Download - Flow
Level 1 - FlowRMT Training - 05 /98
1Level 1Fundamental TrainingFundamental Training
Level 1 - FlowRMT Training - 05 /98
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Topics: Slide No:• Why measure flow? 3 - 4• Flow terminology 5 - 18• Flowmeter selection 19 - 24• DP flowmeters 25 - 46• Velocity flowmeters 47 - 55• Mass flowmeters 56 - 61• Displacement meters 62• Rosemount flow products summary 63• Exercise 64 - 65
ContentsContents
Level 1 - FlowRMT Training - 05 /98
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Safety• Uncontrolled flow rates may cause
– temperature & pressure to reach dangerously high levels– turbines & other machinery to overspeed– tanks to spill
Custody Transfer• the measurement of fluid passing from a supplier to a customer
– cash register of the system– example a local gas station measures how much gas being pumped into the
vehicle for billing– requires high measurement accuracy
Product Integrity• ensuring right amount of blended materials in for example processed food
& gasoline
Why measure flow?Why measure flow?5 Common Reasons5 Common Reasons
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Efficiency Indication• to determine efficiency of process by
– measuring the amount of each input that has gone into the product
– comparing the above measurement to the amount of product producedl
Process Variable Control• Flow rate is measured & controlled during energy transfer
application, for example– heat exchanger
» fluid temperature controlled by varying the flow rate of steam
Why measure flow?Why measure flow?5 Common Reasons5 Common Reasons
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Flow terminologyFlow terminologyFlow Control LoopFlow Control Loop
I/P FIC
TTFT
• Flow Loop Issues:– May be a Very Fast Process
» “Noise” in Measurement Signal May Require Filtering
» May Require Fast-Responding Equipment
– Typically Requires Temperature Compensation
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• Density: rho) = m/V = mass/volume– Mass per unit volume at given operating conditions.– Common units: kg/m3 or lb/ft3 – Density of a liquid varies with temperature– Density of a gas varies with temperature and pressure
Flow terminologyFlow terminologyFluid PropertiesFluid Properties
Liquids Gases
Temperature = Density Temperature = Density Temperature = Density Temperature = Density
Pressure = No change Pressure = Density Pressure = No change Pressure = Density
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For Liquids,
• Specific Gravity =
For Gases,
• Specific Gravity =
Density of liquid at process temperature
Density of water at 15.6°C
Molecular Weight of gas
Molecular Weight of air
Flow terminologyFlow terminologyFluid PropertiesFluid Properties
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• Gas Compressibility Factor: Z-factorZ-factor– Used to correct gas equations for real-gas effects. Accounts for the deviation from the “ideal” situation.
» For an ideal gas Z=1 and PV=nRT(Ideal Gas Law).» The True Gas Law: PV=ZnRT» Z & n Can be found in engineering tables.» R is dependant on units chosen for P, T & V
PV = nRT
Absolute pressure
Volume
Molecular weight
Universal gas constant
Absolute temperature
Flow terminologyFlow terminologyFluid PropertiesFluid Properties
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• Viscosity– Measure of a fluid’s tendency to resist a shearing force, or to resist flow
» A greater force is required to shear high viscosity fluids than low viscosity fluids (viscosity = shear stress/shear rate).» Viscosity normally decreases with an increase in temperature for a liquid, but increases with an increase in temperature for a gas
Force
FluidThickness
Fixed Plate
Area
•Water is 1cP, peanut butter is 10,000 cP
Flow terminologyFlow terminologyFluid PropertiesFluid Properties
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• Fluid Type
– Clean Fluid
» A fluid that is free from solid particles, e.g. clean water.
– Dirty Fluid
» A fluid containing solid particles, e.g. muddy water.
– Slurry
» A liquid with a suspension of fine solids, e.g. pulp and paper, or oatmeal.
– Steam
» Water vapour
– Gas
» Natural gas
Flow terminologyFlow terminologyFluid PropertiesFluid Properties
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Laminar Flow Turbulent Flow
Transition Flow
Flow terminologyFlow terminologyFluid PropertiesFluid Properties
• Flow Profile
Higher velocity in the middle
Lower velocity at the edge
Lower velocity at the edge
Pipe Wall
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0 2000 4000
TransitionLaminar Turbulent
ReynoldsNumber
(Pipe I.D.) ( Velocity) (Density)Viscosity
Rd = ( x v x D)/
m m/s kg/m3
kg/ms
Flow terminologyFlow terminologyFluid PropertiesFluid Properties
• Reynolds number defines the state of fluid flow– Dimensionless number– Indicates flow profile
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Flow conditions; Velocity = 0.5 m/s
density = 995.7kg/m³
Temperature = 25°C
Viscosity = 0.7cP
Pipe ID = 60mm
(1 Poise = 0.1 kg/m s)
i) Find the Reynolds number for the fluid.
ii) Identify the type of flow.
(a) Laminar
(b) Transitional(c) Turbulent
= 42,673
RD = V.d. /
= 0.5 x 0.06 x 995.7 x 1000 /0.7
= 0.7 / 1000 kg/ms
Flow terminologyFlow terminologyFluid PropertiesFluid Properties
Example:
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• Pressure & Temperature changes inside process pipe determines which state the steam is in– Saturated steam (all vapor)
» Steam exactly at its saturation point (SP) temperature & pressure at which liquid turns to vapor (as pressure increases,
saturation temperature increases)
– Superheated steam» Steam when pressure drop below SP» Steam when temperature rise above SP
e.g. at 350 psia, saturation temperature for water is 222°C.Steam at 350 psia & 278°C includes 56°C of super heat
– Quality steam ( mixture of water liquid & vapor)» Condensed steam when pressure rise above SP» Condensed steam when temperature drop below SP
Flow terminologyFlow terminologyFluid PropertiesFluid Properties
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• Texture of inner walls– smooth wall slightly increase fluid velocity– rough wall slightly decrease fluid velocity
• Inside diameter– e.g., doubling the diameter increase flow rate by as
much as 4 times
» Vol. flow rate(Qv) = Cross-section area * Velocity
= D2/4 * Velocity
= D2(/4 x Velocity)
Flow terminologyFlow terminologyPipe Geometry & ConditionsPipe Geometry & Conditions
Qv = (22D)2 * (/4 x Velocity)Qv = 44 (D2 * (/4 x Velocity))
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• Flow Profile Disturbance– factors that cause flow profile to become irregular
» symmetrical profilecaused by reducers or expanders pipe sectionseliminated by inserting appropriate length of straight pipes
» asymmetrical profilecaused by elbows, valves and teeseliminated by inserting appropriate length of straight pipes
» swirlcaused by pumps, compressors, or two pipe elbows in
different planeseliminated by inserting flow conditioners
Flow terminologyFlow terminologyPipe Geometry & ConditionsPipe Geometry & Conditions
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• Metric Unit - m3/s• Others
StdCuft/s - Standard Cubic feet per second StdCuft/min - Standard Cubic feet per minute StdCuft/h - Standard Cubic feet per hour StdCuft/d - Standard Cubic feet per day StdCum/h - Standard Cubic meter per hour StdCum/d - Standard Cubic meter per day NmlCum/h - Normal Cubic meter per hour NmlCum/d - Normal Cubic meter per day
Volumetric Flow Rate
Std - reference to 14.696 psi Atm. at 68 deg.FNml - reference to 101.325 Atm. At 0 deg.C
Flow terminologyFlow terminologyEngineering UnitsEngineering Units
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Mass Flow Rate• Metric Unit - kg/s• Others
lbs/sec - Pounds per second lbs/min - Pounds per minute lbs/hour - Pounds per hour lbs/day - Pounds per day gram/sec - grams per second grams/min - grams per minute grams/hour - grams per hour kg/min - kilograms per minute kg/hour - kilogram per hour
Flow terminologyFlow terminologyEngineering UnitsEngineering Units
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Flowmeter selectionFlowmeter selectionSpecificationSpecification
• Accuracy– % of rate
» uncertainty of flow proportional to flow rate
– % of full scale» uncertainty of flow remains constant
Rate of Flow % of Rate Accuracy Uncertainty Range100 gpm ±2% of 100 gpm 98-102 gpm50 gpm ±2% of 50 gpm 49-51 gpm20 gpm ±2% of 20 gpm 19.6-20.4 gpm
Rate of Flow % of Rate Accuracy Uncertainty Range100 gpm ±2% of 100 gpm 98-102 gpm50 gpm ±2% of 50 gpm 49-51 gpm20 gpm ±2% of 20 gpm 19.6-20.4 gpm
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Flowmeter selectionFlowmeter selectionSpecificationSpecification
• Rangeability (Turndown)– Meter maximum
» maximum flow rate that a flowmeter is capable of readingcommonly used for magnetic, vortex and Coriolis meters
– Application maximum» maximum flowrate that occurs in the process flow of a
particular applicationcommonly used for orifice plates, flow nozzles, and venturi
tubes
• Repeatability– the ability of a flowmeter to produce the same
measurement each time it measures a flow
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Flow Technologies
Mass Volumetric Head
VelocityMeter
PositiveDisplacement
Meter
Coriolis MeterThermal Meter
DP FlowMeter
TargetMeter
AnnubarOrificeVenturiNozzle
Elbow Taps
MagneticVortex
UltrasonicTurbine
Oval Nutating disc
GearGerotor
Flowmeter selectionFlowmeter selectionClasses of FlowmetersClasses of Flowmeters
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.• Displacement Meters– measure volume flow rate Qv directly by
repeatedly trapping a sample of the fluid. » total volume = sample volume * number of samples
High pressure loss
• Head Meters (DP Flow Meters)– measures fluid flow indirectly by creating &
measuring a differential pressure by means of a restriction to the fluid flow
Flowmeter selectionFlowmeter selectionClasses of FlowmetersClasses of Flowmeters
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A reliable flow measurement is dependent upon the correct measurement of A and v.
• Velocity Meters– FLOW is measured inferentially by measuring
VELOCITY through a known AREA.» With this indirect method, the flow measured is the
volume flow rate, Qv. Stated in its simplest term
» QV = A * v whereA: cross-sectional area of the pipev: fluid velocity
»m3/s = m2 * m/s
Flowmeter selectionFlowmeter selectionClasses of FlowmetersClasses of Flowmeters
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• Mass Meters– Infer the mass flow rate via the equation;
»Qm = Qv * where,Qm: the mass flow rate
Qv : the volume flow rate
: fluid density
»kg/s = m3/s * kg.m3
– Consist of 2 devices;» One device will measure fluid velocity» The other device will measure fluid density
Flowmeter selectionFlowmeter selectionClasses of FlowmetersClasses of Flowmeters
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Flow Restriction in Line cause a differential Pressure
Line Pressure
Orifice Plate(Primary Element)
QV= K DP
Constant
DP flowmeterDP flowmeterDP Flow EquationDP Flow Equation
H.P. L.P.
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FE
FT
FIC
Outputs represent true flow only under specified conditions.
Using “constants” in flow equations assumes a static flow environment. For DP flowmeter output to represent true flowtrue flow, the following fluid properties must be constant:
Fluid density Fluid viscosity,
DP volumetric flow
QV= K DPPrimary Element
Pressure Transmitter
Flow Controller
Control Valve
DP flowmeterDP flowmeterDP Flow EquationDP Flow Equation
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• For varying fluid densityfluid density and viscosityviscosity
– Compensation is required to represent TRUE flow
QM= K DP*(P/T) Partial Compensation
Takes care of Density only
Mass Flow, QM = Volumetric flow * Density= m3/s * kg/m3
= kg/s
DP flowmeterDP flowmeterDP Flow EquationDP Flow Equation
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Traditionally way of partially compensated DP mass DP mass flowflow has been accomplished using a “system.”
FE
TTFT
PT FC FICPressure
Transmitter(AP)
Pressure Transmitter
(DP)
Temperature Transmitter + Sensor
Flow Computer
Flow Controller
Control Valve
Primary Element
QM= K DP*(P/T)
DP flowmeterDP flowmeterDP Flow EquationDP Flow Equation
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• 3095 Multivariable3095 MultivariableTMTM Flow Transmitter Flow Transmitter– 3 Process Sensors used as inputs
to Mass Flow Calculation:» RTD Temperature Sensor Input» Differential Pressure Sensor» Piezoresistive Static Pressure Sensor
QM= N Cd E Y d2 DP*(P/T)
These constants takes care of velocity of the fluid friction of the fluid in contact with the pipe viscosity of the fluidto give a fully compensated dynamic flow measurement
K
DP flowmeterDP flowmeterDP Flow EquationDP Flow Equation
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C dActual_flow
Theoretical_flow
• Cd is a correction factor to the theoretical equation.
Equations for calculating Cd are derived from experimental data. Cd is a function of beta ratio and Reynolds number, and is different for each primary element.
Discharge Coefficient (Cd)
• Density is NOT constant for gases. Y 1 1Y 1 f ,,, k P P 1 for
Liquids: k is the isentropic exponent, a
property of gases:k
C p
C v
Gas Expansion Factor (Y1)
= < 1
(Beta ratio = restriction diam. / pipe diam.)
DP flowmeterDP flowmeterDP Flow EquationDP Flow Equation
QM= K DP*(P/T)
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Cd
RD
102 103 104 105
Concentric Square-edge Orifice
GASESLIQUIDS
Discharge Coefficient vs. RD
CONSTANT
DP flowmeterDP flowmeterDP Flow EquationDP Flow Equation
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0 5 104
1 105
1.5 105
2 105
2.5 105
3 105
3.5 105
4 105
4.5 105
5 105
0.59
0.6
0.61
0.62
0.63
0.64
0.65
0.66
Beta = .75Beta = .6Beta = .5Beta = .4Beta = .2
Orifice Plate Discharge Coefficients
Pipe Reynolds Number
Dis
char
ge C
oeffi
cien
t
( 4” Flange Taps )
Discharge Coefficient vs. RD &
Orifice Diam. / Pipe Diam. = Beta d/D =
Beta Values are almost constant
DP flowmeterDP flowmeterDP Flow EquationDP Flow Equation
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0 20 40 60 80 100 120 140 160 180 200 220 240 2600.85
0.9
0.95
1
1000 psi250 psi100 psi50 psi20 psi
Gas Expansion Factors
Differential Pressure (inH2O)
Gas
Exp
ansi
on F
acto
r
( k=1.3, beta = 0.6 )
Gas Expansion Factor vs. DP
LinePressure
The higher the line pressure, the more constant Gas Expansion Factor for a variety of DP
DP flowmeterDP flowmeterDP Flow EquationDP Flow Equation
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Secondary - measures the differential pressure.
SECONDARY
Using well-established conversion coefficients which depends on the type of head meter used and the diameter of the pipe, a measurement of the differential pressure may be translated into a volume rate.
DP Flow Meters consist of two main components:
PRIMARY
Primary - placed in the pipe to restrict the flow.
Orifice, Venturi, nozzle, Pitot-static tube, elbow, and wedge.
DP flowmeterDP flowmeterComponentsComponents
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• Simplest and least expensive.• Constrict fluid flow to produce diff. pressure across the plate.• Produce high pressure upstream and low pressure
downstream.• Flow proportional to square of the flow velocity.• Greater overall pressure loss compared to other primary
devices.• Cost does not increase significantly with pipe size (advantage).
DP flowmeterDP flowmeterOrifice PlateOrifice Plate
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• Gradually narrows the diameter of pipe.• Resultant drop in pressure is measured.• Pressure recovers at the expanding section of the meter.• For low pressure drop and high accuracy reading applications• Widely used in large diameter pipes.
DP flowmeterDP flowmeterVenturi TubeVenturi Tube
High Pressure Side Low Pressure Side
Cross sectionArea A2
CrosssectionArea A1 Flow
P1 P2
Q (Actual) = C x A1 x A2 2 x ( P1 -P2 )
( A12 - A2
2 ) x
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• High velocity flow meter.• Elliptical restriction of flow at nozzle opening.• No outlet area for pressure recovery.• For application where turbulence is high (Re > 50000)
eg.,stream flow at high temperatures.• Pressure drop falls betw. That of venturi tube and orifice plate
(30-95%)
DP flowmeterDP flowmeterFlow NozzleFlow Nozzle
D
D
d
D/2
FLOW
NOZZLE
High Pressure Low Pressure
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P V
g
Pf
f
f
c
f
f
1 1
2
2
2
P Pf f1 2
V f
f
1
Bernoulli’s energy balance for an
incompressible, non-viscous fluid:
In order to measure accurate flow rate, a pitot traverse is required.
• Stagnation Pressure Sensing - measures a point velocity.
V
g P Pf 1
c f f
f
2 12
Theoretical Point Velocity
DP flowmeterDP flowmeterPitot TubePitot Tube
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Fluid Flow
Low (Static) Pressure TapHigh (Impact) Pressure Tap
Static pressure portHigh pressure port
DP flowmeterDP flowmeterPitot TubePitot Tube
• One-point velocity measurement– accuracy affected by changes in velocity profile– tube must be moved back & forth in the flow
stream for average measurement
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High Pressure Tap Low Pressure Tap
Cross section of Annubar
Blunt
Front
Sharp Edge
Blunt
Rear H.P. L.P.
Fluid Flow
DP flowmeterDP flowmeterAveraging Pitot Tube (Annubar)Averaging Pitot Tube (Annubar)
• Include several measurement ports over the entire diameter of the pipeline– more accurate flow measurement than the regular
pitot tube
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• Advantages:– Can be inserted through a small opening.– Can sample the velocity at many points.– Low pressure drop, non-obstrusive.
• Disadvantages:– Pitot traverse requires a technician, and is time-consuming.– Pitot tube is fragile (not suited for industrial app.)– DP signal is low.– Accuracy depends on the velocity profile.– Easily plugged by foreign material in the fluid.
DP FlowmeterDP FlowmeterPitot TubePitot Tube
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DP flowmeterDP flowmeterWedge Flow ElementWedge Flow Element
• inserted in the process pipe• forms a wedged obstruction on the inner wall of
the pipe• usually used with remote seals for measuring
– dirty fluids, slurries & fluids at high viscosity (low RD) that tends to build up or clog orifice plates
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DP flowmeterDP flowmeterV-Cone V-Cone
• high accuracy• normally lab-calibrated• work equally well with short and long straight pipes• for customers who have limited room for straight
piping requirements• can be used with some dirty fluids
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Head MeterHead MeterRotameterRotameter
• Variable-area flowmeters– float inside the tapered tube rises in response to fluid flow rate– pressure is higher at the bottom than the top of the tapered tube– float rests where the dp between upper & lower surfaces of the
float balances the weight of the float– flowrate read direct from scale or electronically
• commonly used for indication only
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Head MeterHead MeterTarget MeterTarget Meter
• A disc is centered in the pipe with surface positioned at right angle to the fluid flow.
• Force of the fluid acting against the target directly measures the fluid flow rate.
• Requires no external connections, seals or purge systems.
• Useful for dirty or corrosive fluids.
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Advantages:• Low cost• Easily installed and/or
replaced• No moving parts• Suitable for most gases
or liquids• Available in a wide
range of sizes and models
Disadvantages:• Square-root head/flow
relationship• High permanent pressure
loss• Low accuracy• Flow rage normal 4:1• Accuracy affected by wear
and/or damage of the flow primary element especially with corrosive fluids.
Head MeterHead MeterTarget MeterTarget Meter
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As the conductive process liquid moves through the field with average velocity V, the electrodes sense the induced voltage.
• Faraday’s Law of electromagnetic induction.
• A voltage will be induced in a conductor moving through a magnetic field.
• E = kBDV
– E = magnitude of induced voltage
– V = velocity of the conductor– D = width of the conductor– B = strength of the magnetic field– k = proportionality constant
Velocity MeterVelocity MeterMagnetic FlowmeterMagnetic Flowmeter
ConductiveProcess Medium
Lining
Field Coils
Sensing Electrodes
SST Tube
Flange
Magnetic Field “B”(Constant Strength)
“E”
“E”
Variable Flow Rate(Feet Per Second)
“D”D
“V”
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Advantages:
• Obstructionless flow
• Unaffected by viscosity, pressure, temperature and density
• Good accuracy
• No RD constraints
• Suitable for slurries and corrosive, nonlubricating, or abrasive liquids
• Wide rangeability (30:1)
Disadvantages:• Liquid must be
electrically conductive• Not suitable for gases• Can be expensive,
particularly in small sizes
• Must be installed so that the meter is always full
Velocity MeterVelocity MeterMagnetic FlowmeterMagnetic Flowmeter
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An alternating voltage is produced as each blades cuts the magnetic lines of flux. Each pulse represents a discrete volume of liquid.
• Consist of multi-blade rotors supported by bearings and enclosed in a pipe section. perpendicular to fluid flow.
• Fluid flow drives the rotor.• Rotor velocity is proportional to
overall volume flow rate.• Magnetic lines of flux created by a
magnetic coil outside the meter.
Velocity MeterVelocity MeterTurbine MeterTurbine Meter
FLOWRotor Blades
Pickup Probe
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Advantages:• High accuracy• Rangeability 10:1• Very good repeatability• Low pressure drops• Can be used on high
viscosity fluids (but with lower turndowns)
Disadvantages:• Moving parts subject to wear• Can be damaged by
overspeeding• High temperature,
overspeeding, corrosion, abrasion and pressure transient can shorten bearing life
• Rather expensive• Filtration required in dirty fluids
Velocity MeterVelocity MeterTurbine MeterTurbine Meter
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Velocity MeterVelocity MeterVortex FlowmeterVortex Flowmeter
Shedder Bar
Vortices
FLOW
Force on Sensor
Sensor
Pivoting Axis
Shedder Bar
Vortex Shedder Force
FLOW
• von karman effect (vortex shedding)– As fluid pass a bluff body, it
separates and generates small eddies/vortices that are shed alternately along and behind each side of the bluff body.
– This vortices cause areas of fluctuating pressure that are detected by a sensor.
– The frequency of vortex generation is directly proportional to fluid velocity.
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Advantages:• Good accuracy• Usually wide flow range• Used with liquids, gases
and steam• Minimal maintenance (no
moving parts)• Good linearity over the
working range
Disadvantages:• Not suitable for abrasive or
dirty fluids• Straight upstream pipe
required equal to 30 times pipe diameter or longer
• Limited by low velocity (RD < 10,000)
Velocity MeterVelocity MeterVortex FlowmeterVortex Flowmeter
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Velocity MeterVelocity MeterUltrasonic FlowmetersUltrasonic Flowmeters
• uses sound waves to determine flow rates of fluids.– Transit-Time Method
» 2 piezoelectric transducers mounted opposing, to focus sound waves between them at 45° angle to the direction of flow within a pipe. In a simultaneous measurement in the opposite direction to fluid flow, a value (determined electronically) is linearly proportional to the flow rate.
Receiver
Transmitter
FLOW
Upstream Transducer
Downstream Transducer
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Velocity MeterVelocity MeterUltrasonic FlowmetersUltrasonic Flowmeters
• uses sound waves to determine flow rates of fluids.– Doppler Effect Method
» One of the 2 transducer mounted in the same case on one side of the pipe transmits sound waves (constant frequency) into the fluid. Solids or bubbles within the fluid reflect the sound back to the receiver element. Frequency difference is directly proportional to the flow velocity in the pipe.
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Advantages:• Non-intrusive,
obstructionless• Wide rangeability (10:1)• Easy to install (especially
for clamp-on version)• Cost virtually
independent of pipe size• The flow measurement is
bi-directional
Disadvantages:• Maximum temperature 150°C• Particular fluid conditions are
required (TOF-type: clean liquids; Doppler-type: particles or impurities in the stream)
• Not very high accuracy (about ±2%)
• Doppler flowmeter clamp-on type requires a pipe of homogeneous material (cement or fibreglass linings must be avoided)
Velocity MeterVelocity MeterUltrasonic FlowmetersUltrasonic Flowmeters
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• Operating Principle– Uses a obsructionless U-shaped tube as a sensor– Applies Newton’s 2nd Law of Motion to determine flow rate.– Force = mass x acceleration– The flow tube vibrates at its natural frequency by an
electromagnetic drive system.
Mass MeterMass MeterCoriolis MeterCoriolis Meter
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• Coriolis Effect– Fluid flowing through the upward moving tube, pushes
downward against the tube.– Fluid flowing out through the downward moving tube,
pushes upward against the tube.– The combination of upward and downward resistive forces
causes the sensor tube to twist (coriolis effect).
Mass MeterMass MeterCoriolis MeterCoriolis Meter
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Mass MeterMass MeterCoriolis MeterCoriolis Meter
• Signal Transmission– The amount the tube twist is proportional to the mass flow
rate of the fluid flowing through it.– Electromagnetic sensors located at each side of the tube
measures the respective velocity of the vibrating tube at these points.
– The sensor sends this information to the transmitter which gives an output signal directly proportional to mass flow rate.
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Advantages:• High accuracy: ±0.25%• Relatively low pressure
drops• Suitable for liquid and
gas flow• Easy to install• Flow range (10:1)
Disadvantages:• Expensive• Mounting is critical (no
vibration)• Heat-tracing is required
in some applications
Mass MeterMass MeterCoriolis MeterCoriolis Meter
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• Works on the principle of heat transfer by the fluid flow– Made up o 3 elements arranged along the direction of motion.
» high accurate temperature sensor at upstream» an electrical heater in between» high accurate temperature sensor at downstream
– The difference between the two temperature readings is proportional to the mass flow rate. (if the thermal properties of the fluid being metered are constant and known).
Mass MeterMass MeterThermal MeterThermal Meter
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Advantages:• No moving parts• Suitable for large size
pipe (insertion type)• Good rangeability (50:1)• Accuracy: ±1% FS• Low permanent pressure
losses
Disadvantages:• Meter sensitive to fluid heat
conductivity, viscosity, and specific heat
• Mostly gas service (only rare liquid service)
• Specific heat of the fluid must be known and constant i.e. the gas must have a constant composition
• Proper operation requires no heat losses due to conductive exchanges though the pipe walls
Mass MeterMass MeterThermal MeterThermal Meter
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• An example of positive displacement meter– Two meshing oval gears rotate as fluid flows through them– Gears trap a known quantity of fluid as they rotate– Each complete revolution of both the gears = 4 * amount of
fluid that fills the space between the gear and the meter body
– volumetric flow rate is directly proportional to the rotational velocity of the gears
Displacement flowmeterDisplacement flowmeterOval Gear MeterOval Gear Meter
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Meter
DP/Orifice
MV/Orifice
MV/Annubar
Magmeter
Vortex
Coriolis
Turbine
Fluids
Liquid,Gas,steam
Liquid,Gas,steam
Liquid,Gas,steam
Conductive Fluids
Liquid,Gas,steam
All
Liquid,Gas,steam
Dirty Fluids
No
No
Some
Yes
Some
Yes
No
Viscosity
Low-Medium
Low-Medium
Low
Any
Low-Medium
Any
Low-Medium
Pipe Size
0.5 - 40in
0.5 - 40in
0.5 - 72+in
0.2 - 36in
0.5 - 8in
0.5 - 6in
0.5 - 24in
Maximum Pressure
6000psig
6000psig
6000psig
1400psig
1400psig
4000psig
6000psig
MaximumTemp.
175°C
200°C
200°C
PressureLoss
Medium-High
Medium-High
Low
Very Low
Low
High*
High
Rosemount flow products Rosemount flow products Summary TableSummary Table
Level 1 - FlowRMT Training - 05 /98
64ExerciseExercise
1. Which of the following would generally provide the best turndown ?
(A) DP - Orifice Plate (C) Magnetic Flowmeter
(B) V.A.Meter (D) Turbine Meter
Which of the following directly measures mass flow rate, and which
volume flow rate. Indicate “M” or “V”
2. Magnetic Flowmeter [ ]
3. Vortex Meter [ ]
4. Coriolis Meter [ ]
5. Non-compensated DP Flowmeter [ ]
6. Fully-compensated DP Flowmeter [ ]
Level 1 - FlowRMT Training - 05 /98
65
7. The following flowmeters all create some pressure loss. Number them in order, beginning with that which create the least loss.
(A) Venturi tube [ ]
(B) Positive displacement meter [ ]
(C) Magnetic flowmeter [ ]
(D) Vortex Meter [ ]
(E) Annubar [ ]
(F) Orifice plate [ ]
ExerciseExercise