Helium-4 is a non-radioactive and light isotope of helium. It is by far the most abundant of the two naturally-occurring isotopes of helium, making up about 99.99986% of the helium on earth. Its nucleus is a boson and an alpha particle, having two protons and two neutrons. Alpha decay is a common decay mode for many radioactive isotopes.
Author(s)
Abstract
The helium-4 working fluid in regenerative cryocoolers operating with the cold end near 4 K deviates considerably from an ideal gas. As a result, losses in the regenerator, given by the time-averaged enthalpy flux, are increased and are strong functions of the operating pressure and temperature. Helium-3, with its lower boiling point, behaves somewhat closer to an ideal gas in this low temperature range and can reduce the losses in 4 K regenerators. An analytical model is used to find the fluid properties that strongly influence the regenerator losses as well as the gross refrigeration power. The thermodynamic and transport properties of helium-3 were incorporated into the latest NIST regenerator numerical model, known as REGEN3.3, which was used to model regenerator performance with either helium-4 or helium-3. With this model we show how the use of helium-3 in place of helium-4 can improve the performance of 4 K regenerative cryocoolers. The effects of operating pressure, warm-end temperature, and frequency on regenerators with helium-4 and helium-3 are investigated and compared. The results are used to find optimum operating conditions. The frequency range investigated varies from 1 Hz to 30 Hz, with particular emphasis on higher frequencies.- The helium-4 working fluid in regenerative cryocoolers operating with the cold end near 4 K deviates considerably from an ideal gas. As a result, losses in the regenerator, given by the time-averaged enthalpy flux, are increased and are strong functions of the operating pressure and temperature.
- Helium 4's nucleus consists of two protons and two neutrons, for an atomic weight of 4. Helium 3, the rarer isotope, has a nucleus of two protons and one neutron. Helium 3 boils at 3.2 Kelvin. This boiling point is one degree colder than that of helium 4. Both helium 4 and helium 3 can be cooled to below their boiling temperatures by reducing.
Advances in Cryogenic Engineering
985
Journals
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Keywords
Cryocoolers, cryogenics, Gifford-McMahon, helium-3, helium-4, numerical analysis, pulse tubes, real gas, refrigeration, regenerators, Stirling, theory
Citation
Helium 4 Electrons
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