Relativistic Polyatomic Gas

The goal of this chapter is to present the relativistic extended thermodynamics (relativistic ET) theory of rarefied polyatomic gases with 14 fields. This is achieved by adopting the closure procedure for the generalized moments of a distribution function that, as in the classical case, depends on an additional continuous variable representing the energy of the internal modes of a molecule. This permits the theory to take into account the energy exchange between translational modes and internal modes of a molecule. First, we consider the non-dissipative Eulerian fluids and we obtain, via MEP, the equilibrium distribution function that is the natural generalization of the Jüttner distribution function. And we evaluate the thermal and caloric equations of state. We prove that the thermal equation of state is the same as that of monatomic gas, while the caloric equation of state is a generalization of the Synge one. Second, we consider a rarefied polyatomic gas with dissipation. We present the theory given recently by Pennisi and Ruggeri (Ann Phys 377:414, 2017). The theory includes the relativistic ET theory of monatomic gases as a singular limit, and it converges to the corresponding RET theory of polyatomic gases in the classical limit. In contrast to a monatomic gas, the dynamic pressure in a polyatomic gas is not small due to the internal motion of a molecule as is the case in the classical limit. Therefore the present theory might be particularly useful in cosmology to describe some aspects of the post-recombination era.