TERMIUM Plus^®

Fiche 1,  Justifications,  Anglais

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Liquid helium existing as a superfluid below the transition point of approximately 2.2°K at 1 atmosphere and having extremely low viscosity and extremely high thermal conductivity.  1, fiche 1, Anglais, - helium%20II

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Superfluid Helium What Is It? As the temperature of helium gas is lowered to approximately 5.2°K, a phase transition to ordinary liquid helium (He I) takes place. The latter is unremarkable and its behavior is identical to any other liquid. As temperature is lowered further (at moderate pressures) helium does not solidify. Rather, it undergoes a phase change to a second liquid phase He II at temperature of about 2.17°K. ... the He II phase persists all the way to absolute zero. ... The He II phase is referred to as superfluid helium because of its remarkable properties, including the ability to flow through microscopic passages [holes as small as 10^-7 centimeters in diameter] with no apparent friction; the quantization of vortices; and the ability to support four wave modes: first sound which is analogous to sound in ordinary gases and liquids, second sound which carries temperature and entropy perturbations with virtually no pressure variations, third sound which are waves on thin films, and fourth sound which are acoustic-like waves in the "superfluid" component of He II.  5, fiche 1, Anglais, - helium%20II

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Superfluid Helium (He II, Superfluidity). Superfluid or Helium II technology has been developed quite successfully in the past decades in both aerospace and magnet cooling systems. ... Other strange properties of superfluid include the Rollin film, mechanocaloric effect and fountain effect.  6, fiche 1, Anglais, - helium%20II

Fiche 1,  Justifications,  Français

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On désigne par Hélium II, l'hélium en dessous de T_lambda. L'hélium superfluide a la propriété bien connue d'avoir une viscosité nulle (il peut traverser de très fins capillaires sans frottement; il a la capacité de pouvoir remonter le long des parois, etc.).  2, fiche 1, Français, - h%C3%A9lium%20II

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En refroidissant sous la pression atmosphérique de l'hélium ordinaire [...], on constate qu'il se liquéfie à 4,2 K. Le liquide ainsi produit (hélium I) n'a rien de particulier, sa viscosité est faible, mais il se comporte comme tous les liquides usuels. En refroidissant ce liquide au-dessous de 2,17 K, on voit apparaître une phase liquide aux propriétés exceptionnelles (hélium II) souvent désignée sous le nom d'hélium superfluide en raison de sa viscosité pratiquement nulle. L'hélium II est également caractérisé par une résistivité thermique pratiquement nulle, on dit que c'est un supraconducteur thermique.  6, fiche 1, Français, - h%C3%A9lium%20II

Fiche 1,  Justifications,  Espagnol