Superfluidity and Dissipative Processes in Liquid He II

A phenomenological theory of superfluidity of He II is constructed upon the two-fluid models of Tisza and Landau. The postulate that phonons partially represent the thermal energy of the liquid is employed to explain the dependence of critical velocities upon the size of the liquid region. A new assumption, of the production of phonons by the motion of large clusters of superfluid particles, provides a description of the transition between superflow and dissipation at flow velocities exceeding critical.