CFD modelling and mixing in stirred tanks

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 ne cessary to establish energy balance in. stirred vessels. Thirdly, it is nec essary to understand the, linkage between the flow field and the design obj ective. All the three aspects have been addressed here. Five different desi gns 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 ex tended to predict the flow field generated by these impellers. It is observ ed that the predictions of turbulent kinetic energy (k) were significantly improved by using zonal modelling. A new method has been proposed to estima te the values of turbulent energy dissipation rate (epsilon). This new meth od gave excellent comparison between the estimated values and CFD simulatio ns. The CFD simulations have been extended to predict the mixing time for d ifferent impellers. The predicted mixing times are in excellent agreement w ith the experimental measurements of Rewatkar and Joshi (1991, Chem. Engng commun. 91, 322-353). (C) 1999 Elsevier Science Ltd. All rights reserved.