CFD-PBM and experimental investigation of a shear thinning fluid in a gas-liquid tank agitated by a helical ribbon impeller

Abstract

• The hydrodynamics of an agitated gas-liquid reactor has been modelled using CFD-PBM method. • PIV measuring technique has been applied to verify simulation results. • The performance of a dual helical ribbon in non-Newtonian fluid with complex rheology has been investigated. • The influence of impeller speed on bubble size distribution, flow field, and viscosity of shear-thinning fluid have been studied. This study focuses on hydrodynamic characteristics of a shear thinning fluid agitated in a 3D multiphase reactor using a dual helical ribbon impeller. A combination of Computational Fluid Dynamics (CFD) simulation and Population Balance Model (PBM) were employed to study the gas-liquid interactions at various impeller speeds. The standard k - ε model and Eulerian multiphase approach were used to predict better quantities of turbulent flow parameters and its characteristics. Particle Image Velocimetry (PIV) was used to measure the velocity field for the model validation. Simulation results indicated that the bubble breakage and coalescence rate was intensified due to an increase in rotational speed. However, bubble breakage is still the dominant phenomenon since the bubbles would hit the walls and blads due to the turbulent intensity. Further, the helical ribbon impeller significantly reduces the viscosity of the fluid and improves the mixing efficiency that is confirming the authors’ previous experimental results. Furthermore, formation of static vortices adversely affects the efficiency of mixing process proving that an increase in impeller speed does not necessarily enhance the mixing perfiormance. Further, the helical ribbon impeller significantly reduced the viscosity of the fluid and enhanced mixing efficiency, thereby confirming the authors’ previous experimental results.