Abstract Summary (Max 250 words)
Paste formulations, exhibiting non-Newtonian rheological characteristics such as shear-thinning behaviour, are a common format used to deliver personal care products. In a full formulation, high-shear mixing is used to achieve agglomerate break-up and powder dispersion into the continuous phase. It is of interest to study the effects of geometry, operating conditions and fluid properties on the flow field in such processes. Sawtooth impellers are a type of high-shear impeller used in paste manufacture. In this work, particle image velocimetry (PIV) was used to investigate custom sawtooth impeller geometries. Flow profiles were obtained for 3 impellers [4, 8 and 16 teeth] agitating various fluids [Newtonian – glycerol solutions (50 - 100 wt. %) and shear-thinning non-Newtonian – Carbopol solution (1.5 wt. %)]. Experiments were carried out at a rheometer scale [D = 15 mm and T = 35 mm]. Mean flow patterns in the vertical plane reveal the position of internal flow recirculation loops above and below the impeller. Deformation of the free surface is also observed as draw-down towards the impeller intensifies as agitation conditions change. Axial and radial velocity profiles are presented as a function of impeller surface area, viscosity and rotational speed. In the horizontal plane, flow patterns show fluid movement through the gaps between impeller teeth and the change in these patterns as the number of teeth increase. Understanding shear rates near and between impeller teeth will underpin studies into manufacturing industrially relevant formulations and their dependence on agitator geometry.
