Phase transition and lambda-line in liquid helium

A hydrodynamical model describing the superfluid phase transition of 4He close to $\lambda$-line is presented. In the work, which generalizes a phase field model of lambda transition previously formulated by the same authors, the independent fields are the density, the temperature, the velocity, the heat flux and a scalar function $f$, linked to the modulus of the wave-function $\psi$, solution of the Ginzburg-Landau equation. In this framework, the heat flux is given by a modified Maxwell-Cattaneo equation. The restrictions on the constitutive quantities are obtained from the entropy principle, using the Liu method of Lagrange multipliers. A maximum theorem is proved that allows the model satisfy the second law of thermodynamics.