Volf Low Measurements

8/18/2019 Volf Low Measurements

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Volume Flow MeasurementsVolume Flow Measurements


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Obstruction MetersObstruction Meters

Orifce Meters

Venturi Meters

Flow Nozzles


3/30

Flow through a NozzleFlow through a Nozzle

2211

21

222111

21

vAvA

ibleincompressvAvA

Avmmm

=ρ=ρ

ρ=ρ

ρ==

1

1

1

1

v

A

mρ

2

2

2

2

v

A

m

ρ

Basic Equations:

a.) Continuity:

mass in = mass out

b.) Bernoulli’s Eqn.

Total pressure is

constant throughout


4/30

pressuredynamicv

2

1

pressuretotalP pressurestaticP

PPv2

1Pv

2

1

Pv2

1

.constessurePr TotalPBernoulli

2

0

02

2

221

2

11

2

0

=ρ

==

=+ρ=+ρ

+ρ=

==



5/30

ρ∆

−

=

ρ∆

−

==

ρ∆

−

=

P2

A

A1

1YCAQ

FlowaleFor

!dealP2

A

A1

1AvAQ

ateFlow

P2

A

A1

1v

2

1

2

2

2

1

2

222

2

1

2

2



6/30

∆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

ρ ρ

ρ

ρ ρ

ρ ρ

=

−=

−=

−=−=∆

when

A

Av

v A

Av

vv P P P



7/30

Y " Compressibility Factor

"1 #or incompressible #low

or w$en ∆P%% Pabs

C" &isc$ar'e Coe##icient

"#(e) and

nature o# speci#ic #low meter

∆P


P


8/30

Flow through a Venturi Meter Flow through a Venturi Meter

!n a venturi* 0.+, % C % 0.+-

Advanta'e

Pressure recovery

/ses little power


9/30

Flow through a Venturi Meter Flow through a Venturi Meter

C

R e

2 10,

µ

ρ= 11

vd

e

0.+-

Based upon t$e conditions in t$e pipe

approac$in' t$e meter


10/30

Back to the NozzleBack to the NozzleP1 P2

P

P1

P2


11/30

$orter and c$eaper t$an venturi

But lar'er pressure drop.

T$us* more power lost in operatin'.

The Nozzle Flowmeter The Nozzle Flowmeter

C

0.-

0.+-

10310,

e


12/30

Flow Through an OrifceFlow Through an Orifce

Meter Meter


13/30


Meter Meter P

1P

2

P

P1

d &


14/30


Meter Meter

4C$eapest and implest4But bi''est pressure drop and power lost (C50. 4 0.6)

4ide 7ote

Pressure drop caused by #riction and turbulence o# s$ear

layer downstream o# vena contracta

CM

A

A

C =

−

2

1

21

1

0.

0.-,

β"d8&0.1 0.-

e

1009

,000

109


15/30

:lbow Flowmeter


16/30

;aminar

Flowmeter


17/30

Pitot-Static TubesPitot-Static Tubes


18/30

Rotameter !ariable-area-Rotameter !ariable-area-

"owmeter "owmeter

Force balance Drag Force

Gravity

Buoyancy

(usually negligible)

cal

usecal use mm

ρ

ρ =

&erived on net

slide


19/30

D

MgA

D

Mg Am

D

Mg V

Mg V

D F

V Am

2

2

22

2

2

ρ ρ

ρ

ρ

ρ

ρ

==

=

==

=

For a #ied 4position* A is #ied. T$en

cal

usecal use

cal use

mm

mm

ρ

ρ

ρ ρ

=

=

otameter

:


20/30

Turbine Flow MetersTurbine Flow Meters


21/30

=orte meters operate on t$e principle t$at w$en a non4streamlined

ob>ect is placed in t$e middle o# a #low stream* vortices are s$ed

alternately downstream o# t$e ob>ect. T$e #re


22/30

Magnetic "owmeter Magnetic "owmeter


23/30

Based upon Faraday’s a!

T$e #luid is t$e conductor* must be electrically conductive.

:"B&=104-

:"volta'e* volts

B"ma'netic #lu density* 'auss

&" len't$ o# t$e conductor* cm

="velocity o# t$e conductor* cm8sec

Magnetic "owmeter Magnetic "owmeter


24/30


25/30

#oriolis Mass Flow Meter #oriolis Mass Flow Meter


26/30


=ibratin' Flow TubeFluid Force is eactin' to =ibration

o# Flow Tube

:nd =iew o# Flow Tube

$owin' Twist

Twist An'le

Twist An'le

Flow

Force

Flow Force

Flow

Flow


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Positive

&isplacement

?eters


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Volf Low Measurements