Constitutive equations for transport of chemical species

Abstract

In this chapter we begin to study the mass transfer of chemical species, defining its basic principles and defining the appropriate quantities of multicomponent flows. In Sect. 14.1 we show that, as the mean velocities of the individual species are different from each other, there are several ways to define the average velocity of a mixture. Accordingly, the separation between convective and diffusive fluxes appearing in the governing equations derived in Sect. 14.2 is not unique, as we stress in Sect. 14.3, where the constitutive relation of the diffusive material fluxes are investigated. The peculiarities of the transport of mass compared to that of heat and momentum are further illustrated in the discussion on boundary conditions in Sect. 14.4, and in the series of pointed questions that are listed in the final Sect. 14.5.