Computational Fluid Dynamics (CFD) Studies to Study the Effect of Liquid Level on the Hydrodynamics in an Agitated Vessel with an Axial and Radial Impeller

Abstract

Hydrodynamics in stirred vessels is vital for transport phenomena for various applications in chemical and environmental systems like aerobic and anaerobic systems, effluent treatment and biological applications like bioreactors. Design of efficient impellers reduces power consumption which contributes to reduction in greenhouse gases especially power obtained from thermal power plants thus decreasing the carbon footprint. In the present work, Computational Fluid Dynamics (CFD) simulations have been carried out for two different Rushton turbines (one axial and one radial flow) for two different height to diameter (H/T) ratio. The model is first validated for a Pitched Blade Turbine Downflow (PBTD) impeller with data available in the literature. A qualitative study of the flow patterns in stirred tanks shows good axial and radial flow profiles for the respective impellers. A decrease in H/T showed higher power consumption for both impellers. The power number (N_p) for these impellers has also been calculated for two H/T ratio and Reynolds number (Re) in the range (2500 < Re < 1000. N_p was found to be a strong function of liquid level for both impellers considered in the study. Interesting trends of variation of N_p with Re have been observed which suggest there is a critical Re where the impellers have least power consum