CFD Simulation Of Multifluid Mixing In A Rotating Liquid Film Reactor

Co-precipitation reactions are one of the most common methods for the preparation of nanomaterials,which are mostly carried out by liquid-liquid mixing.During the reaction process,the microscopic mixing process has an important influence on the product nucleation and crystal growth process,which in turn affects the product structure and properties,among which the reactor structure has a significant effect on the microscopic mixing process.The rotating liquid membrane reactor has a unique confined reaction space and the particle size of the prepared nanomaterials is small and uniformly distributed.However,there are problems such as low mixing efficiency and yield,unstable product mixing effect,and lack of research on the internal microscopic mixing process,which affects the further optimization of the nucleation reactor structure and application scope.To address this problem,this thesis adopts computational fluid dynamics（CFD）technology to simulate the flow field of the rotating liquid membrane reactor,based on the co-precipitation reaction of magnesium hydroxide prepared by sodium hydroxide and magnesium chloride,to study the fluid micro-mixing and reaction process inside the rotating liquid membrane reactor,and obtain the fluid flow field distribution law.The number of inlets,rotor tilt angle and rotational speed of the rotating liquid film reactor were further adjusted to obtain the fluid micro-mixing state and law under different structural parameters of the reactor,which improved the fluid mixing efficiency and realized the structural optimization of the rotating liquid film reactor.The main research results are as follows:（1）By modeling the rotating liquid film reactor in 3D and meshing the liquid film region formed by the stator-rotor gap,setting the mesh boundary conditions,selecting the fluid flow model and solving the parameters,writing the UDF（user defined function）function for the generation of Mg（OH）₂from sodium hydroxide and magnesium chloride based on the flow and reaction model within FLUENT,writing the rotor Based on the flow and reaction model in FLUENT and the UDF（user defined function）for Mg（OH）₂production from sodium hydroxide and magnesium chloride,a profile file of the rotor speed versus time was prepared,and the mixing process of Mg（OH）₂in the rotating liquid membrane reactor was simulated by combining the turbulence model,the dynamic grid model and the component conservation equation,and the mass fraction of Mg（OH）₂and the flow field distribution of fluid mixing in the rotating liquid membrane reactor under different conditions were derived.The fluid mixing in the rotating liquid membrane reactor was simulated at different rotational speeds at an inlet mass flow rate of 0.0001kg·s^-1.The calculation results showed that the mass fraction of magnesium hydroxide increased when the rotational speed was less than 3000 rpm;the mass fraction of magnesium hydroxide in the reactor was 0.7791 at 3000 rpm;the mass fraction of magnesium hydroxide in the reactor was basically stable between 0.5 and 0.7 at other rotational speeds.Under the condition of rotor speed 3000 rpm to simulate the mixing of fluid flow in the reactor with different mass flow rate at the inlet,the study showed that the mass fraction of magnesium hydroxide in the product with mass flow rate of 0.0003 kg·s^-1at the inlet reached the maximum of 0.8119.At this time,the fluid flow rate in the reactor was stable and the fluid mixing effect was the best.The optimum reaction conditions were rotor speed of 3000 rpm and inlet mass flow rate of0.0003 kg·s^-1.（2）The effects of different inlet numbers,rotor tilt angles and rotational speeds on the fluid mixing of the rotating liquid film reactor were investigated.The two-inlet,four-inlet and six-inlet grid models were used respectively,and the results showed that compared with the two-inlet reactor,the four-inlet and six-inlet reactors obviously enhanced the fluid mixing effect and increased the mass fraction of the product magnesium hydroxide.However,the difference of product mass fraction and reactor fluid mixing rate between the two was not significant,and the effect of rotor tilt angle on the four-inlet model was chosen to be further investigated from the cost-economy consideration.The fluid mixing effect in the reactor is better in the range of 72°-76°rotor angle,and the magnesium hydroxide mass fraction is maximum 0.8386 when the rotor tilt angle is 3000 rpm and the product magnesium hydroxide mass fraction is72°.At this time,changing the speed setting,the simulation analysis results found that when the rotor angle is 72°and the speed is 5000 rpm,the number of inlets is 4 and the mass flow rate is 0.0003 kg·s^-1of the rotating liquid film reactor simulation mixing effect is the best,the maximum product yield reaches 0.8817 for the industrial production of magnesium hydroxide process conditions optimization data support.