Q型静态混合器内液滴群分散特性

Dispersion characteristics of droplets in the Q-type static mixer

静态混合器因具有结构紧凑、强化性能优异和连续性生产等优点被广泛应用于过程工业中,但Q型静态混合器(QSM)内多相流分散混合强化机理不完善制约了其在精细化工和原料药绿色生产中的应用。采用计算流体力学(CFD)耦合群体平衡方程对QSM内相含率α≤5%时液滴分散特性进行数值模拟,分析液液界面张力、动力黏度和相含率对液滴群d_(32)的分散行为的影响。标准旋流静态混合器内的d_(32)数值预测结果与实验结果有良好的一致性。模拟结果表明,在z/l=11.5处不同分散相d_(32)减小73%~96%,RL-90-QSM对不同物性介质的分散混合具有高效性和普适性;在高雷诺数和低相含率下,不同分散相流过z/l=0~2时d_(32)破碎速率最大,在z/l=2.5处d_(32)减小51%~90%,d_(32)随混合时间的增加逐渐减小且在z/l=10后趋于稳定;界面张力对混合结果的影响大于动力黏度。

Static mixer is widely used in the process industry due to their advantages of compact structure,excellent intensification performance and continuous production.The enhancement mechanism of multiphase flow and dispersion mixing in Q-type static mixer(QSM)are not adequate,which restricts its application in green production of fine chemicals and green production of active pharmaceutical ingredient.The computational fluid dynamics(CFD)coupled with the population balance equation are used to simulate the flow and dispersion performance of droplets in the QSM.The discrete interval number of droplet size in the class method(CM)is set as 16 groups.The numerical simulation result in the classical helical static mixer has a good agreement with the experimental results.The dispersive mixing performance of different medium in RL-90-QSM are studied under Re=8000~24000.The effects of dynamic viscosity,interfacial tension,and phase volume fraction on the Sauter mean diameter(d_(32))are analyzed,respectively.The Q-type elements have good functions of splitting,recombination,and stretching.At higher Reynolds number and lower phase volume fraction,the average d_(32)values at different cross section obviously decrease in the first group of elements and then gradually decrease with the increase of mixing time.They become stable after z/l=10.The decreasing ratio of d_(32)at z/l=11.5 of benzene,toluene,cyclohexane and silicone oil 50 relative to the inlet droplet diameter(2.50 mm)are in the range of 78%~95%,80%~96%,73%~94%and 82%~96%,respectively.RL-90-QSM has the advantage of high efficiency and universality for dispersion mixing for the medium with different physical properties.The dispersion performance of droplets in liquid-liquid two phase flow with different continuous phase viscosities and discrete phase viscosities is similar.Compared with dynamic viscosity of discrete phase,the interfacial tension has much more influence on the final mixing result.As far as the restrained aggregation be concerned,the breakup performance of droplets is still predominant at dispersed phase volume fraction no more than 5%.