Page 691 - Bird R.B. Transport phenomena

2
Chapter 2

Interphase Transport in

Nonisothermal Mixtures

§22.1 Definition of transfer coefficients in one phase
§22.2 Analytical expressions for mass transfer coefficients

§22.3 Correlation of binary transfer coefficients in one phase
§22.4 Definition of transfer coefficients in two phases
§22.5° Mass transfer and chemical reactions
§22.6° Combined heat and mass transfer by free convection
§22.7° Effects of interfacial forces on heat and mass transfer
§22.8° Transfer coefficients at high net mass transfer rates
§22.9* Matrix approximations for multicomponent mass transport

Here we build on earlier discussions of binary diffusion to provide means for predicting
the behavior of mass transfer operations such as distillation, absorption, adsorption, ex-
traction, drying, membrane filtrations, and heterogeneous chemical reactions. This chap-
ter has many features in common with Chapters 6 and 14. It is particularly closely
related to Chapter 14, because there are many situations where the analogies between
heat and mass transfer can be regarded as exact.
There are, however, important differences between heat and mass transfer, and we
will devote much of this chapter to exploring these differences. Since many mass transfer
operations involve fluid-fluid interfaces, we have to deal with distortions of the interfa-
cial shape by viscous drag and by surface tension gradients resulting from inhomo-
geneities in temperature and composition. In addition, there may be interactions
between heat and mass transfer, and there may be chemical reactions occurring. Further-
more, at high mass transfer rates, the temperature and concentration profiles may be dis-
torted. These effects complicate and sometimes invalidate the neat analogy between heat
and mass transfer that one might otherwise expect.
In Chapter 14 the interphase heat transfer involved the movement of heat to or from
a solid surface, or the heat transfer between two fluids separated by a solid surface. Here
we will encounter heat and mass transfer between two contiguous phases: fluid-fluid or
fluid-solid. This raises the question as to how to account for the resistance to diffusion
provided by the fluids on both sides of the interface.
We begin the chapter by defining, in §22.1, the mass and heat transfer coefficients
for binary mixtures in one phase (liquid or gas). Then in §22.2 we show how analytical
solutions to diffusion problems lead to explicit expressions for mass transfer coefficients.
In that section we give some analytic expressions for mass transfer coefficients at high

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