Page 130 - Chemical Process Equipment - Selection and Design

102 FLOW OF FLUIDS

EXAMPLE 6.7-(continued) 0.02517(0.02068)( low)( 1.2707)’ = 82.08 ft.
E = 0.00015 ft, hf14 = hf24 = hf34 = (0.4)’
h - sfLeZ = 0.0251fLQ’/D5 ft, Velocity head at discharge:
-g,x D
hfl = hfl = h0,

Total head at pumps:

+ 0.88 + 82.08 + 88.65
= 345.36ft.
1.6364 Power
= [ln(2.03(10W5)/D + 6.5/NR,]* ’
= YQ&
For line 45, 0.92(62.4)(10/3)345.36
= 66,088 ft lb/sec
(NRJ4 = 31542 (3.333) = 105,140, 120.2 HP, 89.6 kW.
f4 = 0.01881,
0.02517(0.01881)(4000)(3.333)’ = 88. 65 ft.
(hf )45 = (0.75)5
Procedure:
1. As a first trial assume f, =fi = f3, and find Q, = 1.266 from Eq.
(8).
2. Find Q, and Q3 from Eqs. (6) and (7).
3. With these values of the Qz, find improved values of the and
hence improved values of Q, and Q3 froq Eqs. (6) and (7).
4. Check how closely Q, + Q2 + Q3 - 3.333 = 0.
5. If check is not close enough, adjust the value of Q, and repeat
the calculations.

The two trials shown following prove to be adequate.
Q, 02 Q, Q, 10/3-0, f, - . - . . - .
138 Q2=1.2352*Ql*(Fl,F22^.5 ! im
1.2660 1.5757 0.4739 3.3156 0.0023 0.02069 Proved value
1.2707 1.5554 0.5073 3.3334 0.0001 0.02068 148 Q3=.3977SQl*(Fl,F3>’.5 ! imp
roved value
Summary : 158 X=l8~-3-Ql-Q2-Q3 ! should he
less than 8.9881
Line A$,e f Q h, 168 DISF X,QliQ2,Q3
14 75,152 0.02068 1.2707 82.08 178 GOT# 48 ! choose another Val
24 60,121 0.02106 1.5554 82.08 ue of 121 if condition of ste
34 99,821 0.02053 0.5073 82.08 P lS8 is not 5atisfierj
45 105,140 0.01881 3.3333 88.65 188 END.

EXAMPLE 6.8 Characteristics of the alternate pump drives are:
Economic Optimum Pipe Size for Pumping Hot Oil with a a. Turbines are 3600rpm, exhaust pressure is 0.75bar, inlet
Motor or Turbine Drive
A centrifugal pump and its spare handle 1000gpm of an oil at pressure is 20 bar, turbine efficiency is 45%. Value of the high
500°F. Its specific gravity is 0.81 and its viscosity is 3.0cP. The pressure steam is $5.25/10001bs; that of the exhaust is
length of the line is 600 ft and its equivalent length with valves and $0.75/1000 lbs.
other fittings is 900 ft. There are 12 gate valves, two check valves, b. Motors have efficiency of 90%, cost of electricity is $0.065/kWh.
and one control valve. Cost data are:
Suction pressure at the pumps is atmospheric; the pump head
exclusive of line friction is 120 psi. Pump efficiency is 71%. Material 1. Installed cost of pipe is 7.50 $/ft and that of valves is 600D0.7 $
of construction of line and pumps is 316 SS. Operation is 8000 hr/yr. each, where D is the nominal pipe size in inches.