PERTURBATIONAL THERMODYNAMICS OF COUPLED ELECTROCHEMICAL HEAT AND MASS-TRANSFER

Local equilibrium effect in systems with transport of energy, matter a nd electric charge is shown to be sufficient for local stability of th e processes which satisfy a dissipative variational formalism for pert urbations relaxing to a steady slate. It is postulated that the effect is an extremal property of those thermodynamic systems which minimize dissipation and whose evolution is governed by an extremum principle describing their natural tendency to Fast local relaxations. A pertine nt principle extends that of Onsager's [1] to nonstationary quasilinea r regime and electrochemical transport. Its resulting form describes a n extremum of a functional structure related to grand thermodynamic po tential, the Legendere transform of entropy. The principle is set in t he physical space-time rather than in the three-dimensional (3D) space and, as such, it substantiates the joint role of thermodynamic potent ials and intensity of dissipation. For isolated systems the principle implies a least possible growth of entropy under constraints imposed b y conservation laws, whereas for nonequilibrium steady-states its pert urbational form implies minimum of a work potential at the steady slat e. Phenomenological equations, equations of change and bulk overvoltag e properties can be derived in complex electrochemical systems. Nonequ ilibrium temperatures and chemical potentials are interpreted in terms of the Lagrangian multipliers of conservation constraints. These quan tities converge to the classical thermodynamic intensities when the lo cal equilibrium is attained. Copyright (C) 1996 Elsevier Science Ltd.