How to calculate U factor of a assembly

[sganz]

Hi guys,

I`m trying to calculate the U- Factor (W/m² K) of an 2D assembly. In the pictures you see the simplified problem with the assembly made of steel and stellrock wool. The BC`s are set to the outside walls of the steel parts (Inisde air temp const 41°C, outside temp const 21°C).

So the question is now how can i see the U Factor of the assembly in the results. Is it the Film coefficient in the wall results measured at the outside steel wall with a reference temp= 41° or something else???? I`m a little bit confused about the calculation of U factor inside the CFD.C?

[Anonymous]

Hi,

first of all, you shouldn't use boundary conditions inside the model. As the name indicates, they should be used in 99% of all cases outside, where the model boundary is. In you example, you can pick the edges far off the wall.
Then, finally you will see a temperature at the solid wall, different from those values and calculate the film coefficient (German: Wärmeübergangskoeffizient), like in your screenshot. I'd always use the reference temperature value manually specified, cause the "neal wall temperature" is mesh dependent.

Lastly, I'm not sure if you're really interested in the film coefficient, which just describes what happens on that particular surface, but rather the "thermal transmittance" of the whole wall (German: U-Wert), which has the same unit but a different purpose.

Marco

[sganz]

I`m sorry for the incorrect definition. The thermal transmittance is what I´m looking for in the end.

Is there a way to calculate the thermal transmittance directly in CFD or do we have to do that manually?

[Anonymous]

manually 🙂

or maybe with python scripting