Hydrodynamics evaluation of an internal-loop airlift reactor with Newtonian and shear-thinning fluids: Experimentation vs CFD simulation

The hydrodynamics of an internal-loop airlift reactor was numerically and experimentally characterized. The gas holdup, liquid velocity, shear rate, flow pattern and volumetric oxygen transfer coefficient (k_La) were evaluated as a function of the air velocity and medium rheology. Tap water and CMC solutions were used as Newtonian and non-Newtonian fluids, respectively. The standard κ-ε model was employed for modeling turbulence, and unsteady three-dimensional simulations with the Euler-Euler model were performed. Gas holdup, liquid velocity and k_La measurements were performed for validating simulations. An increase in bubble coalescence and a decrease in k_La was observed with CMC solutions. The presence of recirculation loops inside the riser for CMC solutions is reported, which was not observed with tap water. The higher the CMC concentration, the larger the recirculation region seems to be. Results show that recirculation loops play a substantial role in the reactor’s hydrodynamic performance, and it turns out that the gas holdup in the riser increases with increasing the CMC concentration.

Keywords: Internal-loop airlift reactor, Shear-thinning fluids; Computational Fluid Dynamics; k_La; Flow Pattern.