- **OpenFOAM Running, Solving & CFD**
(*https://www.cfd-online.com/Forums/openfoam-solving/*)

- - **Strange nheptane density**
(*https://www.cfd-online.com/Forums/openfoam-solving/58547-strange-nheptane-density.html*)

I investigated some fluid propI 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(1-T/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? |

I've checked the data and it lI'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 source-files) 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 |

Sorry, my mistake! n-heptane iSorry, my mistake! n-heptane is OK.
It is n-heksadecane 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. |

Yup, something is weird here..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 n-heptane: rho(T=300) = 686.3 rho(T=400) = 601.6 rho(T=500) = 504.0 so supertrapp predicts reasonable values for n-heptane, 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; } |

Hi!
I have a short questionHi!
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 |

Short answer is - nope.
Even 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 re-write 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. |

Thank you, Niklas, for the shoThank 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 triple-point temperature to 1100 K at pressures up to 800 MPa. J. Phys. Chem. Ref. Data 25 (1996) 1509-1596 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) 1061-1155 Boris |

Peng-Robinson EOSDear All,
I want to implement Peng-Robinson 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 |

Good Day Mr. Nordin
Did you know where the NSRDS get their equation for density, surface tensión, etc.? Maybe a good source, I was looking but it seems kind off hard track Kind regards |

All times are GMT -4. The time now is 23:44. |