Abstract
The distribution of circulation time of a tracer particle and the volume of mixing regions were investigated using a pseudoplastic solution at various concentrations of xanthan gum up to 4.6% in a stirred tank with a turbine impeller having six flat blades. When the relative frequency/N of each circulation time was plotted against Nθ (N, agitation speed; θ, circulation time) at various agitation speeds, the distribution curve for solutions of 1.8% (flow behavior index 0.12 and consistency coefficient 26.4 Pa•s0.12) or more xanthan gum shifted to the side of larger values of Nθ with increasing agitation speed, while distribution curves of the same shape were obtained in water or a diluted solution (0.9% xanthan gum). The mean circulation time also increased with increasing agitation speed. This phenomenon was confirmed by measuring the volumes of two mixing regions, the micromixing and the macromixing regions. These volumes increased with increases in the agitation speed, resulting in decreases of the stagnant region.
