Numerical Simulation Of Three-Dimensional Flow Field And Mechanical Analysis In Horizontal Anaerobic Fermentation Stirred Tank

Stirring is significant for the efficiency of anaerobic fermentation.At present,the study of anaerobic fermentation stirred tanks mostly focused on vertical tanks and rarely on horizontal tanks.In this paper,the horizontal anaerobic fermentation stirred tank as the research object,used ANSYS to simulate the three-dimensional flow field and mechanical properties of the horizontal anaerobic fermentation tank.First,in order to study the main influencing factors of the internal flow field of a large-scale horizontal anaerobic fermentation tank,the three-dimensional geometric model of the horizontal stirred tank was established,and the fluid domain mesh was divided,the standard k-ε turbulence model and multiple reference frame method was used to numerical simulate the three-dimensional flow field inside the tank.Through comparative analysis,the influences of the four variables of stirring shaft speed,material viscosity,blade obliquity and blade installation pitch on the flow field characteristics inside the tank were studied.The results show that the rotational speed is optimal in the interval of 3r/min to 5r/min;the increase of viscosity will cause the axial velocity of the fluid in the tank to decrease,and the relative pressure on the surface of the blade will increase;when the obliquity of the blade is 15° and the installation pitch is 350 mm,the axial velocity inside the tank is the most gently.Secondly,in order to ensure the long-term safe and reliable operation of the stirring shaft,the ANSYS software was used to analyze the mechanical properties of the stirring shaft,and the fluid-structure coupling method was used to analyze the stress and its deformation of the stirring shaft under the fluid force.Based on the static mechanical analysis,the modal analysis was performed to obtain the natural frequency of the stirring shaft.The harmonic response analysis was performed to obtain the response of the stirring shaft under the unbalanced state.The results show that the stress and deformation of the agitator shaft are reduced after adding the support structure,the maximum equivalent stress is 5.47 MPa,much less than the allowable stress,the total deformation is 0.19 mm,and the first-order critical speed rotation is 2648.6r/min,it will not reach resonance,so the stirring shaft can be operated safely and reliably for a long time.