settings on External Black Body Temperature

vanki · August 26, 2018, 11:09

When setting the boundary conditions of the radiation model，the radiant temperature could be set different from the convection temperature——External Black Body Temperature.But i really want to know how it works and What is the difference from the convective boundary temperature?

LuckyTran · August 26, 2018, 16:33

They simply are different. Physically the convective temperature is often the temperature of the fluid nearby (because the driving temperature difference is the difference in temperature between the surface and nearby fluid). Radiation can be a far away object, e.g. the sun. So in general, there should be a separate option for convective temperature and radiant temperature. And in Fluent, there is. Rightly so.

vanki · August 27, 2018, 03:40

Thank you very much for your answer. I get it. And can i ask for another question? That is whether the blackbody temperature at the flow inlet or outlet is related to the wall temperature in the calculation domain. How the black body temperature value should be set?

vanki · August 27, 2018, 03:42

Quote:

Originally Posted by LuckyTran

They simply are different. Physically the convective temperature is often the temperature of the fluid nearby (because the driving temperature difference is the difference in temperature between the surface and nearby fluid). Radiation can be a far away object, e.g. the sun. So in general, there should be a separate option for convective temperature and radiant temperature. And in Fluent, there is. Rightly so.

Thank you very much for your answer. I get it. And can i ask for another question? That is whether the blackbody temperature at the flow inlet or outlet is related to the wall temperature in the calculation domain. How the black body temperature value should be set?

LuckyTran · August 27, 2018, 14:24

Radiation that radiates in/out of the inlet or outlet would interact with some objects. Of course this is modeled as a black/gray body radiation in your model.

In my opinion, you should always know your own boundary conditions. I don't know what your model is so I can't tell you what that temperature should be. Is there any radiation effects in your problem? And if you think so, what is the radiation like? Where does that radiation go and where does it come from?

vanki · September 10, 2018, 22:02

Quote:

Originally Posted by LuckyTran

Radiation that radiates in/out of the inlet or outlet would interact with some objects. Of course this is modeled as a black/gray body radiation in your model.

In my opinion, you should always know your own boundary conditions. I don't know what your model is so I can't tell you what that temperature should be. Is there any radiation effects in your problem? And if you think so, what is the radiation like? Where does that radiation go and where does it come from?

ok thanks a lot.

August 26, 2018, 11:09	settings on External Black Body Temperature	#1
vanki New Member vanki Join Date: Aug 2018 Posts: 6 Rep Power: 8	When setting the boundary conditions of the radiation model，the radiant temperature could be set different from the convection temperature——External Black Body Temperature.But i really want to know how it works and What is the difference from the convective boundary temperature?

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August 26, 2018, 16:33		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,743 Rep Power: 66	They simply are different. Physically the convective temperature is often the temperature of the fluid nearby (because the driving temperature difference is the difference in temperature between the surface and nearby fluid). Radiation can be a far away object, e.g. the sun. So in general, there should be a separate option for convective temperature and radiant temperature. And in Fluent, there is. Rightly so.

August 27, 2018, 03:40		#3
vanki New Member vanki Join Date: Aug 2018 Posts: 6 Rep Power: 8	Thank you very much for your answer. I get it. And can i ask for another question? That is whether the blackbody temperature at the flow inlet or outlet is related to the wall temperature in the calculation domain. How the black body temperature value should be set?

August 27, 2018, 14:24		#5
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,743 Rep Power: 66	Radiation that radiates in/out of the inlet or outlet would interact with some objects. Of course this is modeled as a black/gray body radiation in your model. In my opinion, you should always know your own boundary conditions. I don't know what your model is so I can't tell you what that temperature should be. Is there any radiation effects in your problem? And if you think so, what is the radiation like? Where does that radiation go and where does it come from?