The evaporation of oil spills: Development and implementation of new prediction methodology

Abstract

Extensive experimentation was conducted on oil evaporation. The results of the regulation nature of oil evaporation experiments, show that oil is not strictly boundary-layer regulated specifically: 1) The evaporation rate of several oils with increasing wind speed shows that, unlike water, the evaporation rate does not change significantly except for the initial step over 0-level wind. 2) Increasing area does not significantly change oil evaporation rate. 3) Decreasing thickness does not increase oil evaporation rate. 4) The volume or mass of oil evaporating correlates with the evaporation rate. 5) Evaporation of pure hydrocarbons with and without wind (turbulence) shows that compounds larger than nonane and decane are not boundary-layer regulated. The fact that oil evaporation is not strictly boundary-layer regulated implies a simplistic evaporation equation will suffice to describe the process. A simple equation of the form, evaporation = constant X logarithm of time, is sufficient to describe evaporation. The following processes do not require consideration: wind velocity, turbulence level, area, thickness, and scale size. The factors found to be important to evaporation are time and temperature. The equation parameters found experimentally for the evaporation of oils can be related to commonly-available distillation data for the oil. Specifically, it has been found that the distillation percentage at 180°C correlates well with the equation parameters. Relationships enabling calculation of evaporation equations directly from distillation data have been developed. These equations were combined with the equations generated to account for the temperature variations. The results have application in oil spill prediction and modelling. The simple equations can be applied using readily-available data such as sea temperature and time. Old equations required oil vapour pressure, specialized distillation data, spill area, wind speed, and mass transfer coefficients, all of which are difficult to obtain.