# Heat Transfer convergence problem

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

 April 26, 2013, 03:24 Heat Transfer convergence problem #1 New Member   Join Date: May 2009 Posts: 9 Rep Power: 10 Sponsored Links Hi everyone, I want to model heat transfer through a wall in Fluent. I have several layers of material, including some shell conduction. I set freestream T 293K "inside" and 273 K "outside". Now, to check if my calculation is converged, I observe Total Surface Heat flux on faces "in" and "out", and I would expect that the sum of these fluxes would tend to 0. It does indeed tend to it, but very very very slowly and I still have something like 7% error between flux in and flux out, which is I think too much.... I first had a under-relaxation factor quite low, but then I progressively raised it up to 0.99 now, and even if it does help "getting there" faster, it still appears that it will never completely converge (in fact relaxation factor helps just a very little bit). I tried first 2nd order upwind scheme, now I tried QUICK, it doesn't change anything. Residuals are fine. I have 2 different geometries, the problem occurs in both except that in my second geometry, the fluxes are higher, so the error is much less in %. (but it's the same magnitude of error in Watts). Does anybody have an idea on what could be the problem and how to solve it ? Thanks a lot ! savate moh likes this.

April 26, 2013, 06:29
#2
New Member

Join Date: Mar 2013
Posts: 6
Rep Power: 6
Quote:
 Originally Posted by frodooon Hi everyone, I want to model heat transfer through a wall in Fluent. I have several layers of material, including some shell conduction. I set freestream T 293K "inside" and 273 K "outside". Now, to check if my calculation is converged, I observe Total Surface Heat flux on faces "in" and "out", and I would expect that the sum of these fluxes would tend to 0. It does indeed tend to it, but very very very slowly and I still have something like 7% error between flux in and flux out, which is I think too much.... I first had a under-relaxation factor quite low, but then I progressively raised it up to 0.99 now, and even if it does help "getting there" faster, it still appears that it will never completely converge (in fact relaxation factor helps just a very little bit). I tried first 2nd order upwind scheme, now I tried QUICK, it doesn't change anything. Residuals are fine. I have 2 different geometries, the problem occurs in both except that in my second geometry, the fluxes are higher, so the error is much less in %. (but it's the same magnitude of error in Watts). Does anybody have an idea on what could be the problem and how to solve it ? Thanks a lot !
good morning , i need some answers about fluent,i want to now the definition about, and how can i use them : (free stream temperature,heat generation rate, external radiation temperature,and external emissivity)

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Attesz CFX 7 January 5, 2013 04:32 rogbrito CFX 1 January 29, 2012 18:48 siva0182 FLUENT 1 January 29, 2012 09:23 Manoj Padmakarrao Raut Siemens 0 March 17, 2005 01:01 Brian CFX 0 September 13, 2004 01:19