Chapter 14, Problem 14.23P

Insulation degrades (experiences an increase in thermal conductivity) if it is subjected to water vapor condensation. The problem may occur in home insulation during cold periods, when vapor in a humidified room diffuses through the drywall (plaster board) and condenses in the adjoining insulation. Estimate the mass diffusion rate for a 3 m× 5 m wall, under conditions for which the vapor pressure is 0.03 bar in the room air and 0.0 bar in the insulation. The drywall is 10 mm thick, and the solubility of water vapor in the wall material is approximately ${\text{5 × 10}}^{\text{-3}}{\text{kmol/m}}^{\text{3}}\text{×bar}$ . The binary diffusion coefficient for water vapor in the drywall is approximately ${\text{10}}^{\text{-9}}{\text{m}}^{\text{2}}\text{/s}$ .