Research on Coaxial Mixing of Floating Particles in Viscous System
Author:Zheng Yi Jun
Supervisor:jin zhi jiang liu bao qing
Solid-liquid stir is applied widely in various reaction process,such as coacervation,fermentation,and crystallization.The motion states of floating particles on the free surface are more complex than those of sinking particles on the bottom.The influence of viscosity on the floating particles is often neglected in researches,while viscous materials are also common in industrial processes.Meanwhile,the coaxial mixer has better mixing performance in viscous system than the single-axial mixer.A coaxial mixer was first combined with the floating particles to research the solid-liquid mixing and dispersing in viscous system by experiment and simulation.The main research contents and results are listed as follows:(1)The drawdown and dispersing states of floating particles under different rotating modes(co-rotating and counter-rotating modes,down-pumping and up-pumping modes)were compared and analyzed.The axial flow,the radial flow,and the mixed flow impellers were selected to investigate the mixing performance of the typical inner impellers.The co-rotating mode and a down-pumping mixed flow ipmpeller were optimized for the follow-up researches.(2)The influence rules of structure and material properties on the drawdown and dispersing of floating particles were investigated.The correlation of the critical just drawdown Froude number with the inner impeller diameter,the submerged depth,the liquid viscosity,the concentration and size of particles is presented and proved good satisfactory.It is available to provide reference for the design and selection of the solid-liquid stirred vessel for floating particles.The results show that,the inner impeller diameter has the most obvious impact on the critical just drawdown state of the floating particles among the variuos factors,while the particle size has a few effects on the critical just drawdown speed and power.(3)The Euler-Euler two-fluid model and multiple reference frame method were adopted to simulate the liquid velocity distribution and solid concentration distribution under different operating,structure,and material parameters.The drawdown mechanism of floating particles by coaxial mixer was analyzed and proposed.The results show that,the impacts of the impeller diameter and rotating speed on the solid distribution was realized by changing the circular flow.The influences of the particle concentration and size on the liquid velocity field distribution are unconspicuous.