supposed to be at zero kelvins (Tl=0) and zero pressure (pl = 0). The vessels are connected by a so-called superleak. This is a tube, filled with a very fine powder, so the flow of the normal component is blocked. However, the superfluid component can flow through this superleak without any problem (below a critical velocity of about 20 cm/s). In the steady state vs=0 so Eq. implies where the index l (r) applies to the left (right) side of the superleak. In this particular case pl = 0, zl = zr, and pfl = 0 (since Tl = 0). Consequently, This means that the pressure in the right vessel is equal to the fountain pressure at Tr. In an experiment, arranged as in figure 8, a fountain can be created. The fountain effect is used to drive the circulation of 3He in dilution refrigerators. Heat transport Figure 9 depicts a heat-conduction experiment between two temperatures TH and TL 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.. This pressure drives the normal component from the hot end to the cold end according to Here ηn is the viscosity of the normal component, Z some geometrical factor, and 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 pipes 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. Microscopic theory Landau two-fluid approach L. D. Landau's phenomenological and semi-microscopic theory of superfluidity of helium-4 earned him the Nobel Prize in physics, in 1962. Assuming that sound waves are the most important excitations in helium-4 at low temperatures, he showed that helium-4 flowing past a wall would not spontaneously create excitations if the flow velocity was less than the sound velocity. In this model, the sound velocity is the "critical velocity" above which superfluidity is destroyed. (Helium-4 actually has a