Comment on "A Multicomponent Boundary Layer Chemically Coupled to an Ablating Surface"
where Fi and Fj are at most weak functions of the temperature T. The accuracy of the approximation has been assessed in both Refs. 1 and 2 by comparing calculations based thereon with exact values of 3)^ for a variety of chemical systems and for those systems shown to lead to errors of less than roughly 17%. The apparent convenience achieved by the approximation is that there results an explicit relation for the mass flux of species i in terms of the gradient of concentration of species i and of a sum over gradients of all species. It is the purpose of this comment to make two observations about the approximation of Eq. (1) ; the first concerns the absence of any fundamental basis for it. Note that according to the rigid sphere model (the treatment of Fi and Fj as constants appears analogous to the use of such a model)