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WUFI requires assinging boundary conditions to an internal interface

Posted: Thu Nov 07, 2024 4:51 am -1100
by 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

Re: WUFI requires assinging boundary conditions to an internal interface

Posted: Thu Nov 07, 2024 10:00 pm -1100
by 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

Re: WUFI requires assinging boundary conditions to an internal interface

Posted: Mon Nov 11, 2024 7:13 am -1100
by 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

Re: WUFI requires assinging boundary conditions to an internal interface

Posted: Fri Nov 15, 2024 2:12 am -1100
by 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

Re: WUFI requires assinging boundary conditions to an internal interface

Posted: Mon Nov 18, 2024 12:59 am -1100
by 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

Re: WUFI requires assinging boundary conditions to an internal interface

Posted: Mon Nov 18, 2024 9:03 pm -1100
by 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 ยต-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