A spherical droplet of liquid A and radius ro evapo- rates into a stagnant layer of gas B. Derive an expres- sion for the evaporation rate of species A in terms of the saturation pressure of species A, pA(ro) = pA,sat, the partial pressure of species A at an arbitrary radius r, pA(r), the total pressure p, and other pertinent quantities. Assume the droplet and the mixture are at a uniform pressure p and temperature T.
For calibration purposes, you've been asked to calculate the expected evaporation rate (kg/h · m2) for a test with water and air under the foregoing conditions, using the known value of DAB for the vapor-air mixture.