# Energy equation and Enthalpy

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

 January 20, 2001, 15:37 Energy equation and Enthalpy #1 Martin Guest   Posts: n/a Hi. I would like to know if anyone has experienced this and can explain it to me: In Fluent 5.4, when dealing with the plain air flow at around atmosferic conditions, the reported enthalpy of the fluid is calculated based on cp and some small temperature difference (probably from some reference temperature somewhere, because the reference values should be used for postprocessing only), instead of cp and absolute temperature, how it does it for solids, for instance. The enthalpy is supposed to be h= i+pv = cv*T+pv = cp*T , where i stands for the internal energy. The energy E[J/kg] solved in the energy equation in Fluent is E= h-pv+u2/2 = i+u2/2 . As a result of the above the enthalpy of air is computed very low, thus the reported internal energy and total energy are highly negative. Have I missed anything? I also fiddled with the reference value for enthalpy, but it obviously had no effect. My attention to this problem has been drawn due to problems I am trying to resolve with conjugate heat transfer in 3D (a few messages down). Thanks. ddmdddghj likes this.

 January 25, 2001, 18:11 Re: Energy equation and Enthalpy #2 Martin Guest   Posts: n/a Just responding to myself here ... The fact that I neglected is that there is a convention about assigning enthalpy equal to zero to gases at a reference temperature (298K). As a result, the reported internal energy will not be equal to cv*T, but will be highly negative as term p*v is subtracted from enthalpy at atmospheric conditions. aerosjc likes this.

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post Mihail CFX 7 September 7, 2014 06:27 hartinger OpenFOAM Running, Solving & CFD 18 April 23, 2012 07:31 Sas CFX 15 July 13, 2010 08:56 Joseph CFX 14 April 20, 2010 15:45 zhou FLUENT 0 February 24, 2004 00:55

All times are GMT -4. The time now is 03:36.