On the temperature of a rarefied gas in non-equilibrium

This paper addresses the problem of the proper definition of temperature of a gas in non-equilibrium. II shows that the mean kinetic energy of the atoms of a rarefied gas is not a good measure for the thermodynamic temperature, because in general it jumps at a wall, and because it is non-monotone in a one-dimensional process of stationary heat conduction. The jump of the 'kinetic temperature' is calculated and found to be about 5 K in a rarefied gas. The basis for the calculations is provided by the arguments of extended thermodynamics of 14 moments. An essential tool is the minimax principle of entropy production recently postulated by Struchtrup & Weiss [1], because it furnishes one important boundary condition.