CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > OpenFOAM Running, Solving & CFD

Temperature dependent Cp: JANAF tables vs Debye model

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

Reply
 
LinkBack Thread Tools Display Modes
Old   July 12, 2013, 10:40
Default Temperature dependent Cp: JANAF tables vs Debye model
  #1
New Member
 
Join Date: Jul 2013
Posts: 2
Rep Power: 0
antb is on a distinguished road
Hello,

I'm working with an expanding gas from a high pressure to a low pressure cavity. With this expansion comes an extreme cooling of the gas to sub 50 K temps from an initial 300 K (Joule-Thomson effect). I am using for this the rhoCentralFoam solver.

Now I remember reading somewhere that solvers start experiencing problems at very low temperatures, though there didn't seem to be any clear stated reasons as to why. One area I can imagine where there may be a problem is the constant Cp (specific heat) characteristic from most thermophysical models.

To help with this, I know there are JANAF tables to specify a temperature dependant Cp. These tables however usually go from values like 200K to 6000K, while we know that Cp starts to drop dramatically at low temps (<< 200K), although this is substance dependent. Therefore, JANAF tables aren't really of a any use. What I want to know, is how to use a Debye model (http://en.wikipedia.org/wiki/Debye_model), which seems to be perfect at modeling low temps Cp. One way I could imagine going about this is fitting the JANAF polynomial onto the Debye curve, but this seems a bit backward.

If I am not required to play with the Cp value and there exists a simpler method for making simulations more stable at very low temp, please let me know.
antb is offline   Reply With Quote

Old   August 26, 2013, 16:57
Default
  #2
Senior Member
 
immortality's Avatar
 
Ehsan
Join Date: Oct 2012
Location: Iran
Posts: 2,186
Rep Power: 16
immortality is on a distinguished road
Quote:
In thermodynamics and solid state physics, the Debye model is a method developed by Peter Debye in 1912 for estimating the phonon contribution to the specific heat (heat capacity) in a solid
Hi
it seems Debye be related to solids,are you sure it can be used for gases?
__________________
Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King.
To Be or Not To Be,Thats the Question!
The Only Stupid Question Is the One that Goes Unasked.
immortality 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
Newer Janaf Model iyer.arvind OpenFOAM 38 May 14, 2015 07:13
is internalField(U) equivalent to zeroGradient? immortality OpenFOAM Running, Solving & CFD 7 March 29, 2013 02:27
Time Dependent Temperature Dependent BC Analysis RP Main CFD Forum 1 March 28, 2008 02:22
FIDAP and temperature dependent mat properties semetay FLUENT 0 July 11, 2006 13:45
Boussinesq model reference temperature? David Agostinho Main CFD Forum 0 June 23, 2004 10:53


All times are GMT -4. The time now is 21:47.