CFD simulation of hydrodynamics characteristics in a tank with forward-reverse rotating impeller

Abstract

BackgroundA forward-reverse rotating impeller was used in an unbaffled tank to improve the mixing efficiency. Flow field and power characteristics in the tank were numerically studied. MethodsComputational fluid dynamics(CFD) simulations were performed to investigate hydrodynamics in the unbaffled tank. The Reynolds stress turbulence (RST) model along with a sliding mesh approach was used to predict instantaneous flow fields in the stirred tank. Significant findingsFluid in the unbaffled tank flows periodically with the forward-reverse impeller agitation. Zonal flow phenomenon was found for the fluid affected by agitation in different directions. The effects of operating conditions on instantaneous fluid velocity vary with positions in the tank. Flow field characteristics in the forward-reverse agitated unbaffled tank are very different from those in constant agitated unbaffled and baffled tanks. Generally, transient power consumption is only the function of its corresponding transient rotational speed. The averaged impeller power number is a constant and is not affected by maximum rotational speed and cycle time. The averaged power number is the largest in the unbaffled tank with forward-reverse agitation, followed by the baffled tank at a constant agitation, and the smallest in the unbaffled tank at a constant impeller speed.