Definition: | state of helium which, in the pressure vs. temperature curve, is represented by the region surrounded by the melting curve, the vapour pressure curve, and a line (λ line) which connects two points, upper λ point (1,76 K and 3,0 MPa) and lower λ point (2,18 K and 5,0 kPa) Note 1 to entry: Saturated superfluid helium: superfluid helium which exists on the vapour pressure curve below lower λ point in the pressure vs. temperature curve. Note 2 to entry: Pressurized superfluid helium: superfluid helium which exists above the vapour pressure curve below lower λ point in the pressure vs. temperature curve. Note 3 to entry: Superfluid helium has very small viscosity and large thermal conductivity.
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