Page 482 - Chemical process engineering design and economics

Design of Flow Systems 459

Thus, the actual liquid velocity,

gal 1 ft 3 1 min 1
v = 100 —— ————— ——— —————— = 2.520 ft/s (0.768 m/s)
min 7.481 gal 60 s 0.08842ft 2

Velocity Head

The velocity head is usually negligible. This is shown in the following calculation.

2
2
A = TI D /4 = (3.142 / 4) (10.0) = 78.55 ft 2
The velocity in the feed tank is given by

gal 1 ft 3 1 min 1
3
v = 100 —— ————— ———— ———— = 2.836xlO~ ft/s (8.64x10-" m/s)
min 7.481 gal 60 s 78.55ft 2

If the flow in the feed tank is laminar, then a = 1A, but if the flow is turbulent,
then a « 1. Next, calculate the Reynolds number.

pvD
Dp = ____
JXt

lb M lb M
4
u = 0.982 cp (6.72X10" ) ——— = 6.60x10^ —— (9.82x10"" Pa-s)
ft-s-cp ft-s
62.3 lb M 2.836xlO~ 3 ft 10.0 ft

1 f t 3 1 s i
Re = ————————————————— = 267.7
6.60x10-" lb M/ft-s

Because the Reynolds number is less than 2100, the flow in the feed tank is
laminar, and a « Y 2.
The velocity head in the feed tank is

3 2
ocv 2 (2.836xlO~ ) fVVs 2
8
8
H v = —— = ——————————— = 6.244xlO~ ft (1.90xlO~ m)
2g 2 (2) (32.2) ft/s 2

Copyright © 2003 by Taylor & Francis Group LLC