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Unformatted text preview: s linearly proportional to the pressure drop.
(Courtesy of Martin Girard, DH
Instruments, Inc.)  eText Main Menu Pressureequalization chamber  Textbook Table of Contents  Study Guide 6.10 Fluid Meters 397 times. Careful calibration is thus necessary. In Fig. 6.37 the laminarflow concept has
been synthesized into a complete massflow system, with temperature control, differential pressure measurement, and a microprocessor all selfcontained. The accuracy of
this device is rated at 0.2 percent. Bernoulli obstruction theory. Consider the generalized flow obstruction shown in Fig.
6.38. The flow in the basic duct of diameter D is forced through an obstruction of
diameter d; the ratio of the device is a key parameter
d
D (6.122) After leaving the obstruction, the flow may neck down even more through a vena contracta of diameter D2 d, as shown. Apply the Bernoulli and continuity equations for
incompressible steady frictionless flow to estimate the pressure change:
Continuity: Q Bernoulli: 4 p0 p1 D2V1 1
2 2
V1 2
D2V2 4
p2 2
V2 1
2 Horizontal
EGL Moody
loss p1 – p2
HGL
Nonrecoverable
head loss Vena contracta D2
D V1 d = βD V2 ≈ V1 2 ()
D
D2 Dividing
streamline  v v Fig. 6.38 Velocity and pressure
change through a generalized
Bernoulli obstruction meter.  eText Main Menu Deadwater
region  Textbook Table of Contents  Study Guide Chapter 6 Viscous Flow in Ducts Eliminat...
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 Spring '08
 Sakar

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