(98b) Effect of Shear Gap Width on Flow and Power Draw in an Inline Rotor-Stator Mixer
Three-dimensional computational fluid dynamics (CFD) simulation was performed for water in turbulent flow to investigate the effect of shear gap width on the flow field, pumping rate and power draw of a Silverson L4R bench scale inline rotor-stator mixer equipped with a square hole stator head. Sliding mesh simulations of the Reynolds-Averaged Navier-Stokes (RANS) equations were performed using Fluent with the realizable k-Îµ turbulence model and enhanced wall functions. The power draw was determined from the rotor torque and the pumping capacity was calculated from the velocity exiting the stator slots.
The stator dimensions were held constant (inner diameter = 31.3 mm). Several shear gap widths were investigated ranging from the standard shear gap width w = 0.2 mm to the widest one with w = 1.7 mm. It was found that increasing the shear gap width caused a small decrease in pumping capacity. However, the mill head with the standard shear gap draws the most power and power draw decreases significantly with increasing shear gap width. Flow field features such as mean velocity, turbulent kinetic energy and energy dissipation rate are significantly influenced by shear gap width, particularly the extent to which the stator jets penetrate the volute. Examining these quantities provides physical insight into the flow and power results. Motivation for the study will be presented and use of the results will be illustrated by application to the analysis of crystal wet milling experiments performed in these devices.