CFD modelling and mixing in stirred tanks

Abstract

In order to develop rational design procedures for stirred vessels, several important points have to be addressed. Firstly, it is necessary to relate the impeller-vessel geometry to the flow field produced. Secondly, it is necessary to establish energy balance in stirred vessels. Thirdly, it is necessary to understand the linkage between the flow field and the design objective. All the three aspects have been addressed here. Five different designs of axial flow impellers have been studied. The zonal modelling concept used by Sahu et al. (1998 Ind. Engng Chem. Res. 37, 2116-2130.) has been extended to predict the flow field generated by these impellers. It is observed that the predictions of turbulent kinetic energy (k) were significantly improved by using zonal modelling. A new method has been proposed to estimate the values of turbulent energy dissipation rate (ε). This new method gave excellent comparison between the estimated values and CFD simulations. The CFD simulations have been extended to predict the mixing time for different impellers. The predicted mixing times are in excellent agreement with the experimental measurements of Rewatkar and Joshi (1991, Chem. Engng commun. 91, 322-353).