| Definition: | state of helium that, in the pressure vs. temperature curve, is represented by the region surrounded by the melting curve, the vapour pressure curve, and a line ( line) that connects two points, the upper point (1,76 K and 3,0 MPa) and the lower point (2,18 K and 5,0 kPa) Note 1 to entry: Superfluid helium exists in two states: - saturated superfluid helium: superfluid helium that exists on the vapour pressure curve below the lower point in the pressure vs. temperature curve; - pressurized superfluid helium: superfluid helium that exists above the vapour pressure curve below the lower point in the pressure vs. temperature curve. Note 2 to entry: Superfluid helium has very low viscosity and high thermal conductivity. Note 3 to entry: This entry was numbered 815-15-18 in IEC 60050-815:2015.
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