Spherical pellets of 1.0 cm diameter are spray painted with a very thin coat of paint. The paint contains a volatile solvent. The vapor pressure of the solvent at 298 K is 1:17 × 104 Pa, and the diffusivity of the solvent vapor in air at 296 K is 0.0962 cm2/s. The amount of solvent in the wet paint on the pellet is 0.12 g solvent per cm2 of pellet surface area. The molecular weight of the solvent is 78 kg/kg mol.
a. Determine the minimum time to dry the painted pellet if still air at 298 K and 1.0 atm surrounds the pellet.
b. Determine the minimum time to dry the painted pellet if air at 298 K and 1.0 atm pressure flows around the pellet at a bulk velocity of 1.0 m/s.