Page 197 - Modelling in Transport Phenomena A Conceptual Approach

PROBLEMS 177

Assume that oil and water have constant heat capacities of 2.3 and 4.2 kJ/ kg. K,
respectively.
(Answer: a) 1610 kg/ h)

6.2 The following parallel reactions take place in an isothermal, constant-volume
CSTR
A + 2B r = klcA kl = 1.3s-l
3A 4 C T = k2C~ k2 = 0.4s-l

Pure A is fed to the reactor at a concentration of 350 mol/ m3.
a) Determine the residence time required to achieve 85% conversion of species A
under steady conditions.
b) Determine the concentrations of species B and C.
(Answer: a) T = 2.27s b) CB = 309.9mol/m3, cc = 47.7mol/m3)

6.3 Species A undergoes the following consecutive first-order reactions in the
liquid phase in an isothermal, constant-volume CSTR
A~BSC

where kl = 1.5s-1 and = 0.8s-'. If the feed to the reactor consists of pure A,
determine the residence time required to maximize the concentration of species 23
under steady conditions.
(Answer: 0.913 s)

6.4 An isomerization reaction
A+B

takes place in a constant-volume CSTR. The feed to the reactor consists of pure
A. The rate of the reaction is given by

For the maximum conversion of species A at a given residence time, determine the
reactor temperature.

6.5 Two electronic components (IC = 190 W/ m. K) are to be cooled by passing
0.2 m3/ s of air at 25 "C between them. To enhance the rate of heat loss, it is pro-
posed to install equally spaced rectangular aluminum plates between the electronic
components as shown in Figure 6.6.