Page 426 - Modelling in Transport Phenomena A Conceptual Approach

406 CHAPTER 9. STEADY MICROSCOPIC BALANCES WITH GEN.

Therefore, Eq. (9.5-139) becomes

The rate of moles of species A absorbed by the jet is

where CA, is the initial concentration of species A in the jet and c> is the equi-
librium solubility of species A in the liquid. Substitution of Eq. (2) into Eq. (3)
gives
nA = 4 (c> - CA,) d m (4)

9.5.3 Analysis of a Plug Flow Reactor

A plug flow reactor consists of a cylindrical pipe in which concentration, tempem
ture, and reaction rate are assumed to vary only along the axial direction. Analysis
of these reactors are usually done with the following assumptions:
0 Steady-state conditions prevail.

0 Reactor is isothermal.
0 There is no mixing in the axial direction.

The conservation statement for species i over a differential volume element of
thickness Az, as shown in Figure 9.21, is expressed as
(Q Ci)lx - (Q G)lx+Ax + ai YA Az = 0 (9.5141)

where ai is the stoichiometric coefficient of species i and r is the chemical reaction
rate expression. Dividing Q. (9.5141) by Az and taking the limit as Az + 0
gives
(9 .5142)