Global non-equilibrium thermodynamics for steady states like never before

Abstract In this Perspective article, we introduce a new framework for the global non-equilibrium thermodynamics of stationary states. This theory uses the spatial distributions of temperature, density, velocity, and other variables in stationary states as its input. It outputs the global state parameters to describe the system's energy exchange with the environment. The number of state parameters is determined solely by the type of substance in the system and external potentials, regardless of the number of boundary conditions, fluxes within the system, or its specific geometry. The theory offers a second law of non-equilibrium thermodynamics for stationary states, predicting the direction of spontaneous processes between them. When all macroscopic fluxes reach zero, the theory reduces to equilibrium thermodynamics.