The Linearized Theory An Appraisal

While fluxes computed from the linearized equations usually compare favorably with fluxes computed from exact solutions, the same may not always be said for composition profiles (see, e.g., Krishnamurthy and Taylor, 1982). Indeed, the assumption of constant [ ] may sometimes lead to physically impossible composition profiles (see, e.g., Gupta and Cooper, 1971). 

The linearized theory of Toor (1964a) and of Stewart and Prober (1964) is probably the most important method of solving multicomponent diffusion problems. Very often, the method provides the only practical means of obtaining useful analytical solutions of multicomponent diffusion problems. Additional applications of the method are developed in Chapters 8-10 and still more can be found in the literature [see Cussler (1976), Krishna and Standart (1979) and Taylor (1982c) for sources]. 

It takes more time to scotch falsehood and expose fables than it does to set forth something solid and new. 

The complexity of the Maxwell-Stefan equations and the generalized Fick s law have lead many investigators to use simpler constitutive relations that avoid the mathematical complexities (specifically, the use of matrix algebra in applications). In this chapter we examine these effective diffusivity or pseudobinary approaches. 

---