| In the polymerization stirred reactor,it is common to use the multiple axial flow impellers.The multiple impellers can realize the rapid mixing of the fluid in the whole reactor.At the same time,in order to achieve efficient mixing in the axial direction,a draft tube is often used.However,using the draft tube in the stirred tank with large height-diameter ratio requires relatively high cost on initial investment and maintenance.Therefore,it is of great practical significance to realize axial efficient mixing without draft tube in such a tall stirred tank.In this work,the flow field structure in the stirred tank with 5 doubleblade CBY impellers is experimentally investigated.The macroscopic mixing effect in stirred tank was evaluated by tracer particle method and conductivity method.The results show that part of the axial back mixing flow output from the bottom impeller can not reach the level of top impeller,but can be sucked by the middle impellers and therefore leave the axial circulation.Then,the flow fields of multiple CBY impellers under different power consumption were measured by PIV technology.The results show that as the increase of impeller power consumption,the increase of axial backmixing flow is not obvious,resulting in the insufficient utilization of the energy input by the impellers for axial flow cycle.Based on the experimental results on axial circulation of multiple CBY impellers,two optimization schemes of CBY was proposed: adding vertical auxiliary blade,or arc auxiliary blade.The results showed that the vertical auxiliary blade can only intensify the radial flow,while the arc auxiliary blade can improve the axial circulation effect and reduce the energy consumption of the blade to a certain extent.By changing the bending length and tip angle of the arc auxiliary blade,the results showed that the impeller can achieve better axial circulation with a the large bending length and small tip angle. |
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