Attempt ALL questions A1. Two spheres one of radius Ro and the other of radius 2R, are coated in a thin layer of volatile liquid. The coating liquid has an equilibrium vapour pressure Py. Each sphere is surrounded by a large volume of stagnant air at pressure p and temperature T. The coating liquid evaporates from each sphere and diffuses into the surrounding stagnant air with diffusivity D. The total mass transfer rate from each sphere is the product of the molar flux and sphere surface area. What is the ratio between the total mass transfer rate from the larger sphere and the total mass transfer rate from the smaller sphere? (a) 4 log(1/(1 - Pu/p)) (b) 4 (C) 2 log(1/(1 pu/p)) (d) 2 (e) log(1/(1 - Pu/p)) (f) 1, i.e. the total mass flow rates are the same for both spheres