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IDProjectCategoryView StatusLast Update
0003390OpenFOAMBugpublic2019-11-20 12:45
ReporterMSontheimerAssigned To 
PrioritynormalSeveritymajorReproducibilityalways
Status newResolutionopen 
PlatformUnixOSUbuntuOS Version18.04
Product Version7 
Fixed in Version 
Summary0003390: Wrong liquid properties coefficients of ethanol (Cp, h)
DescriptionThe calculation of liquid properties "heat capacity Cp" and "enthalpy h" of ethanol (C2H5OH) based on the NSRDSfunc0 function is wrong due to wrong coefficients. This was found by comparing the OpenFOAM calculations with CoolProp 6.3.0 (see attached image) and literature data.

I don't have access to the NSRDS data base, so I cannot check the coefficients reported there. However, one could also find new coefficients based on the CoolProp database (see additional information).
Steps To ReproduceUse the NSRDS functions implemented in $FOAM_SRC/thermophysicalModels/thermophysicalProperties/thermophysicalFunctions/NSRDSfunctions with the coefficients provided in $FOAM_SRC/thermophysicalModels/thermophysicalProperties/liquidProperties/C2H5OH/C2H5OH.C and calculate heat capacity and enthalpy for different temperatures and compare the results with literature data.
Additional InformationOne can use CoolProp to find new coefficients for ethanol. A least-squares fit within the temperature range T=[200K, 350K] (up to boiling temperature) for NSRDSfunc0 leads to the following coefficients for the heat capacity of ethanol:

Cp_
(
        3086.27257308567,
       -13.9017298192482,
        0.04495256866223873,
       -1.89534803995077e-05,
        0.0,
        0.0
)

with an average error of 0.024% and maximum error of 0.062%.

The coefficients for enthalpy are found by integration, and the integration constant is calculated from enthalpy of formation and latent heat (consistency for "latentHeat"-mode, see https://bugs.openfoam.org/view.php?id=3085):

h_latent = h_vapor - h_liquid => h_latent(T_std) = h_fv - h_liquid(T_std) => h_liquid(T_std) = h_fv - h_latent(T_std).

The latent heat of vaporization is calculated using the OpenFOAM coefficients (since they agree with the CoolProp data), and the enthalpy of formation of vapor is h_fv = -235.31e6 J/kmol (Çengel & Boles: Thermodynamics: An Engineering Approach. 2006), and T_std=298.15K is the standard-state temperature.

This finally leads to the following coefficients:

h_
(
       -6710293.74515003,
        3086.27257308567,
       -6.95086490962410,
        0.01498418955407958,
       -4.73837009987693e-06,
        0.0
)

Results with old and new coefficients are shown in the attached images. Experimental data for Cp are taken from https://webbook.nist.gov/cgi/cbook.cgi?ID=C64175&Mask=2.
TagsNo tags attached.

Activities

MSontheimer

2019-11-18 12:57

reporter  

OpenFOAM_CoolProp_Comparison.png (299,110 bytes)

henry

2019-11-20 12:45

manager   ~0010926

If someone here has access to the NSRDS database it would be REALLY useful if all the liquid properties coefficients could be checked and corrected as necessary.

Issue History

Date Modified Username Field Change
2019-11-18 12:57 MSontheimer New Issue
2019-11-18 12:57 MSontheimer File Added: OpenFOAM_CoolProp_Comparison.png
2019-11-18 12:57 MSontheimer File Added: comparison_old_new_coeffs.png
2019-11-20 12:45 henry Note Added: 0010926