Variables, M:
1. Duty, heat transferred, Q
2. Exchanger area, A
3. Overall coefficient, U
4. Hot-side flow-rate, W1
5. Cold-side flow-rate, W2
6. Hot-side inlet temperature, T1
7. Hot-side outlet temperature, T2
8. Cold-side inlet temperature, t1
9. Cold-side outlet temperature, t2
Total variables = 9
Design relationships, N:
1. General equation for heat transfer across a surface
Q = UAΔTm (Equation 12.1)
Where ΔTm is the LMTD given by equation (12.4)
2. Hot stream heat capacity
)
211 TTCWQ p
=
3. Cold stream heat capacity
)
122 ttCWQ p
4. U is a function of the stream flow-rates and temperatures (see Chapter 12)
Total design relationships = 4
So, degrees of freedom = M – N = 9 – 4 = 5
Problem 1.3
Number of components, C = 3
Degrees of freedom for a process stream = C + 2 (see Page 17)
Variables:
Streams 4(C + 2)
Separator pressure 1
Separator temperature 1
Total 4C + 10