E1C10 09/14/2010
13:4:38 Page 434
0.2
0.4
0.6
0.8
15°
7°
Venturi
Flow nozzle
Square-edged orifice
= 0.436 – 0.86 + 0.59
2
= 0.218 – 0.42 + 0.38
2
(Δp) loss
Δp
1.0
0
20
40
60
80
100
Overall pressure loss, (Δp)
loss
(% of pressure differential)
β
β
β
β
β
= 1 + 0.014 – 2.06
2 + 1.18β
3 (nozzle)
β
β
(orifice)
≈
=
1 –
(1 – C
2 )
4
1 –
1.9
–
(1 – C
2 ) +
C
2
1 –
4
C
2
(Δ p) loss
Δ p
Figure 10.7 The permanent
pressure loss associated with
flow through common obstruction meters. (Courtesy of
American Society of Mechanical Engineers, New York, NY;
compiled and reprinted from
reference 1.)
x
0
( p) loss
Relative pressure drop
Cylindrical
inlet
Convergent
entrance
Divergent
outlet
Throat
7° or 15°
d 0
d 1
p 1
p 2
21°
d 1
Figure 10.8 The Herschel venturi meter with the associated flow pressure drop along its axis.
434 Chapter 10 Flow Measurements