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

Fixed Wall Temperature Pipe With Odd Results

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

Like Tree2Likes
  • 1 Post By Opaque
  • 1 Post By ghorrocks

Reply
 
LinkBack Thread Tools Display Modes
Old   June 13, 2015, 14:15
Default Fixed Wall Temperature Pipe With Odd Results
  #1
Member
 
Kevin Hoopes
Join Date: Oct 2010
Posts: 40
Rep Power: 7
khoopes is on a distinguished road
I am simulating air flow through a pipe. I am setting the wall temperature at 20 [K] less than the inlet temperature. My issue is that the massflow average temperature steadies out near the end of the pipe, and has the logarithmic shape axial distribution that I anticipated, but it steadies out at about 0.5 [K] above the wall temperature, I thought that it would approach the wall temperature and the delta T would approach 0. Is massflow average the correct temperature to use? Also, my mach number is ~0.05, should I use thermal or total energy, or does it mater? The flow is laminar. RE based on pipe diameter of about 400.

Thanks,

Kevin
khoopes is offline   Reply With Quote

Old   June 13, 2015, 15:39
Default
  #2
Senior Member
 
Join Date: Jun 2009
Posts: 290
Rep Power: 9
Opaque is on a distinguished road
May I ask what is odd in the results ?

The fluid will reach the wall temperature at the "infinite length" of the pipe. Is the pipe long enough for the fluid to reach uniform temperature across the section of the pipe. Otherwise, there is a radial profile, and the mass flow average will never be Twall.

Hope the above helps,
sircorp likes this.
Opaque is offline   Reply With Quote

Old   June 14, 2015, 23:31
Default
  #3
Member
 
Kevin Hoopes
Join Date: Oct 2010
Posts: 40
Rep Power: 7
khoopes is on a distinguished road
Quote:
Originally Posted by Opaque View Post
May I ask what is odd in the results ?

The fluid will reach the wall temperature at the "infinite length" of the pipe. Is the pipe long enough for the fluid to reach uniform temperature across the section of the pipe. Otherwise, there is a radial profile, and the mass flow average will never be Twall.

Hope the above helps,
I think what I do not like about the results is that the temperature difference between the wall and the massflow average temperature does not get to zero, but the axial temperature gradient does get to zero. So there is still a 0.5K dt between wall and fluid, but there is no temperature drop in the fluid.

If I am understanding you correctly you are saying maybe it just needs more time to get closer to the wall temp, but I think what I am seeing is that the temperature is not changing anymore.

This leads me to get a zero htc near the end of the tube since I have a finite delta t (from mass flow average) and a vanishingly small q (from enthalpy change). Is this the correct approach to calculate htc?

Thanks for your help.

Kevin
khoopes is offline   Reply With Quote

Old   June 15, 2015, 03:54
Default
  #4
Senior Member
 
Thomas MADELEINE
Join Date: Oct 2014
Posts: 122
Rep Power: 2
Thomas MADELEINE is on a distinguished road
how do you get these result ? (with a plane, a curve ?)

For me supposing you have the average temperature over a small area (massFlowAve), and you get that area closer and closer to the wall it will get closer and closer to your wall temperature.

But your fluid is only at wall temperature at the first integration point of your first cell (in wall direction) so if you want to see the exact wall temperature I will not use an massFlowAve function but directly the temperature (along a radius by example).
Thomas MADELEINE is offline   Reply With Quote

Old   June 15, 2015, 05:56
Default
  #5
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,809
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Are you looking at the total temperature? That will be higher that the static temperature, and the static temperature should match the wall temperature.
sircorp likes this.
ghorrocks is offline   Reply With Quote

Old   June 15, 2015, 07:58
Default
  #6
Member
 
Shane
Join Date: Oct 2009
Posts: 52
Rep Power: 7
sircorp is on a distinguished road
Quote:
Originally Posted by khoopes View Post
I am simulating air flow through a pipe. I am setting the wall temperature at 20 [K] less than the inlet temperature. My issue is that the massflow average temperature steadies out near the end of the pipe, and has the logarithmic shape axial distribution that I anticipated, but it steadies out at about 0.5 [K] above the wall temperature, I thought that it would approach the wall temperature and the delta T would approach 0. Is massflow average the correct temperature to use? Also, my mach number is ~0.05, should I use thermal or total energy, or does it mater? The flow is laminar. RE based on pipe diameter of about 400.

Thanks,

Kevin
Kevin

Did you try to set facet vector temp rather average ? Also near the end of the pipe refine the mesh(Adapt) & check it if you still get 0.5K difference. As the sample size(data points) increases, average may get better.

Shane
sircorp is offline   Reply With Quote

Reply

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
Natural convection in a closed domain STILL NEEDING help! Yr0gErG FLUENT 3 June 12, 2013 02:12
How to adjust wall temperature nutow FLUENT 0 September 4, 2011 05:37
No Slip Wall with Fixed Temperature Boundary Condition Karkoura CFX 7 March 10, 2011 18:23
Deformation of wall by temperature condition Jay FLUENT 0 April 14, 2007 18:06
Pipe wall temperature Fred Uckfield Main CFD Forum 25 May 22, 2000 14:37


All times are GMT -4. The time now is 09:15.