**HELIUM**

Helium provides thermodynamic properties for normal fluid (not superfluid) Helium using the fundamental equation of state developed by Ortiz Vega:

Diego Orlando Ortiz Vega

*A New Wide Range Equation of State for Helium-4*

PhD Thesis, Chemical Engineering

Texas A&M University, August 2013

http://oaktrust.library.tamu.edu/handle/1969.1/151301

There are a few typographical errors in this work that should be noted. The sign for *h* and *b* in Eqn (75) should be positive, not negative as displayed when used with the coefficients in Table 4. Coefficient N4 in Equation (109) should also be positive. Coefficients s0/R and h0/(RT0) need to be adjusted to provide the desired reference state.

The specific enthalpy and entropy values provided by the equation of state are referenced to 0 for saturated liquid at the normal boiling point (4.23 K).

The equation of state is valid for temperatures between the lower l-point temperature (2,172 K) and 1500 K for pressures up to 2000 MPa.

__Viscosity data:__

Arp, V.D., McCarty, R.D., and Friend, D.G., "Thermophysical Properties of Helium-4 from 0.8 to 1500 K with Pressures to 2000 MPa," ** NIST Technical Note 1334**, Boulder, CO 1998.

__Thermal Conductivity Data:__

Hands, B.A. and Arp, V.D.,"A Correlation of Thermal Conductivity Data for Helium," ** Cryogenics**, 21(12):697-703, 1981.

__Surface tension data are provided using the information in:__

Mulero, A., Cachadina, I, and Parra, M.

"Recommended Correlations for the Surface Tension of Common Fluids"

J.Phys. Chem Ref. Data, Vol. 41, No.4, 2012

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The current helium correlation was implemented in version 10.049. Previous versions used an equation of state based on data from McCarty and Arp as provided by Reiner Tillner-Roth, ** Fundamental Equations of State**, Shaker, Verlag, Aachan, 1998 with ancillary equations provided by R.D. McCarty and V.D. Arp, "A New Wide Range Equation of State for Helium", Advances in Cryogenic Engineering, Vol. 35, pp. 1465-1475, 1990. The range of applicability of the thermodynamic properties is from the lambda point temperature 2.1768 K to 1500 K at pressures up to 100 MPa.

Note that there is a missing plus sign before the first summation in equation (2) of the McCarty and Arp paper and the X in table 2 should be defined as (T-TC)/(T1-TC).

The older equation of state is provided for backward compatibility with substance name **Helium_MA**. Note that the values of specific enthalpy and entropy in this implementation are referred to values of 0 at 298.15 K and 101.325 kPa, which differs from the reference state in the current Helium implementation.