Page 241 - Modelling in Transport Phenomena A Conceptual Approach

PROBLEMS 221
J

t

h

Figure 7.4 Schematic diagram for Problem 7.2

(Answer: 4.7 min)

7.3 a) A stream containing 10% species A by weight starts to flow at a rate of
2 kg/ min into a tank, originally holding 300 kg of pure B. Simultaneously, a valve
at the bottom of the tank is opened and the tank contents are also withdrawn at a
rate of 2 kg/ min. Considering perfect mixing within the tank, determine the time
required for the exit stream to contain 5% species A by weight.
b) Consider the problem in part (a). As a result of the malfunctioning of the exit
valve, tank contents are withdrawn at a rate of 2.5 kg/ min instead of 2 kg/ min.
How long does it take for the exit stream to contain 5% species A in this case?
(Answer: a) 104 min b) 95.5 min)

7.4 The following levels were measured for the flow system shown in Figure 7.5.
The cross-sectional area of each tank is 1.5 m2.

0 50 30
1 58 35
2 67 40
3 74 46
4 82 51
5 89 58
6 96 64

a) Determine the value of &in.
b) If the flow rate of the stream leaving the first tank, &, is given as

e=PA
determine the value of p.