Consider a hemispherical droplet of liquid water (species A) on a flat surface, evaporating by molecular diffusion into the surrounding still air (species B). The temperature and the bulk vapor pressure of water in the surrounding still air are kept constant, and you may assume the change in the droplet radius, r, is negligible during this process.
a) What coordinate system best describes this diffusion process?
b) List five reasonable assumptions that will simplify the evaluation of this mass-transfer process.
c) Based on the assumptions, derived a simplified general differential equation that describes the mass transfer of A.
d) Generate an equation for Na as a function of the diffusion coefficient.