The Two-fluid Model
Helium II is usefully regarded theoretically as a mixture of normal fluid and superfluid, having a total density equal to the sum of the densities of the two components. The normal part behaves like any other liquid, and the superfluid part flows without resistance. The proportions of the two components change continuously from all normal fluid at the transition temperature (2.172 K) to all superfluid at zero temperature. More details can be found in the articles on superfluid helium-4 and macroscopic quantum phenomena.
In turbulence, the normal fluid behaves as a classical fluid, and has a classically turbulent velocity field when a superfluid experiences turbulence. In the superfluid component, however, vorticity is restricted to the quantized vortex lines, and there is no viscous dissipation. In turbulence, the vortex lines arrange themselves in an irregular fashion, and this is described as a "vortex tangle". This vortex tangle mediates an interaction between the superfluid and the normal component known as mutual friction.
Read more about this topic: Quantum Turbulence
Famous quotes containing the word model:
“... if we look around us in social life and note down who are the faithful wives, the most patient and careful mothers, the most exemplary housekeepers, the model sisters, the wisest philanthropists, and the women of the most social influence, we will have to admit that most frequently they are women of cultivated minds, without which even warm hearts and good intentions are but partial influences.”
—Mrs. H. O. Ward (1824–1899)