problem with cfx expressions

TallesC · April 22, 2013, 16:15

personnel must enter the equation in the cfx expressions:

Q = stefan*0.7139*(((1114.15^4)[K^4] ) - (Ts^4)[K^4] ) The Stefan-Boltzmann Law

This term is used to heat the pipe, Ts is the surface temperature of geometry in my case is a pipe, the question is how should I call Ts in the expressions cfx??

ghorrocks · April 22, 2013, 18:19

If you are applying this to a surface then simply use T. That is the local surface temperature.

TallesC · April 22, 2013, 20:14

are you sure? I thought the variable T is the temperature at each node of the mesh, not only the surface ...

ghorrocks · April 22, 2013, 20:15

It might be in this case, good point. If the small difference is important to you then I would do a quick check case to test exactly how this is done.

TallesC · April 22, 2013, 21:38

I found this explication in manual cfx:

This is the hybrid temperature field at a wall boundary condition. For Fixed Temperature walls, the wall temperature is the specified value Tw. For all other heat transfer boundary conditions, the wall temperature is backed out from turbulent wall functions when running a turbulent flow model. For laminar flow modelling the wall temperature is just the local fluid temperature at the vertex adjacent to the wall.

April 22, 2013, 16:15	problem with cfx expressions	#1
TallesC Senior Member Talles Caio Join Date: Oct 2012 Location: Brazil Posts: 101 Rep Power: 13	personnel must enter the equation in the cfx expressions: Q = stefan0.7139(((1114.15^4)[K^4] ) - (Ts^4)[K^4] ) The Stefan-Boltzmann Law This term is used to heat the pipe, Ts is the surface temperature of geometry in my case is a pipe, the question is how should I call Ts in the expressions cfx??

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April 22, 2013, 18:19		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,692 Rep Power: 143	If you are applying this to a surface then simply use T. That is the local surface temperature.

April 22, 2013, 20:14		#3
TallesC Senior Member Talles Caio Join Date: Oct 2012 Location: Brazil Posts: 101 Rep Power: 13	are you sure? I thought the variable T is the temperature at each node of the mesh, not only the surface ...

April 22, 2013, 20:15		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,692 Rep Power: 143	It might be in this case, good point. If the small difference is important to you then I would do a quick check case to test exactly how this is done.

April 22, 2013, 21:38		#5
TallesC Senior Member Talles Caio Join Date: Oct 2012 Location: Brazil Posts: 101 Rep Power: 13	I found this explication in manual cfx: This is the hybrid temperature field at a wall boundary condition. For Fixed Temperature walls, the wall temperature is the specified value Tw. For all other heat transfer boundary conditions, the wall temperature is backed out from turbulent wall functions when running a turbulent flow model. For laminar flow modelling the wall temperature is just the local fluid temperature at the vertex adjacent to the wall.