Nonequilibrium temperature and fluctuation–dissipation temperature in flowing gases

The expressions for the nonequilibrium temperature derived from the fluctuation–dissipation theorem and from the differential of the informational nonequilibrium entropy for ideal gases under shear flow are compared. Both temperatures are different, in particular, the thermodynamic temperature derived from the entropy is lower than the local-equilibrium temperature, whereas the effective temperature defined from the fluctuation–dissipation expression is higher than the local-equilibrium temperature.