Film evaporation of drops of different shape above a horizontal plate

On a vapor film, floating drops with volumes of several cm3 are disk-like on horizontal plates, while in contrast, drops with volumes smaller than 0.5 mm3 are spherical. Most of the drops have a volume, and thus a form, between these two boundary shapes. The evaporation time of disk-like drops is represented in a dimensionless manner on the basis of well-known analytical solutions, whereby two newly defined characteristic numbers are introduced. For spherical drops an analytical solution is developed. It is shown that with these characteristic numbers the evaporation time of disks as well as of spheres can be described. However, as a result of changed drop geometry, other values for the exponents of the numbers occur. The evaporation times of intermediate drops, which were determined experimentally by ourselves and taken from the literature, can likewise be described by these characteristic numbers. Their exponents change with the volume between the limit values of the two shapes, sphere and disk.