CFD Investigation of Gear Pump Mixing Available to Purchase

A moving-deforming grid study was carried out using a commercial CFD solver, Fluent® 6.2.16, in order to quantify the level of mixing of a lower viscosity additive (at a mass concentration below 10%) into a higher viscosity process fluid for a large-scale metering gear pump configuration typical in plastics manufacturing. Second order upwinding and bounded central differencing schemes were used to reduce numerical diffusion. A maximum solver progression rate of 0.0003 revolutions per timestep was required for an accurate solution. Fluid properties, additive feed arrangement, pump scale, and pump speed were systematically studied for their effects on mixing. For each additive feed arrangement studied, the additive was fed in individual stream(s) into the pump intake. Pump intake additive variability, in terms of coefficient of variation (COV), was > 300% for all cases. The model indicated that the pump discharge additive COV ranged from 32% for a single centerline additive feed stream to 3.9% for multiple additive feed streams. It was found that viscous heating and thermal/shear-thinning characteristics in the process fluid slightly improved mixing, reducing the outlet COV to 2.3% for the multiple feed stream case. The outlet COV fell to 1.4% for a half-scale arrangement with similar physics. Lastly, it was found that if the smaller unit’s speed were halved, the outlet COV was reduced to 1.1%.