Comparison of k–ε, RSM and LES models for the prediction of flow pattern in jet loop reactor

Abstract

Jet loop reactors (JLR) are frequently employed in the process industry as an alternative to impeller mixers due to the existence of relatively intense convective flow leading to enhanced rate of macro-mixing at the same power consumption. In JLR, close to the nozzle, high shear zone is present and most of the turbulence models fail to predict the jet spreading. As a consequence, the bulk motion (outside the jet region) does not get appropriately described. It may be pointed out, that the bulk region occupies a major portion of the reactor and houses the processes of mixing and chemical reaction.In the present work, CFD simulations have been undertaken by using standard k–ε, RSM and LES turbulence models. It is known that the computationally cheaper models such as k–ε and Reynolds stress model (RSM) have many simplifying assumptions which limit their accuracy. In order to compare the turbulence models, the LES results have been used to evaluate the exact terms in turbulent kinetic energy (k) and turbulent kinetic energy dissipation (ε) transport equations in standard k–ε model and RSM. From the Large eddy simulation (LES) simulations, the time series of velocity and pressure were stored and were subsequently used for the detailed estimations of two terms. The conservation equations for k and ε consist of convective transport, diffusive transport, dispersive transport, production and dissipation. In the following paper, each of these terms has been quantified accurately in the exact form (i.e. without any assumption) and in the modeled form. This has enabled the direct comparison between the two and has given a clear insight into each modeling assumption.