Numerical analysis of high-pressure fluid jets: Application to RTD prediction in supercritical reactors

Computational fluid dynamics is becoming a very important tool in the research and design of new processes. At high pressures, the fluid dynamics behaves very differently than when reduced pressure is lower than unity. The aim of this work is to do an assessment of turbulence models to discern which is the most suitable choice when dealing with supercritical fluids. Two different studies have been carried out: First, an analysis of a turbulent submerged nitrogen jet, secondly a RTD (Residence Time Distribution) analysis of a supercritical carbon dioxide reactor. Both studies have been validated against experimental data. The results show that the Realizable k–ɛ model seems to be the most accurate choice for the simulation of high pressure systems, providing average deviations lower than 18% from experimental values. A methodology based on the solution of a transport equation for the residence time has been used. Using this method, the presence and location of undesirable backmixing zones inside the reactor are better identified. These backmixing zones correspond to the larger eddies present in the reactor, responsible for the long tail of the RTD data, this affect directly to conversion and selectivity.