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Radiation - Emissivity

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Old   December 18, 2013, 12:09
Question Radiation - Emissivity
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Hello

I wish to simulate the heat losses and the radiation of an exhaust pipe.

For now, I am using the 'convection' option for the heat losses. The radiation is thus mobilized with the surface emissivity.

I wish to try the 'environment' option for the heat losses.
Thus, for the radiation, in addition to the 'surface emissivity', appears the 'external emissivitiy'.
What is the difference between the surface and the external emissivities?
Does this external emissivity is relevant in such a case?

Thank you for your help and explanations
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Old   December 19, 2013, 09:54
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External emissivities can be important if the heat exchange between the outer walls of your domain and surrounding environment is significant. I think in your case that you are simulating an exhaust pipe, you can not simulate the whole world around the exhaust pipe. Instead you can use this environment model and external emissivity to consider the heat radiating to environment.
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Old   December 19, 2013, 10:13
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Hello Siamak

Thank you for your answer.
There is indeed huge different in the results computations, when activating the 'external radiation'.

Compared to StarCD, I did not find any 'external radiation' option, but only the 'surfacic radiation' one.
Do you know if there is a way to implement such 'external radiation' in StarCD?

Thanks again for your help
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Old   December 20, 2013, 12:42
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Take a look at the documentation supplied with the software. It shows how this boundary condition can be used in a particular case with car windows.
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external emissivity, heat losses, radiation, surface emissivity

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