Comparing SST and RSM Predictions of Flow Currents and Heat Generation Within an LPDE Autoclave Reactor

An investigation of a Shear Stress Transport (SST) verses a differential Reynolds Stress Model (RSM) is presented. The evaluation tests both models’ ability to predict complex flows and heat generation within an industrial low-density polyethylene (LDPE) reactor. The CFD model consists of a rotating stirrer shaft and temperature dependent polymerization kinetics to simulate the production of LDPE. The geometry consists of multiple paddles, zone baffles, and stirring elements that induce mixing via local shear. Regions of unbounded heat generation throughout the model can negatively impact polymer properties. The initial goal of the study was to understand the formation of hot spots within the reactor. RSM proved to be less diffusive, reporting higher temperatures throughout the reactor. The increase in temperature affected the polymerization kinetics within the model and resulted in a 17% decrease, compared with SST, in catalyst at one of the zonal outlets. The SST model predicted concentrations of hotter fluid isolated near the centralized stirring shaft, while the RSM revealed new mixing patterns with colder currents penetrating into those previously isolated regions. In tracking each tensorial stress, RSM provides a less diffusive approach in simulating the reactor and is shown to be the more desirable model for predicting flow behavior.