Effects of impeller designs and configurations on the flow field in multiple impeller system using Computational Fluid Dynamics (CFD)

The work presents the computational study of the flow field in multiple impellers stirred vessel with various impeller types and configurations at 300rpm, 450rpm and 600rpm. Three types of impellers are investigated, namely the pitched blade impeller (PB), flat blade impeller (FB) and sawtooth impeller (ST). In this study, the flow patterns, turbulent kinetic energy dissipation, and power consumption in dual impellers system have been studied using computational fluid dynamics (CFD) by employing the multiple reference frame (MRF) and realizable k-ɛ turbulence model. The results from PBFB and reversed FBPB indicate efficient and powerful mixing with the merging of flows from both impellers that circulates the entire vessel. Besides, the FB and ST configuration exhibits the mixing characteristics that enhance both dispersion and mixing homogeneity. It is proven in this study that the combination of axial and radial impellers improves the weak mixing zones in the stirred vessel by the complex flow patterns produced. On top of that, utilizing two different impellers could achieve two mixing objectives in a system with the exceptional features of each impeller. The results establish promising effects of the reverse rotation in axial impellers and the arrangement of two different impellers in a multiple impeller system. With the rapid growth of industrialization, understanding the fluid dynamics in a multiple impeller stirred vessel is fundamental to optimize and scale up industrial mixing operations. Hence, the empirical findings in this study will be beneficial in selecting the suitable combination of impellers and the orientations that will enhance industrial mixing operations. Apart from that, the present work also illustrates that the computational technique used can be extremely valuable in determining the fluid dynamics in complex multiple impeller system which is challenging to analyse experimentally.