WUFI

Hello,

I would like to make an air gap between two layers of wood. But I can't find air in the material data. Do I have to make a new data ? Or is there an easier possibility ?
Thank you

S. Raji

Hello,
the air layers you can find in the database, if you choose "Generic Materials" as Source.
Ch. Bludau

Hello

If you had to use an air gap of for example 75 mm, would it be valid to combine a layer of 50 mm with one of 25 mm?

Thanks,
Jeppe

Hello,
the combination of the air gaps is not the right way because there is the convection included. The better way is described in a table in the Wufi Help Text. Just open Help go to Material Data -> Air Layers. Here is described how the air layer is build. For 75mm you have to interpolate the data between 70 and 80 mm. There is also a difference if the air layer connects to a metal surface or non metal surface:
µ* = 0.09 · Rmet / (3.5 · Dx*) = 0.026 · Rmet / Dx*

For vertical air layers, Rnon-met and Rmet may be taken from this table

thickness Rnon-met Rmet
[cm] [m²K/W] [m²K/W]
7 0.176 0.623
8 0.174 0.613

Have fun, Christian

Vielen dank for the quick answer Christian!

I have an additional question: How do i go about creating an L-shaped air gap?

Thanks, Jeppe

Hi Jeppe,
you can create a L-shaped air gap by connecting two boxes. I forgot to mentioned in my last answer that you should use an anisotroph material in Wufi2d for air layers, to assume, that the air can circulate in the gap. So the way closes to the reality should be to connect two boxes and fill them in both directions with different air properties. Just try to inter-/extrapolate the values.
For example you create a L with a thickness of 75mm and a length upwards of 150mm (box1) and a length to the left with 100mm (box2) you should use for box1 an air layer of 75mm in x-direction and air layer of 150mm to the y-direction and for box2 an air layer of 100mm in x and an air layer of 75mm in y-direction.
BTW: You can assign the different directions the following way: In the material window do a left click on the material to assign x and do a right click to assign/unassign the y-direction.
Hope that helps,
Christian