Two-component model for crude oil evaporation and its application to weathering prediction

Abstract

The model approximates a crude oil as a mixture of an evaporating and non-evaporating component of which the physico-chemical properties are calculated by their composing fractions. The ordinary differential equation with separated variables derived from the model yields a concept of the evaporation time constant T Q that is defined by the initial oil properties and thickness, and the ambient temperature and wind speed. The evaporation ratios Q measured in flume tests on six types of Middle East crude oils are analyzed for the elapsed time non-dimensionalized by T Q. The measured values collapse well to a single straight line Q-log(t/T Q) for each type of oil, independently of emulsification and wave disturbance. A single line common to all the six types of oils is enough for rough estimation. A method using the common line or, more accurately, a line derived from the distillation test of each type of oil is proposed for evaporation prediction. Further analyses of the test results reveal the one-to-one correspondence between evaporation and properties (viscosity and density) of evaporated residual water-free oil. Formulae using the correspondence are suggested for estimating the properties of residual oil. The influences of substrates and thickness of an oil slick on evaporation and oil properties were examined in a small-scale laboratory. The laboratory tests are discussed as a useful procedure for obtaining basic prediction data.