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GASPAK Specifications...


GASPAK ( copyright Cryodata Inc.) is a computer program for calculating properties of 33 fluids. The program uses 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 property calculations at higher temperature and pressure limits if needed for your application.

New since Version 3.30:

The 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 temperature 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 These enhancements are from unpublished work by R. D. McCarty, 1996.

Updated coefficients for oxygen enthalpy calculations.

Fugacity is now calculated for all fluids.

Calculated state properties include:




Gibbs and Internal Energy

Specific Heats

Sound Velocity


Joule-Thomson coefficient


Gruneisen parameter

Latent Heat

dP/dT of the saturation line

plus several other PVT derivatives

Calculated transport properties include:


Thermal Conductivity

Thermal Diffusivity

Prandtl number

Transport properties data are not available for all fluids.

A total of 21 different pairs of input parameters are available for specifying the fluid state. These are

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 of Cryodata. It has evolved in concept from the code MIPROPS (now 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 development of GASPAK, the NIST standards of scientific quality have been maintained.


Currently, GASPAK is offered:

As an Excel Add-In (32 bit) function access to property calculations extensively tested on version of Excel from Excel97 through Excel 2010 (including Excel 2010 running on 64 bit OS).  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. 

As an ActiveX DLL (32 bit) for interfacing to a variety of Windows programs. This version is delivered with sample Visual Basic and C++ code, illustrating how to interface your own application to the GASPAK properties.

Fortran77 Source Code.

GASPAK fluid source




VDI Forschungsheft 596 (1979)


NBS Tech Note 1097 (1986)

Butane, iso

NBS Tech Note 1097 (1986)

Butane, normal

NBS Tech Note 1097 (1986)

Carbon dioxide

NIST data (1989)

Carbon monoxide

J. Phys. Chem. Ref. Data; NIST (1989)


NBS Tech Note 1097 (1986)


NBS Tech Note 1097 (1986)


NBS Tech Note 1045 (1981)


J. Phys. Chem. Ref. Data (1986)

Helium (3K to 5000K)

NBS Tech Note 1334 (1989, 1992); Cryodata 1996

Hydrogen, equilibrium

R.D. McCarty, 1996, valid to 5000 K.

Hydrogen, normal

NBS Monograph 168 (1975); valid to 5000 K

Hydrogen, ortho

R.D. McCarty, 1996, valid to 5000 K.

Hydrogen, para

NBS Tech Note 1097; valid to 5000 K (1986)

Hydrogen sulfide

Colo. School of Mines (1993)


USSR std. Reference; Cryodata correlation (1990)


NBS Tech Note 1097 (1986)


NIST Tech Note 1325 (1989)


USSR std. Reference; Cryodata correlation (1991)


NBS Tech Note 648 (1973)


J.Phys.Chem.Ref.Data (1986); valid to 5000 K

Nitrogen trifluoride

NBSIR 8-1632 (1980); NBS Tech Note 1097 (1986)


NBSIR 78-882 (1978); NBS Tech Note 1097 (1986)


Fluid Phase Equilibria (1985)


NBS Tech Note 1097

Water (above 273.16K)

J.P.C.R.D, vol 18, p1537 (1989)


USSR std. Reference; Cryodata correlation (1990)

Refrigerant 11

Univ. Idaho data (1991)

Refrigerant 12

Univ. Idaho data (1991)

Refrigerant 22

USSR std. Reference; Cryodata correlation (1991)

Refrigerant 32

DOE report; NIST data (1993)

Refrigerant 123

DOE report; NIST data (1993)

Refrigerant 124

DOE report; NIST data (1993)

Refrigerant 125

DOE report; NIST data (1993)

Refrigerant 134a

NIST (1993)

Refrigerant 152a

XII Int. Symposium on Thermophysics (1994)

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


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