Experiments were conducted to investigate the range of applicability of a
commonly used assumption for evaporation models of sessile drops, that the
transport mechanism that controls the evaporation is vapor diffusion. The
evaporation rates of sessile drops of 3-methylpentane, hexane, cyclohexane,
and heptane were measured. The radius of the drop contact line was con-
stant during the measurements and drops of radius from 1 mm to 22 mm
were studied. It was found that a diffusion-controlled evaporation model
underpredicts the evaporation rate from 36% to 80% depending on the drop
size. The increase in the evaporation rate was attributed to a second trans-
port mechanism, natural convection of the vapors, and an empirical model
was developed for conditions of combined diffusive and convective transport.
Over the broad range of volatilities and drop sizes studied, the evaporation
rates computed using the combined transport model agree with the measured
values with less than 6% root mean square error.
Kelly-Zion, Peter; Purcell, Christopher J.; Vaidya, Sawan; and Batra, Jaskirat, "Evaporation of Sessile Drops under Combined Diffusion and Natural Convection" (2011). Engineering Faculty Research. Paper 3.
Colloids and Surfaces A: Physicochemical and Engineering Aspects Volume 381, Issue 1-3, 20 May 2011, Pages 31-36