Description
HEPAK (© copyright Cryodata
Inc.) is a computer program for calculating the thermophysical
properties of helium4 (^{4}He) 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 

JouleThomson
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 deltaT to the lambda line, valid for deltaT 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 Excel AddIn (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 AddIn 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 HEPAK properties.
Fortran77 Source Code.
