Experimental Study and CFD-PBM Simulation of the Unsteady Gas-Liquid Flow in an Airlift External Loop Reactor

The performance of external loop airlift reactor (ELALR) strongly depends on local prevailing hydrodynamics. In this work, the hydrodynamics characterization of the gas-liquid flow is performed in a laboratory scale ELALR. The bubbles plume and the velocity field of the riser are captured using Particle Image Velocimetry (PIV) technique and a three-dimensional CFD-PBM simulation is implemented to provide a full description of the flow structure. The effects of superficial gas velocity on the flow structure and the time-averaged liquid velocity are quantitatively investigated and the numerical results are in reasonable agreement with the PIV measurement. The results show that the gas-liquid two-phases flow in the riser is always unsteady, and the bubble plume meandering behavior is observed clearly. Gas holdup increases with the increase of superficial gas velocity, while the liquid axial velocity shows a trend of first increase and then decrease and the maximum is observed at superficial gas velocity of 30 mm/s. With the increase of superficial gas velocity, the probability density function curve becomes flatter, and changes from unimodal to bimodal. This work helps to gain in-depth understanding of the complex fluid hydrodynamics behavior inside an ELALR.