| Microwave irradiation is a very efficient technology to enhance the esterification of biodiesel,but most of the existing microwave reactors are batch reactors.The frequent loading and unloading process in its production process makes its real running time limited.Largecapacity kettle reactor is limited by microwave penetration depth,and the phenomenon of uneven heating easily occurs in the kettle,so it is urgent to design a continuous flow microwave reactor that can realize efficient heat and mass transfer and mixing.Therefore,a continuous jet coupled stirred flow reactor was designed by introducing jet stirring technology to the continuous transformation of the traditional batch microwave stirred tank reactor.Through the coupling effect of jet and stirred flow,the flow mixing in each area of the reactor was enhanced,as well as the heating uniformity.Numerical simulation was used to explore the factors affecting the flow,mixing and solid-liquid suspension characteristics of media in the reactor.Specific research contents and conclusions are as follows:(1)Numerical analysis of flow characteristics in jet-coupled stirred flow reactor.A continuous jet coupled stirred flow reactor was designed and the reactor model was constructed.The steady-state flow in the reactor was simulated using the standard k-ε turbulence model and the multiple reference frame model.It is found that the symmetrical flow field structure in the reactor can be destroyed by the addition of jet,and the change of jet mode has great influence on the flow characteristics in the reactor.Appropriate spacing between the two impellers can not only ensure the synergy between the two impellers,but also effectively reduce the lowspeed region at the top of the reactor(2)Study on flow and mixing characteristics in jet-coupled stirred flow reactor and validation of mean age theory.Three methods,rule of thumb,residence time distribution theory and mean age theory,were used to evaluate the liquid-liquid mixing performance in the reactor,and species model was used to track the diffusion process of tracer in the reactor,which verified the effectiveness of mean age theory.It is found that the mixing performance of counterclockwise jet in the reactor is the best when the rotating speed is 360 r/min and the jet velocity is 0.9 m/s.(3)Study on mixing characteristics of liquid-liquid esterification flow in continuous flow reactor based on mean age theory.Taking the mean age distribution variance as an index,the effects of different working conditions on the mixing performance in the reactor were studied under inclined,vertical and counterclockwise jet modes respectively.It is found that the increase of jet velocity would increase the mean age distribution variance in the reactor and reduce the mixing performance.However,when the jet is inclined,the change of jet path caused by the increase of jet velocity would improve the mixing performance to a certain extent.The results of response surface analysis show that the mixing performance in the reactor is the best when the stirring speed is 274.51 r/min,the jet velocity is 1.47 m/s,and the impeller spacing is103.59 mm.(4)Study on solid-liquid suspension characteristics in continuous flow reactor based on Mixture multiphase model.The solid-liquid suspension characteristics of solid acid particles in alcohol-oil mixture were simulated numerically,and the effects of stirring speed,jet speed,feeding position and feeding concentration were investigated.It is found that the solid-liquid stratification phenomenon in the reactor could be improved significantly with the increase of jet velocity,and the solid phase deposited towards the bottom of the reactor when the feed concentration was too high.According to the relative standard deviation of solid phase concentration distribution,it is found that the solid-liquid suspension uniformity in the reactor is better when the stirring speed is 480 r/min,the jet velocity is 1.5 m/s,and the feeding concentration is 20%. |
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