Simulation Of Flow Field And Liquid Residence Time Distribution Of Continuous Flow Agitated Tank

With the benefits of controlling easily, simpleness, labour-saving and so on, the kettle with agitator is widely used in petrochemical, biological Pharmaceuticals, environmental protection and other fields. It is of great significance to research the fluid flow in the agitated tank for improving the design and guiding the production. The reports about the study are mainly on batch operation, but it has not been reported how the simulation results - the "flow distribution" correspond to the actual state of fluid flow, the flow associate to the results and impact the reaction. Against the situation, in this paper, we use the CFD software to simulate flow field in the tank with the method of pulse to examine the residence time distribution in the tank. By the residence time distribution density function and variance, we analyze the influence of the fluid flow conditions on the reaction.The simulation results show that: whether single or double-blade propeller is used, increasing the speed of agitator or feed flow, the fluid flow rate will also increase and become uniform; Under the same operating conditions, the mixed results of double-propeller are better than the single-propeller; the fluid flow rate will also increase and become uniform, the dead zone will decrease in the case of using the baffle. The experimental results show that: for six straight of the turbine impeller,σ_θ~2 with the double-impeller is significantly higher than that with the single impeller, especially when the liquid flow is 60 L/h and the rotational speed is 1200 rad/min of the agitator,σ_θ~2 increasing from 0.809 to 0.877, 8.41 percent enlarged. So with the double impeller, the fluid flow is closer to full-Francis in the agitator kettle than that with the single one. That is, the new materials are able to mix easily in a short period of time by the double one. Therefore, for the continuous fermentation process which needs mixing instantly, we can choose the agitated tank with the double or more straight six-blade turbine impeller and high-speed operating conditions.