Numerical simulation of mixing process in a stirred tank agitated by side-entering agitators

Computational fluid dynamics (CFD) software FLUENT 6.3 has been employed in the present work to study the flow field and mixing process in a stirred tank equipped with four side-entering agitators. The multi-reference frame (MRF) and standard k-ε turbulent model were used in the simulation. The effects of tracer feeding, detecting positions and impeller speeds on mixing time were investigated. It has been found that the mixing process is dominated by the flow field pattern in the stirred tank. For certain feeding positions, the mixing time detected from the point near the bottom was the shortest while that at the liquid surface region was the longest. For certain detecting positions, comparing with the tracer feeding around the centre part of the tank, the mixing time detected was about 21% shorter when the tracer was fed at the impeller region. The mixing time had a linear relationship with power consumption per unit volume of the tank on a log-log scale.