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

Background: A 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. Methods: Computational 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 findings: Fluid 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 forwardreverse agitation, followed by the baffled tank at a constant agitation, and the smallest in the unbaffled tank at a constant impeller speed. (C) 2021 Taiwan Institute of Chemical Engineers. Published by Elsevier B.V. All rights reserved.

Automated summary

This study investigated the influence of a forward-reverse rotating impeller in an unbaffled tank on flow field and power characteristics. The findings revealed that the fluid in the unbaffled tank flows periodically with the forward-reverse impeller agitation, resulting in zonal flow phenomenon. The effects of operating conditions on instantaneous fluid velocity vary with positions in the tank. The flow field characteristics in the forward-reverse agitated unbaffled tank are significantly different from those in constant agitated unbaffled and baffled tanks.