CFD with population balance model to predict droplet size distribution in submerged turbulent multiphase jets

Abstract

During deepwater oil spill events, oil is released into a relatively stagnant environment (ocean water) in an uncontrolled manner. The oil phase initially emerges as a jet and the gushing oil loses its momentum energy and results in entrainment of surrounding water. The shear interaction between the oil mass and the ambient fluid results in generation of droplets with wide size distribution. In this study, we present a numerical model for predicting the droplet size distribution resulting from the interaction of turbulent oil jets with the surrounding quiescent environment. We achieve this objective by integrating traditional multiphase CFD models with a population balance approach. The developed model has been validated against the experimental observations reported in Johansen et al. [12] The 'Mixture model' has been employed for evaluating flow fields in the system. We restrict our study to the atomization regime, where the droplet disintegration process has a greater significance over the competing coalescence mechanism. The population balance equation has been solved using the 'Class method' and the disintegration of droplets has been modelled by including the breakage kernel suggested by Lehr. [27] The developed model has been used to analyze the effect of dispersed (oil) phase flow rates, the presence of dispersants, and the presence of air in the jet phase on the overall size distribution of oil droplets. We also present a case which compares the droplet size distributions obtained by using the flow field evaluated by a more rigorous Eulerian Two-Fluid model over Mixture model.