Thermodynamic properties calculation
Thermodynamic properties calculation
(OP)
Hi,
I would like to know what equations are used to calculate thermodynamic properties like enthalpy, Cp, entropy at a given temperature and pressure. I know i can use standard tables for these values, but I am curious as to how these are calculated. I am looking for equations in which i can substitute values and get the properties.
Thanks
I would like to know what equations are used to calculate thermodynamic properties like enthalpy, Cp, entropy at a given temperature and pressure. I know i can use standard tables for these values, but I am curious as to how these are calculated. I am looking for equations in which i can substitute values and get the properties.
Thanks





RE: Thermodynamic properties calculation
RE: Thermodynamic properties calculation
1-Given an equation of state and specific heat at (very) low pressure, the properties may be calculated requiring integration.
2-Given specific heat at low pressure and Availability,
A=U-TS, the properties may be calculated requiring differentiation.
RE: Thermodynamic properties calculation
David
RE: Thermodynamic properties calculation
RE: Thermodynamic properties calculation
Tobalcane
"If you avoid failure, you also avoid success."
RE: Thermodynamic properties calculation
RE: Thermodynamic properties calculation
Here is a good example when it comes to enthalpy vs temperature values when the ideal gas assumption is used, enthalpy is a function of temperature only -- also, please note that at the reference conditions having temperature of 298 [K] and pressure of 1 [atm], enthalpy for basic elements such a s carbon, hydrogen, sulfur, oxygen and nitrogen is equal to zero!
http://www.engineering-4e.com
RE: Thermodynamic properties calculation
Best regards
Morten
RE: Thermodynamic properties calculation
RE: Thermodynamic properties calculation
The reason enthalpy of a perfect gas is a function of temp (only) is that CP at low pressure is a function of temp.
dh=CpdT+ d(p*tau)/dtau|v dv = Tds - pdv
where Cp is spec heat, p is pressure , tau = 1/T where T is absolute temp v is spec vol, s entropy
For a perfect gas pv=RT p*tau= R/v Therefore
d(p*tau)/dtau|v= 0 and dh=CpdT
Since Cp at low pressure (perfect gas) is a function of T, then h= hreference + integral CpdT ( from Treference to T).
RE: Thermodynamic properties calculation
equation from 1st and 2nd laws should be:
de=CvdT-d(p*tau)/dtau|v dv = Tds - pdv
which shows that internal energy is a function of temp only for a perfect gas.
Similarly
dh=cpdT+ d(v*tau)/dtau|p dp = Tds +vdp
For pgas d(v*tau)/dtau|p=0 and therfore h is function of T,
RE: Thermodynamic properties calculation
Tobalcane
"If you avoid failure, you also avoid success."
RE: Thermodynamic properties calculation
I'll be a bit more blunt than the previous posters: Are you requesting this information for a school project or homework?
Patricia Lougheed
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RE: Thermodynamic properties calculation
If they are based on experimental data like MortenA said, it answers my question. If not can some one just show to evaluate h,s,Cp,u,rho etc say for saturated steam at 10bar?
And this is not for any homework or project.
RE: Thermodynamic properties calculation
<http://www.nist.gov/srd/PDFfiles/jpcrd242.pdf>
RE: Thermodynamic properties calculation
A=U-Ts, etc and equation 5.20 of your reference to NIST.
RE: Thermodynamic properties calculation
RE: Thermodynamic properties calculation
Less accurate estimates may be obtained from the equations of state such as Redlich-Kwong, etc. that are less precise though less complicated, but you still need the enthalpy data.
Numerically you have to generate code to construct partial derivatives of the basic data.
All of the references sited by other posters are a good starting point.
Good luck, the effort is quite the learning experience