A Weakly Nonideal Bose Gas Model Leading to the Fountain Effect

The ordinary thermodynamics corresponds to the equilibrium ground state of the system. We present a model making it possible to construct a “second thermodynamics”, an analogue of an equilibrium state of a superfluid, based on which we explain the effect of the appearance of a “bottleneck” in a thin capillary for a moving superfluid if it is heated to the critical point in the second thermodynamics.