Details:DiffusionResistanceFactorMoistureDependent

Diffusion Resistance Factor, Moisture-dependent

The diffusion resistance factor (µ-value) of the dry material is a basic material parameter and thus indispensable. If, in addition, the dependence of the diffusion resistance factor on the moisture content must be taken into account, WUFI can optionally employ a table with the relevant data. WUFI interpolates linearly between table entries.

Please note, however, that in mineral building materials the (fictitious) decrease of the diffusion resistance factor with increasing moisture content is due to surface diffusion [1] and may therefore also be included in the capillary conduction. In this case, using a constant diffusion resistance factor and choosing appropriate liquid transport coefficients is more advisable.

During the calculation WUFI performs iterations where it samples small regions of the tabulated curve. Very sharp bends in the curve may throw the iteration off and thus impede its convergence. In such a case, the curve should be smoothed by inserting additional points. A large number of entries may slow the search in the table, however.

The definition of the diffusion resistance factor (µ-value) is discussed in the topic Water Vapor Diffusion.

Even if you do not explicitly use a moisture-dependent diffusion resistance factor, WUFI will treat it as moisture-dependent if the moisture content exceeds the free saturation wf. For details see the discussion of the Diffusion Resistance Factor Dry.

Literature:

[1]	Krus, M.: Moisture Transport and Storage Coefficients of Porous Mineral Building Materials. Theoretical Principles and New Test Methods Fraunhofer IRB Verlag, 1996