CalebBell
commented
7 months ago Hi Eric,
You are correct - this is an issue, one difficult to remedy today in thermo. Not all methods are available for all chemicals. Methods are based on different data sets, and developed by authors of varying capacities. Modifying your example to show the methods used for each chemical, we can see the HTCOSTALDFIT and MMSNM0 methods are somewhat sub-par and don't display the correct trend in all cases.
I hope a more accurate data source becomes available that can replace those two for these components. I am happy with the issue being in thermo and staying open until it is fixed; the HTCOSTALDFIT and MMSNM0 methods aren't buggy, just under performing.
Sincerely, Caleb
from thermo import ChemicalConstantsPackage
n_paraffins = ['n-C6', 'n-C7', 'n-C8', 'n-C9', 'n-C10',
'n-C11', 'n-C12', 'n-C13', 'n-C14', 'n-C15', 'n-C16', 'n-C17', 'n-C18', 'n-C19', 'n-C20',
'n-C21', 'n-C22', 'n-C23', 'n-C24', 'n-C25', 'n-C26', 'n-C27', 'n-C28', 'n-C29', 'n-C30',
'n-C31', 'n-C32', 'n-C33', 'n-C34', 'n-C35', 'n-C36', 'n-C37', 'n-C38', 'n-C39', 'n-C40',
'n-C41', 'n-C42', 'n-C43', 'n-C44', 'n-C45', 'n-C46', 'n-C47', 'n-C48', 'n-C49', 'n-C50']
constants, packages = ChemicalConstantsPackage.from_IDs(n_paraffins)
for a, b, c in zip(constants.names, constants.rhol_60Fs_mass, packages.VolumeLiquids):
print("{0:20}: {1} kg/m^3 from method {2}".format(a, round(b, 3), c.method))
hexane : 663.383 kg/m^3 from method HEOS_FIT
heptane : 687.596 kg/m^3 from method HEOS_FIT
octane : 706.183 kg/m^3 from method HEOS_FIT
nonane : 721.529 kg/m^3 from method HEOS_FIT
decane : 733.863 kg/m^3 from method HEOS_FIT
undecane : 743.692 kg/m^3 from method HEOS_FIT
dodecane : 752.737 kg/m^3 from method HEOS_FIT
tridecane : 756.957 kg/m^3 from method DIPPR_PERRY_8E
tetradecane : 765.155 kg/m^3 from method DIPPR_PERRY_8E
pentadecane : 770.036 kg/m^3 from method DIPPR_PERRY_8E
hexadecane : 775.049 kg/m^3 from method HEOS_FIT
heptadecane : 774.043 kg/m^3 from method DIPPR_PERRY_8E
octadecane : 774.123 kg/m^3 from method DIPPR_PERRY_8E
nonadecane : 775.741 kg/m^3 from method DIPPR_PERRY_8E
eicosane : 771.17 kg/m^3 from method DIPPR_PERRY_8E
heneicosane : 796.868 kg/m^3 from method HTCOSTALDFIT
docosane : 778.837 kg/m^3 from method HEOS_FIT
tricosane : 799.489 kg/m^3 from method HTCOSTALDFIT
tetracosane : 802.598 kg/m^3 from method HTCOSTALDFIT
pentacosane : 793.723 kg/m^3 from method HTCOSTALDFIT
hexacosane : 800.671 kg/m^3 from method HTCOSTALDFIT
heptacosane : 765.35 kg/m^3 from method HTCOSTALDFIT
octacosane : 797.185 kg/m^3 from method HTCOSTALDFIT
nonacosane : 777.126 kg/m^3 from method MMSNM0
triacontane : 682.918 kg/m^3 from method MMSNM0
hentriacontane : 752.603 kg/m^3 from method MMSNM0
dotriacontane : 834.028 kg/m^3 from method MMSNM0
tritriacontane : 747.243 kg/m^3 from method MMSNM0
tetratriacontane : 744.29 kg/m^3 from method MMSNM0
pentatriacontane : 739.241 kg/m^3 from method MMSNM0
hexatriacontane : 625.765 kg/m^3 from method MMSNM0
heptatriacontane : 735.882 kg/m^3 from method MMSNM0
octatriacontane : 736.663 kg/m^3 from method MMSNM0
nonatriacontane : 737.428 kg/m^3 from method MMSNM0
tetracontane : 840.562 kg/m^3 from method MMSNM0
hentetracontane : 738.813 kg/m^3 from method MMSNM0
dotetracontane : 739.439 kg/m^3 from method MMSNM0
tritetracontane : 740.005 kg/m^3 from method MMSNM0
tetratetracontane : 844.711 kg/m^3 from method MMSNM0
pentatetracontane : 741.159 kg/m^3 from method MMSNM0
hexatetracontane : 741.654 kg/m^3 from method MMSNM0
heptatetracontane : 742.141 kg/m^3 from method MMSNM0
octatetracontane : 742.71 kg/m^3 from method MMSNM0
nonatetracontane : 743.094 kg/m^3 from method MMSNM0
pentacontane : 743.562 kg/m^3 from method MMSNM0
(Perhaps this issue should be opened in chemicals... but since I'm using Thermo and you are the maintainer of both Thermo and Chemicals, I'm posting here)
The densities of the normal paraffins seem to be inconsistent. For example n-C30 (=n-triacontane=638-68-6) from thermo shows density=682.91. I have two online sources that claim the density to be 775.0 (link) and 779.7 (link).
Another example is tritriacontane (CAS=630-05-7), which Thermo reports 747.24, but it actually should be around 903.2 (source)
I observed this inconsistency for normal paraffins upto C50 (didn't check beyond that). Thermo gives acceptable density values for some, but some doesn't. The common sense is that the density should increase with increasing carbon number (or molecular weight) but the density reported by Thermo doesn't agree with this.
Example: