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Emissivity for boundary condition

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Old   July 16, 2004, 09:48
Default Emissivity for boundary condition
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ereiss
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I am modeling the heat flow in a concrete floor heated with imbedded hot water pipes. For the top surface boundary condition I am using the mixed thermal conditions, where I can input the external emissivity and temperature for the radiative heat transfer. I can't find any place (such as "define materials") to input the emissivity of the concrete surface though. Even if I select radiation under "define models" I can't find any place to provide the surface emissivity. How does FLUENT calculate this? Does it assume an emissivity of the boundary of 1? Thanks for any information you can provide.
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Old   July 16, 2004, 12:13
Default Re: Emissivity for boundary condition
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Bob
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What Radiation model are you using?
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Old   July 16, 2004, 12:59
Default Re: Emissivity for boundary condition
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ereiss
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I am not using a radiation model. I am just using the energy model but, I can still use a mixed boundary condition that incorporates both convection and radiation. It is the radiation part that I don't know how FLUENT calculates.
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Old   July 25, 2004, 04:48
Default Re: Emissivity for boundary condition
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nazeem
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Dear ereiss ,you should take a global convection coeficient which includes conv+radiation

h=24.1*e-4*epsilon*pow(T,1.61)

epsilon :emissivity ,T temperature

and you write a UDF for this......
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Old   August 10, 2012, 01:27
Red face External radiation
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Quote:
Originally Posted by nazeem
;113968
Dear ereiss ,you should take a global convection coeficient which includes conv+radiation

h=24.1*e-4*epsilon*pow(T,1.61)

epsilon :emissivity ,T temperature

and you write a UDF for this......
Dear Nazeem,
Could you please write the equation a bit clearly? And is it possible for you to give a reference for that, so that I can make some study. Another request is, I am modeling a conjugate heat transfer problem (liquid coolant flow through a tube), in which I have to give three boundary conditions on the outer surface of the tube: (non-uniform) functional heat flux as heat input, radiation loss and convection loss. But I don't understand how can I ensure all of these 3 at a time.
Could you please suggest me? I'll be happy if you may text me in my email.

Regards
n7310889 (murad99me@yahoo.com)
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