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Time constants for moisture diffusion through a permeable barrier into an airspace
Author(s) -
Pinnes Edward L.
Publication year - 1979
Publication title -
polymer engineering and science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.503
H-Index - 111
eISSN - 1548-2634
pISSN - 0032-3888
DOI - 10.1002/pen.760190711
Subject(s) - constant (computer programming) , thermal diffusivity , humidity , diffusion , materials science , fick's laws of diffusion , mechanics , moisture , volume (thermodynamics) , permeability (electromagnetism) , time constant , thermodynamics , air permeability specific surface , composite material , physics , chemistry , computer science , engineering , biochemistry , membrane , electrical engineering , programming language , layer (electronics)
This paper arose from a study of the use of polymeric materials to protect humidity‐sensitive items from damp ambient conditions. A one‐dimensional model for the Fickian diffusion of moisture through a permeable wall into a volume of air is considered. The humidity in the airspace asymptotically approaches equilibrium with the exterior, and the time constant is defined as the time to reach 1–1/ e of its ultimate value. Exact and approximate solutions are considered. Depending on the system geometry and properties, the time constant is either permeability‐controlled or diffusivity‐controlled, or somewhere in between. Under certain conditions, there exists an optimum combination of airspace depth and wall thickness that maximizes the time constant.