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Reflecting/bouncing thermal radiation

ErikClacey
9-Granite

Reflecting/bouncing thermal radiation

I'm using the thermal model in Creo 3.0 Simulate. If I have a U-shaped part/radiator in a vacuum with two surfaces at some distance apart from eachother, and apply a heat load at the bottom and radiative surfaces on the remaining surfaces, I want to see how warm it gets inside the U vs the outside. In a vacuum, heat can only move avay from the part via thermal radiation. The inside should get warmer since the thermal radiation from each face "sees" an equally warm face.

The same applies if I have two parts close to each other in an assembly, in a vacuum. They are not physically thermally connected, so conduction is not possible. If one part gets warm the thermal radiation should heat the other part. Can this be done?


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4 REPLIES 4
ehaenen
4-Participant
(To:ErikClacey)

Hello Erik

In Simulate thermal, radiation is defined the other way around. You enter for a surface the heat that it "sees". You do this by entering an emissivity (how easily the surface accepts heat through radiation , Emissivity - Wikipedia, the free encyclopedia) and the ambient temperature.

So it is not actually possible to define a surface temperature and have Simulate determine what temperature the opposing surface in the U will get (in vacuum).

I've used it though with useful effect. You can try and find out how sensitive a design is when radiation is or is not taken into account.

Does this help?

Erik

Ïf you know the radiative power emitted from one component/surface, and how much of that power is absorbed by the other component, then yes, you can apply this as a heat load on the component where you want to calculate the temperature distribution.

If you don't know this, then it's more complicated.

I don't have the formulae for thermal radiation in my head, but I guess you can look that up. I'm not sure however, how accurate a hand calculation is. Thermal radiation can be more or less directional / diffuse, just as a surface can be matte or shiny. Knowing the emittance coefficient of your surface is maybe not so easy, but you can get some guidance here:

Emissivity - Wikipedia, the free encyclopedia

If you have access to FloEFD (which I happen to have), then you can set up an analysis and calculate the heat transfer between the components. FloEFD will take radiation, convection and conduction into account. You will also include the cooling effect of the air (or other fluid) that circulate around the hot components. FloEFD has an extensive library of fluids, solid materials and radiative surfaces.

FloEFD is a CAD-embedded software for flow/heat simulation. It is particularly good at simulating the coupled problem of flow and heat transfer.

I can do the analysis for you, for a fee of course. From your description, the problem/geometry does not seem to be too complicated. A stationary analysis (the conditions that occur after a long time, when flow field and temperatures have stabilized) can be done quickly, but if you want to run a transient analysis, then that can be more time consuming. Drop me a message in case you are interested...

/Mats Lindqvist/

Ok. Well, we have a proper thermal analysis software suite that can handle this situation correctly, so no worries there. I was just hoping to be able to do the analysis directly in Creo Simulate. It seems then that this functionality may be missing in Simulate.

For future reference: another possible software to use is RadTherm.

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