Homogenization energy in a stirred tank

Mixing in stirred tanks influences conversion of reactants for fast reactions, and the efficiency of a mixing process can be determined from the power consumption and mixing time, which are the two parameters that define homogenization energy. In this study, the computational fluid dynamics (CFD) and laser Doppler velocimetry (LDV) techniques were employed to study the effect of the Rushton turbine bottom clearance on the flow field, mixing time and power consumption in a stirred tank. Experimental and simulation studies were conducted in a tank with and without a draft tube where a conductivity meter and decolourization methods were employed in validating the mixing time simulation results. A good agreement between the experimental and simulation results for the flow field and mixing time was obtained. The results showed a reduction in mixing time and power consumption at a low impeller clearance, with reference to the standard clearance, and a further reduction of the same parameters was obtained for a system fitted with a draft tube. At the low clearance, there was an increase in mixing efficiency by 46%, for a system without draft tube and 61% for that with the draft tube.