CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Software User Forums > ANSYS > CFX

Mass Flow Rate is not converging

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   December 7, 2010, 03:08
Default Mass Flow Rate is not converging
  #1
New Member
 
Ghulam Destgeer
Join Date: Nov 2010
Posts: 4
Rep Power: 15
destgir448 is on a distinguished road
I'm analyzing heat transfer and pressure drop in a heat exchanger. All the residuals are converging up till (at least) 10^-3. But some residuals' lines do not go below 10^-3 mark.
After completion of solution, when I check Mass Flow Rate at the Inlet which I initially assigned as Inlet Boundary Condition, do not remain same. In fact, Mass Flow Rate becomes significantly low. In addition, if I apply velocity as the Inlet condition, velocity remains same at the inlet, but again when I calculate mass flow rate, it gives very low value.

I need to know, how can I make Mass Flow rate to converge. At least mass flow rate should remain same at the inlet as I assign as a boundary condition.

Your help would be highly appreciated.

Thanks,
Ghulam
destgir448 is offline   Reply With Quote

Old   December 7, 2010, 17:48
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,830
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
http://www.cfd-online.com/Wiki/Ansys...gence_criteria
ghorrocks is offline   Reply With Quote

Old   December 9, 2010, 07:55
Default
  #3
New Member
 
Ghulam Destgeer
Join Date: Nov 2010
Posts: 4
Rep Power: 15
destgir448 is on a distinguished road
Thanks a lot ghorrocks... It was really helpful...
destgir448 is offline   Reply With Quote

Old   December 10, 2010, 07:18
Default
  #4
New Member
 
Ghulam Destgeer
Join Date: Nov 2010
Posts: 4
Rep Power: 15
destgir448 is on a distinguished road
I have followed the instructions and the solution converged to 1e-4 in 50 iterations. But the mass flow rate which I applied as the inlet boundary condition (i.e. value 0.02 kg/s) do not remain same after the solution. As Mass Flow rate is a boundary condition, it should remain same, but the mass flow rate turns out to be 0.0001 kg/s when I calculate it in post processing (Mass Flow over area average ~0.0001kg/s). what should I do to make it remain same as I specify it in the beginning.

Regards,
ghulam Destgeer

Last edited by destgir448; December 10, 2010 at 08:01.
destgir448 is offline   Reply With Quote

Old   December 11, 2010, 05:13
Default
  #5
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,830
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Something is not right in your simulation setup when that happens. Do you have warnings about reverse flow?

Also, how are you calculating mass flow rate? Use the mass flow rate calculator in CFD-Post. Mass Flow over area average is not the correct way of calculating it.
ghorrocks is offline   Reply With Quote

Old   December 11, 2010, 05:55
Default
  #6
New Member
 
Ghulam Destgeer
Join Date: Nov 2010
Posts: 4
Rep Power: 15
destgir448 is on a distinguished road
Thank you so much for your reply.

You are right, i was not calculating mass flow rate in the right way... now it is OK. I got my results.

Thanks,
Ghulam Destgeer
destgir448 is offline   Reply With Quote

Reply

Tags
cfx, convergance, mass flow

Thread Tools Search this Thread
Search this Thread:

Advanced Search
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 Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
Mass flow rate eddie FLUENT 15 July 19, 2017 09:31
How can apply mass flow rate boundary condition? Sima Phoenics 1 December 1, 2007 18:55
negative global mass flow rate Gimli FLUENT 0 April 21, 2006 07:17
mass flow rate error Masood FLUENT 0 May 22, 2005 00:32
Beginner---Value of mass flow rate Wang Xin Phoenics 2 May 10, 2003 02:30


All times are GMT -4. The time now is 21:14.