Study On Fluid Micro-mixing Mechanism In The Quick Reaction System

Micro-mixing is mainly referred to the mixing process of material homogenization from the smallest scale of turbulent dispersion- Kolomogrov scale to the molecular scale after turbulent diffusion. The mixing process of small scale has great influence on the mixing process of fast and complicated reaction system(Such as the high temperature propylene chlorination reaction, cyclohexanone oxime rearrangement reaction, etc.) The concentration distribution of product, the product quality and operating stability of the product etc. are closely connected with the micro-mixing process. Because the reaction rate is so quickly that is completed or nearly completed before homogenous mixing. As a result, It has great significance to study the mechanism of fluid micro-mixing and establish responding theoretical model in fast reaction system, It helps us to design and optimization of reactor,improve the product selectivity, avoid uneven mixing materials to form local high concentration phenomenon and inhibit the side-reaction caused by high concentration phenomenon.In the already existing literatures, the micro-mixing model mainly has two categories. One is empirical model, and the other is the structure model. Empirical models are mainly coalescence and re-dispersion model, double/three-environment model, the interaction by exchange with the mean model and so on. The structure models are lamellar structure model, thin sheet structure model, the vortex engulfment model and so on. For empirical model, there is a major defect of the model by introducing one or several parameters, and these parameters haven’t the actual physical meaning, these parameters can relate each other through math expressions,the model lack of the basis of fluid mechanics. For structure models, only consider the deformation rate of one direction. At last, the model is simplified to consider material convection diffusion in a local infinitesimal stripes. Due to this kind of model simplification, model described by the mixed process have a certain deviation with the actual situation. In this paper, aiming at the shortage of the previous model, a new mechanism of micro-mixing model is put forward.The model in our work considering the complexity of the turbulent flow structure,scale breakage dynamics, and the mixing process of rich material region undermulti-dimensional convection and diffusion synergistic effect. That is, the model coupling the multidimensional tensile, shear and entrainment mechanism. According to the material of convection and diffusion transport equation, we built a new micro-mixing model equation, and derived the expression of the velocity field of the new model. After deriving the new constructed model equation, we introduce the series- competition reaction system(i.e. the reaction of ?-naphthol and benzene sulfonic acid diazonium salt formatie azo dye system), and discuss the effects of material molar volume ratio, viscosity, diffusion coefficient, the initial concentration of reactants to the selectivity of products, the effects of which reflects the impact of these factors on the micro-mixing homogenization. Then, for the fly temperature,burning or carbonization phenomenon in the industrial, we try to use the new micro-mixing model equation combined with rapid strong exothermic reaction system(we select the propylene chlorination in high temperature whose dynamics and physical parameters can be easily obtained) to explain these phenomena. Studies show that when the molar volume of the material is different, the thickness and the layer number of entrainment is also different; When the viscosity is changed, the reaction selectivity increasing with the increase of the viscosity; When the diffusion coefficient is changed, the reaction selectivity decreases with the increase of diffusion coefficient,and the changes is obvious within a certain range change; At the same time the reaction selectivity increases with increasing of the concentration of reactants; When considering the influence of temperature, it can be seen that the local reaction area there is a temperature gradient. All these has certain guiding significance to study micro-mixing in the future. After these for the study of industrial reaction micro-mixing has certain guiding significance.