CFD Online Logo CFD Online URL
Home > Forums > CFX

Difference between sum(Wall Heat Flow)@Wall1 and areaInt(Wall Heat Flux)@Wall1

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

LinkBack Thread Tools Display Modes
Old   October 11, 2009, 12:25
Default Difference between sum(Wall Heat Flow)@Wall1 and areaInt(Wall Heat Flux)@Wall1
New Member
Dan Rhys
Join Date: Oct 2009
Posts: 1
Rep Power: 0
danr is on a distinguished road
I'm doing a 2D steady state simulation of a hot pipe in a cold pipe filled with air, with CFX12.
I've prescribed the inner pipe and outer pipe walls at fixed temperatures, and want to find out how much heat is transferred between them by natural convection (no radiation, SST turbulence model). The grid is a one cell thick slice (1mm), with symmetry boundaries either side.

When converged, the heat flowing through the inner wall and outer wall are equal and opposite (sum = 0, as you would expect with a steady state solution).

Previously I've relied on the expression "areaInt(Wall Heat Flux)@Wall1" to give me the heat transfer in [W], but in cfx12 have also opted to save "Wall Heat Flow" to the results files. The values for "sum(Wall Heat Flow)@Wall1" are exactly half that of the flux derived values - dimensions also in [W].

I've done this with many simulations with additional pipes etc and the values always differ by a factor of 2.

Does anyone know why they differ and which is the correct value?

danr is offline   Reply With Quote

Old   October 11, 2009, 17:37
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 14,202
Rep Power: 110
ghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the roughghorrocks is a jewel in the rough
Very strange. You should report this to CFX support as it may be a bug.

I suspect the areaInt(Wall Heat Flux) is the correct number as it should take the integration points into account properly. sum(Wall Heat Flow) would not take into account the integration points so would probably be an approximation. But it is strange the difference is a factor of 2 exactly each time.

I would check the results against the heat flows reported in the output file. I am pretty sure areaInt will be the correct one.
ghorrocks is offline   Reply With Quote


cfx12, heat flow, heat flux, heat transfer

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

All times are GMT -4. The time now is 12:32.