Macromixing study for various designs of impellers in a stirred vessel

The effect of the impeller designs and impeller clearance level (C/T) on power consumption, mixing time and air entrainment point in a single liquid phase under turbulent conditions (Re > 104) were investigated. Different impeller designs including conventional and new designs, were used to consider both axial and radial flow impellers. The electric conductivity method, suspended motor system and observation method were employed to determine the mixing time, the power consumption and the air entrainment point, respectively. The reduction in the impeller clearance level form T/3 to T/6 resulted in a decrease in power number values for up-flow pumping impellers while it was increased for down-flow pumping. The same trend was observed for the mixing time results. Moreover, axial flow impellers and specially HE3 are preferable for higher agitation speeds due to the less air entrainment. The results verified that the axial flow impellers and specifically down-flow impellers are more efficient than the radial flow impellers. ANFIS-Fuzzy C–means (ANFIS–FcM) and nonlinear regression were used to develop models to predict the mixing time based on the energy dissipation rate and clearance. The results verified that the model predictions successfully fit the experimental mixing time data

The effect of various designs of six-curved blade impellers on reaction rate analysis in liquid–liquid mixing vessel

The mixing efficiencies of impellers vary according to their designs. In this work, the effects of 6-curved-blade impellers of different curvature angles and central disk sizes on the reaction in a stirred vessel were investigated and the results were compared to that of a Rushton turbine. The impeller efficiency was defined by the ratio of reaction rate to power consumption, (rA/P). The experiments were performed at the rotational speeds of 5, 6 and 7 rps. The interaction among the experimental parameters was investigated using Response Surface Methodology. The rA/P values were found to decrease with increasing curvature angles. The lowest rA/P value was obtained for the impeller with curvature angle of 140°. The result showed that the results for Rushton turbine was relatively low compared to curved-blade impellers and increase in central disk size did not significantly affect rA/P. In conclusion, curved-blade impellers were more economically efficient than Rushton turbine

Liquid-liquid mixing in stirred vessels: a review

Liquid-liquid mixing is a key process in industries that is commonly accomplished in mechanical agitation systems. Liquid-liquid mixing performance in a stirred tank can be evaluated by various parameters, namely minimum agitation speed, mixing time, circulation time, power consumption, drop size distribution, breakup and coalescence, interfacial area, and phase inversion. The importance of these liquid-liquid mixing parameters, the measurement method, and the results are discussed briefly. Input parameters such as impeller type, power number, flow pattern, number of impellers, and dispersed phase volume fraction, in addition to physical properties of phases such as viscosity and density, are reviewed. Scale-up aspects are also included. © 2013 Copyright Taylor and Francis Group, LLC