Expressions for the gas phase in a multiphase material

Abstract

This is the third of three chapters (9–11) that focus on developing expressions for a single phase in a multiphase material. In this chapter, the transport of “conserved” quantities that occurs predominantly (or only) through the gas phase is treated. In doing so, it is also necessary to account for the interphase exchange of “conserved” quantities through the internal (interphase) boundary surfaces that the gas phase shares with adjacent phases in the (multiphase) material--that is, gas/solid and/or gas/liquid boundary surfaces. Examples of such processes include, but are not limited to, drying, chemical vapor infiltration, certain gas/solid reactions, corrosion processes, and so on. And, as in Chapter 10, it will be seen that it is often the topological features (particularly the connectivity) of the gas-filled pore space that play a central role in both the intraphase transport, as well as the interphase exchange, of various “conserved” quantities. This is particularly true when the gas phase of interest only partially fills the pore space, such as in a pore space that is partially saturated with liquid. As a result, it is valid to think of the gas-phase portion of such a partially saturated pore space as being complementary to the liquid-phase portion of the same pore space: gas is where liquid isn’t. And, when this liquid is a wetting liquid (or fluid)--so that the gas in this situation is the non-wetting fluid--the gas must reside preferentially in the pores of radius r > R. [See also Eqn. (10.2.12).] In fact, this complementary relationship between the gas- and liquid-filled portions of the pore space makes the task of describing the intraphase transport and interphase exchange of “conserved” quantities in the gas phase a much simpler task than it might otherwise be: an analogy may be drawn in most cases between the quantities for the liquid phase--in terms of φL and S--and those for the gas phase--in terms of φG and (1-S). Moreover, since many of the expressions that are needed for the gas phase have effectively already been described in Chapter 10 (i.e., for the liquid phase), a much less detailed description is needed here. As a result, the length of Chapter 11 will be seen to be much shorter than that of Chapter 10.KeywordsPore SpaceMass DiffusivityKnudsen DiffusionMultiphase MaterialChemical Vapor InfiltrationThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.