CFD Simulation Study On The Flow And Mixing Performance Of Shear Thinning Fluid Inside SMX Static Mixer

Static mixer is a widely used industrial mixing equipment,without mechanical rotating parts,easy to install and use.Among them,the SMX static mixer has the advantages of good mixing effect and reduced pressure when used for non-Newtonian fluid mixing.At present,there are few studies on the flow characteristics and mixing laws of shear thinning fluids in SMX static mixers.At the same time,the mechanism of the influence of the structural parameters of the SMX static mixer on the mixing effect is still unclear.In this paper,the computational fluid dynamics(Computational Fluid Dynamics,CFD)method is used to simulate the shear thinning fluid flow and mixing process in the SMX static mixer.Combined with the CFD simulation results,the fluid flow and mixing mechanism in the SMX static mixer are analyzed and explained,and the influences of the structural parameters on the mixing effect is studied to guide the industrial application of the SMX static mixer.The flow rule of shear thinning fluid in SMX static mixer was systematically studied.Compared with Newtonian fluids,the viscosity and velocity field distribution of shear thinning fluids in SMX static mixers was uneven:under laminar flow conditions,the velocity gradient was smaller,and the average viscosity of the fluid in the mixing unit was large;under turbulent conditions,the velocity gradient was large,and the average viscosity of the fluid in the mixing unit was small.The maximum speed in the mixing element could reach to 2.5 times of the inlet speed.With the increase of the flow rate,although the viscosity of the fluid was decreased,the overall pressure drop of the mixer was still significantly increased.Therefore,the laminar flow should be selected for the mixing of the shear-thinning fluid.The mixing regularity of shear thinning fluid in SMX static mixer was systematically studied.Increasing the flow rate helped to improve the mixing effect of the fluid,but the increase in flow rate would cause a significant increase in pressure drop.Considering the pressure drop and mixing effect comprehensively,for the xanthan gum-water system and mash-concentrated sulfuric acid system,a suitable inlet flow rate was given.The calculation results showed that when the fluid flowed through the mixing element,the radial flow and confluence of the fluid were achieved under the guidance and cutting of its internal structure.Due to the certain angle of the plates,the radial mixing of the fluid was strengthened,thereby promoting its uniform distribution in the radial direction.The effect of the structural parameters of the SMX static mixer on the mixing effect of non-Newtonian fluids was systematically studied.As the number of plates increases,the division of the fluid was strengthened,the velocity gradient inside the mixing element was increased,the overall viscosity was effectively reduced,fluid flow and mixing were promoted,and the overall pressure drop continued to increase.As the width of the plate increases,the velocity gradient of the shear-thinning fluid in the mixer increased,the viscosity decreased,and the mixing effect was improved.The overall pressure drop trend was to decrease first and then increase.Considering the pressure drop and mixing effect comprehensively,the recommended number of plates for the SMX static mixer used for shear thinning fluid mixing was 8-10,and the recommended plate width range was between 0.0275 m and 0.03m.