Power and mixing time study involving a Maxblend® impeller with viscous Newtonian and non-Newtonian fluids

Physical investigations have been carried out to characterize the power consumption and the mixing time in a vessel equipped with a Maxblend (R) impeller (Sumitomo Mechanical Equipment, Japan). The laminar, transition and turbulent flow regimes were investigated using viscous Newtonian and non-Newtonian shear-thinning fluids. For the determination of the mixing times, a discolouration method based on a fast acid-base reaction was used in conjunction with image analysis to generate mixing evolution curves. Three vessel sizes were used from which the influence of the scale on the mixing efficiency and the power consumption could be determined. With the geometrically similar mixers used here, it was clearly shown that power and efficiency do not depend on the scale, under certain conditions. The power consumption was found almost identical as that of an anchor but far lower than that of a double helical ribbon impeller. The power and shear constants, K-p and K-s, were found very sensitive to small variations in the bottom clearance. The K-s value remained almost constant for a wide range of flow indices. The dimensionless mixing time, Nt(m), decreased with the reciprocal of the Reynolds number in the laminar flow region. Based on data from the literature, a comparison with many different large impellers also indicated that the Maxblend technology makes better use of the mixing power in the upper part of the laminar regime and in the low turbulent regime.