Phonon model of heat radiation into superfluid helium by a solid with a flat surface

This paper reviews the quasiparticle model of superfluid helium and its application to describe heat transfer between a heated solid and superfluid helium. In this case, a problem is considered in which the surface of the heater is flat and the helium is at practically zero temperature. Under these conditions, heat transfer between solid and superfluid helium is determined by the transformation of the phonons of the solid into helium phonons. The work considers certain types of such transformation—elastic processes of phonon transformation, in which the number of phonons is conserved, and inelastic processes, in which the number of phonons changes. The main attention in this work is paid to the development of a quantum-mechanical approach for calculating the contribution of various polarizations phonons of solid to the heat flux formation, its magnitude, and angular distribution. The results of the work are used to explain the experimentally observed features of heat transfer from a heated solid to superfluid helium.