Effect of shear forces on fine particle retention

An inverted cone is investigated as an alternate stirrer for a dynamic drainage jar. The cone is used to generate a known uniform shear field over the wire. Drainage rates are compared between the cone and the standard propeller stirrers. Both stirrers show a minimum in the drainage rate curve at 750 rpm and indicate filtercake formation even though the drainage rate is less than 100 mL in 30 seconds. The data for the propeller indicate filtercake formation at high stirring rates while the cone data do not. The retention curves for the two stirrers are similar in magnitude. However, at high stirring rates, the propeller and cone data show that retention goes to zero and a plateau, respectively. The influence of adding a retention aid is reported.