Page 486 - Chemical process engineering design and economics

Design of Flow Systems 463

Velocity Head

We showed that the velocity head in the feed tank is negligible. The velocity head
in the boiler will also be negligible. We will not repeat the calculation for the
boiler.

Pressure Head

32.2 49.7
gcp 2
H P2 = ——— = ——— ——— 144 = 114.9 ft (35.0 m)
g p 32.2 62.3

Friction Head

E 1.5 xlO" 1
• = 5.886x10" 4
D 0.2557

62.3 (4.338) (0.2557)
Re = ———————————— = 1.047xl0 5
6.60x10""

From Figure 8.16, 4f= 0.205. The computations for friction head on the discharge
side of the pump, H FD, are completed in Table 8.4.1.

Valve Pressure Drop
So far, the frictional head does not include the frictional pressure drop across the
control valve. To insure good process control, the designer specifies the pressure
drop across the valve. The pressure drop should be about 33% of the frictional
pressure drop for a linear valve.

(AH) V
———————— = 0.33
(AH) F' + (AH) V

where (AH)' is the frictional pressure drop in the flow system, excluding the fric-
F
tional pressure drop across the control valve. Now, convert the 5 psi drop across
the heat exchanger to head.

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