Numerical simulation of oil spill diffusion behavior under the influence of salinity and temperature at the substrate

Oil spills in the ocean resulting from accidents can cause significant water pollution across large areas. When a dispersed oil film on the water surface comes into contact with an ignition source, it may ignite and lead to a severe marine fire. Currently, research on the microscopic mechanisms through which oil properties and substrate environments influence the dynamic diffusion behavior of oil is relatively limited.

In this study, a multiphase flow model was developed using the ANSYS FLUENT software to investigate the dynamic evolution and diffusion mechanisms of oil on the substrate under various influencing factors. Using numerical simulation, diffusion kinetics of oil films on substrates with different properties were studied under various environmental conditions, focusing mainly on three variables: (1) substrate salinity (deionized water, 20 g/kg, 30 g/kg, and 40 g/kg), (2) water content of the oil (crude oil, 20%, 40%, and 60%), and (3) substrate temperature (20 ℃, 30 ℃, and 40 ℃). This study mainly emphasizes the effects and regulatory roles of these three influencing factors on the dynamic diffusion behavior of oil films.

The results indicate a direct correlation between the salinity of the substrate and the diffusion rate of the oil film. Increased salinity elevates the density and surface tension of the substrate, promoting the diffusion of the oil film. The water content of oil affects its physical properties, such as density, viscosity, and surface tension. Higher water content leads to higher viscosity, which inhibits the diffusive movement of the oil on the substrate and ultimately reduces the diameter of the diffused oil film. Analysis of the oil film diffusion rate contour map revealed that during the initial diffusion stage, gravity acts as the primary driving force, causing rapid diffusion in a radial direction. Over time, surface tension dominates and slows down the diffusion process at the oil film edges. With an increase in substrate temperature, the viscosity and surface tension of the oil decrease, thus promoting the diffusion of the oil film. The ratio of the diameter to the thickness of the oil film also affects the diffusion trend. At higher temperatures, this ratio varies significantly, indicating vigorous movement of the oil film in the initial stages. Formulas for predicting the diameter of the diffused oil film under varying conditions of salinity, water content, and temperature were derived based on power-law functions and showed good agreement with simulation results.

Oil spills in marine environments spread at a faster rate with an increase in salinity. The water content in oil films also affects the diffusion rate: oil films with high water content spread at a slower rate compared with those with low water content. Furthermore, water temperature has a significant effect on oil spilling; high water temperature makes the diffusion behavior of the oil film more intense. Numerical simulation characterizes the dynamic diffusion features of oil under diverse environmental conditions, laying a theoretical foundation for the prediction of slick diffusion of oil during spill incidents.