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

Double pipe heat exchanger with SST k-w turbulence model

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

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   July 15, 2015, 12:33
Default Double pipe heat exchanger with SST k-w turbulence model
  #1
New Member
 
Join Date: Apr 2015
Posts: 11
Rep Power: 9
MStudent is on a distinguished road
I've made quite a few threads lately, but it seems I just can't understand what I'm doing wrong... And I'm seriously running out of time

Here is my problem:

A counterflow double pipe heat exchanger was chosen for it's simplicity.
Through the inner pipe flows a gas starting at 600C (873K) going to about 50C (323K), this is a laminar flow according to previous calculations..
Water flow through the annulus starting at a temperature of 6C (279K), again according to previous calculations this is a turbulent flow with a Reynolds number of approx. 80 000.
The diameter of the water inlet and outlet is 19.05 mm
From LMTD, etc equations the pipe needs to be 3.5 m long




  • I'm using the pressure based solver, and I've set the gravity to -9.81m/s in the z direction...


  • The model is set to SST k-w with all model constants still as standard.


  • For the cell zone conditions I've only changed the materials and set the inner pipe "flow" to laminar zone


  • For the boundary conditions:
-the inlets are set to velocity inlets and I've calculated the velocity by means of 'flow through a certain area'. the turbulence factors I've decided to used (because they where easiest to find/know) are turbulent intensity (from the ansys guide I=0.16(Dh)^(-1/8))and hydraulic diameter (for both of which I've simply used the inlet diameter of the fluid 19.05 mm)
-the outlets are set to pressure outlet and the thermal backflow is still set at the standard 300K
-the wall I've left standard (non slip condition, etc)



  • I haven't touched the dynamic mesh or the reference values
  • velocity coupling is set to SIMPLE and for discretization I've set certain factors to second order upwind (see pic)







What I get from this seems to be a very efficient heat exchanger when looking at the contours of static temperature...The does also seem to be an instability in the x-direction when looking at the scaled residuals...





http://s12.photobucket.com/user/MStu...tml?sort=3&o=3
http://s12.photobucket.com/user/MStu...tml?sort=3&o=5
http://s12.photobucket.com/user/MStu...tml?sort=3&o=6
http://s12.photobucket.com/user/MStu...tml?sort=3&o=7




Please help me out with this problem, I can't seem to understand this problem or what I'm doing wrong, my degree hangs in the balance and I'm seriously running out of time...
Also, I'm sorry to make this so pic heavy, but as they say 'a picture tells a thousand words'.





Thanks for any help you can give me,


MStudent
MStudent is offline   Reply With Quote

Old   May 21, 2016, 03:31
Default
  #2
Senior Member
 
Shamoon Jamshed
Join Date: Apr 2009
Location: Karachi
Posts: 348
Rep Power: 16
Shamoon Jamshed is on a distinguished road
Send a message via Skype™ to Shamoon Jamshed
The main issue may be in the flow direction which is specified in the cell zone condition. Here in your image. it is in z direction while the other figures suggest that they should be in x direction. Please put x=1 and z=0
Shamoon Jamshed is offline   Reply With Quote

Reply

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
CFD by anderson, chp 10.... supersonic flow over flat plate varunjain89 Main CFD Forum 18 May 11, 2018 08:31
Parallel User Defined Real Gas Model aeroman FLUENT 4 July 1, 2015 07:09
Error finding variable "THERMX" sunilpatil CFX 8 April 26, 2013 08:00
UDF for Heat Exchanger model francois louw FLUENT 2 July 16, 2010 03:21
Convective Heat Transfer - Heat Exchanger Mark CFX 6 November 15, 2004 16:55


All times are GMT -4. The time now is 01:45.