March 2, 2023 at 9:46 am
Rémi Gérard-Marzan
Subscriber

 

 

Hello again Dave,

Here is some feedback from your suggestions.

I have modelled radiation in a very simple cylinder : one of the bottom (inner) faces models the Earth, at 15°C (so 288,15°K), while all the other inner faces of that cylinder model outer space, at 4°K. I have run a steady-state thermal analysis by applying radiation to all these surfaces, all with an emissivity of 1, and alternatively with an Open configuration or a Perfect configuration. The image below will show you an exploded view of that setup, with the radiating surfaces for “espace” (“outer space” in French) being highlighted. The disk at the foreground is the Earth.

Now, the surface of Earth in that setup is 76.905 m². Given an emissivity of 1 and a temperature of 288.15K, I would expect the “Emitted Radiation” value to be equal to 30,061.6W. However, both in the “Open” and in the “Perfect” enclosures, I can read in the thermal probe that the “Emitted Radiation” value is actually equal to 29,317.0W. So, similarly to the case I mentioned in the opening post, there is a significant difference here. 

Even more surprisingly, when reviewing the thermal probe for Space, since this is a perfect black-body, I would expect reflected radiationto be equal to 0. Maybe, due to numerical errors, I could understand an actually non-zero value, provided it is very small. However, I can read that the computed “Reflected Radiation” to be equal to 45.426W. This is a surprisingly high amount.

So that’s it. Do you have any clues as to why all this happens?

Best regards and thank you for your help so far.

Rémi