Pumping capacity of inline dynamic mixers and its effect on process flow control

A semi-empirical (dimensional) model has been developed to predict the performance of an inline dynamic mixer within a specific application to ensure effective process design and operation. Inline dynamic mixers (or rotor-stator mixers) are known to behave like centrifugal pumps, particularly when operating at high rotor speeds. A mismatch between the process flowrate and the mixer's inherent pumping action can result in either high or low pressure at the inlet of the rotor-stator mixer, which can influence process control. Experiments were conducted at pilot scale using three models of inline dynamic mixers from Silverson Machines Ltd., with water as the process fluid. A wide range of flowrates and rotor speeds were covered where the pressures at the inlet and outlet of the Silverson were measured in each condition. A good correlation (R2 = 0.9998) between Silverson inlet pressure, process flowrate and rotor tip speed has been established but the expression requires knowledge of the nominal flowrate of the mixer model at a benchmark rotor tip speed. This reported model can serve as design criteria when selecting mixer models even at production scale.