Page 171 - Modelling in Transport Phenomena A Conceptual Approach

6.1. CONSERVATION OF CHEMICAL SPECIES 151

Therefore, Eq. (6.1-2) takes the form

Sometimes it is more convenient to work on molar basis. Division of Eqs. (6.1-2)
and (6.1-5) by the molecular weight of species i, Mi, gives

(6.1-6)

and

where ni and ci are the molar flow rate and molar concentration of species i,
respectively.

Example 6.1 The liquid phase reaction

A+2B+C+2D

takes place in an isothermal, constant-volume stirred tank wactor. The rate of
reaction is expressed by

r = k CACB with k = 0.025 L/ mol. min

The feed stream consists of equal concentrations of species A and B at a value
of lmoI/L. Determine the residence time required to achieve 60% conversion of
species B under steady conditions.

Solution

Assumption

1. As a result of perfect mixing, concentrations of species within the reactor are
uniform, i-e., = (ci)sys.