During cold weather periods, vapor in a room diffuses through the dry wall and condenses in the adjoining insulation. This process decreases the thermal resistance and degrades the insulation. Consider a condition at which the vapor pressure in the air at 25°C inside a room is 3 kPa, and the vapor pressure in the insulation is negligible. The 3-m-high and 10-m-wide dry wall is 12-mm thick with a solubility of water vapor in the wall material of approximately 0.007 kmol/m³.bar, and diffusion coefficient of water vapor in the wall is 0.2 × 10^-9 m²/s. Determine the mass diffusion rate of water vapor through the wall.

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Room 25°C PA.1 = 3 kPa Vapor diffusion Dry wall Insulation