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- Q19904196 subject Q7415569.
- Q19904196 subject Q8431293.
- Q19904196 abstract "In the field of cryogenics, helium [He] is utilized for a variety of reasons. The combination of helium’s extremely low molecular weight and weak interatomic reactions yield interesting properties when helium is cooled below its critical temperature of 5.2 K to form a liquid. Even at absolute zero (0K), helium does not condense to form a solid. In this state, the zero point vibrational energies of helium are comparable to very weak interatomic binding interactions, thus preventing lattice formation and giving helium its fluid characteristics. Within this liquid state, helium has two phases referred to as helium I and helium II. Helium I displays thermodynamic and hydrodynamic properties of classical fluids, along with quantum characteristics. However, below its lambda point of 2.17 K, helium transitions to He II and becomes a quantum superfluid with zero viscosity.Under extreme conditions such as when cooled beyond Tλ, helium has the ability to form a new state of matter, known as a Bose–Einstein condensate (BEC), in which the atoms virtually lose all their energy. Without energy to transfer between molecules, the atoms begin to aggregate creating an area of equivalent density and energy. From observations, liquid helium only exhibits super-fluidity because it contains isolated islands of BECs, which have well-defined magnitude and phase, as well as well-defined phonon–roton (P-R) modes. A phonon refers to a quantum of energy associated with a compressional wave such as the vibration of a crystal lattice while a roton refers to an elementary excitation in superfluid helium. In the BEC’s, the P-R modes have the same energy, which explains the zero point vibrational energies of helium in preventing lattice formation.When helium is below Tλ, the surface of the liquid becomes smoother, indicating the transition from liquid to superfluid. Experiments involving neutron bombardment correlate with the existence of BEC’s, thereby confirming the source of liquid helium’s unique properties such as super-fluidity and heat transfer. Though seemingly paradoxical, cryogenic helium systems can move heat from an area of relatively low temperature to an area of relatively high temperature. Though this phenomenon appears to violate the second law of thermodynamics, experiments have shown this to prevail in systems where the area of low temperature is constantly heated, and the area of high temperature is constantly cooled. It is believed this phenomenon is related to the heat associated with the phase change between liquid and gaseous helium.".
- Q19904196 thumbnail Helium_atomic_diagram.png?width=300.
- Q19904196 wikiPageWikiLink Q106667.
- Q19904196 wikiPageWikiLink Q1086480.
- Q19904196 wikiPageWikiLink Q111059.
- Q19904196 wikiPageWikiLink Q124131.
- Q19904196 wikiPageWikiLink Q130825.
- Q19904196 wikiPageWikiLink Q13534105.
- Q19904196 wikiPageWikiLink Q176555.
- Q19904196 wikiPageWikiLink Q177045.
- Q19904196 wikiPageWikiLink Q186608.
- Q19904196 wikiPageWikiLink Q192116.
- Q19904196 wikiPageWikiLink Q46202.
- Q19904196 wikiPageWikiLink Q560.
- Q19904196 wikiPageWikiLink Q7415569.
- Q19904196 wikiPageWikiLink Q81182.
- Q19904196 wikiPageWikiLink Q826582.
- Q19904196 wikiPageWikiLink Q8431293.
- Q19904196 wikiPageWikiLink Q910137.
- Q19904196 comment "In the field of cryogenics, helium [He] is utilized for a variety of reasons. The combination of helium’s extremely low molecular weight and weak interatomic reactions yield interesting properties when helium is cooled below its critical temperature of 5.2 K to form a liquid. Even at absolute zero (0K), helium does not condense to form a solid.".
- Q19904196 label "Helium cryogenics".
- Q19904196 depiction Helium_atomic_diagram.png.