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September 8, 2008, 07:48 
I investigated some fluid prop

#1 
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Tomislav Sencic
Join Date: Mar 2009
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I investigated some fluid properties and I found a strange low density for heptane used in OpenFOAM.
In src/thermophisicalModels/liquids/C7H16 is said that density is described by NSRDSfunc5 with coefficients (61.38396836, 0.26211, 540.2, 0.28141). In src/thermophysicalModels/thermophisicalFunctions/NSRDSfunctions/NSRDSfunc5.h is given the function: return a/pow(b,1+pow(1T/c,d)) When I print this on a graph, I obtain a density that is lower than 360kg/m3, while I think it should be over 700kg/m3. Beside other sources, the NIST pages on the web http://webbook.nist.gov/chemistry/fluid/ conferm that it should be around 700kg/m3. Is it a mistake or I am missing something? 

September 8, 2008, 10:31 
I've checked the data and it l

#2 
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Niklas Nordin
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I've checked the data and it looks ok to me.
at what temperature and pressure are you looking? approximate values... rho(T = 300) = 679 rho(T = 400) = 585 rho(T = 500) = 446 rho(T = 540) = 270 the data is using the NSRDS functions and coefficients (reference is in the sourcefiles) and is only valid at around athmospheric pressures and up to critical temperature (around 540 K), but I'd say that accuracy around critical conditions is probably poor. NIST also reveals that at p=1bar liquid does not exist above ~370K (which is ~normal boiling point) at 100 bar NIST yields rho(300K) ~ 687 rho(500K) ~ 509 rho(540K) ~ 463 so not too shabby by NSRDS neglecting the pressure influence Id say 

September 9, 2008, 03:12 
Sorry, my mistake! nheptane i

#3 
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Tomislav Sencic
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Sorry, my mistake! nheptane is OK.
It is nheksadecane C16H34 that has strange low density: coeffs: rho_(61.94656776, 0.25442, 720.6, 0.3238), func: return a_/pow(b_, 1 + pow(1  T/c_, d_)); aproximate values rho(T = 300) = 355 rho(T = 400) = 332 rho(T = 500) = 305 rho(T = 540) = 293 I do not have the refference, but I would expect that C16H34 has bigger density. 

September 9, 2008, 07:07 
Yup, something is weird here..

#4 
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Niklas Nordin
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Yup, something is weird here...
I ran hexadecane in supertrapp and got this: p = 100 bar. rho(T=300) = 790.2 rho(T=400) = 708.4 rho(T=500) = 637.6 for nheptane: rho(T=300) = 686.3 rho(T=400) = 601.6 rho(T=500) = 504.0 so supertrapp predicts reasonable values for nheptane, but that is not a guarantee that it will do so for hexadecane, however, its supposed to be pretty accurate for hydrocarbons. so I then ran hexadecane in openfoam and got this. rho(T=300) = 768.8 rho(T=400) = 697.9 rho(T=500) = 618.9 so Im guessing the mistake is on your side. this was my setup in thermophysicalProperties. liquidComponents ( C16H34 ); liquidProperties { C16H34 C16H34 defaultCoeffs; } 

September 16, 2008, 17:57 
Hi!
I have a short question

#5 
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Boris Elling
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Hi!
I have a short question to those of you who solve the equation of state for a number of liquids. The NIST webpage includes calculations for greenhouse gases like C02 and CH4. Are these equations included in Openfoam or in some other software (together with the sourcecode)? thanks! Boris 

September 17, 2008, 02:08 
Short answer is  nope.
Even

#6 
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Niklas Nordin
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Short answer is  nope.
Even shorter is  no haha. A while back i implemented Peng Robinson EOS and sent it to Henry, but it has not been included yet and I think its because he really wants to rewrite the entire thermo treatment before making it into an even bigger beast. For ideal gases it's ok, but its hard to extend it to handle mixtures with complex mixing rules. 

September 17, 2008, 10:40 
Thank you, Niklas, for the sho

#7 
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Boris Elling
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Thank you, Niklas, for the short answer. I am also interested in EOS calculators outside of Openfoam. As long as these are open source, it shouldn't be too difficult to access them from Openfoam.
I am asking, because the project freesteam.sourceforge.net was mentioned in another post, which calculates the IAPWS water and steam properties. In fact the IAPWS formulation appears to be based on the methane formulation, and so I am wondering whether the following two references have been the target of a project like freesteam, which would be interesting for atmospheric modelling: Span, R., Wagner, W. A new equation of state for carbon dioxide covering the fluid region from the triplepoint temperature to 1100 K at pressures up to 800 MPa. J. Phys. Chem. Ref. Data 25 (1996) 15091596 Setzmann, U., Wagner, W. A new equation of state and tables of the thermodynamic properties for methane covering the range from the melting line to 625 K at pressures up to 1000 MPa. J. Phys. Chem. Ref. Data 20 (1991) 10611155 Boris 

June 29, 2009, 06:52 
PengRobinson EOS

#8 
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Hamed Aghajani
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Dear All,
I want to implement PengRobinson EOS, and make use of it in carbon dioxide high pressure release. I think it is not included yet as Niklas mentioned; I coludn't find it, at least. Would you please let me have you advise on the how to derive it suitable for OF. As I had a look into current perfect gas Eos, it seems the psi(rho/P) parameter is more important than rho. Because, later rho is been calculate by, rho = p_*psi Please let me have your kind advise, Best Hamed 

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