Study On Chaotic Mixing Intensification Of Liquid-Liquid In Mixer Settler

Mixer settler is mainly composed of mixing chamber and clarification chamber.Because of its advantages of simple structure,stable operation,convenient operation and strong adaptability,it is currently the most widely used extraction and separation equipment.However,traditional mixer settler also has the problems of low separation efficiency,serious emulsification and high energy consumption,which seriously reduces the efficiency of extraction and separation.Impeller is main component of mixing chamber and the choice of impeller has a direct influence on mixing performance.Therefore,design and optimization of impeller is an important means for enhancing liquid-liquid mixing in mixing settler.There is an isolation zone in mixing chamber,which reduces the mixing effects of liquid-liquid.Rigid-flexible combination impeller was is to destroy the isolation zone,so that more fluid could enter chaotic region and enhance the mixing of liquid-liquid.It has important value to improve the mixing effect of mixer settler.In this thesis,firstly,the pressure data signals were collected by experiments,and largest Lyapunov exponent?LLE?was calculated to characterize the fluid chaos in mixing chamber.The law of liquid-liquid chaos mixing enhancement for rigid-flexible combination impeller was discussed.Then,Particle Image Velocimetry?PIV?was used to study the influence of rigid-flexible combined impeller on structure and velocity field distribution of continuous phase.Effects of impeller structure,aperture ratio and baffles on flow field were discussed.Finally,method of Computational Fluid Dynamics?CFD?simulation was used to study the mixing of liquid-liquid,and the strengthening of mixing was analyzed by rigid-flexible combination impeller.The results showed that:?1?When the speed was 200r?min^-1,LLE of Double Rigid-flexible Rushton Turbine impeller?DRFRT?system was 68.4%higher than that of Double Rushton Turbine?DRT?impeller system.When aperture ratio was 10.7%,chaotic mixing effect of flow field was the best.Compared with Rushton Turbine?RT?impeller system,LLE of Rigid-flexible Rushton Turbine?RFRT?impeller system was about 11.5%higher.The installation of baffles could improve LLE,chaotic mixing of flow field was strengthened.Through PIV measurement,it was found that rigid-flexible combination impeller could eliminate the mixed isolation zone and improve the flow velocity of the continuous phase.Baffles deflected axial flow of flow field,increased axial and radial velocity,eliminated vortex phenomenon occurring in mixing process.?2?In double impeller system,CFD simulation showed that holdup of dispersed phase in mixing chamber of DRFRT system was obviously higher than that of RT system.When the speed was 200r?min^-1,holdup of dispersed phase???in mixing chamber was the highest,which was 0.161.Rigid-flexible combination impeller could effectively eliminate the mixed“dead zone”between upper and lower blades,making the velocity distribution of dispersed phase more homogeneous and improving the mixing effect.The addition of baffles increased holdup of dispersed phase by about75%,and improved the mixing effect of liquid-liquid.?3?In single impeller system,when the rotational speed was 100r?min^-1 and150r?min^-1,holdup of dispersed phase in RFRT system was the highest,which was0.162.The installation of baffles increased holdup of dispersed phase by about 52%,and reduced the reflux in mixing chamber,made distribution of dispersed phase more uniform and improved the mixing efficiency of fluid.?4?Comparing single impeller and double impeller,it was found that RFRT impeller is more favorable dispersion of dispersed phase,improved holdup of dispersed phase and reduced aggregation near axis,so that distribution of dispersed phase in mixing chamber was more uniform.Compared with DRFRT system,power number decreased by about 40%,head number increased by about 48%,and flow number decreased by about 50%.In summary,rigid-flexible combination impeller could enhance chaotic mixing of fluid through rigid blade's shearing action and multi-body motion of flexible piece,and the isolation mixed zone was destroyed.