Superfluid liquid helium refers to the state of liquid helium when it undergoes a phase transition called the helium-4 superfluid transition. At very low temperatures, below 2.17 Kelvin (or -270.98 degrees Celsius), helium-4 can exhibit remarkable properties, including zero viscosity and infinite thermal conductivity, which are characteristic of superfluidity.
When helium-4 is in its superfluid state, it behaves as if it has lost all internal friction, allowing it to flow with virtually no resistance. This property is known as zero viscosity, which means that it can move through extremely narrow channels and capillaries without any loss of energy due to friction. It also has infinite thermal conductivity, meaning it can efficiently transport heat.
Moreover, superfluid helium-4 exhibits other fascinating phenomena. It can climb up and flow over the walls of a container, defying gravity. It can also flow through very tiny openings, such as capillaries, without any measurable resistance. These properties arise due to the formation of a quantum mechanical state known as a Bose-Einstein condensate, where a large number of helium atoms occupy the same quantum state.
When superfluid helium is dissolved in normal liquid helium, the properties of the normal liquid can change. The dissolved superfluid acts as impurities in the normal liquid helium, causing disruptions in its flow. These impurities can induce vortices or whirlpools within the liquid helium, disrupting the superfluid behavior. As a result, the normal liquid helium may lose some of its superfluid properties and exhibit increased viscosity or resistance to flow. The degree of disruption depends on the concentration of the superfluid helium and the temperature. At very low temperatures, the effects of dissolved superfluid helium are more pronounced.