The paper deals with the theory of actions on thermodynamical systems. It is proved that if an action has the conservation property at least at one state then it has the conservation property at every state and admits an everywhere defined continuous potential. An analogous result for semi-systems is also proved.
We overview the notion of entropy in thermodynamics. We start from the smooth case using differential forms on the manifold, which is the natural language for thermodynamics. Then the axiomatic definition of entropy as ordering on a set that is induced by adiabatic processes will be outlined. Finally, the viewpoint of category theory is provided, which reinterprets the ordering structure as a category of pre-ordered sets.
Extended thermodynamics is based on a set of equations of balance which are supplemented by local and instantaneous constitutive equations so that the field equations are quasi-linear differential equations of first order. If the constitutive functions are subject to the requirements of the entropy principle, one may write them in symmetric hyperbolic form by a suitable choice of fields. The kinetic theory of gases, or the moment theories based on the Boltzmann equation, provide an explicit example...
The postulates of macroscopic thermodynamics give us the possibility to endow the set of thermodynamic states with the structure of a riemannian manifold. Two alternatives are available: the first one is to introduce on the set of thermodynamic equilibrium states a metric induced by an embedding metric space (extrinsic approach), the second one is to introduce the stability metric (intrinsic approach). Between the two choices the second one looks more promising on the basis of its capability of...
We discuss the different roles of the entropy principle in modern thermodynamics. We start with the approach of rational thermodynamics in which the entropy principle becomes a selection rule for physical constitutive equations. Then we discuss the entropy principle for selecting admissible discontinuous weak solutions and to symmetrize general systems of hyperbolic balance laws. A particular attention is given on the local and global well-posedness of the relative Cauchy problem for smooth solutions....