Note on the summational invariant and corresponding local Maxwellian for the Enskog equation

Abstract: The summational invariant and the corresponding local Maxwellian that are compatible with the Enskog equation are discussed, with special interest in the presence of a boundary. The local Maxwellian corresponding to the summational invariant is restrictive compared to the case of the Boltzmann equation in the sense that a radial flow and time-dependent temperature are forbidden. However, a rigid body rotation with a constant angular velocity is admitted as in the case of the Boltzmann equation. The influence of the presence of a boundary is also discussed in simple situations.