Training - Flow

Flow

Level 1 - Fundamental Training

Level 1 Fundamental Training

1

Level 1 - Flow

Contents Topics: • Why measure flow? • Flow terminology • Flowmeter selection • DP flowmeters • Velocity flowmeters • Mass flowmeters • Displacement meters • Flow products summary • Exercise

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Slide No: 3-4 5 - 18 19 - 24 25 - 46 47 - 55 56 - 61 62 63 64 - 65

Level 1 - Flow

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Flow

Level 1 - Fundamental Training Why measure flow? 5 Common Reasons

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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 Level 1 - Flow

Why measure flow? 5 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

Level 1 - Flow

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Flow

Level 1 - Fundamental Training Flow terminology Flow Control Loop

5

• 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 I/P

FIC

FT

TT

Level 1 - Flow

Flow terminology Fluid Properties •

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Density: ρ (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

Liquids

Gases

↑ Temperature = ↓ Density ↓ Temperature = ↑ Density

↑ Temperature = ↓ Density ↓ Temperature = ↑ Density

↑ Pressure = No change ↓ Pressure = No change

↑ Pressure = ↑ Density ↓ Pressure = ↓ Density

Level 1 - Flow

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Flow

Level 1 - Fundamental Training Flow terminology Fluid Properties

7

For Liquids, • Specific Gravity =

Density of liquid at process temperature Density of water at 15.6°C

For Gases, •

Specific Gravity =

Molecular Weight of gas Molecular Weight of air

Level 1 - Flow

Flow terminology Fluid Properties

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• Gas Compressibility Factor: Z-factor – Used to correct gas equations for real-gas effects. Accounts for the deviation from the “ideal” situation. Absolute pressure

Absolute temperature

PV = nRT Volume

Universal gas constant Molecular weight

» » » »

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

Level 1 - Flow

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Flow

Level 1 - Fundamental Training Flow terminology Fluid Properties •

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Viscosity – Measure of a fluid’s tendency to resist a shearing force, or to resist flow

Area Fluid Thickness

Force

•Water is 1cP, peanut butter is 10,000 cP

Fixed Plate

» 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 Level 1 - Flow

Flow terminology Fluid 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 Level 1 - Flow

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Flow

Level 1 - Fundamental Training Flow terminology Fluid Properties

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• Flow Profile

Pipe Wall

Lower velocity at the edge

Higher velocity in the middle

Lower velocity at the edge

Laminar Flow

Turbulent Flow Transition Flow

Level 1 - Flow

Flow terminology Fluid Properties

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• Reynolds number defines the state of fluid flow – Dimensionless number – Indicates flow profile

Laminar 0

4000

2000

m

Reynolds Number

Turbulent

Transition

m/s

kg/m3

(Pipe I.D.) ( Velocity) (Density) Viscosity kg/ms

Rd = (ρ x v x D)/μ Level 1 - Flow

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Flow

Level 1 - Fundamental Training Flow terminology Fluid Properties

13

Example: Flow conditions; RD =

μ = =

Velocity = 0.5 m/s density = 995.7kg/m³ V.d.ϕ / μ Temperature = 25°C = 0.7 / 1000 kg/ms Viscosity = 0.7cP 0.5 x 0.06 x 995.7 x 1000 /0.7 Pipe ID = 60mm (1 Poise = 0.1 kg/m s) 42,673

i) ii)

Find the Reynolds number for the fluid. Identify the type of flow. (a) (b) (c)

Laminar Transitional Turbulent Level 1 - Flow

Flow terminology Fluid Properties

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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 Level 1 - Flow

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Flow

Level 1 - Fundamental Training Flow terminology Pipe Geometry & Conditions

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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 = πD2/4 * Velocity = D2(π/4 x Velocity)

Qv Qv

= =

(2 2D)2 * (π/4 x Velocity) 4 (D2 * (π/4 x Velocity)) Level 1 - Flow

Flow terminology Pipe Geometry & Conditions

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• Flow Profile Disturbance – factors that cause flow profile to become irregular » symmetrical profile ⇒caused by reducers or expanders pipe sections ⇒eliminated by inserting appropriate length of straight pipes

» asymmetrical profile ⇒caused by elbows, valves and tees ⇒eliminated by inserting appropriate length of straight pipes

» swirl ⇒caused by pumps, compressors, or two pipe elbows in different planes ⇒eliminated by inserting flow conditioners Level 1 - Flow

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Flow

Level 1 - Fundamental Training Flow terminology Engineering Units

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Volumetric Flow Rate • Metric Unit• Others ⇒ StdCuft/s ⇒ StdCuft/min ⇒ StdCuft/h ⇒ StdCuft/d ⇒ StdCum/h ⇒ StdCum/d ⇒ NmlCum/h ⇒ NmlCum/d

Std Nml

m3/s - Standard Cubic feet per second - Standard Cubic feet per minute - Standard Cubic feet per hour - Standard Cubic feet per day - Standard Cubic meter per hour - Standard Cubic meter per day - Normal Cubic meter per hour - Normal Cubic meter per day

- reference to 14.696 psi Atm. at 68 deg.F - reference to 101.325 Atm. At 0 deg.C Level 1 - Flow

Flow terminology Engineering Units Mass Flow Rate • Metric Unit• Others ⇒ lbs/sec ⇒ lbs/min ⇒ lbs/hour ⇒ lbs/day ⇒ gram/sec ⇒ grams/min ⇒ grams/hour ⇒ kg/min ⇒ kg/hour

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kg/s - Pounds per second - Pounds per minute - Pounds per hour - Pounds per day - grams per second - grams per minute - grams per hour - kilograms per minute - kilogram per hour

Level 1 - Flow

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Flow

Level 1 - Fundamental Training Flowmeter selection Specification

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• Accuracy – % of rate » uncertainty of flow proportional to flow rate Rate of Flow 100 gpm 50 gpm 20 gpm

% of Rate Accuracy ±2% of 100 gpm ±2% of 50 gpm ±2% of 20 gpm

Uncertainty Range 98-102 gpm 49-51 gpm 19.6-20.4 gpm

– % of full scale » uncertainty of flow remains constant Rate of Flow 100 gpm 50 gpm 20 gpm

% of Rate Accuracy ±2% of 100 gpm ±2% of 50 gpm ±2% of 20 gpm

Uncertainty Range 98-102 gpm 49-51 gpm 19.6-20.4 gpm Level 1 - Flow

Flowmeter selection Specification

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• Rangeability (Turndown) – Meter maximum » maximum flow rate that a flowmeter is capable of reading ⇒commonly used for magnetic, vortex and Coriolis meters

– Application maximum » maximum flowrate that occurs in the process flow of a particular application ⇒commonly 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 Level 1 - Flow

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Flow

Level 1 - Fundamental Training Flowmeter selection Classes of Flowmeters

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Flow Technologies Mass

Volumetric

Head

Coriolis Meter Thermal Meter

Positive Velocity Meter Displacement Meter

DP Flow Target Meter Meter

Magnetic Vortex Ultrasonic Turbine

Oval Nutating disc Gear Gerotor

Annubar Orifice Venturi Nozzle Elbow Taps Level 1 - Flow

Flowmeter selection Classes 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

Level 1 - Flow

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Flow

Level 1 - Fundamental Training Flowmeter selection Classes of Flowmeters

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• 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 where ⇒A: ⇒v:

cross-sectional area of the pipe fluid velocity

» m3/s = m2 * m/s A reliable flow measurement is dependent upon the correct measurement of A and v.

Level 1 - Flow

Flowmeter selection Classes of Flowmeters

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• Mass Meters – Infer the mass flow rate via the equation; » Qm = Qv * ρ where, ⇒Qm: ⇒Qv : ⇒ρ :

the mass flow rate 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

Level 1 - Flow

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Flow

Level 1 - Fundamental Training DP flowmeter DP Flow Equation

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Flow Restriction in Line cause a differential Pressure Line Pressure (Primary Element) Orifice Plate

H.P.

L.P.

QV= K

DP Constant Level 1 - Flow

DP flowmeter DP Flow Equation Pressure Transmitter

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Flow Controller FIC

FT

DP volumetric flow Control Valve

Primary Element

FE

QV= K

DP

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 flow, flow the following fluid properties must be constant: Fluid density Fluid viscosity, Level 1 - Flow

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Flow

Level 1 - Fundamental Training DP flowmeter DP Flow Equation

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• For varying fluid density and viscosity – 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

Level 1 - Flow

DP flowmeter DP Flow Equation

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Traditionally way of partially compensated DP mass flow has been accomplished using a “system.”

Pressure Transmitter PT (AP)

Pressure Transmitter (DP) FT

Flow Computer FC

TT Temperature Transmitter + Sensor FE

QM= K

FIC Flow Controller Control Valve

Primary Element

DP*(P/T) Level 1 - Flow

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Flow

Level 1 - Fundamental Training DP flowmeter DP Flow Equation

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Discharge Coefficient (Cd) • Cd is a correction factor to the theoretical equation. QM= K

DP*(P/T)

Cd

Actual_flow Theoretical_flow

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. (Beta ratio = restriction diam. / pipe diam.)

Gas Expansion Factor (Y1) • Density is NOT constant for gases. Y 1 f β , k , ΔP , P 1

for Liquids:

k is the isentropic exponent, a property of gases:

k

Y1 1 Cp Cv

=<1 Level 1 - Flow

DP flowmeter DP Flow Equation

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Discharge Coefficient vs. RD Cd

Concentric Square-edge Orifice

CONSTANT 102

103

104

LIQUIDS

105

RD

GASES Level 1 - Flow

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Flow

Level 1 - Fundamental Training DP flowmeter DP Flow Equation

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Discharge Coefficient vs. RD & β Orifice Plate Discharge Coefficients 0.66

( 4” Flange Taps )

Discharge Coefficient

0.65 0.64

Beta Values are almost constant

0.63 0.62 0.61

0.6 0.59

4 5 10

0

5 1 10

5 1.5 10

Beta = .75 Beta = .6 Beta = .5 Beta = .4 Beta = .2

5 5 5 2 10 2.5 10 3 10 Pipe Reynolds Number

5 3.5 10

5 4 10

5 4.5 10

5 5 10

Orifice Diam. / Pipe Diam. = Beta ⌫ d/D = β Level 1 - Flow

DP flowmeter DP Flow Equation

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Gas Expansion Factor vs. DP Gas Expansion Factors

Gas Expansion Factor

1

0.95

0.9

0.85

Line Pressure

The higher the line pressure, the more constant Gas Expansion Factor for a variety of DP 0

20

40

1000 psi 250 psi 100 psi 50 psi 20 psi

60

80

100 120 140 160 180 200 220 240 260 Differential Pressure (inH2O)

( k=1.3, beta = 0.6 ) Level 1 - Flow

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Flow

Level 1 - Fundamental Training DP flowmeter Components

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DP Flow Meters consist of two main components: Primary

-

Secondary -

SECONDARY

placed in the pipe to restrict the flow. Orifice, Venturi, nozzle, Pitot-static tube, elbow, and wedge. measures the differential pressure. 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. PRIMARY Level 1 - Flow

DP flowmeter Orifice Plate

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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).

Level 1 - Flow

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Flow

Level 1 - Fundamental Training DP flowmeter Venturi Tube • • • • •

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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. High Pressure Side

Low Pressure Side P1 P2

Cross section Area A1 Flow

Cross section Area A2

Q (Actual) =

C x A1 x A 2 x ( A12 - A22 )

2 x ( P1 -P2 ) ρ

Level 1 - Flow

DP flowmeter Flow Nozzle

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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%) D

D/2

High Pressure

Low Pressure

FLOW D

d

NOZZLE Level 1 - Flow

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Flow

Level 1 - Fundamental Training DP flowmeter Pitot Tube

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Bernoulli’s energy balance for an incompressible, non-viscous fluid: Pf 1

Pf 2

Pf 1

Vf 1

ρf

ρf

V f 12

+

=

2 gc

Pf 2

ρf

• Stagnation Pressure Sensing - measures a point velocity.

Theoretical Point Velocity

Vf 1 =

(

2 gc Pf 2 − Pf 1

ρf

)

In order to measure accurate flow rate, a pitot traverse is required. Level 1 - Flow

DP flowmeter Pitot Tube

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High (Impact) Pressure Tap

Low (Static) Pressure Tap

Fluid Flow

High pressure port

Static pressure port

• One-point velocity measurement – accuracy affected by changes in velocity profile – tube must be moved back & forth in the flow stream for average measurement Level 1 - Flow

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Flow

Level 1 - Fundamental Training DP flowmeter Averaging Pitot Tube (Annubar (Annubar)) High Pressure Tap

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Low Pressure Tap

Sharp Edge Blunt

H.P.

L.P.

Front

Blunt Rear

Cross section of Annubar

Fluid Flow

• Include several measurement ports over the entire diameter of the pipeline – more accurate flow measurement than the regular pitot tube Level 1 - Flow

DP Flowmeter 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 timeconsuming. – 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.

Level 1 - Flow

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Flow

Level 1 - Fundamental Training DP flowmeter Wedge Flow Element

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• 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

Level 1 - Flow

DP flowmeter V-Cone

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• • • •

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

Level 1 - Flow

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Flow

Level 1 - Fundamental Training Head Meter Rotameter

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• 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

Level 1 - Flow

Head Meter Target Meter

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• 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.

Level 1 - Flow

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Flow

Level 1 - Fundamental Training Head Meter Target Meter

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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. Level 1 - Flow

Velocity Meter Magnetic Flowmeter

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• Faraday’s Law of electromagnetic Conductive induction. Process • A voltage will be induced in a Medium conductor moving through a Lining magnetic field. Sensing • E = kBDV

“V”

“D”

Variable Flow Rate (Feet Per Second) SST Tube Flange

D

“E”

Electrodes

– E = magnitude of induced voltage – – – –

V = velocity of the conductor D = width of the conductor “E”field B = strength of the magnetic k = proportionality constant

Field Coils

Magnetic Field “B” (Constant Strength)

As the conductive process liquid moves through the field with average velocity V, the electrodes sense the induced voltage. Level 1 - Flow

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Flow

Level 1 - Fundamental Training Velocity Meter Magnetic Flowmeter 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)

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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

Level 1 - Flow

Velocity Meter Turbine Meter • Consist of multi-blade rotors supported by bearings and enclosed in a pipe section. perpendicular to fluid flow. • Fluid flow drives the rotor. Rotor Blades • Rotor velocity is proportional to overall volume flow rate. • Magnetic lines of flux created by a magnetic coil outside the meter.

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Pickup Probe

FLOW

An alternating voltage is produced as each blades cuts the magnetic lines of flux. Each pulse represents a discrete volume of liquid.

Level 1 - Flow

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Flow

Level 1 - Fundamental Training Velocity Meter Turbine Meter Advantages: • High accuracy • Rangeability 10:1 • Very good repeatability • Low pressure drops • Can be used on high viscosity fluids (but with lower turndowns)

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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

Level 1 - Flow

Velocity Meter Vortex Flowmeter

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• von karman effect (vortex shedding) – As fluid pass a bluff body, it Sensor Force on separates and generates Sensor small eddies/vortices that are shed alternately along and FLOW behind each side of the bluff Vortex Pivoting body. Shedder Axis Force – This vortices cause areas of fluctuating pressure that are Shedder Bar detected by a sensor. – The frequency of vortex Shedder Bar generation is directly proportional to fluid velocity. FLOW

Vortices Level 1 - Flow

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Flow

Level 1 - Fundamental Training Velocity Meter Vortex Flowmeter

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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)

Level 1 - Flow

Velocity Meter Ultrasonic Flowmeters

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• 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. Transmitter Upstream Transducer

Receiver

FLOW

Downstream Transducer Level 1 - Flow

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Flow

Level 1 - Fundamental Training Velocity Meter Ultrasonic Flowmeters

53

• 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.

Level 1 - Flow

Velocity Meter Ultrasonic Flowmeters 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

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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) Level 1 - Flow

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Flow

Level 1 - Fundamental Training Mass Meter Coriolis Meter

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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.

Level 1 - Flow

Mass Meter Coriolis 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).

Level 1 - Flow

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Flow

Level 1 - Fundamental Training Mass Meter Coriolis Meter

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• 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.

Level 1 - Flow

Mass Meter Coriolis Meter Advantages: • High accuracy: ±0.25% • Relatively low pressure drops • Suitable for liquid and gas flow • Easy to install • Flow range (10:1)

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Disadvantages: • Expensive • Mounting is critical (no vibration) • Heat-tracing is required in some applications

Level 1 - Flow

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Flow

Level 1 - Fundamental Training Mass Meter Thermal Meter

59

• 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).

Level 1 - Flow

Mass Meter Thermal Meter Advantages: • No moving parts • Suitable for large size pipe (insertion type) • Good rangeability (50:1) • Accuracy: ±1% FS • Low permanent pressure losses

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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 Level 1 - Flow

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Flow

Level 1 - Fundamental Training Displacement flowmeter Oval Gear Meter

61

• 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

Level 1 - Flow

Flow products Summary Table

62

Meter

Fluids

Dirty Fluids

Viscosity

DP/Orifice

Liquid,Gas,steam

No

Low-Medium 0.5 - 40in

6000psig

Medium-High

MV/Orifice

Liquid,Gas,steam

No

Low-Medium 0.5 - 40in

6000psig

Medium-High

Some

Low

0.5 - 72+in 6000psig 0.2 - 36in

MV/Annubar Liquid,Gas,steam

Pipe Size

Maximum Maximum Pressure Pressure Temp. Loss

Low

Magmeter

Conductive Fluids Yes

Any

Vortex

Liquid,Gas,steam

Some

Low-Medium 0.5 - 8in

1400psig

Coriolis

All

Yes

Any

4000psig

200°C

High*

Turbine

Liquid,Gas,steam

No

Low-Medium 0.5 - 24in

6000psig

200°C

High

0.5 - 6in

1400psig

175°C

Very Low Low

Level 1 - Flow

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Flow

Level 1 - Fundamental Training

Exercise

63

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 - Flow

Exercise

64

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 [ ]

Level 1 - Flow

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