Study On Chaotic Mixing Characteristics Of Fluid In Punched Rigid-flexible Impeller Stirred Reactor

Stirred reactors are widely used in chemical,metallurgical,pharmaceutical and food process industries,and are the core equipment in related production processes.As the critical component of the stirred reactor,the impeller provides the required energy to the fluid in the stirred tank,make the fluid form into a suitable flow field,which affects the efficiency and degree of the momentum transport,energy transport,quality transport and chemical reaction process.Traditional rigid impeller mainly transmits energy to the fluid through the shearing action of the impeller.About 70%of the input energy of the impeller is consumed at the outer edge of the impeller blade and the trailing vortex behind the impeller blade,and the fluid mixing efficiency is low.Therefore,the design and optimization of the impeller has become a hot spot in fluid mixing strengthening research.Based on the chemical process intensification and fluid chaotic mixing reinforcement theory,a new method to intensify the fluid chaotic mixing process by punched rigid flexible impeller was proposed based on the preliminary study of rigid flexible impeller.It is expected that the high-speed jet generated by the self-rotation of the punched rigid flexible impeller will strengthen the local eddy diffusion of the flow field,cause the structure instability of the flow field,induce the fluid into the chaotic mixing state,and strengthen the fluid chaotic mixing process.The chaotic characteristics and mixing performances in single-phase,solid-liquid two-phase,and gas-liquid two-phase systems in punched rigid flexible impeller stirring reactor were studied through experiments.The flow field characteristics of single-phase system,the solid-liquid suspension characteristics of solid-liquid two-phase system,and the gas-liquid dispersion behavior of gas-liquid two-phase system were studied by computational fluid dynamics?CFD?.At the same time,rigid flexible impeller was applied to intensify the manganese ore leaching process.Solid-liquid two-phase suspension characteristics and fluid-structure interaction behavior of impeller in a manganese ore leach tank were studied,and the manganese ore leaching time,leaching rate and power consumption in manganese ore leaching process were studied.The main conclusions are as follows:?1?Single phase system1)Based on the fluid chaotic mixing reinforcement theory,the study on intensification of single-phase fluid chaotic mixing by chaotic motor coupled with punched rigid-flexible impeller was carried out.The chaotic characteristics and mixing performance of fluid mixing process in the four stirring systems of R-RT impeller,RF-RT impeller,PRF-RT impeller and chaotic motor coupled with PRF-RT impeller were comparatively studied,the chaotic characteristic parameters,mixing time and mixing efficiency of the four stirring systems were obtained.Results show that,at the Reynolds number of 210,compared with R-RT impeller and RF-RT impeller system,the LLE of PRF-RT impeller system was increased by 35.4%and 14.9%,respectively,and NTm of PRF-RT impeller system was shortened by 47.7%and 29.0%,respectively.Compared with PRF-RT impeller system,the LLE of chaotic motor coupled PRF-RT impeller system was increased by 16.7%and NTm of chaotic motor coupled PRF-RT impeller system shortened by 38.1%.Meanwhile,the fitting relation between Tm and Pv was obtained.R-RT impeller system,T_m=164.61P_v^-0.548;RF-RT impeller system,T_m=130.71 P_v^-0.558;PRF-RT impeller system,T_m=98.54 P_v^-0.603;Chaotic motor coupled with PRF-RT impeller system,T_m=61.79 P_v^-0.682.In addition,the fractal dimension of the chaotic attractors in the four stirring systems were calculated.Under the same power consumption,compared with R-RT impeller,RF-RT impeller and PRF-RT impeller,PRF-RT impeller coupled with chaotic motor can effectively increase the fractal dimension of chaotic attractors in the mixing system,improve the chaotic mixing degree of the mixing system and strengthen the fluid chaotic mixing process.2)The flow field characteristics of R-RT impeller,RF-RT impeller and PRF-RT impeller were comparatively studied through numerical simulation,and the hydrodynamic properties of three types of impeller systems were obtained.Results showed that PRF-RT impeller can effectively increase the axial velocity of the fluid and reduce the size of trailing vortex behind the impeller blade compared with R-RT impeller and RF-RT impeller under the same power consumption.It indicated that PRF-RT impeller can effectively improve the impeller energy efficiency and intensify the eddy diffusion process in the stirred tank.?2?Solid-liquid two-phase system1)Based on the process intensification and turbulence theory,the suspension behavior of solid-liquid two-phase strengthened by dual rigid-flexible combination impeller was studied.The chaotic characteristics and solid-liquid suspension characteristics of solid-liquid two-phase mixing process in the three stirring systems of DR-PBDT impeller,DRFC-PBDT impeller,and DPRFC-PBDT impeller were experimental studied,and the chaotic characteristic parameters,axial local solid concentration distribution and solid-liquid suspension degree in three stirring systems were obtained.Results show that,at the Reynolds number of Re?2?10⁵,compared with DR-PBDT impeller and DRFC-PBDT impeller system,the LLE of DPRFC-PBDT impeller system was increased by 69.3%and 19.3%,respectively.The axial local solid concentration distribution in system was more uniform and the solid-liquid suspension was higher.At the same time,the fractal dimension of the chaotic attractors in the four stirring systems were calculated.Under the same power consumption,compared with DR-PBDT impeller and DRFC-PBDT impeller,DPRFC-PBDT impeller can effectively increase the fractal dimension of chaotic attractors in the solid-liquid mixing system,and improve the solid-liquid chaotic mixing degree.2)The solid-liquid suspension characteristics of DR-PBDT impeller,DRFC-PBDT impeller and DPRFC-PBDT impeller were comparatively studied through numerical simulation,and the velocity distribution,turbulent kinetic energy distribution,solid holdup distribution and solid particles suspension state were obtained.Results showed that,under the same power consumption,compared with DR-PBDT impeller and DRFC-PBDT impeller,DPRFC-PBDT impeller can effectively increase the turbulent degree and turbulent kinetic energy dissipation rate,enhance the axial velocity of solid particle,reduce the amount of accumulated solid particles,and improve the solid-liquid suspension degree.?3?Gas-liquid two-phase system1)Based on the process intensification and cavitation theory,the dispersion behavior of gas-liquid two-phase strengthened by dual rigid-flexible impeller was studied.The chaotic characteristics,power consumption characteristics,and gas-liquid dispersion characteristics of gas-liquid two-phase mixing process in the three stirring systems of DR-RT-PBDT impeller,DRF-RT-PBDT impeller,and DPRF-RT-PBDT impeller were experimental studied.Results show that,at the Froude number Fr=0.66,compared with DR-RT-PBDT impeller and DRF-RT-PBDT impeller system,the LLE of DPRF-RT-PBDT impeller system was increased by 20.25%and 9.61%,respectively.Under the same power consumption,DPRF-RT-PBDT impeller can effectively increase the fractal dimension of chaotic attractors in the gas-liquid mixing system.At the same ventilation number Flg,RPD of the DPRF-RT-PBDT impeller system>RPD of the DRF-RT-PBDT impeller system>RPD of the DR-RT-PBDT impeller system.At the same time,DPRF-RT-PBDT impeller can increase the local gas holdup,reduce the bubble size,and strengthen the bubble dispersion and breakage process.2)The gas-liquid dispersion characteristics of DR-RT-PBDT impeller,DRF-RT-PBDT impeller and DPRF-RT-PBDT impeller were comparatively studied through numerical simulation,and absolute pressure of the impeller,water shear strain rate,local gas holdup distribution,and bubble size distribution were obtained.Results showed that,compared with DR-RT-PBDT impeller and DRF-RT-PBDT impeller,DPRF-RT-PBDT impeller can reduce the differential pressure before and after the impeller blades and the cavitation size,increase the liquid phase shear rate,strengthen the bubble breakage and dispersion process,and improve the uniformity of gas dispersion.?4?Application research of rigid-flexible combination impeller in manganese ore leaching stirred tankA pilot test of manganese ore leaching in a stirred tank with a rigid-flexible impeller was carried out,and the solid-liquid suspension characteristics in manganese ore leaching process was studied.The fluid-structure interaction behavior of the impeller,solid-liquid suspension characteristics,manganese ore leaching time,manganese ore leaching rate,and power consumption in manganese ore leaching process were analyzed.At the agitation speed of 58 s^-1,compared with conventional rigid impeller,when the wire rope was installed at the outer end of rigid-flexible combination impeller blades,the wire rope length was 1.2Hs,the maximum deformation was 65.02 times of that of rigid impeller,and the maximum equivalent stress was 6.848times of that of rigid impeller.Rigid-flexible combination impeller can effectively increase the interaction between the impeller and the fluid,improve the axial velocity of solid particles,increase the solid-liquid two-phase suspension degree in the leaching tank,and improve the solid-liquid chaotic mixing degree.Compared with rigid impeller,rigid-flexible impeller can shorten the manganese leaching time by nearly 1 hour,and enhance the manganese leaching rate by 3%at expense of 1.98 kW·h per hour.The pilot manganese ore leaching tank was modified with rigid-flexible combination impeller can generate an economic benefit of 420,000 yuan per year.In summary,based on the chemical process intensification and fluid chaotic mixing reinforcement theory,a new method to intensify the fluid chaotic mixing process by punched rigid flexible impeller was proposed in this dissertation.The fluid chaotic mixing characteristics in the punched rigid-flexible impeller stirred reactor was reached by experiment and numerical simulation,a new method to cause the structure instability of the flow field was established,which realized the efficient and energy-saving mixing of fluid.In addition,the study on the application of rigid-flexible combination impeller to intensify manganese ore leaching process was carried out,and the new technology of intensifying manganese ore leaching process with rigid-flexible combination impeller was tested and the high-efficiency leaching of manganese ore was realized.