Extended irreversible thermodynamics

Summary

Extended irreversible thermodynamics is a theory of non-equilibrium thermodynamics in which the fluxes, such as the heat flux, are independent state variables. The entropy then depends on the fluxes as well as on the classical variables, and the fluxes obey their own evolution equations with relaxation times. This leads to hyperbolic transport equations, such as the Cattaneo–Vernotte equation for heat, with finite speeds of propagation. It is used for fast processes and high frequencies, where classical theory based on local equilibrium fails.