Reconsider Prob. 14–77. In order to reduce the migration of water vapor through the wall, it is proposed to use a 0.051-mm-thick polyethylene film with a permeance of 9.1 × 10^-12 kg/s·m² · Pa. Determine the amount of water vapor that will diffuse through the wall in this case during a 24-h period.

Data From problem 77

The diffusion of water vapor through plaster boards and its condensation in the wall insulation in cold weather are of concern since they reduce the effectiveness of insulation. Consider a house that is maintained at 20°C and 60 percent relative humidity at a location where the atmospheric pressure is 97 kPa. The inside of the walls is finished with 9.5-mm-thick gypsum wallboard. Taking the vapor pressure at the outer side of the wallboard to be zero, determine the maximum amount of water vapor that will diffuse through a 3-m × 8-m section of a wall during a 24-h period. The permeance of the 9.5-mm-thick gypsum wallboard to water vapor is 2.86 × 10^-9 kg/s·m² · Pa.

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Room 20°C 97 kPa 60% RH Plaster board -9.5 mm Outdoors Vapor diffusion