Helium cryogenic properties

The values in these tables were generated from the NIST REFPROP software (Lemmon, E.W., McLinden, M.O., and Huber, M.L., NIST Standard Reference Database 23 Reference Fluid Thermodynamic and Transport Properties—REFPROP, National Institute of Standards and Technology, Standard Reference Data Program, Gaithersburg, Md., 2002, Version 7.1). The primary source for the thermodynamic properties is McCarty, R.D., and Arp, V D., A New Wide Range Equation of State for Helium, Ado. Cryo. Eng. 35 1465-1475,1990. The source for viscosity is 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, Colo., 1998. The source for thermal conductivity is Hands, B. A., and Arp, V. D., A Correlation of Thermal Conductivity Data for Helium, Cryogenics, 21(12) 697-703,1981. 

Plate-fin exchangers provide a very large heat transfer surface per unit volume and are relatively inexpensive per unit area. They are not mechanically cleanable and are ordinarily used only with very clean fluids. This combination of properties fits them very well for a wide variety of cryogenic applications, such as air separation helium separation, purification, and liquefaction liquefied natural gas production and separation of light hydrocarbons. They are also used in higher-temperature gas-to-gas services. 

The final electrical connections to the STM can be done with copper wires. A small amount of helium is used as an exchange gas to anchor the temperature of the whole assembly to the cryogenic fluid. The body of the STM can be made out of copper, which will respond quickly to temperature changes for variable temperature measurements and provide a uniform temperature environment for the tunnel junction. One has to estimate the differential thermal contraction of the component parts to make sure that a tunnel junction separation set at room temperature is sufficiently large to prevent tip crash on cooling. Other materials like Macor or Invar , which closely match the thermal expansion properties of the piezoelectric transducers, are used as well but take more time to thermally stabilize. Some references are given in [6.30-6.43]... 

Alloys, and Compounds Low-Temperature Phase Equilibria Helium-3 and Helium-4 Low-Temperature Crystallography Cryogenic Insulation Systems The Mechanical Properties of Materials at Low Temperatures Cryopumping... 

It is important not only to consider the hazards associated with the low temperatures of cryogens, but to remember that each cryogen itself may have other hazardous properties specifle to that particular chemical. Liquid nitrogen and liquid helium present only asphyxiation hazards as gases while carbon... 

Equations (la), (2) and (3) were combined and coded for solution on a Burroughs Datatron 205 computer. Properties of the most common cryogenic fluids (oxygen, nitrogen, argon, hydrogen and helium) were expressed as a function of pressure and the problem solved for various. initial pressure conditions. 

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