Study On The Mixing And Deformation Characteristics Of Flexible-Blade Impeller

Stirring and mixing operations are used as a basic unit operation in various industries,such as food,pharmaceutical,wastewater treatment,etc.The stirrer has a direct influence on the characteristics of the flow field,the stirring effect and the mixing efficiency by changing it's structural forms.Related studies had found that the fluid-solid interaction is stronger during the stirring process due to the different material properties of the flexible stirrer,which makes the advantages of the flexible stirrer have certain advantages in the stirring and mixing operations.Based on this topic,the traditional Rushton and the flexible Rushton(obtained by replacing the original rigid blades with blades of the same size rubber material)were studied.The mixing characteristics of the two kinds of impellers were compared and analyzed by using PLIF experimental test and CFD numerical simulation;And the micro-strain characteristics of the flexible Rushton were experimentally studied by the infinite torque test technique.The mixing characteristics of the two kinds of impellers in the water-based stirring tank were analyzed by comparing the data obtained by the PLIF experiment.The data includes the Rhodamine 6G concentration distribution map,histogram of fluorescerthe concentration values of the Rhodamine 6G,etc.The results showed that the value of the mixing time is gradually decreasing with the increase of the rotational speed.The mixing time of the flexible Rushton is smaller.And the time for the Rhodamine 6G to diffuse to the near liquid level(P4)and the bottom of the tank(P1)are shorter.The flexible Rushton can disperse the Rhodamine 6G more quickly,and the mixing efficiency and speed are superior to the traditional Rushton.The mixing time and tracer concentration distribution of the two types of impellers at different monitoring points were analyzed by CFD numerical simulation.The results show that the response curve of the tracer concentration increases with time and then decreases.After a period of fluctuation,it gradually becomes balanced.The mixing time obtained near the edge of the impeller is relatively small,and the mixing time measured away from the impeller is relatively large.This is consistent with the experimental measurements.The magnitude of the mixing time and the degree of fluctuation of the concentration curve are related to the position of the monitoring point.The mixing time is not much different when the rotation speed is constant and the stirring medium is different.And the difference lies in the fluctuation degree of the concentration curve.In the three planes of z=30 mm,z=100 mm and z=170 mm,the tracer distribution in the flexible Rushton is better,and the tracer concentration is higher of the traditional Rushton in the plane of z=240 mm,but the tracer distribution in the flexible Rushton is closer to the centerline of the tank.Finally,the strain variation of the flexible Rushton was measured by the infinite torque test technique.The main conclusions obtained are as follows:The strain curve of the flexible Rushton is similar to the sinusoidal curve,floating around a certain value(mean value).And the mean value of the strain becomes larger with the increase of the rotational speed.The variation of the maximum,minimum and mean values of the strain with the rotation speed are basically similar,and all become larger with the increase of the rotational speed,which proves that the interaction between the fluid and the impeller is continuously enhanced with the increase of the rotational speed;The fluctuation range of the strain increases with the increase of the rotation speed in the lower speed range,but when the speed reaches 2 r/s.the fluctuation range decreases with the increase of the speed.