Study On Mixed Flow Characteristics Of Stirred Reactor

In this paper,the bio-reaction system of filamentous fungi(Rhizopus oligorhizopus)was used to study the bio-reaction equipment(agitated fermenter)by means of computational fluid dynamics simulation,mainly considering the shear,dissolved oxygen and other parameters and the mixing of flow field inside the equipment.Firstly,the traditional stirred fermentation tank was simulated.The results show that the simulation results are in good agreement with the experimental results,which shows that the computational fluid dynamics simulation method can better show the internal mixing situation of fermentation equipment.The results show that in a certain range,the gas holdup increases with the increase of apparent gas velocity in the stirred fermenter.At the initial stage,the gas holdup increases rapidly,and then decreases with the further increase of apparent gas velocity.The relationship between gas holdup and stirring speed also shows this trend.Secondly,because filamentous fungi(Rhizopus oligorhizopus)can not tolerate higher shear stress and have higher requirements for dissolved oxygen conditions,the traditional stirred fermenter was improved and optimized.It is planned to add mesh cloth as a carrier for the growth of bacteria,so as to improve the mixing situation in the flow field and the growth of bacteria.After the design,improvement and comparison of the cloth,the immobilized fermentation form with square mesh cloth as carrer was determined and analyzed by means of computational fluid dynamics simulation.The results show that the mixture of flow field is improved obviously by adding mesh cloth as carrier,the dispersion of bubbles is enhanced,the residence time of bubbles in liquid phase is increased,which is beneficial to the growth of bacteria and the formation of target products.Finally,because the six-straight-blade disc turbine is prone to cavitation and shear force is large,a new impeller combination is considered,which is composed of six-back-curved-blade disc turbine blade instead of six-straight-blade disc turbine blade.After calculation,design and improvement,the blade size was determined and the corresponding model was established.After the simulation calculation,it is found that the shear rate distribution produced by the impeller combination is relatively uniform,and the "dead angle" can be effectively avoided.To a certain extent,it plays a better role in dispersing bubbles.