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182 Chapter 4

UocU 0 3077(553.5)
From Equation 4.7.9, the required fouling resistance for the condenser,

4
4
4
2
5
2
= Rfi +R fo = 2.5xlO" + 1.0xlO- = 3.5xlO- m -K/W(6.16xlO~ h-ft -°F/Btu)
Therefore,
Thus, the condenser will be adequate for the service. Because the available foul-
ing resistance is greater than the required fouling resistance, the condenser will last
longer than the specified time before cleaning.

Table 4.7 Summary of Equations for Rating a Heat Exchanger ______

First subscript: Process stream = 1,2,3 or 4
Second subscript: Component =1 or 2

Mass Balance

m 3 '=m4 (4.7.1)

Energy Equation

Q = h 3, 2m3'-h4, 2m (4.7.2)

Rate Equation

(4.7.3)
Q = U 0 A 0 F(At) LM
F = f(tj', , t 3', t 4') — Equation 4.10 (4.7.4)
t 2
(At) LM = f(ti', t 2, t 3', V) — Equation 4.2 (4.7.5)

Economic Relations

1 3' - 1 2 = approach At — Table 4.5 (4.7.6)

Thermodynamic Properties

h 3j2 = f(t 3') (4.7.7)

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