Explicit specification of Water Vapor Transfer Coefficients

[hs]

In order to directly apply the design conditions against the internal condensation issued by MLIT of GOJ,
it requires to specify the water vapor transfer coefficients explicitly.
If the user defined is checked, convective heat transfer coefficient can be explicitly specified, however there is nothing to do with the water vapor transfer coefficient.

I assumes even in the current Wufi Pro that the water vapor transfer coefficient Bp (kg/sqm/s/Pa) is derived from the following
relation, that is, described in the Ph.D Thesis of Dr. Kuenzel,

Bp = 7 e-09 ak

where ak is the convective heat transfer coefficient (W/sqm/K).

Please confirm my presumption that described above and let me know if it is possible to change the implemented Lewis relation.

Best regards,

[veitner]

You are right. Additionally WUFI adds the supplied sd-value (if any) to vapour transfer coefficient (it transforms the bp to an sd-value and adds the user defined sd-value - during calculation this effective sd-value is transformed back to the water vapour transfer coefficient).
But you can enter a negative sd-value. The negative sign is used as a flag to ommit the bp=7 e-09 ak part and to use the sd-value only.
You just need to express your bp in terms of a sd-value.

This functionality is not documented and could be dropped or changed in the future.

Regards
Veit