study of mixing time of non-Newtonian fluids in stirred tank

The knowledge of mixing time is of fundamental importance for mixing investigation in agitation systems. In fact, this characteristic controls the performance of the mechanically agitated tanks and has a direct influence on the cost of the agitation process. Experimental study of the mixing timeof non-Newtonian shear-thinning fluids is presented in this paper. The purpose of this study is to analyze the effect of the rotational speed of the impeller N (rpm), tracer injection point andconductivity probe location on mixing time. Experimentally, mixing time was determined using aconductivity meter. For each experiment, a pulse of electrolyte was added to the liquid bulk. Themixing time is the time which is taken for the fluctuation of the response signal to be below 5% ofthe concentration achieved at perfect mixing. To measure the mixing time, one parameter is variable and other parameters are considered constant. The measurements were conducted in baffled agitated vessel with inner diameter of 0.3 m equipped with dual 6-blade Rushton turbinelocated centrically in the vessel. The experimental results show that the mixing time decreases byincreasing the rotational speed of the impeller. It can conversely increase the power consumption. The variation of mixing time versus the probe and injection locations is at first in a decreasing trend, while it then turns to be on the increase.

Keywords:

mixing time , non-newtonianfluids , CMC