Ultrasonics Flow Measurement

Theory: Terms & DefinitionsTheory: Terms & Definitions

ULTRASOUND

Frequency (f ):

Subsonic 0 to 20 Hz

Audio 20 Hz to 20 kHz

Ultrasonic >20 kHz

f cyclessecond

=

λ proportional to 1f

λ


ULTRASOUND

Materials (different materials support different frequencies):

Solids 1 MHz to 100 MHz

Liquids .25 MHz to 5 MHz

Gases 20 kHz to 200 kHzFr

eque

ncy,

f

Density, ρ


SPEED OF SOUND (c)

How Fast a Sound Wave Moves Through a Given Medium

Property of a Material

c = f (Temperature)

c ≠ f (Frequency)

Gases

H2OLiquids

Temperature, °C

c

74

Density, ρ

c

Speed of Sound Examples:

SS = 6500 m/s

H2O = 1500 m/s

Air = 330 m/s

@ 25°C


Atte

nuat

ion

Distance

f (material)ATTENUATION

Reduction in Amplitude of the Ultrasonic Signal• Dissipation

• Reflection

• Absorption

ATTEN = 1/GAIN

How Loud? More Attenuative

Less Attenuative

MOLECULAR LEVEL


TRANSDUCER

Electrical Energy Mechanical Energy

Mechanical Energy Electrical Energy

Piezoelectric Effect

Transducer is Both Transmitter and Receiver

V V V

V V V

TRANSMIT

RECEIVE:

Theory: Doppler TechniqueTheory: Doppler Technique

DOPPLER PRINCIPLE

When sound of a given frequency reflects off a moving object, the reflected frequency is shifted in proportion to the velocity of the moving object.

XMITRCV

V

θ

Theory: Doppler TechniqueTheory: Doppler Technique

PROBLEMS

Scatterer Size

Scatterer Reflectability

Scatterer Velocity ≠Fluid Velocity

Clean Fluids

~10% Accuracy

V = (F F ) c2F COS

T R

T

−θ

V = Scatterer Velocity

FT = Transmitted Frequency

FR = Received Frequency

θ = Angle of Sound Beamwith Respect to Flow Axis

c = Sound Speed of the Fluid

Theory: Transit Time TechniqueTheory: Transit Time Technique

Transducer is Both Transmitter and Receiver

Ultrasonic Pulses

Transit Times

Upstream direction, tup

Downstream direction, tdn

tup = Ultrasound is Decelerated by Flow

tdn = Ultrasound is Accelerated by Flow

Analogous to a Flowing River

t t

t t t

V f( t)

Q V A

up dn

up dn

>

= −

=

= ×

∆

∆

UP

DOWN

V


V = Fluid Velocityc = Fluid Sound Speedtup = Transit Time in the

Upstream Directiontdn = Transit time in the

Downstream Direction∆ t = Transit Time DifferenceP = Acoustic Path Through FluidL = Axially Projected Path

Through Fluidθ = Path Angle

DN

UP

V

LPθ


NO FLOW

DISTANCE RATE TIME

TIME DISTANCERATE

= ×

=

t Pc

t Pc

t t t 0

up

dn

up dn

=

=

= − =∆

WITH FLOW

t Pc -Vsin

t Pc+ Vsin

t t t

up

dn

up dn

=

=

= −

θ

θ

∆

V

V

θθ

θθ

c

c

DN

UP

Vθ

LP

Theory: Transit Time TechniqueTheory: Transit Time Technique 1

t c - sin

P 1

t c + Vsin

P

t t

t

c + VsinP

- c - VsinP

t

t = 2Vsin

P

V Psin

t

t

.

Since sin LP

.

V PL

t

t

.

up dn

dn up

up dn

dn up

dn up

= =

= − =

−

= −

=

= −

θ θ

θ θ

θ

&

∆1 1

1 1

21 1

21 12

θ

θ

Theory: Transit Time TechniqueTheory: Transit Time TechniqueVELOCITY

V P2L

t tt t

2 up dn

dn up=

−

×

SOUND SPEED

tt t

2

c = Pt

avg = dn up

avg

+

Q = Velocity × Cross-Sectional Area

Q = V × A

VOLUMETRIC


CLAMP-ON

Refraction

Snell’s Law

Built-In Correction for Liquid Property Changes

csin

csin

csin

1

1

2

2

3

3θ θ θ= =

c1

θ1c2θ2

θ3c3

L

S

W.T.

c1 = Wedge Sound Speedc2 = Wall Sound Speedc3 = Fluid Sound SpeedS = Transducer Spacing

Theory: Fluid DynamicsTheory: Fluid Dynamics

FLOW PROFILEThe Shape of the Flow Due to Friction and Viscous Forces in the Pipe

REYNOLDS #The Measure of the Shape of the Flow Profile

Re = Reynolds #

V = Fluid velocity

ID = Pipe ID

ν = Kinematic viscosity

(ft2/sec or m2/sec)

Re =×V IDν

ν absolute viscosityfluid density

=


FLOW PROFILE REGIONSLaminar:

• Stratified, parabolic profileRe = 0 to 2000

Transitional:

• Undefined profileRe = 2000 to 4000

Turbulent:

• Flattened profileRe = >4000


FLOW PROFILE FACTOR (kRe)

Diametrical Interrogations

Theoretical Correction Factor

Based on Re

Nikuratze’s Equation

V = kRe × Velocity

Ranges:

laminar = 0.75transitional ≈ 0.85turbulent = 0.91 - 0.99

NOTE: A 10:1 change in v results in <1% change in flow.

Example: V = 5 ft/sec and ID = 6”v = 10×10-6 v = 100×10-6

Re = 250,000 Re = 25,000kRe = 0.944 kRe = 0.934

k = 11.119 0.011 log ReRe −

Theory: Fluid DynamicsTheory: Fluid DynamicsSTRAIGHT-RUN REQUIREMENTS

Fully Developed Flow Profile

10 Upstream/5 Downstream dia.

Disturbances

• bends

• valves

• wells

• tees

• insertions

10∅ 5∅


STRAIGHT-RUN REQUIREMENTSHorizontal Flowing Up

Vertical Flowing Up

What if I Don’t Have 15 Diameters?• 2/3 up, 1/3 down• multipath• flow straighteners• accuracy cannot

be quantified• repeatability

10∅ 5∅

Liquid Flow: DiagnosticsLiquid Flow: Diagnostics

SIGNAL STRENGTH (SSup, SSdn)

Amplitude of the Received Signals


SOUND SPEED (SNDSP)

Measured “c”

Independent of Programmed “c”

“The More Accurate the Measured Sound Speed Value, the More Accurate the Flow Reading”

Tables In Manuals

c Pt

tT T

2

avg

avgup dn

=

=+


SIGNAL QUALITY (Qup, Qdn)

Shape of Received Signal

Coded Transmits

Q > |300|

Pipes < 4”, Q > |180|

• 4-Bit Code

TRANSMIT

RECEIVE


SIGNAL PEAKS (Pup, Pdn)

Window Position

Programmed “c”

“500,” Centered Signal

<100, No Signal

>900, No Signal

Tracking Window10000

t = P/c

Liquid Flow: Signal ProcessingLiquid Flow: Signal Processing

“WINDOW POSITIONING”

Based on Programmed Sound Speed

• Time =

• +20%

Reduces ProcessorTime

Avoids Short Circuit

DistanceRate

“c”

t = 0

TRANSMITCODEDSIGNAL

SHORTCIRCUIT

RECEIVED SIGNAL

“c”

WINDOW


CODED SIGNALS

BAD CORRELATION

GOOD CORRELATION

≈∆t

tdn

tup

CORRELATION

Signal Quality


∆t MEASUREMENT

Cross Correlation

More Accurate

1 Nanosecond Resolution

CORRELATION tdn

CORRELATION tup

∆t

Liquid Flow: Application Liquid Flow: Application ConsiderationsConsiderations

FULL PIPES ONLY

Accuracy

Signal Loss

Q = V × A


Bubbles to top

ENDVIEW

TOPVIEW

Sediment to bottom

L

L/2

SINGLE PHASE OR MULTIPHASE

Mount the Transducers on the Sides of the Pipe

3 O’Clock / 9 O’ClockPosition

Single vs Double Traverse

Transducer Frequency


PIPE CONDITION

Clean Outside Surface!

• Rust/PaintCouplant

• Good contactInside Build Up

• Attenuation• Transducer frequency• Accuracy

Single vs. Double Traverse

VS IDID


PIPE SIZE

Overall Range: 1/2” to 200” (12 mm to 5 m)

Transducer Selection• 1/2” to 2” • 2” to 200”

Clamping Fixture Selection

Transducer Frequency

• 0.5 MHz for large pipes


PIPE MATERIAL

Metals• Carbon Steel• Stainless Steel• Copper• Aluminum • Cast Iron• Brass• Ductile Iron

WT

c2


PIPE MATERIALPlastics• PVC• Polypropylene• Polyethylene• CPVC• PVDF• Nylon• Acryllic

WT

c2


PIPE MATERIAL

Wall Thickness

Sound Speed (C2)

Liners

Concrete No Clamp-On

WT

c2


VELOCITY EXPECTED

Good: V > 1.0 ft/s (0.3 m/s)

Minimum Detectable Velocity

• V = 0.1 ft/s (0.03 m/s)• Accuracy

Maximum: V < 40 ft/s (12m/s)

Resolution of ∆t

• Higher velocity = more ∆t

Slide Rule

EQUATIONSArea =

Q = V × A

USEFUL CONVERSIONS

1 Gallon = 0.13368 ft3

1 Barrel = 42 gallons

1 Liter = 0.001 m3

π ID2

2


vsTEMPERATURE

Transducer Type

Clamp-On

•Couplant type•Couplantmaintenance

vs


PIPING ORIENTATION

Horizontal = Good

Vertical Flowing Up = Good• Ensures full pipe

Vertical Flowing Down = Less Desirable


STRAIGHT-RUN REQUIREMENTSFully Developed Flow Profile10 Upstream/5 Downstream DiameterDisturbances

• Bends

• Valves

• Wells

• Tees

• Insertions

10∅ 5∅


STRAIGHT-RUN REQUIREMENTSHorizontal/Vertical Flowing Up

What If I Don’t Have 15 Diameters?

• 2/3 up, 1/3 down

• Multipath

• Flow straighteners

• Accuracy cannot be quantified

• Repeatability

10∅ 5∅


VISCOSITY

Maximum ~300 centistokes

Attenuation

Low Reynolds Number

Atte

nuat

ion

Viscosity300

less

more

Liquid Systems: ComponentsLiquid Systems: Components

Electronics

CouplantClampingFixture

Cable

Transducers

CLAMP-ONElectronics

• Portable

• Dedicated

• Transmitter

Transducers

Clamping Fixture

Cable

Couplant

Liquid Systems: ClampLiquid Systems: Clamp--on on TransducersTransducers

TRANSDUCER #

Liquid Systems: ClampLiquid Systems: Clamp--on on TransducersTransducers

SMALL PIPES

ADJUSTABLE FIXED

VELCRO/SSSTRAPS

Liquid Systems: Clamping FixturesLiquid Systems: Clamping Fixtures

SINGLETRAVERSE

DOUBLETRAVERSE

LARGER PIPES


BLOCK STYLE (CF-BL)

Permanent Installations

Stainless Steel Straps

“Hose Clamp” Tightening Mechanism

Must Specify Pipe Size


DOUBLE TRAVERSE

SINGLE TRAVERSE

MAGNETIC (MC)

Cabon Steel Pipes ONLY!

Liquid Systems: ComponentsLiquid Systems: Components

CABLE

TRANSDUCERS

FLOWCELL

ELECTRONICS

WETTED

Flowcell

• Spoolpiece• Pipe couplings• Saddles

Cable

Liquid Systems:Wetted Liquid Systems:Wetted TransducersTransducers

STANDARD VERSION

1” NPT

Liquid Systems:Wetted Liquid Systems:Wetted TransducersTransducers

EXTENDED WELL DESIGN

Liquid Systems: TransducersLiquid Systems: Transducers

ADAPTER

Hybrid System• Removal of transducers

NOTE: WT-1/P TRANSDUCERS WITHOUT EXTENDED WELL ARE USED

Liquid Systems: Liquid Systems: FlowcellsFlowcells

SPOOL PIECES

Process Connection• Plain ends (welding)

• Flanged ends

Transducer Connection• 1” NPT

• Socket weld/Panadapta

PLAIN END

FLANGED END


PIPE COUPLINGS (PC)Weld Distortion

Pipe Coupling Kit• Single traverse

1" NPT

WELDS = OD

WELD


SADDLESWelding Not Possible• Ductile iron

• Cast iron

• Concrete

1” NPT

Liquid FlowmeterLiquid Flowmeter

REASONS FOR USING ULTRASONICWide Range of Pipe Sizes, 1/2” to 200”

Turn-Down Ratio

Pressure Drop

Bi-Directional Flow

Maintenance

No Moving Parts

“Clamp-On” Independent of Pipe Size (Cost)


REASONS FOR USING ULTRASONIC

Corrosive Fluids

High-Temperature Fluids

Radioactive Fluids

Purity

Multichannel Capability

Cost of Installation

Liquid FlowmeterLiquid FlowmeterTYPICAL APPLICATIONS

AcidsCorrosive, Erosive& Toxic LiquidsChemicalsCryogenics• LPG• LNG• Argon

Petroleum Products

• Benzene Propane

• Ethylene Crude Oil

• Solvents Fuels

• Lube Oil Xylene

Water

Waste Water

Seawater


TYPICAL USESBalancing Systems

Batching

Billing/Accounting

Check Metering

Heating/Cooling

Efficiency Studies

Flow Surveys

Leak/Rupture Detection

Process Control

Large/Small Pipes


INDUSTRYPetrochemical

• Refining• Chemical processing• Process control

Power

• Fossil fuel• Nuclear• Hydroelectric

Food & Beverage

Energy Management• Hot water• Chilled water

Manufacturing

Medical


INDUSTRY

Pharmaceutical

Pulp & Paper

Semiconductor Manufacturing• Ultra-pure liquids

• Deionized water

Sewage Treatment

Water & Waste Water Management

Aerospace

Agriculture

Gas Flow MeasurementGas Flow Measurement

DIFFERENCES FROM LIQUID

No Clamp-On!

Slower Sound speeds

• Longer transit times

Greater Attenuation

• Lower frequencies

• 30 to 500 kHz

UP

DOWN

V

Gas Flow MeasurementGas Flow MeasurementEQUATIONS

Standard Flow• Gases are compressible• Pressure• Temperature

Standard Conditions• Base pressure = 1 atm (14.7 psia)• Base temperature = 20 C → 293 K

= 68 F → 528RVelocity• Calculate VACT

*The velocity the transducers are exposed to.

Q Q PP

TT

Q V AREA

STD ACTf

b

b

f

ACT ACT

= × ×

= ×

→

NOTE: MUST USE ABSOLUTE PRESSURE & TEMPERATURES IN CALCULATIONS.

Gas Flow MeasurementGas Flow Measurement

EQUATIONS

Mass Flow• kg/hr

• lb/hr

Density• Constant

• Derived MW

M = Mass Flow

V = Actual Velocity

A = Cross-Sectional Area

ρ = Density

P = Pressure (Absolute)

T = Temperature (Absolute)

R = Universal Gas Constant

MW = Molecular Weight

ρ P ( M W )R (T)

=

.M VA= ρ.

Short-Circuit Signal

Some sound energy

shears off through the surface of the pipe

Emitting Transducer

Receiving Transducer

The short-circuit signal travels very quickly to the receiving transducer since it is traveling through a solid – the pipe wall

The sound refracts

through the pipe wall

Emitting Transducer


The sound travels

through the gas

Emitting Transducer


The sound refracts through the other

wall

…and is received by

the downstream transducer

Emitting Transducer


The correct receive signal is the one that travels through the flow – not through the pipe wall

Emitting Transducer

When the sound hits the inside pipe wall, a lot of the signal reflects back into the pipe

This is due mainly to the mismatch in soundspeedsfor the solid wall versus the gas flowing in the pipe

Steel Pipe

Emitting Transducer

The amount of sound strength energy traveling through the gas is only 0.007%0.007% of what was transmitted

Steel Pipe

Emitting Transducer

There is another reflection point when the sound hits the other side of the pipe’s inside wall

Steel Pipe

Emitting Transducer

Here, again, a lot of the signal strength is lost

Steel Pipe

Emitting Transducer

The remaining sound energy that gets to the receiving transducer is only 0.00000049%0.00000049% of that transmitted!

Steel Pipe

t0

POOR SNR (SIGNAL TO NOISE RATIO)

MAKES SIGNAL DETECTION TOO DIFFICULT

New InnovationsNew InnovationsPrimary Innovation

New Transducer Technology :

• SNR

• Increase Signal

• Reduce Noise

New InnovationsNew Innovations

t0

REDUCE NOISE INCREASE SIGNAL

New Innovations: More SignalNew Innovations: More SignalPrimary Innovation

New Transducer Technology : • More signal output with

same applied excitation voltage.

• 5-10x More Signal Amplitude than traditional xducers

• Low Mode Conversion• Highly Efficient

Think of transducer as ‘turbo-charged’

New Innovations: More SignalNew Innovations: More SignalPrimary Innovation

New Transducer Technology :

• Cleaner Signal Shape

• Less Ringing

• Less Prone to Cycle Skipping

• Larger Receive Area

New Innovations: More SignalNew Innovations: More SignalInnovation

More Attention Paid to Alignment

• Clamping Fixture System–Axially–Circumference

• Less Attenuation

• Precise Installation

New Innovations: Less NoiseNew Innovations: Less NoiseInnovation

Less Noise

Short Circuit Dampening

• Dampening Material

• Attenuates Surface Waves

• Attenuates Short Circuit

Application Considerations

Straight RunMinimum requirements:

• 20D upstream• 10D downstream• More is Better

20∅ 10∅

Application ConsiderationsApplication Considerations

FLOW

-1.0 -0.8 -0.6 -0.4 -0.2 -0.0 0.2 0.4 0.6 0.8 1.0

Normalized Horizontal Position (X)

-1.0

-0.8

-0.6

-0.4

-0.2

-0.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ized

Ver

tical

Pos

ition

(Y)

0.900

0.9

28

0.956

0.956

0.9

83

0.983

0.983

0.983

1.011

1.039

-1.0 -0.8 -0.6 -0.4 -0.2 -0.0 0.2 0.4 0.6 0.8 1.0

Normalized Horizontal Position (X)

-1.0

-0.8

-0.6

-0.4

-0.2

-0.0

0.2

0.4

0.6

0.8

1.0

Nor

mal

ized

Ver

tical

Pos

ition

(Y)

0.900

0.900

0.900

0.9

00 0

.928

0.956

0.983

1.011

1.039

1.06

7

1.094 1.122 10D100D

Application Considerations

Straight RunThe more straight run, the better!

This is a VERY GOOD

installation

Presentation Facilitated by

Insertech (Caribbean) Limited in conjunction with Panametrics

Ultrasonics Flow Measurement

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