Page 409 - Civil Engineering Formulas

336 CHAPTER TWELVE

ECONOMICAL SIZING OF
DISTRIBUTION PIPING

An equation for the most economical pipe diameter for a distribution system for
water is
fbQ a S 1/7
3
D 0.215 (12.138)
aiH a
where D pipe diameter, ft (m)
f Darcy–Weisbach friction factor
b value of power, $/hp per year ($/kW per year)
3
3
Q average discharge, ft /s (m /s)
a
2
S allowable unit stress in pipe, lb/in (MPa)
a in-place cost of pipe, $/lb ($/kg)
i yearly fixed charges for pipeline (expressed as a fraction of total
capital cost)
H average head on pipe, ft (m)
a
VENTURI METER FLOW COMPUTATION
Flow through a venturi meter (Fig. 12.27) is given by
2
Q cKd 2 2 h 1 h 2 (12.139)
4 2g
K (12.140)

B1 (d 2 d 1 ) 2

h – h 2
1
Main section
Throat
21° 5°–7°

5 Throat connection
4
Main connection 3 Flow-rate scale
2
1

FIGURE 12.27 Standard venturi meter.