采用格子Boltzmann方法模拟解吸过程中的Rayleigh对流

Simulation of Rayleigh Convection in Desorption Process by Lattice Boltzmann Method

应用二维非稳态格子Boltzmann方法研究了异丙醇-水溶液和丙酮-乙酸乙酯溶液解吸过程中Rayleigh对流的临界开始时间、流动特征及其对界面传质的影响,并与相关文献对比.结果表明,临界开始时间随界面浓度增加呈先缓慢增大再迅速增大最后趋于稳定的变化趋势.Rayleigh对流结构经历了从有序到无序的发展过程,是不断更新的耗散结构.Rayleigh对流主要作用于液相主体,使液相主体具有较大的湍动速度(10-4～10-3m/s).液相主体中存在许多循环流动,促进了界面更新及界面与液相主体之间液体的交换与混合.传质增强因子(介于2～6之间)表明Rayleigh对流能有效提高解吸过程传质速率,强化界面传质过程.

A two-dimensional time-dependent lattice Boltzmann method was used for simulation of critical onset time and flow characterization of Rayleigh convection and its effect on interfacial mass transfer in the processes of isopropyl alcohol desorption from water and acetone desorption from ethyl acetate. The characteristics of Rayleigh convection are experimentally verified by literature data. The results indicate that the critical onset time slowly increases in the beginning, then sharply increases and finally becomes stable with interfacial concentration. Rayleigh convection patterns are dissipative structure with the continuous renewal feature, which experience the development from order to disorder. Rayleigh convection has effect mainly on the liquid bulk, leading to larger turbulent velocity （10^-4～ 10^-3 m/s） in it. There are many circular flows in the liquid bulk, which impel exchange of the liquid between the interfacial vicinity and liquid bulk, and promote the renewal of interfacial liquid. Mass transfer enhancement factor from 2 to 6 indicates that the Rayleigh convection can effectively promote the mass transfer rate for desorption and intensify interfacial mass transfer.