  A dark Friedman-Robertson-Walker fluid governed by a non-linear inhomogeneous
equation of state is considered which can be viewed as a conveniently simple
paradigm for a whole class of models which exhibit phase transitions from a
non-phantom towards a phantom era (superacceleration transition). From another
side, such dark fluid models may describe also quintessence-like cosmic
acceleration. Thermodynamical considerations for the processes involved, which
are of great importance in the characterization of the global evolution of the
corresponding universe, are given too. Connecting the proposed equation of
state with an anisotropic Kasner universe with viscosity, we are led to the
plausible conjecture of a dark fluid origin of the anisotropies in the early
universe.
