Evaporation is an important component in oil spill models.
Various approaches for oil evaporation prediction are
summarized. Models can be divided into those models that
use the basis of air‐boundary‐regulation or those that use
liquid diffusion‐regulated evaporation physics. Studies
show that oil is not air boundary‐layer regulated such as it is
for water evaporation, which implies that a simplistic
evaporation equation suffices to accurately describe the
process. The following processes do not require
consideration: wind velocity, turbulence level, area and scale
size. The factors important to evaporation are time and
temperature. Oil evaporation does show a thickness effect,
although not as pronounced as that for air‐boundary‐layer
regulated models. A thickness adjustment calculation is
presented for diffusion‐regulated models. This new model is
applicable to thicknesses greater than about 1.5 mm. In the
case of thin slicks, this adjustment is not relevant as oils
typically spread to less than that in a short time.
The use of air‐boundary‐models results in three types of
errors: air‐boundary‐layer models cannot accurately deal
with long term evaporation; second, the wind factor results
in unrealistic values and finally, they have not been adjusted
for the different curvature for diesel‐like evaporation.
Further, these semi‐empirical equations require inputs such
as area, etc., that are unknown at the time of the spills. There
has been some effort on the part of modellers to adjust airboundary‐
layer models to be more realistic on the long‐term,
but these may be artificial and result in other errors such as
under‐estimation for long‐term prediction. A comparison of
models shows that on a very short term, such as a few hours,
most models yield similar results. However, as time
increases past a few days, the errors with air‐boundary‐layer
regulated models are unacceptable. Examples are given
where errors are as large as 100% over a few days.
