Diffusive Lorentz gases and multibaker maps are compatible with irreversible thermodynamics

We show that simple diffusive systems, such as the Lorentz gas and multibaker maps, are perfectly compatible with the laws of irreversible thermodynamics, despite the fact that the moving particles, or their equivalents, in these models do not interact with each other, and that the dynamics takes place in low-dimensional phase spaces. The interaction of moving particles with scatterers provides the dynamical mechanism responsible for an approach to equilibrium, under appropriate conditions. This analysis provides a refutation of the criticisms expressed recently by Cohen and Rondoni (Physica A 306 (2002) 117).