Editing Superfluid helium-4 (section)

=== Heat transport ===
Figure 9 depicts a heat-conduction experiment between two temperatures <math display="inline">T_H</math> and <math display="inline">T_L</math> connected by a tube filled with He-II. When heat is applied to the hot end a pressure builds up at the hot end according to Eq.{{EquationNote|7|(7)}}. This pressure drives the normal component from the hot end to the cold end according to

{{NumBlk2|:|<math display="block">\Delta p = -\eta_nZ\dot V_n.</math>|9}}

Here <math display="inline">\eta_n</math> is the viscosity of the normal component,<ref>Zeegers, J. C. H. ''Critical velocities and mutual friction in <sup>3</sup>He-<sup>4</sup>He mixtures at low temperatures below 100 mK'', thesis, Appendix A, Eindhoven University of Technology, 1991.</ref> <math display="inline">Z</math> some geometrical factor, and <math display="inline">\dot V_n</math> the volume flow. The normal flow is balanced by a flow of the superfluid component from the cold to the hot end. At the end sections a normal to superfluid conversion takes place and vice versa. So heat is transported, not by heat conduction, but by convection. This kind of heat transport is very effective, so the thermal conductivity of He-II is very much better than the best materials. The situation is comparable with [[heat pipe]]s where heat is transported via gas–liquid conversion. The high thermal conductivity of He-II is applied for stabilizing superconducting magnets such as in the [[Large Hadron Collider]] at [[CERN]].