The Phenomenological Relations

Abstract

In the first chapter we had assumed the existence of variables which are dependent on position r in space and on time t. Such local variables are the deviations α (r, t) and β( r, t) as well as the conjugate variables X(r, t) and Y(r, t). In order to specify these variables as thermodynamic variables we extend the assumption of the existence of local variables to the assumption of local equilibrium. This means that all thermodynamic functions of state which we know in equilibrium thermodynamics exist as well in irreversible thermodynamics for each space element of the system. The relations between the local thermodynamic functions are the same as those in equilibrium thermodynamics. Thus, e.g., the local temperature T(r, t) is defined by an equation of state T(ϱ, u), where the mass density ϱ = ϱ (r, t) and the specific internal energy u = u(r, t), which is the same as has been observed by experiments on equilibrium systems [6].