Study On Improving Anti-winding Performance Of Submersible Mixer With Blade Sweeping And Raking

As a sewage treatment equipment,submersible mixer's mixing performance has important influence on the quality of sewage treatment.In practical application,the types of pollutants in sewage are various,including many fibrous pollutants,which can lead to blade winding.With it comes,flow channel is blocked,power increases due to load aggravation,and water mixing quality declines.Therefore,studying how to improve anti-winding performance of submersible mixer has great practical significance.The content of this paper mainly includes(1)The winding critical position on the blade of the prototype submersible agitator is observed by conducting the winding test of the impeller.The winding critical point is at 0.75 blade height.There is fiber winding on the inlet edge between the hub and the critical point,and no winding between the critical point and the shroud(2)If the fiber hanging on the inlet edge can slip away from the blade,the angle of the flow direction and the tangent of the inlet edge must be less than a certain value,thus the concept of minimum winding angle is proposed.Theoretical analysis and two-dimensional winding test of inclined plates show that the minimum winding angle of woollen fibers is 63°.(3)The angle between the inlet edge of the prototype blade and the tangential velocity of the circumference on 2 dimensions is calculated,which is not consistent with the critical winding position of the winding test.So the angle between the inlet edge and the three-dimensional velocity should be considered.Methods for solving the angle between the tangent of the inlet edge of the three-dimensional blade and flow direction are established.(4)Through the analysis of the curved-sweep model,it is determined that the swept back can reduce the winding angle and improve the anti-winding performance of the impeller.According to above flow analysis on 2 dimensions,a sweep angle is first prepared.The final sweep angle is corrected to 40° by calculation and comparison.(5)Analyzing the geometric model to determine that the blade should be properly tilted forward.Through comparative analysis,a 6° forward tilt angle is adopted based on the backward-swept blade.Forerake can reduce the winding angle near the hub,but has little effect on the winding angle near the shroud.(6)The flow characteristics of the blade before and after modification are analyzed.The low-pressure area at the inlet side of the optimized blade is greatly reduced,and the lowest pressure is higher,so the suction force of the blade is smaller,which is conducive to the fiber falling off;The corner of the streamline on the inlet edge is smaller,and the streamline is straighter,which is conducive to improving the fiber passability;The abrasion of the blade surface is less,so the surface is smoother,which is helpful for the fiber to be washed away from the blade.(7)The changes of mixing field and external characteristics before and after modification are compared.The energy consumption will be increased when the blade is swept back and tilted forward.However,the flow velocity is large in the final optimized impeller channel,the dead water area of in the pool is small,and the mixing is sufficient near the wall.(8)The winding test of the optimized impeller is performed.The result shows that the inlet edge is free of winding,which verifies the feasibility of controlling the winding of agitator blades based on the minimum winding angle.