volume flow measurements. obstruction meters u orifice meters u venturi meters u flow nozzles
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Volume Flow MeasurementsVolume Flow Measurements
Obstruction MetersObstruction Meters Orifice Meters
Venturi Meters
Flow Nozzles
Flow through a NozzleFlow through a Nozzle
2211
21
222111
21
vAvA
ibleincompress
vAvA
Avm
mm
1
1
1
1
v
A
m
2
2
2
2
v
A
m
Basic Equations:
a.) Continuity:
mass in = mass out
b.) Bernoulli’s Eqn.
Total pressure is constant throughout
pressuredynamicv
2
1
pressuretotalP
pressurestaticP
PPv2
1Pv
2
1
Pv2
1
.constessurePrTotalP
Bernoulli
2
0
02
2
221
2
11
2
0
Flow through a NozzleFlow through a Nozzle
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
P21
2
1
222
22
2
1
21
222
211
22221
12
1
2
1
2
1
2
1
2
1
when
A
Av
vA
Av
vvPPP
Flow through a NozzleFlow through a Nozzle
Y = Compressibility Factor
=1 for incompressible flow or when P<< Pabs
C= Discharge Coefficient
=f(Re) and
nature of specific flow meterP
Flow through a NozzleFlow through a Nozzle
P
Flow through a Venturi MeterFlow through a Venturi Meter
In a venturi, 0.95 < C < 0.98
Advantage:
Pressure recovery
Uses little power
Flow through a Venturi MeterFlow through a Venturi Meter
C
Re
2 x 105
11vde
R
0.98
Based upon the conditions in the pipe approaching the meter
Back to the NozzleBack to the NozzleP1 P2
P
P1
P2
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
Flow Through an Orifice Flow Through an Orifice MeterMeter
Flow Through an Orifice Flow Through an Orifice MeterMeter
P1 P2
P
P1
d D
Flow Through an Orifice Flow 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
AC
2
1
21
1
0.6
0.85
=d/D0.1 0.8
Re
100k
5000
10k
Elbow Flowmeter
Laminar Flowmeter
Pitot-Static TubesPitot-Static Tubes
Rotameter, variable-area-Rotameter, variable-area-flowmeterflowmeter
Force balance Drag Force Gravity Buoyancy
(usually negligible)
cal
usecaluse mm
Derived on next slide
D
MgA
D
MgAm
D
MgV
MgV
DF
VAm
2
2
22
2
2
For a fixed x-position, A is fixed. Then
cal
usecaluse
caluse
mm
mm
Rotameter
Equations
Turbine Flow MetersTurbine Flow Meters
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 liquid flowing in the pipeline.
Magnetic flowmeterMagnetic flowmeter
Based upon Faraday’s 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
Magnetic Flow Meter
Coriolis Mass Flow MeterCoriolis Mass Flow Meter
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
Coriolis Mass Flow MeterCoriolis Mass Flow Meter
Positive Displacement Meters