Are Onsager's reciprocal relations necessary to apply Thermodynamic Extremal Principles?

Onsager's Reciprocal Relations between thermodynamic forces and fluxes, for which Onsager was awarded the Nobel Prize, automatically follow from Thermodynamic Extremal Principles. Thus, the Principles are up to now non-applicable for the treatment of experimentally determined or theoretically modeled non-reciprocal systems as e.g. those in the magnetic field. However, we can demonstrate that adding of a certain barrier constraint as bilinear form of thermodynamic forces and fluxes accounted by the Thermodynamic Extremal Principles provides to non-reciprocal relations between the thermodynamic forces and fluxes. Such a novel idea may contribute to a better understanding of physics behind non-reciprocal systems. (C) 2019 Elsevier Ltd. All rights reserved.