Phenomenological coefficients and frames of reference for transport processes in liquids and membranes. Part 1.—Resistance coefficients, friction coefficients and generalised diffusivities in isothermal systems

Abstract

Phenomenological descriptions of transport processes in isotropic, non-reacting systems are discussed in terms of resistance coefficients, friction coefficients, generalised diffusivities and conductance coefficients. These quantities are defined rigorously, and it is shown that, for a non-viscous system containing n species, there is a set of (n– 1)² independent coefficients whether or not the system is at mechanical equilibrium. If the coefficients are symmetric, then the number of independent coefficients is reduced to n(n–1)/2. It is also shown that resistance and friction coefficients and generalised diffusivities are invariant under transformations among frames of reference moving at different velocities. Conductance coefficients do not possess this invariance, but do preserve symmetry when they are defined properly. If any set of conductance or resistance coefficients is symmetrical, then the symmetry of any other set is implied.