  Building on a general variational framework for multi-fluid dynamics, we
discuss finite temperature effects in superfluids. The main aim is to provide
insight into the modelling of more complex finite temperature superfluid
systems, like the mixed neutron superfluid/proton superconductor that is
expected in the outer core of a neutron star. Our final results can also (to a
certain extent) be used to describe colour-flavour locked quark superconductors
that may be present at the extreme densities in the deep neutron star core. As
a demonstration of the validity of the model, which is based on treating the
excitations in the system as a massless ``entropy'' fluid, we show that it is
formally equivalent to the traditional two-fluid approach for superfluid
Helium. In particular, we highlight the fact that the entropy entrainment
encodes the ``normal fluid density'' of the traditional approach. We also show
how the superfluid constraint of irrotationality reduces the number of
dissipation coefficients in the system. This analysis provides insight into the
more general problem when vortices are present in the superfluid, and we
discuss how the so-called mutual friction force can be accounted for in our
framework. The end product is a hydrodynamic formalism for finite temperature
effects in a single superfluid condensate. This framework can readily be
extended to more complex situations.
