
[Sponsors] 
June 13, 2015, 14:15 
Fixed Wall Temperature Pipe With Odd Results

#1 
Member
Kevin Hoopes
Join Date: Oct 2010
Posts: 42
Rep Power: 9 
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 

June 13, 2015, 15:39 

#2 
Senior Member
Join Date: Jun 2009
Posts: 573
Rep Power: 13 
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, 

June 14, 2015, 23:31 

#3  
Member
Kevin Hoopes
Join Date: Oct 2010
Posts: 42
Rep Power: 9 
Quote:
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 

June 15, 2015, 03:54 

#4 
Senior Member
Thomas MADELEINE
Join Date: Oct 2014
Posts: 126
Rep Power: 4 
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). 

June 15, 2015, 05:56 

#5 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,837
Rep Power: 100 
Are you looking at the total temperature? That will be higher that the static temperature, and the static temperature should match the wall temperature.


June 15, 2015, 07:58 

#6  
Member
Shane
Join Date: Oct 2009
Posts: 52
Rep Power: 9 
Quote:
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 

Thread Tools  
Display Modes  


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 