Numerical Simulation And Analysis Of Flow Field And Solid-liquid Suspension In Stirred Tanks

Mixing equipment is widely used in mechanical, chemical, pharmaceutical, metallurgical, sewage treatment, food and other industrial process because of its flexible operation, good mixing effect, large contact area and strong applicability. Among them, the stirring operation of solid-liquid flow is one of the most common operation in the stirring. Because of its wide application in industry is paid much attention. The study of solid-liquid suspension and flow field in stirred tank has important significance to industrial production, so its research is one of the hot topics to scholars at home and abroad. In recent years, the scale of stirred reactor is increasing, the uneven problem of mixing phases is gradually obvious and growing, and the current mechanical process is developing to "green", saving energy, so the requirement of product recovery rate and product quality is increasing. Rational design and right selection to mixing equipment are particularly important. But at present, the selection and the design of mixing equipment are still mainly dependent on small scale experimental results and the method of theoretical and semi-empirical. The detailed distribution of flow field in stirred tank is not clear understanding because of the limitation of technology and conditions. And lack the deeper understanding about the amplifying laws of stirred reactors. Besides, the experimental simulation has long period, large deviation and high cost. The new interdisciplinary computational fluid dynamics (CFD) technology provides new ideas and new methods to solve the above problems. Its technical advantages make the numerical simulation of flow field in stirred tank become one of the hot research in stirring, but the numerical simulation of flow field and solid-liquid suspension in stirred tank has not formed relatively perfect theory. This paper is mainly based on CFD technology and using multiple reference frame and standard k-ε model to carry on solid-liquid two phase system numerical simulation of45degree four oblique leaves turbine blade stirred tank. It also analyzes the influence of stirring speed, blade clearance from the bottom and other factors on the flow field’s distribution and solid particle’s distribution and the power consumption.The research results show that the impeller off-bottom clearance has great influence on the flow field and solid-liquid suspension states in stirred tanks. Low impeller off-bottom clearance is conducive to solid suspension, but power consumption is relatively large when the impeller off-bottom clearance is too low. And the clear liquid layer appears easily at too small of the impeller off-bottom clearance. Increasing the stirring speed can improve the effect of mixing, but taking power consumption, durability and other factors into account, stirring speed is not the bigger the better. We must consider all these factors to determine the appropriate stirring speed. These factors such as impeller clearance from the bottom, solid particle diameter and solid volume concentration all have influence on stirring power. Power consumption varies with the impeller clearance from the bottom under the same conditions; three work conditions of C=T/4, C=T/5, C=T/6, the condition of C=T/4consumes minimal power. Power consumption increases with the increasing diameter of solid particle under the same conditions. Under the same stirring speed, power consumption increases with the decreasing concentration of the solid.