doiSerbia

CFD simulation of the hydrodynamics and mixing time in a stirred tank

Ochieng Aoyi (Department of Chemical Engineering Vaal University of Technology, Private Bag X Vanderbijlpark, South Africa)
Onyango Maurice S. (Department of Chemical and Metallurgical Engineering Tshwane University Technology, Pretoria, Private Bag X Pretoria, South Africa)

Hydrodynamics and mixing efficiency in stirred tanks influence power draw and are therefore important for the design of many industrial processes. In the present study, both experimental and simulation methods were employed to determine the flow fields in different mixing tank configurations in single phase system. The laser Doppler velocimetry (LDV) and computational fluid dynamics (CFD) techniques were used to determine the flow fields in systems with and without a draft tube. There was a reasonable agreement between the simulation and experimental results. It was shown that the use of a draft tube with the Rushton turbine and hydrofoil impeller resulted in a reduction in the homogenization energy by 19.2% and 17.7%, respectively. This indicates that a reduction in the operating cost can be achieved with the use of a draft tube in a stirred tank and there would be a greater cost reduction in a system stirred by the Rushton turbine compared to that stirred by a propeller.

Keywords: Draft tube, CFD, solids concentration, stirred tank, simulation