Study On Optimization Of Internal Flow And Mixing Efficiency Of Blade Mixing Agitator

Paddle mixer is widely used in various sewage treatment processes,and it is one of the core equipment in the mixing stage.The problem of low mixing efficiency is becoming increasingly prominent.The problems of convection and mass transfer are involved in the operation of the blade mixer,and there are many factors affecting its mixing efficiency.The optimization of its internal flow and mixing efficiency has important academic significance and engineering application value.In this paper,the model of a paddle mixing agitator is taken as the research object.The internal flow characteristics,efficiency indexes and influencing factors of different schemes of agitators under partial baffle conditions are compared and analyzed by means of numerical calculation,experimental measurement and orthogonal analysis.The main research work and achievements of this paper are as follows:Numerical calculation and PIV test measurement were carried out for single-phase flow in paddle agitator,and the influence rule of paddle speed and inclination Angle on inward flow was compared and analyzed.The results show that the numerical calculation is in good agreement with the results of PIV test,and the mixing effect can be effectively improved with the increase of blade speed.When D1/D2=0.696,the upand-down types of 60° and 90° blades are radial circulation flow,and the rotation direction is opposite.The center position of circulating flow of 60° blade is higher than that of 90° blade.The flow velocity at the bottom of the groove is small and is less affected by blade factors.Based on the single-phase numerical calculation,the influences of inlet and outlet factors of circular and square agitator tanks as well as geometrical factors of blade diameter and inclination Angle were comparatively studied.The results show that when the flow velocity is small,the inlet flow will increase the velocity gradient at the baffle on the right side of the inlet pipe of the circular stirred tank,and the influence on the flow in other regions can be ignored.The flow pattern in the square stirred tank is basically the same under the condition of inlet and outlet,and there are weak mixing zones with different strengths behind the baffle of the square stirred tank.When the blade Angle is 90°,the flow patterns of blades with different diameters are radial flows with opposite handedness.When the blade Angle is 45°or 60°,with the decrease of the distance between the baffle and the blade edge,the blade flow pattern gradually evolves from axial circulation to radial circulation,and the center of the circulation flow below it moves downward.Based on the evaluation indexes of power,mixing time and mixing energy per unit volume,unsteady numerical simulation and orthogonal range and variance analysis were carried out for liquid-liquid mixing process under different impeller diameters and inclination schemes.The results show that the convective diffusion plays a dominant role in the mixing process above the blade,while the natural diffusion only achieves mixing under the blade and there is a mixing dead zone.Nagata Jinji power empirical formula has some limitations in use;The influence weight of blade diameter on power and mixing time is greater than that of blade inclination,and the influence weight of blade inclination on mixing energy per unit volume is greater than that of diameter.The electrical conductivity test device of impeller type mixing and stirring was built,and the solution concentration in the stirred tank under different schemes was tested and analyzed.The evolution law of solution concentration in the mixing process was revealed,and the influence law of impeller geometric parameters on mixing time was preliminarily clarified.The results show that the conductivity increases linearly with the increase of solution concentration,and there is a significant correlation between them.With the increase of stirring time,the solution concentration in the stirred tank shows a trend of rapid oscillation increasing at first and then tending to be stable.The rapid increasing process of blades with different geometric parameters has obvious differences.When the blade diameter is unchanged,the mixing time of the blade with45° Angle is the shortest.When the blade Angle is constant,the mixing time of160 mm blade is the shortest.According to the 95% rule,the mixing time values of numerical calculation and test are basically the same,and the maximum relative error is 6.8%.