CFD Online Logo CFD Online URL
Home > Forums > Main CFD Forum

BC for constant heat flux

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

LinkBack Thread Tools Display Modes
Old   July 16, 1998, 09:48
Default BC for constant heat flux
Posts: n/a

I am doing heat transfer calculations for duct flows with an in house code. The constant temperature BC was already written but I want to use constant heat flux BC in periodic flow case and I am using a finite volume code, any suggestions?

  Reply With Quote

Old   July 16, 1998, 10:36
Default Re: BC for constant heat flux
Jonas Larsson
Posts: n/a
It's impossible to give an answer to that without further details.

The simple answer is that you just set

dT/dn = 1/k * q

on the wall-face of the control-volume when you derive your equations. q is given by you as a boundary condition.

How this should be implemented in your code depends entirely on what kind of code it is, how it is structured, which solution variables you are using, if you are resolving the boundary layer or if you are using wall function etc.
  Reply With Quote

Old   July 17, 1998, 15:02
Default Re: BC for constant heat flux
Philip Zwart
Posts: n/a
If your code is a finite volume code this should be dead easy. Then the boundary conditions simply represent the flux integral through the boundary faces, which in your case is just the specified heat flux times the face area; ie, just dump q*A into the right-hand side of your equation. Then, after the equations are solved, you can back out the boundary temperature using the relationship

q = -k dT/dn

(or analogous expression if wall functions are used, as Jonas pointed out).

I'd also like to mention that some people have a far more convoluted approach to implementing boundary conditions in FV methods. The text by Hoffman & Chiang, for instance, wants to move the storage location for cells adjacent to the boundary onto the boundary face itself, so that the conservation equation for cells adjacent to the boundary is discarded for T-specified walls. This can lead to conceptual inconsistencies, including the need to apply flux-specified boundary conditions iteratively (rather than directly as above). Also, ambiguity issues similar to those mentioned in another thread from a few days ago can arise.

Hope this helps.
  Reply With Quote


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

Similar Threads
Thread Thread Starter Forum Replies Last Post
Sign of Heat Flux at wall Kyung FLUENT 2 February 26, 2016 17:25
Calculating heat flux hugo17 OpenFOAM Post-Processing 4 May 27, 2015 12:47
Variable name for heat flux peterle CFX 4 February 13, 2014 03:21
Heat Flux at wall in a conjugate heat transfer problem Chander CFX 2 July 9, 2011 22:22
Heat Flux Wall Boundary Confusion. Joee FLUENT 1 August 21, 2010 12:20

All times are GMT -4. The time now is 19:04.