Simulation of flow generated by an axial-flow impeller: batch and continuous operation

Abstract

It is important to extend and to validate computational flow models to simulate continuous operation of stirred vessels and to capture possible interaction of feed inlet/outlet with the flow generated by impellers. In the present work, we have developed and used a computational model to understand the flow generated by an axial flow impeller in a batch and a continuously operated baffled vessel. A multiple reference frames approach was used to simulate flow generated by the Mixel TT impeller in stirred vessel. The predicted velocity results show reasonably good agreement (qualitative as well as quantitative) with the experimental data. Characteristics of flow around blades of Mixel TT were studied using the computational model. The computational model was extended to simulate flow and mixing in a continuous operation. Simulations were carried out to understand the interaction of the jet emanating from the feed pipe and the flow generated by the impeller. Model predictions were compared with published experimental data, obtained by laser Doppler velocimetry. The differences and similarities between batch and continuous operation are highlighted. Mixing simulations were carried out to examine possible short-circuiting and non-ideal behaviour of the continuous operation of the stirred vessel. Influence of the impeller speed, feed rate and location of inlet/outlet on mixing and on the extent of non-ideality of flow was studied. The computational model and results discussed in this work will be useful for understanding the mixing process in continuous-flow stirred vessels.