
[Sponsors] 
October 8, 2009, 02:29 
Diff bet total energy & thermal energy model??

#1 
New Member
Vijesh Joshi
Join Date: Mar 2009
Posts: 10
Rep Power: 9 
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.. 

October 8, 2009, 05:17 

#2 
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,559
Rep Power: 97 
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. 

October 8, 2009, 15:53 

#3 
New Member
Join Date: Jun 2009
Posts: 8
Rep Power: 9 
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 16:35. 

October 8, 2009, 17:58 

#4  
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 12,559
Rep Power: 97 
Quote:


October 9, 2009, 09:56 
which book gives details of models??

#5 
New Member
Vijesh Joshi
Join Date: Mar 2009
Posts: 10
Rep Power: 9 
Dear friends,
thanks for the reply... Which text book covers details of heat transfer models?? 

October 9, 2009, 10:31 

#6 
Senior Member
George
Join Date: Mar 2009
Location: Birmingham, UK
Posts: 257
Rep Power: 10 
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 

Thread Tools  
Display Modes  


Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
ATTENTION! Reliability problems in CFX 5.7  Joseph  CFX  14  April 20, 2010 15:45 
transported PDF for combustion (total energy PDF)  mathieu ourliac  Main CFD Forum  0  April 10, 2008 05:38 
What is the total energy for incompressible fluid?  Harry Dong  Main CFD Forum  12  February 4, 2006 01:55 
Water vapour condensation in CFX5.7.1  hdj  CFX  1  November 27, 2005 08:15 
Why FVM for highRe flows?  Zhong Lei  Main CFD Forum  23  May 14, 1999 13:22 