Convective heat transport in two-phase superfluid/vapor ⁴He system

We have recently shown that under certain cryogenic conditions heat can flow from a colder but constantly heated body to a hotter but constantly cooled body. Specifically, we have provided experimental evidence that heat flows through normal liquid and gaseous phases of 4He from the constantly heated, but cooler, bottom plate of a Rayleigh–Bénard convection cell to its hotter, but constantly cooled, top plate. Here we report results of a modified experiment, where the bottom normal liquid helium layer is replaced by superfluid 4He, providing, together with a superfluid film covering the entire cell interior, an effective thermal short-circuit. Applied heat input of order 1 W to the bottom plate results in simultaneous heating of the entire cell: this physical process can be viewed, at least approximately, as a series of subsequent equilibrium states, until upon reaching the superfluid transition the non-equilibrium processes described in our previous study [Proc. Nat. Acad. Sci. USA 110, 8036 (2013)] are fully recovered.