Modeling the Breakup of Oil-Particle Aggregates in Turbulent Environments for Projectile Penetration.

After an oil spill incident, the spilled oil slicks are observed to migrate to the shoreline area. Under the turbulent conditions, they break into small droplets and are suspended in the water column. The dispersed droplets are expected to interact with the suspended particles and form the oil-particle aggregates (OPAs), which significantly changes the transport of the oil. Instead of an earlier assumption that particles cover the oil surface, thus preventing further breakage or aggregation of OPAs, recent studies demonstrated that particles act like projectiles penetrating the oil droplets, resulting in the breakage of OPAs over a longer period of time. A model looking into the OPA breakup through two breakup mechanisms was proposed for the first time. The first method depicted the breakup of one large OPA into two daughter droplets owing to the turbulent nature, while the second method demonstrated the tear of the OPA surface layer caused by particle uprooting. The model was then calibrated by an experimental study targeting crude oil with varied viscosities, along with previous experimental investigations. Three key factors were identified accounting for the breakage of OPAs, where the increase in particle concentration in the natural environment and the increase in turbulent energy of the surrounding flows benefited the breakage of OPAs, and the increase in oil viscosity suppressed the breakage due to large resistance to shear stress. Besides these elements, the impact of the particle shape on the penetration depth was discussed. The model serves as a fundamental theory to describe the evolution of OPAs for fragmentation behavior.