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

Pipe Flow Heat Transfer

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

Reply
 
LinkBack Thread Tools Display Modes
Old   January 17, 2011, 08:10
Default Pipe Flow Heat Transfer
  #1
Senior Member
 
Saima
Join Date: Apr 2009
Location: Canada
Posts: 140
Rep Power: 8
Saima is on a distinguished road
Hello,

I am working on a pipe flow(hot air, compressible) for which i have boundary conditions:
Pin = 533 Kpa
Tin = 700 K
mass flow rate: 0.68 kg/sec (outlet)

This pipe is insulated witha another material. I know k =0.70, and outside temperature in 343 K.

Now i have to figure out wat will be the surface temperature after applying this insulation.

I did some basic calculation from heat transfer book (conduction+convection) for pipe in radia direction and found TSur = 400K., its like convection...conduction ...and then convection

But when i tried this in CFX by giving the above boundary conditions plus wall with heat transfer coefficient (h = 1/R: from analytical convection+conduction), it gave me surface temperature 698K.

1. Am i applying the right boundary condition for Heat Transfer on wall?

2. Do i have to do meshing for insulation material as well?

What will be the right way to applying heat transfer boundary condition for hot air inside pipe pluse insulated wall and then natural convection?


Kindly guide me.

Regards,

Last edited by Saima; January 17, 2011 at 08:29.
Saima is offline   Reply With Quote

Old   January 17, 2011, 17:55
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,935
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
I would model this including the pipe and insulation (at least initially) so you do not have to specify a boundary condition on the inside of the pipe. On the outside of the pipe you can specify a combined convection and radiation boundary - CFX does not support this but are pretty easy to derive and apply.

You may be able to ignore radiation on the inside of the pipe providing the pipe internal temperature is constant enough. If this is the case the radiation will cancel out and can then be ignored.
ghorrocks is online now   Reply With Quote

Old   January 30, 2011, 03:50
Default
  #3
Senior Member
 
Saima
Join Date: Apr 2009
Location: Canada
Posts: 140
Rep Power: 8
Saima is on a distinguished road
yes, i calculated combined (Cond+Convection) cefficient and i can specify outer temperature (environment) as well.

I am taking SST and total energy model is it ok?

When i did hand calculation it gave me Tsur = 477 K. I took insulation as well.

But after solving problem in CFX it was not give me that temperture, it is around 655K. In CFX i have include insulation but when i am given h comined it has effect of both.

Kindly let me Is this the right way?

Regards.
Saima is offline   Reply With Quote

Old   January 30, 2011, 05:41
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,935
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Are you sure your simulation is accurate? See http://www.cfd-online.com/Wiki/Ansys..._inaccurate.3F

Are you sure your hand calculation is accurate?
ghorrocks is online now   Reply With Quote

Old   January 30, 2011, 09:52
Default
  #5
Senior Member
 
Saima
Join Date: Apr 2009
Location: Canada
Posts: 140
Rep Power: 8
Saima is on a distinguished road
Hello,

I did hand calculation from heat transferbook by taking cylinder in layers (Conduction+Convection) and for sure that are accurate.

Is it possible, i cans end you cfx file by email.

Regards,
Saima is offline   Reply With Quote

Old   January 30, 2011, 17:41
Default
  #6
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 10,935
Rep Power: 85
ghorrocks has a spectacular aura aboutghorrocks has a spectacular aura aboutghorrocks has a spectacular aura about
Quote:
and for sure that are accurate.
Um, right. What did you use for the convection coefficient? How accurate was that?

Please don't send me the files, I don't have time to look at them.
ghorrocks is online now   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
Flow around pipes - heat transfer coefficient on the wall of pipe doodek Main CFD Forum 2 November 23, 2009 09:48
Convective / Conductive Heat Transfer in Hypersonic flows enigma Main CFD Forum 2 November 1, 2009 23:53
Concentric tube heat exchanger (Air-Water) Young CFX 5 October 6, 2008 23:17
axial flow around a cylinder -heat transfer model? Ralf Schmidt FLUENT 0 March 21, 2006 04:29
How to simulate heat transfer and water flow arwang FLUENT 1 April 26, 2005 10:20


All times are GMT -4. The time now is 03:30.