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Problems with applying emissivity

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Old   June 15, 2020, 02:35
Default Problems with applying emissivity
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Hi guys!


I am trying to use the S2S radiation model for my simulation of a flat plate collector. I initially created the geometry, ran the simulations and validated the model. Now I am trying to change some dimensions and do some optimizations.



I created the geometry exactly like I did in the first case (with one modified dimension) and did the meshing too similarly and now trying to simulate with Fluent.



In the first case, I had to apply emissivity to the normal boundary (wall), lets say.. absorber_sheet_top_edge, only.



But in the newer geometry, it lets me apply the emissivity value only to the shadow boundary! Only to absorber_sheet_top_edge-shadow.

This happened to every other boundary as well!



I got quite high efficiencies with this newer model (less thermal losses). I suspect its more because the S2S model not working normally, than because of the slightly modified geometry.


Help me out here.

What am I doing wrong?
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Old   June 15, 2020, 05:34
Default Emissivity
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Using S2S, radiation travels only through the fluid medium without being affected by it. You have both, solid and fluid, zones in your case. In first case, the names, such as, absorber_sheet_top_edge, belong to the fluid zone, while in the second case their shadows are adjacent to the fluid zones while the name without shadow belong to the solid zone. It doesn't matter. These are just names. You can change those if you want, but it would not affect the simulation. So, you can just go ahead and run the simulation by applying the emissivity values.
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Old   June 15, 2020, 07:13
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Quote:
Originally Posted by vinerm View Post
Using S2S, radiation travels only through the fluid medium without being affected by it. You have both, solid and fluid, zones in your case. In first case, the names, such as, absorber_sheet_top_edge, belong to the fluid zone, while in the second case their shadows are adjacent to the fluid zones while the name without shadow belong to the solid zone. It doesn't matter. These are just names. You can change those if you want, but it would not affect the simulation. So, you can just go ahead and run the simulation by applying the emissivity values.
Thank you very much for your reply
Appreciate it.

What is strange for me was why the names are different when I used the exact same method to create the geometry and mesh. I checked and rechecked if I selected the wrong edges or forgot some edges, while selecting the boundaries and cell zones. But no, all were same.

Anyway, I will disregard the name differences and proceed as you suggested.
Thanks again!
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