Mathematical modelling and numerical simulation of two-phase gas-liquid flows in stirred-tank reactors

Abstract

This paper presents the mathematical modelling and numerical simulation of the turbulent, two-phase flow of liquid and gas in a gas-induced agitated stirred-tank reactor, using Computational Fluid Dynamics (CFD) techniques. The reactor used as an application demonstration of the developed model is the ozone-induced one, first designed and modeled by Yang et al. (1999). A three-dimensional (3D), transient, Euler-Euler two-phase flow model is developed and used to investigate the turbulent flow and mixing of liquid and bubbles in the stirred-tank reactor, applying the sliding mesh approach. Turbulence is simulated by means of several available models, the Renormalization Group (RNG) k-ε model being the one finally recommended as the most appropriate of the ones studied, for the present application. Two-way coupling between the two phases is modeled by means of appropriate inter-phase interaction relations. The study focused on bubbles of one size group (mean aerodynamic diameter of 2.5E-03 m), but it is easily extended to any number of sizes. It is concluded that the predicted overall flow field pattern and the mixing of both phases around the two blades of the simulated baffled stirred vessel, as well as inside and outside of the main tube of the reactor, are physically plausible, appear reasonably accurate, and are, therefore, satisfying. Keywords: Computational Fluid Dynamics, Two-phase flow, Dispersed flow, Reactor mixing, Sliding mesh, Baffled stirred-tank reactor