Mixture properties

[mtaktnk]

I'm user REFPROP ver.10 and calculate the mixture properties with Excel add-in. I have a problem with calculating "Temperature" from "Pressure and Enthalpy" in Mixture of para-hydrogen and methane. Under the mixture rate 40%mass of para-hydrogen, calculated value of Excel add-in is different from Refprop software. However, calculated temperature of 0%mass of para-hydrogen ( = 100% methane) with Excel add-in is the same as Refpro software. I have no idea to avoid this issue at once, so want to know correct way to calculate the properties or alternative method.

Versions

REFPROP Version:10.0 Operating System and Version:Windows 10
**Access Method:Excel [How you are accessing REFPROP (i.e. Python, other wrapper)]

Additional Information

[NickAtNight62]

When I setup that mixture in RefProp I get a warning message: 117: Binary interaction parameters are not presently available for this mixture; alternative mixing rules from a similiar substance have been used.

Followed by: Enthalpy/entropy reference state calculation failed to converge for the specified mixture. reference values set for each pure component will be used instead.

Followed by: the equation parameters for mixtures composed of natural gas fluids come from the 2008 GERG model (see reference in Help file). the default pure fluid equations of state in REFPROP are not the same as those used in the GERG model, rather they are more complex with lower uncertainties. The GERG equations for the pure fluids are shorter, less complex, and faster, but slightly less accurate. To use the GERG model as published choose the corresponding option under Options/preferences. The preference screen also has an option to use the AGA8 model for calcuatlions.

[NickAtNight62]

In Refprop: under View mixing parameters, it is using: Mixing rule KW7 Kunz and Wanger model for the methane-hydrogen mixture BetaT 1.0 gammaT 1.3526 Fij 1.0 BetaV 1.0 GammaV 1.0187

[NickAtNight62]

Lets see, so what is going on...

1. The pure-properties results are the same (0% Parahydrogen or 100% parahydrogen) in both Refprop and Excel
2. I can duplicate your results, but for 40% Parahydrogen, I get the error '#[PHFLSH error 248] Single-phase iteration did not converge for P = 0.4 MPA and H = 8480.88 J/mol.
3. The issue is probably in the mixing rules that are being applied.
4. We can test this by running the case of 0.01 Parahydrogen. That gives a temp of 584 K. Compare to 0% parahydrogen temp of 405K.
5. So we get a correct result with pure methane, but when a small amount of parahydrogen is added, we get erroneous results.
6. I forget how to check what mixing rules are being applied in Excel.

[nist-aharvey]

@NickAtNight62 I expect that your apparent discontinuity between pure methane and 0.01 para-H2 is because by default REFPROP uses a different reference state for mixtures than for a pure component. If you go into Options, Reference State, and check the box "Apply Reference State to Each pure component" you should get continuity with the pure-component endpoints.

The original problem is probably a matter of REFPROP having difficulty converging sometimes when components of a mixture have very different volatility. I think @ianhbell may have suggestions for improving that. I believe there are also some issues with use of mass fractions in REFPROP 10.0 -- it is always a good idea to try the calculation with mole fraction as the composition variable (which is the natural variable for mixture thermodynamics and what REFPROP uses internally) to see if that fixes the problem.

[NickAtNight62]

I expanded your review a bit more. There are 4 regions:

1. From 100% to 42% Parahydrogen, the results are close. Error fits polynomial: error=0.0022x^2-0.407+14.979. R2=0.9806 (orange line). Results get progressively worse as we lower the parahydrogen. RefProp MethanParahydrogen March2023.xlsx

2. From 41% to 34% Parahydrogen, we get an error in Excel. That plots as a 'zero' value on my excel plot. Please ignore.

3. From 33% to 0.01% Parahydrogen, the results start off bad and get attrocious ! Error =-0.0266x^2+3.3392x-181.03 R^2=0.999. (blue line) CAUTION: THIS PLOT USES THE SECOND Y AXIS ON THE RIGHT. THAT WAS SO I COULD SHOW BOTH PLOTS ON ONE CHART.

4. From 0.05 to 0% Parahydrogen. Only two points, so didn't bother to trend the results.

See attached Excel file

[NickAtNight62]

RefProp MethanParahydrogen March2023.xlsx

[NickAtNight62]

Methane Parahydrogen March 2023.txt

[NickAtNight62]

Note: System does not support a *.rfp file. Could not upload that.

[ianhbell]

You can rename the .rfp file to .txt

[mtaktnk]

Thank you for replying my issue. Following the comments, I also calculated the properties with mole fraction as the composition variable, but the results was not good (please look at the attached chart). Even though calculating error disappear, difference between Excel add-in and Refprop is huge under 80% mole fraction of para-hydrogen. As NickAtNight62 showed above, temperature calculated from pressure and enthalpy in Refprop approach to quadratic function. So I will calculate temperature with approximate functions and interpolation of them, at present.

[mtaktnk]

And also I tried to calculate temperature from specific pressure and density, and compare the results from Excel add-in and Refprop. In this case, the temperature value from each methods shows good agreement. (with some errors in Excel add-in)

In NickAtNight62' comment, Followed by: Enthalpy/entropy reference state calculation failed to converge for the specified mixture. reference values set for each pure component will be used instead.

I understood that calculation of mixture properties with enthalpy/entropy in Excel add-in is difficult and should be avoided.

[NickAtNight2017]

If you look in C:\Program Files(x86)\Refprop you will find a file labeled HMX.BNC That file sets the Mixing properties that Refprop will be using. The only time I see Parahydrogen listed is for the Parahydrogen/Orthohydrogen mixture.

I suspect that you will need the Parahydrogen/Methane mixture added to this file, with the same parameters set as those reported above in the Refprop program.

I do not know how you check what Mixing rules the Excel program is using. Don't know how the Refprop program is getting the parameters it is using if the parameters are not in the HMX.BNC file.

?Parahydrogen/Orthohydrogen                                [PH2/OH2]
?ideal mixture
  8d757b4a/8d757b4b
    XR0      1.             1.             1.             1.             0.             0.             0. 0. 0. 0. 0. 0.
    TC1     -0.00066932776  0.00030452149  0.             0.             0.             0.             0. 0. 0. 0. 0. 0.
    VC1      1.2268439e-06  7.4675821e-05  0.             0.             0.             0.             0. 0. 0. 0. 0. 0.
!
?Hydrogen/Deuterium                                        [H2/D2]
?I.H. Bell and E.W. Lemmon, JCED, 2016. DOI:10.1021/acs.jced.6b00257; MAPD: 0.87% from 150 bubble-point pressures
  8d757b40/639b18a0
    XR0      1.0087153      0.99511        1.             1.             0.             0.             0. 0. 0. 0. 0. 0.
    TC1      0.43594975    -0.81988847    -0.10252257    -0.84503691     0.57703816    -0.17357626     0. 0. 0. 0. 0. 0.
    VC1     -0.0029824454  -0.0012893186  -0.010439783    0.031459786   -0.035038004    0.016263248    0. 0. 0. 0. 0. 0.
!

[ianhbell]

In this case, the "similar fluid" mixing rule is used, which if you open the parahydrogen fluid file you see a line like:

8d757b40  (hydrogen)                      !Alternative fluid for mixing rules   :AltID:

which says that when you need the interactions for pH2 + methane, just use the ones for eH2 + methane

[NickAtNight62]

Ah, so it is using the Methane/Hydrogen parameters in the HMX.BNC file?

?Methane/Hydrogen [C1/H2] ?Kunz and Wagner (2007) 8ae7a700/8d757b40 KW7 1. 1.352643115 1. 1.018702573 1. 0. 0. 0. 0. 0. 0. 0. TC5 66.626615 445.38361 -381.30154 0. 0. 0. 0. 0. 0. 0. 0. 0. VC5 -0.369107 0.59576944 -0.23854726 0. 0. 0. 0. 0. 0. 0. 0. 0. TRN -0.28 0.207 0.99 0.98 0. 0. 0. 0. 0. 0. 0. 0. PR1 0.0156 0. 0. 0. 0. 0. 0. 0. 0. 0. 0. 0.

So that is the first setup warning: [SETUP warning -117] Binary interaction parameters are not presently available for this mixture; alternative mixing rules from a similar substance have been used.

The next warning was for Natural gas mixtures. Saying the 2008 GERG model was being used.

The first line, (KW7) is the BetaT, GammaT, Fij, BetaV and GammaV values respectively that refprop shows.

"Literature reference for Methane/Hydrogen Kunz and Wagner (2007) Kunz, O., Klimeck, R., Wagner, W., Jaeschke, M. The GERG-2004 Wide-Range Equation of State for Natural Gases and Other Mixtures. GERG Technical Monograph 15. Fortschr.-Ber. VDI, VDI-Verlag, Duesseldorf, 2007.Kunz, O. and Wagner, W. The GERG-2008 Wide-Range Equation of State for Natural Gases and Other Mixtures: An Expansion of GERG-2004. J. Chem. Eng. Data, 57(11):3032-3091, 2012.Methane-Hydrogen"

[NickAtNight62]

Correct parameters are applied from the paper (see page 3077 of Ref)

Which get fed into Equations 16 and 17. (page 3041 of Ref)

[NickAtNight62]

@ianhbell - So how does he check to see what mixing rule is being used in the Excel spreadsheet?

[ianhbell]

Not easily. The GETKTVdll function is what you need, or use the GUI.

[NickAtNight62]

Yes, that is the function. In the help it is a Legacy API. Here is the HELP information.

subroutine GETKTVdll(icomp, jcomp, hmodij, fij, hFmix, hfij, hbinp, hmxrul, hmodij_length, hFmix_length, hfij_length, hbinp_length, hmxrul_length)

Retrieve mixture model and parameters for a specified binary mixture. This subroutine should not be called until after SETUP has been called. The order of icomp and jcomp do not matter, the routine returns the parameters as stored in the HMX.BNC file. To determine if the compositions are backwards, call HMXORDER. If calling SETMIX with the same parameters, an error will be returned if the components are backwards.

Kunz-Wagner model (KW0)	Lemmon-Jacobsen model (LJ6)
fij(1) = betaT	fij(1) = zeta
fij(2) = gammaT	fij(2) = xi
fij(3) = betaV	fij(3) = Fij
fij(4) = gammaV	fij(4) = beta
fij(5) = Fij	fij(5) = gamma
fij(6) = ‘not used’	fij(6) = ‘not used’

Parameters:

icomp [int,in] :: Component i jcomp [int,in] :: Component j hmodij [char,out] :: Mixing rule for the binary pair i,j (e.g., KW0, LJ6, XR0, or LIN) (character*3) fij (6) [double,out] :: Binary mixture parameters (array of dimension nmxpar; currently nmxpar is set to 6); the parameters will vary depending on hmodij; hFmix [char,out] :: File name (character*255) containing parameters for the binary mixture model hfij [char,out] :: Description of the binary mixture parameters (character*8 array of dimension nmxpar) The parameters will vary depending on hmodij. hbinp [char,out] :: Documentation for the binary parameters (character*255) hmxrul [char,out] :: Description of the mixing rule (character*255) hmodij_length [int] :: length of variable hmodij (default: 3) hFmix_length [int] :: length of variable hFmix (default: 255) hfij_length [int] :: length of variable hfij (default: 255) hbinp_length [int] :: length of variable hbinp (default: 255) hmxrul_length [int] :: length of variable hmxrul (default: 255)

[NickAtNight62]

@ianhbell - So how we make the call to that function in Python or Visual Basic?
Is there some existing sample code? Is there a way to call this from the new API, or do we have to use the legacy API? Is there a way to view the parameters in visual basic debug mode?

---

In Excel,

1. Turn on Developer mode.
   
2. From Developer, open Visual Basic
3. Refprop uses: refrprop_Ribbon.xlam, Refprop.xla
4. In Refprop.xla, Look at the Refprop10Code Module. That shows the Code as to how to call the REFPROPdll library function. The GETKTVdll call would be similar to that. Not quite sure how we tie that call into the existing Refprop module.

5. We want to look at the existing icomp,jcomp properties being used. if we specify them independently, we don't see what it is using.

   Someone developed this sample code: https://trc.nist.gov/refprop/LINKING/SAMPLE.BAS

Attribute VB_Name = "Module1" DefDbl A-H, O-Z DefLng I-N Const ncmax = 20 'Maximum number of components in the mixture (do not change unless the Refprop Fortran code is also changed with the same number in the CONSTS.INC file) Const iPropMax = 200 'Number of output properties available in ALLPROPS (also do not change).

Private Declare Sub REFPROPdll Lib "REFPROP.DLL" (ByVal hFld As String, ByVal hIn As String, ByVal hOut As String, iUnitNumb As Long, iMass As Long, iFlag As Long, a As Double, b As Double, zm As Double, Output As Double, ByVal hUnits As String, iUnits As Long, x As Double, y As Double, x3 As Double, q As Double, ierr As Long, ByVal herr As String, ln1 As Long, ln2 As Long, ln3 As Long, ln4 As Long, ln5 As Long)

Sub Example()

' Example program that uses the routines in REFPROP. ' ' Refprop uses a default set of units, these being: ' K, kPa, mol/dm^3, mole fraction, J/mol, J/mol-K, m/s, uPa-s, W/m-K, and N/m ' ' Refprop 10 comes with two new subroutines, labeled as ALLPROPS and REFPROP, ' that allow the user to access nearly all properties in the Refprop program. ' One additional routine allows the setting of options and flags to change ' how the program works. The details of these routines are given at the top ' of the file REFPROP.FOR for the first two, and at the bottom for the last one. ' Examples are given below. ' ' The examples here are split into two pieces. The first shows the new method ' to obtain properties. The second shows the old method. The method to use ' depends on your needs. For simple calculations, then the use of the ' techniques in the first method works very well. For applications ' that require heavy computational needs, the second method will be faster ' by calling directly the routines needed due to the higher overhead required ' in the ALLPROPS and REFPROP routines to search for the correct routines ' to call for each calculation. ' Dim hFld As String, hIn As String, hOut As String, hUnits As String, herr As String Dim Output(iPropMax) As Double, z(ncmax) As Double, x(ncmax) As Double, y(ncmax) As Double, x3(ncmax) As Double Dim ymass(ncmax) As Double, ymole(ncmax) As Double o = 1000#

'New methods for obtaining properties from the REFPROP and ALLPROPS subroutines (see notes at top of file)

'...Get the DLL number of the REFPROP DLL. Call REFPROP(" ", " ", "DLL#", 0, 0, 0, 0, 0, z, Output, hUnits, q, ierr, herr)

'...When Refprop was installed, an environmental variable called RPPrefix was setup so that Refprop can find ' the fluid files. To manually set the path to these files, use the following lines. ' Call REFPROPdll ("c:\Program Files (x86)\Refprop","Path"," ", ' & 0,0,0,0d0,0d0,z,Output,hUnits,iUnit,x,y,x3,q,ierr,herr) ' if (ierr>0) then msgbox herr

'...Load nitrogen as a pure fluid (this can also be done in the call to REFPROP). 'Call SETFLUIDS("nitrogen", ierr) 'Call ERRMSG(ierr, herr) 'If the error message is desired, call ERRMSG with the value of ierr returned from the line above. If (ierr > 0) Then MsgBox herr

'...Calculate the density, isobaric heat capacity, viscosity, and thermal conductivity at a given '...temperature and pressure with the REFPROP subroutine. T = 300 'K P = 1 'MPa iU = 2 'Units in mass SI (see the REFPROP.FOR file for a complete list of the unit systems available). iMass = 0 'Send composition in mole percent if 0, mass percent if 1. Call REFPROP("nitrogen", "TP", "D,Cp,Vis,Tcx", iU, iMass, 0, T, P, z, Output, hUnits, q, ierr, herr) If (ierr > 0) Then MsgBox herr 'write (*,1000) 'T,P,D,Cp,Vis,Tcx ",ierr,iU,T,P,Output(1:4) D = Output(1) 'Density - kg/m^3 Cp = Output(2) 'Cp - kJ/(kg-K) eta = Output(3) 'Viscosity - uPa-s tcx = Output(4) 'Thermal conductivity - mW/(m-K)

'...Calculate the specific volume at a given temperature and pressure with the REFPROP1 subroutine '...in English units and composition in mass fractions for 70% methane and 30% ethane. 'Call SETFLUIDS("methane;ethane", ierr) 'If (ierr > 0) Then MsgBox herr z(1) = 0.7 z(2) = 0.3 iMass = 1 'Mass fractions for composition iU = 5 'Flag to use English units T = 50 'F P = 100 'psia Call REFPROP("methane;ethane", "TP", "V", iU, iMass, 0, T, P, z, Output, hUnits, q, ierr, herr) 'Volume in ft^3/lbm v = Output(1) If (ierr > 0) Then MsgBox herr 'write (*,1000) "T,P,V ",ierr,iU,T,P,V

'...Calculate other thermodynamic properties with a call to ALLPROPS now that '...the temperature and density are known. Use molar SI as input units. 'Call REFPROPdll1(" ", "m", 0, iMass, 0#, 0#, z, wm, q, ierr, herr) 'Get the molar mass. Call REFPROP("F", "K", "UNITCONV_T", 0, 0, 0, T, 0#, z, Output, hUnits, q, ierr, herr) 'Convert the temperature from F to K. T = Output(1) Call REFPROP("ft^3/lbm", "mol/dm^3", "UNITCONV_D", 0, 0, 0, v, wm, z, Output, hUnits, q, ierr, herr) 'Convert the volume in ft^3/lbm to density in mol/dm^3. D = Output(1)

  'iU = 1   'Molar SI
  'iMass = 1 'Mass fractions
  'hOut = "Z,s,Cv,Cp,W"
  'Call ALLPROPS(hOut, iU, iMass, 1, t, d, z, Output, hUArray, iUArray, i, herr)
  'If (i > 0) Then MsgBox herr
  'write (*,1000) 'D,Z,s,Cv,Cp,w     ",ierr,iU,D,Output(1:5)
  'zz = Output(1) 'Compressibility factor
  's = Output(2) 'Entropy - J/(mol-K)    This entropy will not match that from the GUI because the reference state applied to the mixture is set differently.  See the call to SETREF below to change this.
  'w = Output(5) 'Speed of sound - m/s

'...Calculate the liquid saturation pressure and the mole and mass fractions in the vapor phase. 'Call SETFLUIDS("methane;ethane;propane", ierr) 'Either this or the call to REFPROP in the next section is valid. iU = 2 'Flag to use mass SI units, for SI units with celsius, use 3. iMass = 1 T = 200 'K z(1) = 0.8 z(2) = 0.15 z(3) = 0.05 hOut = "P,Dliq,Dvap,xmassliq,xmassvap,xmoleliq,xmolevap" 'The string "xmassvap" is the y mass fractions because of the "vap" appended to the end. The string "xmass" simply means composition on a mass basis. Call REFPROP(" ", "Tliq", hOut, iU, iMass, 0, T, 0#, z, Output, hUnits, q, ierr, herr) 'The liquid and vapor mole fractions are returned in the x and y arrays. Note: Always mole fractions for x, y, and x3. If (ierr > 0) Then MsgBox herr P = Output(1) 'MPa Dl = Output(2) 'Saturated liquid density - kg/m^3 Dv = Output(3) 'Saturated vapor density - kg/m^3 'ymass(1:3)=Output(7:9) 'Because the xmass and xmole inputs to REFPROP have more than one output, the Output() array does not line up with the inputs. Thus, the outputs for xmassliq are in slots 7 to 9, for xmassvap in 10 to 12, etc. 'ymole(1:3)=Output(13:15) 'The ymole outputs are in slots 13 to 15, but are actually the same as the values returned in the array y in the call to the REFPROP routine. This example shows how the pieces are linked together. 'write (,1000) 'P,Dl,Dv,ymass ",ierr,iU,P,Dl,Dv,ymass(1:3) 'write (,1000) ' xmole,ymole ",ierr,iU,x(1:3),ymole(1:3) 'The x() array values returned from the REFPROP routine are the same as those in slots 10 to 12 for the xmoleliq string, and in this example are also the same as the input array z() except on a molar basis.

'...Setup a mixture of natural gas components and calculate the enthalpy given pressure and entropy. D = 2 'kg/m^3 iU = 3 'Use mass SI with T in Celsius iMass = 0 'Use molar composition z(1) = 0.7 z(2) = 0.2 z(3) = 0.1 Call REFPROP("methane;ethane;propane", "Dliq", "T,P,S,H,W", iU, iMass, 0, D, 0#, z, Output, hUnits, q, ierr, herr) If (ierr > 0) Then MsgBox herr 'write (*,1000) 'D,T,P,S,H,W ",ierr,iU,D,Output(1:5) T = Output(1) 'C P = Output(2) 'MPa h = Output(4) 'kJ/kg

'...Setup the predefined mixture R410A.MIX and calculate the liquid state at 300 K and the properties of the vapor state in equilibrium with the liquid state. T = 300 'K iU = 2 'Use mass SI iMass = 1 'Use mass composition Call REFPROP("R410A.MIX", "Tliq", "Pliq,Dliq,Dvap,xmassliq(1),xmassliq(2),xmassvap(1),xmassvap(2)", iU, iMass, 0, T, 0#, z, Output, hUnits, q, ierr, herr) If (ierr > 0) Then MsgBox herr P = Output(1) 'MPa Dliq = Output(2): Dvap = Output(3) 'kq/m^3 Note carefully: Dvap is not at the input composition (50/50 R32/R125), but at the equilibrium composition given by y1 and y2 below. X1 = Output(4): X2 = Output(5) 'These should be 50 and 50, the liquid composition for this state. Y1 = Output(6): Y2 = Output(7) 'These will be the equilibrium composition in the vapor phase.

'...Call with R410A again but this time for a two-phase state at 300 K and 0.8 quality. iMass = 0 'Use mole composition and molar quality q = 0.8 Call REFPROP("", "TQ", "P,D,Dliq,Dvap,qmass,qmole", iU, iMass, 0, T, q, z, Output, hUnits, q, ierr, herr) If (ierr > 0) Then MsgBox herr P = Output(1) 'MPa D = Output(2): Dliq = Output(3): Dvap = Output(4) 'kq/m^3 D is the overall density of the two phase state at the R410A composition. Dliq and Dvap are not the densities at the R410A composition (50/50 R32/R125), but at the equilibrium compositions for x and y (not returned in this call). 'The following checks are very important to make sure you sent the program the correct units for quality. qmass = Output(5) 'Mass quality, which will equal the input q if iMass=1 qmole = Output(6) 'Molar quality, which will equal the input q if iMass=0

  'For additional calculations, there is no need to send the fluid file name again.
  Call REFPROP("", "TP", "D,H,S", iU, iMass, 0, T, P, z, Output, hUnits, q, ierr, herr)

  End

End Sub

Sub REFPROP(hFld As String, hIn As String, hOut As String, iUnits As Long, iMass As Long, iFlag As Long, a As Double, b As Double, z() As Double, Output() As Double, hUnits As String, q As Double, ierr As Long, herr As String) Dim hFld2 As String 10000, hIn2 As String 255, hOut2 As String 255, hUnits2 As String 255, herr2 As String * 255 Dim iUnits2 As Long, iMass2 As Long, iFlag2 As Long, iUCode2 As Long, ierr2 As Long Dim a2 As Double, b2 As Double, z2(ncmax) As Double, x(ncmax) As Double, y(ncmax) As Double, x3(ncmax) As Double, q2 As Double, Output2(iPropMax) As Double

hFld2 = hFld: hIn2 = hIn: hOut2 = hOut iUnits2 = iUnits: iMass2 = iMass: iFlag2 = iFlag a2 = a: b2 = b For i = 1 To ncmax: z2(i) = z(i): Next Call REFPROPdll(hFld2, hIn2, hOut2, iUnits2, iMass2, iFlag2, a2, b2, z2(1), Output2(1), hUnits2, iUCode2, x(1), y(1), x3(1), q2, ierr2, herr2, 10000&, 255&, 255&, 255&, 255&) For i = 1 To iPropMax: Output(i) = Output2(i): Next hUnits = hUnits2 iUCode = iUCode2 hUnits = hUnits2 q = q2 ierr = ierr2 herr = herr2 If Trim(hFld2) <> "" Then For i = 1 To ncmax: z(i) = z2(i): Next End If

End Sub

---

[ianhbell]

Something like this?:

import os
os.environ['RPPREFIX'] = os.getenv('HOME')+'/REFPROP10'

import numpy as np
root = os.getenv('RPPREFIX')
import ctREFPROP.ctREFPROP as ct
RP = ct.REFPROPFunctionLibrary(root)
RP.SETPATHdll(root)

z = [0.9206,0.0714,0.0078,0,0,0.0002]
znorm = np.array(z)/sum(z)
ierr = RP.SETFLUIDSdll('METHANE;ETHANE;PROPANE;BUTANE;PENTANE;NITROGEN')
print(ierr)
print(RP.GETKTVdll(1,2))

yielding

0
GETKTVdlloutput(hmodij='KW1', fij=array('d', [0.996336508, 1.049707697, 0.997547866, 1.006617867, 1.0, 0.0]), hFmix='HMX.BNC', hfij='BetaT   GammaT  BetaV   GammaV   Fij   not used', hbinp='Methane/Ethane\r\nKunz and Wagner (2007)', hmxrul='KW1  Kunz and Wagner model for the methane-ethane mixture')

[ianhbell]

There is the FIJMIX output in the REFPROPdll function, but it doesn't give the string information I think.

[NickAtNight62]

Something like this?:

Yes, exactly like that. Wow. That is easy to do in Python.

The Excel/Visual Basic is still a bit of a mystery on how to do it. (Probably very similar to the call in the GUI - since that is/was in Basic.

[NickAtNight62]

@ianhbell Well, I might have fat fingered it, but I got inconsistent results in the GUI interface!?!

Using the mixture, for pure Methane, I got a temp of 403.65 C for Ethalpy 2000 kJ/kg and Pressure 400 kPa.

Using pure methane, for same conditions, I got 405.5 C.

The Parahydrogen also gave different results. -132.75 C for the mixture. -129.49 C for pure parahydrogen.

The Excel spreadsheet results (original posters first post) also gave the 405.5 C and the -129.49 C result (same as for the single substance properties in the GUI)

[ianhbell]

What do you mean by inconsistent? You need to be ensuring that you set the same reference states in each case.

[nist-aharvey]

Yes, this last problem is almost certainly a matter of reference states. Remember that the absolute value of enthalpy is meaningless (you can only talk about enthalpy change between two states) so setting the zero of the reference state is arbitrary and REFFPROP by default does something different for mixtures than it does for pure components. You can get consistency of reference states between pure and mixture calculations in the GUI by choosing Options, Reference State, and Apply Reference State to "Each pure component".

[NickAtNight62]

Something like this?:

Still not able to get the was not able to get the GETKTVdll function to work. However, I modified the Sample code from above (Sample.Bas) and got that to run, Code shown below. Spreadsheet attached.

• the unmodified Sample.bas is in Module1
• the modified version, specfic to the above problem is in Module2.

This code calls Refprop from the Visual Basic app. It then returns the results to the spreadsheet.

The result was a bit of a surprise. See Plot 1 and 2 below.

The surprise: The VBA results matched the Refprop results !

The results from the Forumula entered into the spreadsheet still differs from both Refprop GUI and the VBA generated results.

Changing the spreadsheet formula from Mass to Mole composition also did not help.

I narrowed down where the problem starts/stops.

• It starts at 0.000075 mass fraction Parahydrogen in Methane. (0.0006 mole fraction)
• There is a VERY sharp temperature break in the results, where an error of 194.73, 223.16, & 273.28 K suddenly appears.

We cannot say when the error disappears exactly, there are two transitions. The first is to the flash error result. This occurs at:

• 0.33507 mass fraction Parahydrogen in Methane (0.8004 mole fraction)
• ALL three conditions start/end at the same compositions. That may indicate that the coding error is in the Composition section of the software for the Excel spreadsheet..

The second transition occurs at:

• 0.417476 mass fraction Parahydrogen in Methane (0.8508 mole fraction).
• We now switch from flash errors to results that are reasonably close to the other results (GUI Refprop, VBA in Excel)
• As in the first two transitions, all three conditions transition at the same time.

Perhaps the VBA version is using a different reference property than the Excel version. The instructions to change reference state for the Excel spreadsheet are attached. perhaps a different reference condition was used in the Sample.bas from the default spreadsheet.

'Attribute VB_Name = "Module1"
DefDbl A-H, O-Z
DefLng I-N
Const ncmax = 20   'Maximum number of components in the mixture (do not change unless the Refprop Fortran code is also changed with the same number in the CONSTS.INC file)
Const iPropMax = 200 'Number of output properties available in ALLPROPS (also do not change).

Private Declare Sub REFPROPdll Lib "REFPROP.DLL" (ByVal hFld As String, ByVal hIn As String, ByVal hOut As String, iUnitNumb As Long, iMass As Long, iFlag As Long, a As Double, b As Double, zm As Double, Output As Double, ByVal hUnits As String, iUnits As Long, x As Double, y As Double, x3 As Double, q As Double, ierr As Long, ByVal herr As String, ln1 As Long, ln2 As Long, ln3 As Long, ln4 As Long, ln5 As Long)

Sub Example2()

'     Nicks Version
'     Example program that uses the routines in REFPROP.
'
'     Refprop uses a default set of units, these being:
'       K, kPa, mol/dm^3, mole fraction, J/mol, J/mol-K, m/s, uPa-s, W/m-K, and N/m
'
      Dim hFld As String, hIn As String, hOut As String, hUnits As String, herr As String
      Dim Output(iPropMax) As Double, z(ncmax) As Double, x(ncmax) As Double, y(ncmax) As Double, x3(ncmax) As Double
      Dim ymass(ncmax) As Double, ymole(ncmax) As Double
      o = 1000#

'***New methods for obtaining properties from the REFPROP and ALLPROPS subroutines***  (see notes at top of file)

'...Get the DLL number of the REFPROP DLL.
      Call REFPROP(" ", " ", "DLL#", 0, 0, 0, 0, 0, z, Output, hUnits, q, ierr, herr)

'...When Refprop was installed, an environmental variable called RPPrefix was setup so that Refprop can find
'   the fluid files.  To manually set the path to these files, use the following lines.
'     Call REFPROPdll ("c:\Program Files (x86)\Refprop","Path"," ",
'    &       0,0,0,0d0,0d0,z,Output,hUnits,iUnit,x,y,x3,q,ierr,herr)
'     if (ierr>0) then msgbox herr

'...Calculate the Temperature at a given Enthalpy and Temperature with the REFPROP1 subroutine
      'Call SETFLUIDS("methane;ethane", ierr)
      'If (ierr > 0) Then MsgBox herr
      z(1) = 1#
      z(2) = 0
      iMass = 1 'Mass fractions for composition
      iU = 3  'Flag to use SI units with C
      'iU = 2  'Flag to use SI units with K
      'iU = 1  'Flag to use SI units
      H = 2000  'kJ/kg
      P = 0.4 'MPaa

' For Enthalpy (H) and Pressure (P) of 2000, 1500 adn 1000 kJ/kg  and 400,300,200 kPaa respectively
' For parahydrogen/methane compsitions from 100% to 0%
Dim Number As Integer
Dim Offset As Integer
Offset = 3

For Number = 0 To 100 Step 1

'For number As Double = 100 to 0 Step -1

   z(1) = 1 - (Number / 100)
   z(2) = (Number / 100)

      Call REFPROP("parahydrogen;methane", "HP", "T,D", iU, iMass, 0, H, P, z, Output, hUnits, q, ierr, herr) 'Temperature in K
      T = Output(1)
      D = Output(2)
      If (ierr > 0) Then MsgBox herr

' Call SETUPdll(ncomp, hFiles, hFmix, hrf, ierr, herr, hFiles_length, hFmix_length, hrf_length, herr_length)
' Call GETKTVdll(" ", " ", "DLL#", 0, 0, 0, 0, 0, z, Output, hUnits, q, ierr, herr)
' Call GETKTVdll(icomp, jcomp, hmodij, fij, hFmix, hfij, hbinp, hmxrul, hmodij_length, hFmix_length, hfij_length, hbinp_length, hmxrul_length)

'Results
      Range("A" & Number + Offset).Value = z(1)
      Range("B" & Number + Offset).Value = z(2)
      Range("C" & Number + Offset).Value = H
      Range("D" & Number + Offset).Value = P
      Range("E" & Number + Offset).Value = T

Next

'Next set
      H = 1500  'kJ/kg
      P = 0.3 'MPaa

For Number = 0 To 100 Step 1

'For number As Double = 100 to 0 Step -1

   z(1) = 1 - (Number / 100)
   z(2) = (Number / 100)

      Call REFPROP("parahydrogen;methane", "HP", "T,D", iU, iMass, 0, H, P, z, Output, hUnits, q, ierr, herr) 'Temperature in K
      T = Output(1)
      D = Output(2)
      If (ierr > 0) Then MsgBox herr

'Results
      Range("H" & Number + Offset).Value = z(1)
      Range("I" & Number + Offset).Value = z(2)
      Range("J" & Number + Offset).Value = H
      Range("K" & Number + Offset).Value = P
      Range("L" & Number + Offset).Value = T
Next

'Next set
      H = 1000  'kJ/kg
      P = 0.2 'MPaa

For Number = 0 To 100 Step 1

'For number As Double = 100 to 0 Step -1

   z(1) = 1 - (Number / 100)
   z(2) = (Number / 100)

      Call REFPROP("parahydrogen;methane", "HP", "T,D", iU, iMass, 0, H, P, z, Output, hUnits, q, ierr, herr) 'Temperature in K
      T = Output(1)
      D = Output(2)
      If (ierr > 0) Then MsgBox herr

'Results
      Range("O" & Number + Offset).Value = z(1)
      Range("P" & Number + Offset).Value = z(2)
      Range("Q" & Number + Offset).Value = H
      Range("R" & Number + Offset).Value = P
      Range("S" & Number + Offset).Value = T
Next

      End

End Sub

Sub REFPROP(hFld As String, hIn As String, hOut As String, iUnits As Long, iMass As Long, iFlag As Long, a As Double, b As Double, z() As Double, Output() As Double, hUnits As String, q As Double, ierr As Long, herr As String)
Dim hFld2 As String * 10000, hIn2 As String * 255, hOut2 As String * 255, hUnits2 As String * 255, herr2 As String * 255
Dim iUnits2 As Long, iMass2 As Long, iFlag2 As Long, iUCode2 As Long, ierr2 As Long
Dim a2 As Double, b2 As Double, z2(ncmax) As Double, x(ncmax) As Double, y(ncmax) As Double, x3(ncmax) As Double, q2 As Double, Output2(iPropMax) As Double

  hFld2 = hFld: hIn2 = hIn: hOut2 = hOut
  iUnits2 = iUnits: iMass2 = iMass: iFlag2 = iFlag
  a2 = a: b2 = b
  For i = 1 To ncmax: z2(i) = z(i): Next
  Call REFPROPdll(hFld2, hIn2, hOut2, iUnits2, iMass2, iFlag2, a2, b2, z2(1), Output2(1), hUnits2, iUCode2, x(1), y(1), x3(1), q2, ierr2, herr2, 10000&, 255&, 255&, 255&, 255&)
  For i = 1 To iPropMax: Output(i) = Output2(i): Next
  hUnits = hUnits2
  iUCode = iUCode2
  hUnits = hUnits2
  q = q2
  ierr = ierr2
  herr = herr2
  If Trim(hFld2) <> "" Then
    For i = 1 To ncmax: z(i) = z2(i): Next
  End If

End Sub

Refprop Help on reference states:

Reference State

Reference State

When large differences in enthalpy and entropy occur between REFPROP and tables of properties given in handbooks, please note:

The absolute values of enthalpy, entropy, and energy at a single state point are meaningless. It is only the difference between two different state points that matter. Thus, the value for a single state point can be set to any arbitrary value. Many handbooks set the arbitrary state point so that the values of these properties are positive for most liquid or gas states. You can change the values of the arbitrary state points by going to the Options/Reference State menu. Your choice of options can be permanently saved in the graphical interface by selecting Options/Save Options, and then saving the options under the file name ‘defaults.prf’.

To change the default in the Excel file, press Alt-F11 to bring up the VB code. If the code does not appear, make sure the project explorer is visible (View/Project Explorer), then click on modules, and then on module1. Then search for the call to SETREF, and change the second input from 2& to 1&. More information on this can be found in your REFPROPFortran directory in the file SETUP.FOR under the SETREF subroutine.

The reference states for enthalpy and entropy are entered in the Reference dialog. There are three common choices for the reference state on which the values of enthalpy and entropy are based. These three common choices are: 1.Setting enthalpy and entropy to zero for the saturated liquid at the normal boiling point (designated as NBP). 2.Setting enthalpy and entropy to zero for the saturated liquid at -40 °C (designated as ASHRAE). 3.Setting enthalpy to 200 kJ/kg and entropy to 1.0 kJ/(kg-K) for the saturated liquid at 0 °C (designated as IIR).

In addition, the reference state can be set manually by specifying values of the enthalpy (h) and entropy (s) at arbitrary values of temperature (T) and pressure (P).

When working with mixtures, the default setting can be used for each pure fluid, or the reference state values of enthalpy and entropy can be specified at the currently defined composition.

The exergy reference state and definition can be selected based on the user’s preference.

The reference state choices are saved with other Preferences when the Save Current Options command is selected. It is restored to a previously saved option with the Retrieve Options command or Open command.

RefpropIssue Rev1.xlsx