance from blades is0.4m, and mixing shaft speed is300r/min, we can get a good mixing effect, the distribution of flow and pressure field is more stable, and it can better meet the practical application.