Question 2
Consider the following cascade of heat exchangers,
100°F
T$_1$
T$_2$
500°F
Hex 1
Hex 2
Hex 3
300°F
400°F
600°F
T$_5$
T$_4$
T$_3$
Find the minimum total surface area of the three heat exchangers.
Data: mc$_p$ = 1000 (Btu h$^{-1}$ F$^{-1}$) (all streams)
Exchanger
U (Btu h$^{-1}$ ft$^{-2}$ F$^{-1}$)
Area (ft$^2$)
Duty (Btu h$^{-1}$)
1
120
A$_1$
Q$_1$
2
80
A$_2$
Q$_2$
3
40
A$_3$
Q$_3$
Marking criteria
- Formulate the optimisation problem (equations and words, justifying use of
equations)
- Show spreadsheet implementation - professionally constructed, logical input output
structure, results clearly demonstrated.
- Discussion and quantification of any uncertainty associated with the result.