Problems evaluating HeatFlux

mak86 · September 11, 2010, 13:14

Dear all,
I have modelled a conjugate heat transfer problem. Results and temperature field seem to be ok but when I try to define the heat flux through areas by defining an expression I get zero value.
I use the following expression:
ave(Heat Flux)@targetarea
What is the problem?
Another problem is that the monitor points defined in the CFX-Pre does not appear in the CFD-Post. what should I do to fix this?
Thanks

ghorrocks · September 11, 2010, 22:41

You should use the areaAve() function, not the ave function. The ave function just does an arithmetic average of the nodal values with no regard to the element size.

Are you talking about a heat flux on a wall or in the middle of the flow?

Monitor points do not get transferred to CFD-Post. You have to define them again as points in CFD-Post.

mak86 · September 12, 2010, 04:15

thanks, I have tried the areaAve but I got the same result. I'm trying to evaluate the heat flux at fluid-solid interface. Thanks again

ghorrocks · September 13, 2010, 07:50

The ave() and areaAve() functions will only return the same value if the mesh size is constant. You should use the correct areaAve() function so if in future you move to graded meshes you calculations will be correct.

I think the variable you are looking for is Wall Heat Transfer.

mak86 · September 13, 2010, 09:17

Thanks.
I searched the variable list but there is no Wall Heat Transfer variable.

September 11, 2010, 13:14	Problems evaluating HeatFlux	#1
mak86 New Member Join Date: Jul 2010 Posts: 23 Rep Power: 17	Dear all, I have modelled a conjugate heat transfer problem. Results and temperature field seem to be ok but when I try to define the heat flux through areas by defining an expression I get zero value. I use the following expression: ave(Heat Flux)@targetarea What is the problem? Another problem is that the monitor points defined in the CFX-Pre does not appear in the CFD-Post. what should I do to fix this? Thanks

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September 11, 2010, 22:41		#2
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 18,001 Rep Power: 146	You should use the areaAve() function, not the ave function. The ave function just does an arithmetic average of the nodal values with no regard to the element size. Are you talking about a heat flux on a wall or in the middle of the flow? Monitor points do not get transferred to CFD-Post. You have to define them again as points in CFD-Post.

September 12, 2010, 04:15		#3
mak86 New Member Join Date: Jul 2010 Posts: 23 Rep Power: 17	thanks, I have tried the areaAve but I got the same result. I'm trying to evaluate the heat flux at fluid-solid interface. Thanks again

September 13, 2010, 07:50		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 18,001 Rep Power: 146	The ave() and areaAve() functions will only return the same value if the mesh size is constant. You should use the correct areaAve() function so if in future you move to graded meshes you calculations will be correct. I think the variable you are looking for is Wall Heat Transfer.

September 13, 2010, 09:17		#5
mak86 New Member Join Date: Jul 2010 Posts: 23 Rep Power: 17	Thanks. I searched the variable list but there is no Wall Heat Transfer variable.