# Emissivity for boundary condition

 Register Blogs Members List Search Today's Posts Mark Forums Read

 July 16, 2004, 09:48 Emissivity for boundary condition #1 ereiss Guest   Posts: n/a 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.

 July 16, 2004, 12:13 Re: Emissivity for boundary condition #2 Bob Guest   Posts: n/a What Radiation model are you using?

 July 16, 2004, 12:59 Re: Emissivity for boundary condition #3 ereiss Guest   Posts: n/a 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.

 July 25, 2004, 04:48 Re: Emissivity for boundary condition #4 nazeem Guest   Posts: n/a 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......

August 10, 2012, 01:27
#5
New Member

n7310889
Join Date: Aug 2012
Posts: 26
Rep Power: 5
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