The flux of water vapour through glass fiber insulation depends on the gradients of the concentration of the water vapour and the temperature in accordance with a generalized form of Fick's Law, viz.
JV/ρν=-α(1/ρν dρν/dx) - β(1/TdT/dx)
The diffusion coefficient for the density gradient is related to the permeability obtained from an isothermal permeance test. The coefficient associated with the temperature gradient is derived from measured values of the heat flux through a specimen of fibrous insulation in both a wet and dry condition.
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References
1.
1. Kumaran, K.K. (April 1987). Moisture Transport Through Glass-Fiber Insulation in the Presence of a Thermal Gradient , Journal of Thermal Insulation, 10: 243-255 .
2.
2. Tong, T.W., McElroy, D.L. and Yarbrough, D.W. (1985). Transient Radiation and Conduction Heat Transfer in Porous Thermal Insulations, Journal of Thermal Insulation, pp. 9-13.Also as Paper No. 84 WA/HT-102, (1984). ASME Winter Annual Meeting.
