Modeling dispersed phase holdup and conditions of flooding in a pulsed disc and doughnut solvent extraction column

Pulsed disc and doughnut solvent extraction columns (PDDCs) have emerged as an efficient alternative to conventional mixer-settlers and pulsed sieve plate extraction columns for nuclear spent fuel extraction. This study discusses the feasibility of the turbulent volume of fluid (VOF) and hybrid multi-fluid Eulerian multiphase methods to predict the dispersed phase holdup and flooding conditions of an experimental PDDC with 7.5-cm internal diameter. Analysis of axial holdup and axial velocity was incorporated to rationalize the droplet breakage and coalescence along the column. The onset of local and total flooding was modeled and compared using both methods. The evolution of recirculating zones revealed insightful information about local holdup distributions during flooding. Unlike conventional Eulerian multiphase modeling, the VOF method described accurately the holdup and the onset of local flooding, but a finer mesh was required. Alternatively, the hybrid multi-fluid Eulerian method could capture accurately turbulent length scales while predicting the holdup and flooding conditions, but required optimization of the dispersed phase droplet diameter through multiple iterations.