HEPAK Specifications...

Description

HEPAK (© copyright Cryodata Inc.) is a computer program for calculating the thermophysical properties of helium-4 (⁴He) from fundamental state equations.

The state equations are valid from 0.8 Kelvin or the melting line to 1,500 Kelvin, including the superfluid range, the lambda line, and liquid vapor mixtures.  As a function of pressure, calculations are valid up to 1,000 bars, except between 80 and 300 Kelvin where they are valid to 20,000 bars.

HEPAK development continues, based on new reference data combined with minor corrections of the existing code around the critical point and at high pressure in the liquid. Also, new development will extend down to 0 K, rather than being terminated at 0.8 K.

Calculated state properties include:

	PVT
	Enthalpy, Entropy, Gibbs and Internal Energy
	Specific Heats
	Sound Velocity, including 2nd and 4th sound in the superfluid
	Compressibility
	Joule-Thomson coefficient
	Expansivity
	Gruneisen parameter
	Latent Heat
	dP/dT of the saturation line
	several other PVT derivatives
	Lambda line location as a function of P,V,or T
	Normal fluid density fraction in Helium II
	Mutual friction and conductivity function in He II
	State properties (as listed above) within microdegrees of the Lambda line.

Other calculated properties include:

	Viscosity down to 1.2 K
	Thermal Conductivity down to 3 K
	Dielectric Constant
	Refractive Index
	Fluid Surface Tension

A total of 41 different pairs of input parameters (i.e., pressure and temperature, density and internal energy, saturation line and entropy) are available for specifying the fluid state. Included in the input parameter list are both isochoric and isobaric delta-T to the lambda line, valid for delta-T as small as 50 microkelvin.

HEPAK is written by Vincent Arp, Bob McCarty, and Jeff Fox, using code from Brian Hands of the Oxford University Cryogenics Laboratory. HEPAK is referenced to NIST Technical Note 1334 (1989), by Arp and McCarty, then employed at NIST, and an update of this Technical Note (1998) by D.G. Friend, V. Arp, and R.D. McCarty.

HEPAK is fully consistent with the updated NIST standard reference data for helium. It is also consistent with the International Temperature scale of 1990, defined by helium vapor pressure from 1.2 to 5.0 K.

Availability

Currently, HEPAK is offered:

As an ActiveX DLL (version 3.41) 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 HEPAK properties.

As a DOS executable program with an Excel Add-In function-only interface (version 3.40).  Fortran77 source code is available with this version.  The basic DOS program is supplied as a "stand-alone, keyboard input " version, with options for input from and output to user-defined files. The code has been tested and verified to operate in a DOS window in the Windows 3.1, 95/98/2000/NT4/XP operating systems.  Only calculational bugs and DOS interface bugs are being fixed in this version.  Bugs in the Excel Add-In function access are not being fixed in preference to migrating this entire code to the ActiveX version.