CO_(2)吸收过程Rayleigh对流传质特性格子-Boltzmann模拟

Lattice Boltzmann Simulation of Rayleigh Convection Mass Transfer Characteristics for CO_(2) Absorption Process

在化工吸收过程中,浓度梯度导致的Rayleigh对流对气液界面传质具有重要影响,但其强化传质机理尚不明确。本文采用格子Boltzmann方法研究乙醇与甲醇吸收CO_(2)过程Rayleigh对流传质特性,将模拟图像与实验观测结果进行对比,并采用不同传质模型对气液传质通量进行分析。结果表明:模拟得到的Rayleigh对流结构形状、形态演变等与实验结果具有良好的一致性;界面传质扰动是Rayleigh对流发生的必要条件,在扰动强度10^(-6)≤CD≤10^(-5)kg/m^(3)区间内,Rayleigh对流临界时间与理论预测值的最大误差约10%;Rayleigh对流的发生及演化过程可分为三个阶段:扩散传质阶段、Rayleigh对流起始阶段、Rayleigh对流演化阶段;对气液传质通量进行预测时,表面散度模型的预测效果优于小涡模型,但表面散度模型预测结果与模拟传质通量具有1 s的相位差,速度与浓度场并不完全同步;基于Rayleigh对流发生及演化过程的分阶段性,提出混合模型描述Rayleigh对流传质特性,该模型对传质通量预测的拟合度超过0.9,能很好地预测溶液吸收CO_(2)的传质过程。

In chemical absorption process,Rayleigh convection induced by concentration gradient has an important effect on mass transfer at gas-liquid interface,but the mechanism of its enhanced mass transfer is still unclear.In this paper,lattice Boltzmann method is used to study the mass transfer characteristics of Rayleigh convection in the process of CO_(2) absorption by ethanol and methanol.The simulation were compared with the experimental observation results,and different mass transfer models were used to analyze the gas-liquid mass transfer flux.The results showed that the simulated and experimental results are in good agreement in terms of the structure shape,morphological evolution;In the value range of disturbance intensity 10^(-6)<Cp<10^(-5) kg/m^(3),the maximum error between simulation and theoretical prediction of critical time is about 10%;The occurrence and evolution of Rayleigh convection can be divided into three stages:Diffusion mass transfer stage,Rayleigh convection initial stage and Rayleigh convection evolution stage.When predicting the gas-liquid mass transfer flux,the prediction effect of the surface divergence model is better than the small eddy model.However,there is a phase difference of is between the predicted results of the surface divergence model and the Simulate mass transfer fux,the velocity and concentration field are not completely synchronized;Based on the stages of Rayleigh convection generation and evolution,a hybrid model is proposed to describe the mass transfer characteristics of Rayleigh pairs.The fitting degree of the this model for the prediction of mass transfer fux is more than 0.9,which means that the hybrid model can well predict the mass transfer process of the solution absorption of CO_(2).