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

Diff bet total energy & thermal energy model??

Register Blogs Community New Posts Updated Threads Search

Like Tree9Likes
  • 4 Post By ghorrocks
  • 5 Post By Bak_Flow

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   October 8, 2009, 03:29
Default Diff bet total energy & thermal energy model??
  #1
New Member
 
Vijesh Joshi
Join Date: Mar 2009
Posts: 10
Rep Power: 17
vijeshjoshi23 is on a distinguished road
Hello everyone,
What is the diff bet total energy model and thermal energy model (HEAT TRANSFER MODELS) ?? when to use total energy model and when to use thermal energy model?? what are the parameters on which it depends on??

plz reply...

thank you..
vijeshjoshi23 is offline   Reply With Quote

Old   October 8, 2009, 06:17
Default
  #2
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,844
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
The "thermal energy" option activates the enthalpy/temperature equation, but does include compressibility effects. It is used for low speed thermal models like AC flows, combustion, heat exchangers, etc.

The "total energy" option activates the full enthalpy equation, including compressibility effects. It is used for high speed flows (Ma>0.3) or anywhere else where compressibility is important.
ghorrocks is offline   Reply With Quote

Old   October 8, 2009, 16:53
Default
  #3
New Member
 
Join Date: Jun 2009
Posts: 8
Rep Power: 17
Bak_Flow is on a distinguished road
Hi Vijesh,

a further way to think of when thermal energy or total energy option should be selected is to look at the equations solved. In thermal energy we are advecting h. In total energy we are advecting h + 0.5*V^2. If you look at the processes taking place say it is flow and heat transfer on some surface you can compare the size of the terms. If you solve for total energy there will be a temperature recovery as you stagnate the flow. How big is this relative to the heat transfered?

Also note that is always correct to solve total energy.....so why do we not solve it all the time? Unfortunatly it adds complexity and might affect robustness due to additional coupling! That is life with our current CFX techology.....if you can neglect something or make it constant...the solver always runs more robustly.

Regards.............Bak_Flow

PS Glenn I don't really like your term "full enthalpy equation" better is Total Enthalpy or the Full Energy Equation ie D/Dt(h + 0.5*V^2), where h + 0.5*V^2 is the Total or Stagnation Enthalph!

Last edited by Bak_Flow; October 8, 2009 at 17:35.
Bak_Flow is offline   Reply With Quote

Old   October 8, 2009, 18:58
Default
  #4
Super Moderator
 
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,844
Rep Power: 144
ghorrocks is just really niceghorrocks is just really niceghorrocks is just really niceghorrocks is just really nice
Quote:
PS Glenn I don't really like your term "full enthalpy equation" better is Total Enthalpy or the Full Energy Equation ie D/Dt(h + 0.5*V^2), where h + 0.5*V^2 is the Total or Stagnation Enthalph!
Point taken, thanks.
ghorrocks is offline   Reply With Quote

Old   October 9, 2009, 10:56
Default which book gives details of models??
  #5
New Member
 
Vijesh Joshi
Join Date: Mar 2009
Posts: 10
Rep Power: 17
vijeshjoshi23 is on a distinguished road
Dear friends,
thanks for the reply... Which text book covers details of heat transfer models??
vijeshjoshi23 is offline   Reply With Quote

Old   October 9, 2009, 11:31
Default
  #6
Senior Member
 
ckleanth's Avatar
 
George
Join Date: Mar 2009
Location: Birmingham, UK
Posts: 257
Rep Power: 18
ckleanth is on a distinguished road
i think you need a basic thermodynamics book, and after then look into how the models work.

a good undergraduate book is fundamentals of heat and mass transfer by Frank P. Incropera and David p. DeWitt
__________________
Top 4 tips
1. Knowledge is everything and Ignorance is dangerous.
2. Understand your limitations and try to eliminate them.
3. Get yerself a bike and hoon the chuffer. You will soon learn why dogs like to hang their heads out the car window.
4. Please before asking any questions on how to run simulations in CFX, go though all the tutorials
ckleanth is offline   Reply With Quote

Reply


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
ATTENTION! Reliability problems in CFX 5.7 Joseph CFX 14 April 20, 2010 16:45
transported PDF for combustion (total energy PDF) mathieu ourliac Main CFD Forum 0 April 10, 2008 06:38
What is the total energy for incompressible fluid? Harry Dong Main CFD Forum 12 February 4, 2006 01:55
Water vapour condensation in CFX-5.7.1 hdj CFX 1 November 27, 2005 08:15
Why FVM for high-Re flows? Zhong Lei Main CFD Forum 23 May 14, 1999 14:22


All times are GMT -4. The time now is 01:29.