ABSTRACT
This chapter discusses the principles of conservation of mass, momentum, and energy, as well as the conservation of a mass species in a multicomponent mixture. It considers the flow fields composed of mixtures of different chemical species rather than a single component fluid. In a multicomponent fluid, each species, in addition to its macroscopic displacement due to the flow, also diffuses with respect to the mixture. In multicomponent mixtures, the diffusion term is more complicated than Fick’s law, and the diffusion of each species depends on the pair binary diffusion coefficients of that species with respect to all other components in the mixture. However, Fick’s law becomes accurate in a multicomponent mixture when all the pair diffusivities in the mixture are equal. Although the fluid conservation equations are usually solved in Eulerian frame for convenience, the conservation principles themselves are originally Lagrangian.
