GASPAK Specifications…


GASPAK is a series of physics-based algorithms for calculating properties for 33 fluids. The codes use fundamental state equations which are valid from the triple point and melting line, through the saturation line and liquid-vapor mixtures, to high temperature and pressure (the High T and P limits are different for each fluid and listed in the User’s Guide documentation).  Please contact Horizon Technologies for an evaluation of available property calculations at higher temperature and pressure limits if needed for your application.

Latest additions:

  • Helium, hydrogen, and nitrogen property calculations have been extended to higher temperature limits – helium up to 5000 K.
  • Molecular disassociation is calculated for hydrogen and nitrogen. Properties at lower temperatures are unchanged.
  • Ortho-hydrogen and equilibrium-hydrogen have been added to the fluids library. These enhancements are from unpublished work by R. D. McCarty, 1996.
  • Oxygen enthalpy calculations use updated coefficients.
  • Fugacity is now calculated for all fluids.

Calculated state properties include:

  • PVT
  • Enthalpy, Entropy, Gibbs and Internal Energy
  • Specific Heats
  • Sound Velocity
  • Compressibility
  • Joule-Thomson coefficient
  • Expansivity
  • Gr√ľneisen parameter
  • Latent Heat
  • dP/dT of the saturation line
  • …plus several other PVT derivatives

Calculated transport properties include:

  • Viscosity
  • Thermal Conductivity
  • Thermal Diffusivity
  • Prandtl number

Transport properties are not available for all fluids or at all state property conditions.

A total of 21 different pairs of input parameters are available for specifying the fluid states:

  • Single phase and liquid-vapor mixtures: (P,T), (P,D), (P,H), (P,S), (P,U), (P,X), (X,T), (S,T), (D,H), (D,S), (D,U), (H,S)
  • Saturation line plus one of (P), (T), (D), (S), (H), or (U)
  • Melting line plus one of (P), (T), or (D)

GASPAK was developed by Vincent Arp, Bob McCarty, and Jeff Fox, formerly of NIST and then Cryodata. It evolved in concept from the MIPROPS code (known as NIST-12) written by Bob McCarty before his retirement from NIST (formerly NBS) and documented in NBS Technical Note 1097 (1986).

GASPAK differs fundamentally from NIST-12 in the following key features:

  • Based on a variable-term Helmholtz equation rather than the 32-term BWR equation, and usable with a wider variety of published fluid equations.
  • Mathematically much more stable for calculations in the neighborhood of the saturation lines near the critical and triple points.
  • Available with a variety of user-friendly input-output options, described above.

Throughout its development and evolution into the commercially available GASPAK codes, the NIST standards of scientific quality have been maintained.


Currently, GASPAK is offered:

  • As an Excel Add-In (works in 32bit and 64bit Excel and Windows OS) function access to property calculations extensively tested on version of Excel from Excel97 through Excel 2016.  The Excel Add-In has also been tested on the MAC Excel 2011 version with property calculations working correctly and occasional messaging glitches that are currently being debugged.
  • CURRENTLY SUSPENDED FOR RE-WRITE As an ActiveX DLL for interfacing to a variety of Windows programs. This version is delivered with sample interface code illustrating how to interface your own application to the GASPAK properties.
  • Fortran Source Code (will be suspended once ActiveX DLL re-write is completed).

GASPAK Property Data and Algorithm Sources

Note: fluids which are valid to 5000 K have been updated by R.D. McCarty in unpublished work,1996. Only the high temperature properties have changed from the below works.

AmmoniaVDI Forschungsheft 596 (1979)
ArgonNBS Tech Note 1097 (1986)
Butane, isoNBS Tech Note 1097 (1986)
Butane, normalNBS Tech Note 1097 (1986)
Carbon dioxideNIST data (1989)
Carbon monoxideJ. Phys. Chem. Ref. Data; NIST (1989)
DeuteriumNBS Tech Note 1097 (1986)
EthaneNBS Tech Note 1097 (1986)
EthyleneNBS Tech Note 1045 (1981)
EthyleneJ. Phys. Chem. Ref. Data (1986)
Helium (3K to 5000K)NBS Tech Note 1334 (1989, 1992); Cryodata 1996
Hydrogen, equilibriumR.D. McCarty, 1996, valid to 5000 K.
Hydrogen, normalNBS Monograph 168 (1975); valid to 5000 K
Hydrogen, orthoR.D. McCarty, 1996, valid to 5000 K.
Hydrogen, paraNBS Tech Note 1097; valid to 5000 K (1986)
Hydrogen sulfideColo. School of Mines (1993)
KryptonUSSR std. Reference; Cryodata correlation (1990)
MethaneNBS Tech Note 1097 (1986)
MethaneNIST Tech Note 1325 (1989)
NeonUSSR std. Reference; Cryodata correlation (1991)
NitrogenNBS Tech Note 648 (1973)
NitrogenJ.Phys.Chem.Ref.Data (1986); valid to 5000 K
Nitrogen trifluorideNBSIR 8-1632 (1980); NBS Tech Note 1097 (1986)
OxygenNBSIR 78-882 (1978); NBS Tech Note 1097 (1986)
OxygenFluid Phase Equilibria (1985)
PropaneNBS Tech Note 1097
Water (above 273.16K)J.P.C.R.D, vol 18, p1537 (1989)
XenonUSSR std. Reference; Cryodata correlation (1990)
Refrigerant 11Univ. Idaho data (1991)
Refrigerant 12Univ. Idaho data (1991)
Refrigerant 22USSR std. Reference; Cryodata correlation (1991)
Refrigerant 32DOE report; NIST data (1993)
Refrigerant 123DOE report; NIST data (1993)
Refrigerant 124DOE report; NIST data (1993)
Refrigerant 125DOE report; NIST data (1993)
Refrigerant 134aNIST (1993)
Refrigerant 152aXII Int. Symposium on Thermophysics (1994)