Radiation heat transfer rate

stefdc · March 4, 2016, 05:04

Hi, what is exactly the definition of radiation heat transfer rate? I've already seen the manual, but I don't understand the real meaning. what does it include?

LuckyTran · March 5, 2016, 20:08

Heat may be transferred between objects via photons through electromagnetic radiation.

Please see: https://en.wikipedia.org/wiki/Black-body_radiation

stefdc · March 6, 2016, 02:52

Thank you for answering me! I've just read the page on internet, but I don't understand why in fluent the values obtained in report--fluxes--radiation heat transfer rate are very different to the values obtained with the stefan boltzman law applied to the all surfaces with the view factors calculated in fluent. Do you have any idea?

LuckyTran · March 6, 2016, 10:38

Because Stefan-Boltzmann law only describes the radiation emitted by a blackbody. It does not include radiation from other surfaces. It also does not say anything about radiation from the original object that is reflected back. Real surfaces have emissivities far from 1 and view factors far from 1.

stefdc · March 6, 2016, 12:01

Thank you again. I have a big furnaces, about 20mX7mX7m with the wall at 1400K. I'm studying the heat lost during the transient of the opening of the door with a dynamic simulation, but I have problem with the radiation heat flux because if i check the report--fluxes--radiation heat transfer rate, I obtain values around 200.000 W. I think this value is not real considering the dimension and the temperature of the furnace. I'm using the S2S model and I registered the Surface Integral---wall fluxes--radiation heat flux on a surface I created behind the door in order to capture the heat flux during the transient of the opening but these values are strange. Do you think there is a problem with the model I made? Thank you for helping me.

March 4, 2016, 05:04	Radiation heat transfer rate	#1
stefdc New Member stefania Join Date: Feb 2016 Location: Italy Posts: 20 Rep Power: 10	Hi, what is exactly the definition of radiation heat transfer rate? I've already seen the manual, but I don't understand the real meaning. what does it include?

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March 5, 2016, 20:08		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,743 Rep Power: 66	Heat may be transferred between objects via photons through electromagnetic radiation. Please see: https://en.wikipedia.org/wiki/Black-body_radiation

March 6, 2016, 02:52		#3
stefdc New Member stefania Join Date: Feb 2016 Location: Italy Posts: 20 Rep Power: 10	Thank you for answering me! I've just read the page on internet, but I don't understand why in fluent the values obtained in report--fluxes--radiation heat transfer rate are very different to the values obtained with the stefan boltzman law applied to the all surfaces with the view factors calculated in fluent. Do you have any idea?

March 6, 2016, 10:38		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,743 Rep Power: 66	Because Stefan-Boltzmann law only describes the radiation emitted by a blackbody. It does not include radiation from other surfaces. It also does not say anything about radiation from the original object that is reflected back. Real surfaces have emissivities far from 1 and view factors far from 1.

March 6, 2016, 12:01		#5
stefdc New Member stefania Join Date: Feb 2016 Location: Italy Posts: 20 Rep Power: 10	Thank you again. I have a big furnaces, about 20mX7mX7m with the wall at 1400K. I'm studying the heat lost during the transient of the opening of the door with a dynamic simulation, but I have problem with the radiation heat flux because if i check the report--fluxes--radiation heat transfer rate, I obtain values around 200.000 W. I think this value is not real considering the dimension and the temperature of the furnace. I'm using the S2S model and I registered the Surface Integral---wall fluxes--radiation heat flux on a surface I created behind the door in order to capture the heat flux during the transient of the opening but these values are strange. Do you think there is a problem with the model I made? Thank you for helping me.