Volume flow Measurements
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Transcript of Volume flow Measurements
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Volume Flow MeasurementsVolume Flow Measurements
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Obstruction MetersObstruction Meters
Orifice Meters
Venturi Meters
Flow Nozzles
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Flow through a NozzleFlow through a Nozzle
2211
21
222111
21
vAvA
ibleincompressvAvA
Avmmm
==
=
==
1
1
1
1
v
A
m
2
2
2
2
v
A
m
Basic Equations:
a.) Continuity:
mass in = mass out
b.) Bernoullis Eqn.
Total pressure is
constant throughout
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pressuredynamicv
2
1
pressuretotalPpressurestaticP
PPv2
1Pv
2
1
Pv2
1
.constessurePrTotalPBernoulli
2
0
02
2
221
2
11
2
0
=
==
=+=+
+=
==
Flow through a NozzleFlow through a Nozzle
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=
==
=
P2
A
A1
1YCAQ
FlowalReFor
IdealP2
A
A1
1AvAQ
RateFlow
P2
A
A1
1v
2
1
2
2
2
1
2
222
2
1
2
2
Flow through a NozzleFlow through a Nozzle
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P21
2
1
22
2
2
2
2
1
21
2
22
2
11
2
2221
12
1
2
1
2
1
2
1
2
1
=
=
=
==
when
A
Av
vA
Av
vvPPP
Flow through a NozzleFlow through a Nozzle
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Y = Compressibility Factor
=1 for incompressible flow
or when P
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Flow through a Venturi MeterFlow through a Venturi Meter
In a venturi, 0.95 < C < 0.98
Advantage:
Pressure recovery
Uses little power
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Flow through a Venturi MeterFlow through a Venturi Meter
C
Re
2 x 105
= 11
vd
e
R
0.98
Based upon the conditions in the pipe
approaching the meter
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Back to the NozzleBack to the NozzleP1 P2
P
P1
P2
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Shorter and cheaper than venturi
But larger pressure drop.
Thus, more power lost in operating.
The Nozzle FlowmeterThe Nozzle Flowmeter
C
0.86
0.98
103105
Re
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Flow Through an OrificeFlow Through an Orifice
MeterMeter
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Flow Through an OrificeFlow Through an Orifice
MeterMeterP
1P
2
P
P1
d D
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Flow Through an OrificeFlow Through an Orifice
MeterMeter
-Cheapest and Simplest-But biggest pressure drop and power lost (C~0.6 - 0.7)
-Side Note:
Pressure drop caused by friction and turbulence of shear
layer downstream of vena contracta
CM
A
A
C =
2
1
21
1
0.6
0.85
=d/D0.1 0.8
Re
100k
5000
10k
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Elbow Flowmeter
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Laminar
Flowmeter
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Pitot-Static TubesPitot-Static Tubes
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Rotameter, variable-area-Rotameter, variable-area-
flowmeterflowmeter
Force balanceDrag Force
Gravity
Buoyancy
(usually negligible)
cal
usecaluse mm
=
Derived on next
slide
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D
MgA
D
MgAm
D
MgV
MgV
DF
VAm
2
2
22
2
2
==
=
==
=
For a fixed x-position, A is fixed. Then
cal
use
caluse
caluse
mm
mm
=
=
Rotameter
Equations
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Turbine Flow MetersTurbine Flow Meters
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Vortex meters operate on the principle that when a non-streamlined
object is placed in the middle of a flow stream, vortices are shed
alternately downstream of the object. The frequency of the vortex
shedding is directly proportional to the velocity of the liquidflowing in the pipeline.
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Magnetic flowmeterMagnetic flowmeter
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Based upon Faradays Law
The fluid is the conductor, must be electrically conductive.
E=BDVx10-8
E=voltage, volts
B=magnetic flux density, gauss
D= length of the conductor, cm
V=velocity of the conductor, cm/sec
Magnetic flowmeterMagnetic flowmeter
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Magnetic Flow
Meter
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Coriolis Mass Flow MeterCoriolis Mass Flow Meter
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Coriolis Mass Flow MeterCoriolis Mass Flow Meter
Vibrating Flow TubeFluid Force is Reacting to Vibration
of Flow Tube
End View of Flow Tube
Showing Twist
Twist Angle
Twist Angle
Flow
Force
Flow Force
Flow
Flow
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Coriolis Mass Flow MeterCoriolis Mass Flow Meter
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Positive
Displacement
Meters
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