The major objectives of oil weathering simulation models are to predict both the mass of oil remaining in a slick over time and the chemical composition and physical properties of the slick and the movement of the oil slick on the seas. Predictive oil weathering models which generate material balances for both specific compounds and psuedo-compounds (true boiling point distillation cuts) in a crude oil spill have been developed. Composite models have also been developed to provide realistic predictions on the environmental fate and behavior of oil spills. These models are applicable to open ocean oil spills, spills in estuaries and lagoons and spills on land. The oil weathering processes included in the model are evaporation, dispersion, dissolution, emulsification and slick spreading. The models are based on physical property data, such as oil/air interracial surface tension, oil viscosity and mass transfer (rate) coefficients.
Modelling of Oil Weathering Processes
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In general, reasonable correlations between predicted oil weathering behaviour and observed chemical changes have been obtained. Simulated models are capable of predicting oil weathering behaviour in real spill situations. However, further work is needed to validate existing oil weathering models under higher turbulence regimes. This would facilitate assessments of environmental impact of petroleum pollution and site specific contingency plan activation.
In assessing the environmental impacts of petroleum pollution in aquatic environment, it is important to be able to develop predictive mathematical models to estimate the rate at which petroleum spreads and enters into the water column. The predictions from models of the spreading rate, concentration content due to dissolution and dispersion and exposure times can be used to predict the toxic effect of petroleum once introduced into the aquatic environment. These predictions would provide information on the effect of physical properties of the petroleum spill on the spreading rate and spreading rate coefficient, dissolution rate and its coefficient, and dispersion rates and its coefficient. These predictive models provide these information as functions of the physical properties, aquatic dimensions and characteristic flow velocity or angular velocity or frequency or period of oscillation or rotation as vortex and spherical aquatic mediums of the petroleum spill.
If a quantity of raw petroleum slick is placed on an aquatic surface at constant pressure and temperature, so that initially, petroleum is present in a monolayer of appreciable thickness, then the free surface energy of the petroleum-water is given by the total energy.
Once petroleum spills into aquatic environments, it is divided into discrete parcels and a set of spatial coordinates is assigned to each parcel. These parcels are observed to advect with the surrounding water body and diffuse as a result of random processes. These random processes are actually influenced by the characteristics flow velocity; this in turn influences the concentration distribution pattern.
However, the aquatic environments have characteristic natural flow conditions (vortex, cylindrical, 2-dimensional vortex or cylindrical etc.) Which are really a function of the velocity field U that are found to influence the dissolution and dispersion rates of petroleum spills in water. It is worthwhile to develop the velocity distribution of some natural flow conditions that can be used to model the dissolution and dispersion rates of petroleum in aquatic environments.
The pressure exerted by the petroleum spill on aquatic environment at any point in the flow is an essential hydrodynamic model applicable to petroleum spreading, dissolution and dispersion rates. The significance of pressure analysis provides knowledge that the pressure that could be applied to a spreading velocity is zero.
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