Study On Flow Field Simulation And Design Optimization Of Stirred Reactor Based On CFD

Stirred reactors are widely used in agricultural,chemical,pharmaceutical,biological fermentation,and metallurgical industries to achieve mixing between materials.In order to promote economic development and achieve green production and energy saving at the same time,it is required to have good mixing performance in the stirred reactor,and further,it is necessary to carry out optimization research on the process parameters and the structure of the stirred equipment.In recent years,the computational fluid dynamics(CFD)method has been widely used in the simulation study of the flow field in a stirred reactor,providing a reliable way for the design and optimization of the stirred reactor.In addition,the development of chaotic mixing theory also provides a reliable basis for exploring the mixing effect in stirred reactors.In this paper,the fermentation experiment of pullulan polysaccharide production by Aureobasidium pullulans was carried out in a stirred bioreactor firstly,and the gas holdup of different agitation speeds and gas flow rates in the reactor at a certain moment were measured.The CFD method was used to establish a numerical model of gas-liquid two-phase flow in a stirred bioreactor,and the gas holdup of the fluid at the same time and under the same working conditions were obtained.The comparison results showed that experiment and simulation have good consistency,which verified the accuracy and reliability of the CFD model.Secondly,the viscosity of the fermentation broth of Aureobacidium pullulans in the stirred bioreactor was measured experimentally.Biomass concentration of Aureobasidium pullulans was correlated with consistency index and flow behavior index,and consistency index was correlated with duration of fermentation time.The regression equations had high coefficients of determination(R~2>0.95).The low,medium and high viscosity stages were determined during the whole fermentation process.The CFD simulation of the flow field in the reactor at three stages were performed,and combined with Taguchi's method,effects of impeller type,gas flow rate,and agitation speed and their significant levels on gas holdup and power consumption were evaluated by means of range analysis and ANOVA,and the optimized process schemes were proposed.Then,the PIV technology was used to study the mixing process of the single-phase water system in the stirred reactor,and the axial velocity,radial velocity and turbulent kinetic energy data of the flow field were obtained.A numerical model under the same system was established using the LES method.The flow parameters obtained by experiments and simulations were compared,and they were found to have good agreement,which verified the accuracy and reliability of the model.Finally,referring to other literatures on the design concept of the impeller,a new type of twisted inclined baffle was developed.A numerical model of the flow field in the stirred reactor with a new type baffle was established using the LES method.The time series of the system variables of the flow field in the stirred reactor with a standard baffle and a new type baffle were collected.The numerical model of the flow field in the stirred reactor under the new type baffle was established using the LES method.Time series of the system variables of the flow field in the sub-plate stirred reactor.Largest Lyapunov Exponent and power consumption of the flow field under the two baffles were compared and analyzed.The results showed that the power consumption of the new type baffle was the same as that of the standard baffle,but it had a larger Largest Lyapunov Exponent,so the chaotic mixing performance of the new type baffle was better.