WUFI requires assinging boundary conditions to an internal interface

[Lxr_Energy]

Hello,

I'm trying to do a moisture analysis for a multi-layer structure. when I go to surface/weather to set up boundary conditions, WUFI 2D asks to assign a boundary condition to an internal layer interface which is not exposed to the climate. Does that mean I did something wrong with the geometry?

Thanks,
Ray

[Christian Bludau]

Hi Ray,
if unidentified cavities (or holes) are left in the construction, a boundary condition must be assigned to them.
This could be used, for example, to take in account for heating pipes.
Normally, however, the construction should be modeled without cavities. Also for air cavities a layer must be created.
Christian

[Lxr_Energy]

Hi Christian,

Thanks for the reply. If I have cavities/holes in my assembly, for example, for heating pipes or air cavities, shall I use the "air layers" defined in the materials database? The reason why I'm asking is because it seems like the air layers pre-defined in the database are of certain thicknesses, and I don't know if for a custom air layer of specific thickness, shall I create new material in the database and modify the materail parameters, or I can just use the existing air layers in the database and change its thickness?

Thanks,
Ray

[Christian Bludau]

Hi Ray,
the air layers shall not be changed in thickness or combined, as they contain effective values for radiation and convection. See program help for air layers, there is a description on how to calculate other thickness.
I would recommend to set the right thickness in direction of the main temperature gradient and use this for both directions.
Christian

[katinkar]

Hello,
What type of air layer is recommended to use when consideirng the "air layer" inside a HUP column (horizontal cross section)? There is one option of air layers between metallic surfaces (d=10mm) but my air space is much greater than this ...

Do I need to create one myself, if yes, what are the properties I need to take extra into account for the steel surfaces?
Then, would it affect the moisture transport of my component if I anyway set the steel material of the HUP to be vapour impermeable?? (read: does it matter how I model this air space then?)

Thanks in advance,

Katinka

[Christian Bludau]

HI Katinka,

I'm not familiar with HUP. What is that?

Generally, if you do not need to know, what is happening in the column (in case it is a closed profile filed with air), you can model it as one material the profile and the air layer with a high µ-value and an effective value for lambda from profile and filled air.

Regarding the air layers with metallic surfaces please see the program help. Search for "air" or "topic 22", in there a description is given on how to calculate values for other thickness.

Christian