Liu procedure is applied to special relativistic fluids. It is shown that a reasonable
relativistic theory is an extended one, where the basic state space contains the
momentum density. This property follows from the structure of the energy-momentum
balance and the Second Law of thermodynamics. Moreover, we derive that the
entropy depends on both the energy density and the momentum density in a specific
way, indicating that the local rest frame energy density cannot be interpreted as the
internal energy, and that the local rest frame momentum density should be
considered, too. The corresponding constitutive relations for the stress and the
energy flux are derived.
Keywords
relativistic nonequilibrium thermodynamics, Liu procedure,
relativistic internal energy
