An experimental technique was developed that uses infrared tomography to measure the three-dimensional vapor distribution above an evaporating sessile drop. The technique was applied to measure the vapor distributions above evaporating drops of hexane and 3-methylpentane (3MP) at room temperature and pressure. The molecular masses of these two species are heavier than air and the vapor from the evaporating drop forms a flat, disk-shaped cloud. A Fourier transform infrared spectrometer (FTIR) was used to measure the spectral absorbance along a set of paths passing through the vapor cloud. From a set of path-averaged absorbance measurements, a two-dimensional spatial concentration distribution was determined using a computed tomography routine. A three-dimensional concentration distribution was obtained from multiple two-dimensional distributions obtained at different elevations above the drop.
The vapor distributions for both hexane and 3MP differ significantly from the values predicted by the solutions for diffusion-limited evaporation and indicate the effect of buoyancy-induced convection of the vapor. These measurements are the first quantitative measurements of the vapor distribution above a sessile drop and are important for advancing the understanding of the vapor phase transport mechanisms, and thus sessile drop evaporation.
P.L. Kelly-Zion, C.J. Pursell, N. Hasbamrer, B. Cardozo, K. Gaughan, K. Nickels, Vapor distribution above an evaporating sessile drop, International Journal of Heat and Mass Transfer, Volume 65, October 2013, Pages 165-172, ISSN 0017-9310, http://dx.doi.org/10.1016/j.ijheatmasstransfer.2013.06.003.
International Journal of Heat and Mass Transfer