Study And Modeling Of The Weathering Of Spilled Oils At Sea

The prevention and cure of the spilt oils pollution is an important task of the protection of marine environment. The study of the weathering of spilt oils is the base of the prediction and control of oil spills. The process of evaporation and emulsification, which are the most important in the weathering of spilt oils, has been studied in this thesis. A weathering prediction model, which will be an important tool in oil spill contingency reaction, has also been developed. The evaporation of some oils and their emulsifies was modeled with pan evaporation method, and the characteristics of the evaporation in different states was inspected. The equations of evaporation rate and the factors of inhibitory action of emulsification on evaporation have been obtained. The dynamics mechanism of emulsification has been discussed based on the observation and analysis of the characteristics of oil and water motion. The processes of spilt oils weathering have been integrated by the composition and states of oils in this prediction model. The main content is:1. Through the pan evaporation experiments, in which the effects of wind speed, area and mass on the evaporation process has been studied, it is found that the behaviors of mixed and pure liquids have different characteristics, which cannot be explained by the theory of boundary layer control and basic evaporation. According to the feature of oils, the evaporation of crude oils is not controlled by the boundary layer and the prediction equation based on the water evaporation equation is not correct theoretically. It is first suggested that the evaporation of mixtures has three steps, which are the transfer of volatile components to the surface from the inside, the transfer of the components to gas boundary-layer from the surface and the transfer of them to the environment from the boundary-layer. Which step is the control one dominates the characteristics of the whole evaporation. With the mechanism mentioned above, either the results of the experiments here or the ones in literatures can be explained reasonably.2. Thought the pan evaporation, it has been found that the evaporation of Shengli Crude oil is controlled by the first step and the effect of wind velocity is small. The prediction equation is dw/dt^k d ?2 A ju,Y HCT /t, which is related with the liquid characters and states (e.g. thickness, area, viscosity) and is independent of wind speed. Under low wind (<1 m/s), the effect of wind on the evaporation of diesel is evident and becomes inevident when the wind becomes faster than 1 m/s. When the film of diesel becomes thinner, the control step of the evaporation will change from the first to the second step. Therefore, the prediction equation has different form under different conditions, that is, when d>lmm and without stir, the equation is dw/dt = k d"" A ny HaU'/2 t i/2, when d