VDROP: A comprehensive model for droplet formation of oils and gases in liquids - Incorporation of the interfacial tension and droplet viscosity

Knowledge of the droplet size distribution (DSD) of spilled oil is essential for accurate prediction of oil dissolution and biodegradation. To predict DSD in turbulent flow, understanding the two resisting forces to droplet breakup are important: oil-water interfacial tension (IFT) and oil viscosity. Most existing predictive models consider only resisting force to droplet breakup due to IFT. However, in situations (e.g., high oil viscosity or low IFT) when oil viscosity becomes important, neglecting the resistance to breakup due to oil viscosity overestimates the extent of droplet breakage, and produces erroneously droplets of smaller size than reality. For these reason, we introduced a comprehensive conceptual-numerical model, VDROP, capable of simulating the transient droplet size distribution (DSD) in turbulent regimes while accounting for both oil viscosity and the oil-water IFT in resisting breakup. The residence time of high viscosity (and/or small IFT) oils in systems is more important than that of the low viscosity (and/or large IFT) oils. An expedient formulation was introduced to account for the residence time of high viscosity oils. Results showed that the model was able to reproduce the transient droplet size distribution of both low and high viscosity oils. VDROP was then used to provide the DSD of oils in breaking waves, and various IFT (due to usage of surfactant) and oil viscosities were considered. The results show that the transient DSD of high viscosity oils was bimodal and converged to unimodal when approaching steady state, which occurred within 2. h for considered case.