Module 10 Flow Measurement

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Energy Systems Engineering Technology

Flow Module Page 1

College of Technology

Instrumentation and Control

Module # 4 Flow Measurement

Document Intent:

The intent of this document is to provide an example of how a subject matter expert might teach

Flow Measurement. This approach is what Idaho State University College of Technology is

using to teach its Energy Systems Instrumentation and Control curriculum for Flow

Measurement. The approach is based on a Systematic Approach to Training where training is

developed and delivered in a two step process. This document depicts the two step approach

with knowledge objectives being presented first followed by skill objectives. Step one teachesessential knowledge objectives to prepare students for the application of that knowledge. Step

two is to let students apply what they have learned with actual hands on experiences in a

controlled laboratory setting.

Examples used are equivalent to equipment and resources available to instructional staff

members at Idaho State University.

Flow Measurement Introduction:

This module covers aspects of Flow measurement as used in process instrumentation and control.

Flow measurement addresses essential knowledge and skill elements associated with measuringFlow. Students will be taught the fundamentals of Flow measurement using classroom

instruction, demonstration, and laboratory exercises to demonstrate knowledge and skill mastery

of Flow measurement. Completion of this module will allow students to demonstrate mastery of

knowledge and skill objectives by completing a series of tasks using calibration/test equipment,

Flow indicating, and Flow transmitting devices.




Flow Module Page 2

References

This document includes knowledge and skill sections with objectives, information, and examples

of how pressure measurement could be taught in a vocational or industry setting. This documenthas been developed by Idaho State University’s College of Technology. Reference material used

includes information from:

American Technical Publication – Instrumentation, Fourth Edition, by Franklyn W. Kirk,

Thomas A Weedon, and Philip Kirk, ISBN 979-0-8269-3423-9 (Chapter 5)

Department of Energy Fundamentals Handbook, Instrumentation and Control, DOE-

HDBK-1013/1-92 JUNE 1992, Re-Distributed by http://www.tpub.com




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STEP ONE

Flow Measurement Course Knowledge Objectives

Knowledge Terminal Objective (KTO)

KTO 4. Given examples, EVALUATE Flow measurement fundamentals as they apply to

measuring Flow process variables to determine advantages and disadvantages

associated with different types of devices used to indicate, measure, and transmit

Flow.

Knowledge Enabling Objectives (KEO)DEFINE FLUID FLOW and its importance as a process variable. KEO 4.1.

DESCRIBE FLOW RATE as it applies to flow measurement.KEO 4.2.

DESCRIBE TOTAL FLOW as it applies to flow measurement.KEO 4.3.

DESCRIBE the characteristics of FLUID FLOW to include Physical Properties,KEO 4.4.

Reynolds Number, and Compressibility.

DESCRIBE how pressure, temperature, and volume define GAS LAWS forKEO 4.5.

Boyle’s Law, Charles’ Law, Gay- Lussac’s Law, and the Combined Law .

DESCRIBE the concept associated with DIFFERENTIAL PRESSUREKEO 4.6.

FLOWMETERS.

DEFINE what a PRIMARY FLOW ELEMENT is. KEO 4.7.

DESCRIBE what an ORIFICE PLATE is and how it used to measure flow. KEO 4.8.

DESCRIBE what a FLOW NOZZLE is and how it used to measure flow.KEO 4.9.

DESCRIBE what a VENTURI TUBE is and how it used to measure flow.KEO 4.10.

DESCRIBE what a LOW-LOSS FLOW TUBE is and how it used to measureKEO 4.11.

flow.




Flow Module Page 4

DESCRIBE what a PITOT TUBE is and how it used to measure flow.KEO 4.12.

DESCRIBE OPERATING PRINCIPLES associated with DIFFERENTIALKEO 4.13.

PRESSURE FLOWMETERS to include the Bernoull i Equation and the Vena

Contracta Point .

DESCRIBE why locations for DIFFERENTIAL PRESSUREKEO 4.14.

CONNECTIONS of FLOWMETERS vary.

DESCRIBE how DIFFEENTIAL INSTRUMENT LOCATIONS areKEO 4.15.

determined for L iquid, Gas, and Steam flow applications.

DESCRIBE how BLOCKING VALVES AND MANIFOLDS are used forKEO 4.16.measuring differential measurements associated with flow.

DESCRIBE how VARIABLE-AREA FLOWMETERS maintain a constantKEO 4.17.

differential pressure and allows the flow area to change with flow rate.

DESCRIBE how ROTAMETERS are used and how they measure flow.KEO 4.18.

DESCRIBE how MODIFIED ROTAMETERS are used as PURGE ORKEO 4.19.

BYPASS METERS.

DESCRIBE how METERING-CONE and SHAPTE-FLOAT & ORIFICEKEO 4.20.

VARIABLE-AREA METERS measure flow.

EXPLAIN operating principles associated with VARIABLE-AREAKEO 4.21.

FLOWMETERS.

DESCRIBE how MECHANICAL FLOWMETERS measure flow to includeKEO 4.22.

the following Posit ive-Displacement Flometers : Nutating Disc, Rotating-

Impeller, and Sliding Vane.

DESCRIBE how TURBINE METERS and PADDLE WHEEL METERSKEO 4.23.

measure flow.

DESCRIBE how MAGNETIC METERS measure flow.KEO 4.24.




Flow Module Page 5

DESCRIBE how MAGNETIC VORTEX SHEDDING METERS measureKEO 4.25.

flow.

DESCRIBE how ULTRASONIC FLOWMETERS measure flow.KEO 4.26.

DESCRIBE how MASS FLOWMETERS measure flow to include aKEO 4.27.

CORIOLIS METER and a THERMAL MASS METER .

DESCRIBE how ACCESSORY FLOW DEVICES function and how they areKEO 4.28.

used.

EXPLAIN how different FLOW SWITCHS function and how they are used toKEO 4.29.

include: DIFFERENTIAL PRESSURE SWITCHES, BLADE SWITCHES,

THEREMAL SWITCHES, and ROTAMETER SWITCHES.

EXPLAIN how OPEN-CHANEL WEIRS and PARSHALL FLUME FLOWKEO 4.30.

MEASUREMTNS function and how they are used.

EXPLAIN how a BELT WEIGHING SYSTEM is used to measure a solidsKEO 4.31.

flow.




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FLOW MEASURMENT

DEFINE FLUID FLOW and its importance as a process variable. KEO 4.1.

FLUID FLOW is the movement of liquids in pipes or channels, and gases or vapors in pipes or

ducts. A fluid is a material that flows and takes the shape of its container. All liquids and gases

are fluids.

Measuring flow is an important process variable which requires the use of many types of

instruments and scientific principles. It is often more convenient to measure the flow of a fluid by measuring some other characteristic that varies in a predictable and reliable way with the rate

of flow, such as a drop in pressure caused by restriction in a pipeline. This is drop in pressure is

commonly used as well as a host of other methods.

FLUID FLOW is an important process variable that needs to be monitored and controlled not

only in our homes and communities, but throughout all aspects of industry in the world. Fluids

can be harmless, toxic, caustic, acidic, or volatile and to measuring them requires not only

accuracy, but constant control at all times.

DESCRIBE FLOW RATE as it applies to flow measurement.KEO 4.2.

FLOW RATE is the quantity of fluid passing a point at a particular moment. Flow rate is

expressed in volumetric or mass units. The common volumetric units used in the United States

are Gallons per Minute (gpm) or Gallons per Hour (gph). Also in the United States metric units

used are Liters per Minute, Cubic Meters per Hour, and Cubic Centimeters per Minute. The unit

of Mass in the United States is Pounds per Hour and the Metric unit of Mass is Kilograms per

Hour.

DESCRIBE TOTAL FLOW as it applies to flow measurement.KEO 4.3.

TOTAL FLOW is the quantity of fluid that passes a point during a specific time interval. An

example would be the Flow Rate of pumping a fluid may be given in gallons per hour and the

Total Flow is the total gallons pumped.




Flow Module Page 7

Flow is measured in many units. Conversion tables like the table below are used to convert from

one unit to another:

Figure 5-1 page 167

SUMMARY

Fluid flow is the movement of liquids in pipes or channels, and gases or vapors in pipes

or ducts.

A fluid is a material that flows and takes the shape of its container.

All liquids and gases are fluids.

Flow rate is the quantity of fluid passing a point at a particular moment.

Total flow is the quantity of fluid that passes a point during a specific time interval.

DESCRIBE the characteristics of FLUID FLOW to include Physical Properties,KEO 4.4.

Reynolds Number, and Compressibility.




Flow Module Page 8

A FLUID FLOW’s most important characteristic that affects its flow is whether the fluid is a

liquid, gas, or vapor. This is because at certain temperatures and pressures, most fluids can

change phase between vapor, liquid, or solid. An example would be water that when heated

becomes steam and when cooled becomes ice. Gases can also be condensed to a liquid like liquid

nitrogen or liquid oxygen, or a solid like dry ice.

A number of Physical Properties common to most fluids that influence the selection of the

method chosen to measure fluid flow include: Pressure, Velocity, Density, Viscosity,

Compressibility, Electrical Capacitance and Conductance, Thermal Conductivity, and the

response to Sonic Impulses, Light, or Mechanical Vibration. All of these properties allow for

the measurement of these fluids to determine Flow Rate and Total Flow. The fact that so many

properties and characteristics can be measured account for the wide variety of flowmeters.

In addition to Physical Properties of fluids, there are other factors that affect flow. They includeconfiguration o the pipes or ducts; the location, style, and number of valves; and changes in

elevation of the fluid. The most important factors affecting fluid flow are the properties of the

fluid, the Reynolds Number describing the type of flow, and the Compressibility of the fluid.

Physical Propert ies greatly affecting the measurement of flow include Density, Specific

Gravity, and Viscosity.

Density is a measurement of Mass per Volume with common units of density being pounds per

cubic foot (lb/ft3 or lb/cu ft) and grams per cubic centimeter (g/cm

3 or g/cu cm). Density varies

with changes in temperature.

Specific Gravity is the ratio of density of a fluid to the density of a reference fluid. For liquids

this reference is usually water. For gases, the reference fluid is dry air. When two liquids that do

not mix are in a container, the one with the lowest specific gravity will float on top of the one

with the greater specific gravity. An example would be most oils having a specific gravity of

from 0.75 to 0.85 at ambient temperature mixed with a fluid like water having a specific gravity

of 0.998 the oil will rise to the top and float on the surface of the water. Gasoline would also

float on top of water. Oils and fuel are examples of fluids called organic fl uids and solutions

containing water are called aqueous fl uids .

Absolute Viscosity is the resistance to flow of a fluid and has units of Centipoise (cp) .

Kinematic Viscosity is the ration of absolute viscosity to fluid density and has units of

Centi stokes (cS) .




Flow Module Page 9

The following picture illustrates how Viscosity is affected by temperature and other factors

which normally decreases with increasing temperatures:

Figure 5-2 page 168

Many fluids must be preheated before being pumped. A property of fluid flow that describes the

type of flow is the Reynolds Number .

The Reynolds Number of a fluid is the ratio between the inertial forces moving a fluid and

viscous forces resisting that movement. The Reynolds Number describes the nature of the fluid

flow. This number has no units of measure and is calculated from velocity or flow rate, density,

viscosity, and the inside diameter of the pipe. Reynolds Numbers commonly range from 100 to

1,000,000. However, they can be higher or lower than these values.

The following picture illustrates the relationship of Reynolds Number and F low Profiles :




Flow Module Page 10

Figure 5-3 page 169

Velocity is the speed of fluid in the direction of flow and typically is expressed in ft/sec. A

Streamline is a line that shows the direction and magnitude of smooth flow at every point across

a pipe profile. A Flow Profile is a representation of the Velocity of a fluid at different points

across the pipe or duct as depicted in the above picture.

Laminar Flow is the smooth fluid flow that has a F low Profile that is parabolic in shape with no

mixing between the stream lines. Laminar F low in pipes occurs at Reynolds Numbers below




Flow Module Page 11

about 2100. A cross section of a Laminar Flow is a parabolic Flow Profile , with the maximum

Velocity in the center and the minimum Velocity at the pipe walls.

Turbulent Flow is fluid flow in which the Flow Profile is a flattened parabola, the streamlines

are not present, and the fluid is freely intermixing. Turbulent Flow in pipes typically occurs at

Reynolds Numbers above about 4000. The exact shape of the flattened profile depends on the

Reynolds Number .

There is a sudden transition between Laminar Flow and Turbulent Fl ow as the flow rate

increases and normally occurs at Reynolds Numbers between 2100 and 4000. Many Flowmeters

require Turbulent Fl ow and specify Reynolds Numbers above 10,000 to ensure that Turbulent

Flow is the prevailing condition.

Compressibility is a determination as to whether or not a fluid can be compressed. An

incompressible fluid is a liquid fluid where there is very little change in pressure. Liquids areessentially incompressible. As an example, fluid power systems transmit power through an

impressible hydraulic fluid. A compressible fluid is a fluid where the volume and density

change when subjected to a change in pressure. Gases and Vapors are examples of

compressible fluids.

A F lowing Condition is the pressure and temperature of the gas or vapor at the point of

measurement. A Standard Conditi on is when an acceptable set of temperature and pressure

condition is used as a basis for measurement.




Flow Module Page 12

SUMMARY

A fluid flow’s most important characteristic that affects its flow is whether the fluid is a

liquid, gas, or vapor.

Physical properties common to most fluids that influence the selection of the methodchosen to measure fluid flow include:

o Pressur e, Velocity, Density, Viscosity, Compressibi l ity, El ectr ical Capacitance

and Conductance, Thermal Conductivity, and the response to Soni c Impul ses,

L ight, or M echanical Vibration .

The most important factors affecting fluid flow are the properties of the fluid, the

Reynolds Number describing the type of flow, and the Compressibility of the fluid.

The Reynolds Number of a fluid is the ratio between the inertial forces moving a fluid

and viscous forces resisting that movement and describes the nature of the fluid flow.

Compressibility is a determination as to whether or not a fluid can be compressed.

An incompressible f lu id is a liquid fluid where there is very little change in pressure.

L iquids are essentially incompressible.

A compressible fl uid is a fluid where the volume and density change when subjected to a

change in pressure.

Gases and Vapor s are examples of compressible fluids.




Flow Module Page 13

DESCRIBE how pressure, temperature, and volume define GAS LAWS forKEO 4.5.

Boyle’s Law, Charles’ Law, Gay- Lussac’s Law, and the Combined Law .

Gas Laws show how gases behave with changes in temperature, pressure and volume. Gas Laws

are used to determine the volume of gas at one set of pressure and temperature conditions when

data from another set of conditions are known. The following figure depicts three gas laws,

Boyle’s, Charles’, and Gay-Lussac’s with their corresponding calculations:

Figure 5-4 Page 171




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Boyle’s Law is a gas law that states that the absolute pressure of a given quantity of gas varies

inversely with its volume provided the temperature remains constant.

Boyle’s Law

P2 = Final Pressure (in psia)

P1 = Initial Pressure (in psia)

V2 = Final Volume (in cubic units)

V1 = Initial Volume (in cubic units)

Charles’ Law is a gas law that states the volume of a given quantity of gas varies directly with

its absolute temperature provided the pressure remains constant.

Charles’ Law

T2 = Final Temperature (ino

R)T1 = Initial Temperature (in

oR)

V2 = Final Volume (in cubic units)

V1 = Initial Volume (in cubic units)

Gay-Lussac’s Law is a gas law that states that the absolute pressure of a given quantity of a gas

varies directly with its absolute temperature provided the volume remains constant.

Gay-Lussac’s Law




Flow Module Page 15

T2 = Final Temperature (inoR)

T1 = Initial Temperature (inoR)

V2 = Final Volume (in psia)

V1 = Initial Volume (in psia)

The three gas laws can be combined into one equation, called the Combined Gas Law in order

to simplify calculations as depicted below:

Figure 5-5 page 172

Combined Law




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V = Volume (in ft3 or other volumetric terms)

P = Pressure (in psia or other absolute pressure terms)

T = Temperature (inoR or

oK)

All Subscripts refer to different sets of conditions.

SUMMARY

Gas Laws show how gases behave with changes in temperature, pressure and volume.

Gas Laws are used to determine the volume of gas at one set of pressure and temperature

conditions when data from another set of conditions are known.

Boyle’s Law is a gas law that states that the absolute pressure of a given quantity of gas

varies inversely with its volume provided the temperature remains constant.

Charles’ Law is a gas law that states the volume of a given quantity of gas varies directly

with its absolute temperature provided the pressure remains constant.

Gay- Lussac’s Law is a gas law that states that the absolute pressure of a given quantity of

a gas varies directly with its absolute temperature provided the volume remains constant.

The three gas laws can be combined into one equation, called the Combined Gas Law in

order to simplify calculations.

DESCRIBE the concept associated with DIFFERENTIAL PRESSUREKEO 4.6.

FLOWMETERS.

A pressure difference is created when a fluid passes through a restriction in a pipe. The point of

maximum developed differential pressure is between the upstream of the restriction and the

pressure downstream of the restriction, at the point of highest velocity. The shape and

configuration of the restriction affects the magnitude of the differential pressure and how much

of the differential is recoverable.

Differential Pressure flowmeters are commonly used throughout industry and are called

Differential Pressure Transmitters or DP Cells. Devices that restrict a flow and measure itsdifferential pressure are called primary flow elements and they work together with the DP

Devices to provide critical measurement and control of fluids.

DEFINE what a PRIMARY FLOW ELEMENT is. KEO 4.7.




Flow Module Page 17

Primary Flow Elements are devices that create or detect a pressure drop as fluid flows through

a pipeline. Primary Flow Elements are designed to provide accuracy, low cost, ease of use, and

pressure recovery, but not necessarily all in the same element. Examples of Primary Flow

elements include: Orifice Plates, Flow Nozzles, Venturi Tubes, Low-Loss Flow Tubes, and

Pitot Tubes.

DESCRIBE what an ORIFICE PLATE is and how it used to measure flow. KEO 4.8.

An ORIFICE PLATE is a primary flow element consisting of a thin circular metal plate with a

sharp-edged round hole in it and a tab that protrudes from the flanges. The tab has orifice plate

information stamped onto it. This information usually includes: Pipe Size, Bore Size, Material,

and Type of Orifice.

Orifice plates are not always reversible so the stamping information is on the upstream face ofthe plate. The Orifice is held in place between two special pipe flanges called orifice flanges. The

below picture illustrates flow being straightened after going through pipe 90o

fittings to allow a

smooth non turbulent flow upstream of the orifice plate (Straightening Vanes remove flow

disturbances upstream of an orifice plate):

Figure 5-6 page 173.




Flow Module Page 18

Orifice Plates are simple, inexpensive, and replaceable. The hole in the plate is generally in the

center (concentric) by may be off-center (eccentric). Eccentric plates are usually used to prevent

excessive build up of foreign material or gases on the inlet side of the orifice. Some orifice plates

will have a smaller hole near the top of the plate to release any build up of gases that may be

present.

Orifice Plates have a straight run requirement of about 20 times the pipe diameter before the

orifice and 6 times the pipe diameter after the orifice plate to provide the most accurate

differential pressure. Orifice plates have the poorest recovery of differential pressure (50%) of

any of the primary flow elements.

DESCRIBE what a FLOW NOZZLE is and how it used to measure flow.KEO 4.9.

A similar primary flow element to the orifice plate is the Flow Nozzle. A Flow Nozzle is a primary flow element consisting of a restriction shaped like a curved funnel that allows a little

more flow than an orifice plate and reduces the straight run pipe requirements associated with

orifice plates.

The Flow Nozzle is mounted between a pair of flanges like an orifice plate. The pressure sensing

taps are located in the piping a fixed distance upstream and downstream of the flow nozzle. The

following picture depicts a typical Flow Nozzle:

Figure 5-7 page 174




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DESCRIBE what a VENTURI TUBE is and how it used to measure flow.KEO 4.10.

A VENTURI TUBE is a primary flow element consisting of a fabricated pipe section with a

converging inlet section, a straight throat, and a diverging outlet section. The static pressure

connection is located at the entrance to the inlet section. The reduced pressure connection is in

the throat. Venturi tubes are much more expensive than orifice plates, but are more accurate and

recover 90% or more of the differential pressure. This recovery reduces the burden on pumps and

the cost of power to run them. Venturi Tubes are frequently used to measure large flows of

water. A Venturi Tube is depicted below:

Figure 5-7 page 174




Flow Module Page 20

DESCRIBE what a LOW-LOSS FLOW TUBE is and how it used to measureKEO 4.11.

flow.

A LOW-LOSS FLOW TUBE is a primary flow element consisting of an aerodynamic internal

cross section with the low-pressure at the throat as depicted below:

Figure 5-7 page 174

Low-Loss Flow Tubes are used for a higher energy efficiency of up to 97%, but are very

expensive. Low-Loss Flow Tubes are often used in applications where the line pressure is low

and therefore the pressure recovery must be high. Low-Loss Flow Tubes can often pay for

themselves in energy savings in a short time as the following picture illustrates:

Figure 5-8 page 174

Venturi Tube and Low-Loss Flow Tubes are the most efficient Primary Flow Element




Flow Module Page 21

DESCRIBE what a PITOT TUBE is and how it used to measure flow.KEO 4.12.

A PITOT TUBE is a tube inserted into the piping or water flow to measure the impact pressure.

A Pitot Tube is a flow element consisting of a small bent tube with a nozzle opening facing into

the flow stream.

NOTE: Pitot Tubes are also used in other applications to measure water flow of a river or

stream and on air craft to measure air flow to determine the speed of an aircraft is flying.

The Pitot Tube Nozzle is called the impact opening and senses the velocity pressure plus the

static pressure. The Static Pressure is sensed at the pipe wall perpendicular to the fluid stream.

Pitot tubes are commonly used to measure air velocity in ducts and for measuring air speed of

planes in flight.

A Standard Pitot Tube is depicted below:

Figure 5-9 page 175

A standard Pitot Tube senses the impact pressure at only one point in the center of the flow path.This is the high pressure tap as the pressure is greater in the center as it is on the walls of the pipe

due to pipe resistance to the flow. Even though the velocity varies across the whole stream, it is

greater in the middle of the flow stream. For example if a Pitot Tube were used to measure river

water flow, the impact opening would be inserted the middle of the river as the water moves

faster there than at the sides of the river banks due to the resistance of the river banks.




Flow Module Page 22

To overcome the disadvantage of only having one impact point to measure the flow, an

Averaging Pitot Tube was developed as depicted below:

Figure 5-9 page 175

The advantage of the Averaging Pitot Tube is that you have several sensing points to average the

flow reading for a more accurate flow rate reading; therefore they are improved devices for

measuring flow.




Flow Module Page 23

SUMMARY

A pressure dif ference is created when a fluid passes through a restriction in a pipe.

The point of maximum developed dif ferential pressure is between the upstream of therestriction and the pressure downstream of the restriction, at the point of highest velocity.

Primary Flow Elements are devices that create or detect a pressure drop as fluid flows

through a pipeline.

An Or if ice Plate is a primary flow element consisting of a thin circular metal plate with a

sharp-edged round hole in it and a tab that protrudes from the flanges and this tab has

orifice plate information stamped onto it.

Ori f ice plates are not always reversible so the stamping information is on the upstream

face of the plate.

Ori f ice plates have the poorest recovery of differential pressure (50%) of any of the

primary flow elements.

A F low Nozzle is a primary flow element consisting of a restriction shaped like a curved

funnel that allows a little more flow than an orifice plate.

A Venturi Tube is a primary flow element consisting of a fabricated pipe section with a

converging inlet section, a straight throat, and a diverging outlet section.

Ventur i tubes are much more expensive than orifice plates, but are more accurate and

recover 90% or more of the differential pressure.

Ventur i Tubes are frequently used to measure large flows of water.

Low-Loss F low Tubes are used for a higher energy efficiency of up to 97%, but are very

expensive. Low-Loss F low Tubes are often used in applications where the line pressure is low and

therefore the pressure recovery must be high.

A Pitot Tube is a tube inserted into the piping or water flow to measure the impact

pressure.

A Pitot Tube is a flow element consisting of a small bent tube with a nozzle opening

facing into the flow stream.

There are two types of Pi tot Tubes : A Standard Pitot Tube and an Averaging Pitot

Tube .




Flow Module Page 24

DESCRIBE OPERATING PRINCIPLES associated with DIFFERENTIALKEO 4.13.

PRESSURE FLOWMETERS to include the Bernoull i Equation and the Vena

Contracta Point .

OPERATING PRINCIPLES of all differential pressure flowmeters are based on equations

developed by Daniel Bernoulli , a late 18th

century Swiss Scientist. His experiments related to

the pressure and velocity of flowing water. He determined that at any point in a closed pipe there

were three types of head pressure present:

1. Static Head Pressure due to elevation

2. Static Head Pressure due to applied pressure

3. Velocity Head Pressure.

The different types of head pressure can be converted to each other by changes in flow. The

Bernoull i Equation states that the sum of the heads of an enclosed flowing fluid is the same atany two locations.

Differential Pressure Flowmeters primary flow elements, have pressure measured upstream and

downstream of the flow element. The flow steam contracts slightly before it passes through the

flow element and continues to do so until it reaches maximum contraction, and then slowly

expands until it again fills the pipe. This concept is depicted below:

Figure 5-10 page 176

The Vena Contracta is the point of lowest pressure and the highest velocity downstream frfom a

primary flow element. According to the Bernoull i Equation , the velocity increases and the




Flow Module Page 25

pressure decreases as fluid flows through the restriction. The actual location of the Vena

Contracta point varies with flow rate and design of the flow element.

Di ff erential Pressure Measurements: For turbulent flow, the flow rate is proportional to the

square root of the differential pressure. This square root relationship affects the Rangeability of

the flow metering system. Rangeability or Turndown , is the ratio of the maximum flow to the

minimum measurable flow at the desired measurement accuracy.

This is a Character istic of the I nstrument and is not adjustable. For example, if the maximum

measurable flow rate of a flowmeter were 100 gpm of water and the minimum rate were 20 gpm

of water, the Rangeability or Turndown , is 5 to 1 (5:1) as depicted in the below picture:


The above picture depicts how flow varies with the square root of pressure drop, restricting the

meter from full flow to 20% if flow.

Flow measurement is only accurate as long as the flowing conditions remain the same as when

the system was designed. Changes in pressures and temperature are common in gas and vapor

flow measurements. Liquid flow measurements are usually more consistent.

Flowing conditions that differ from the original flowmeter design calculation can result in

significant errors. When the original design conditions and the actual flowing conditions are

known, the flowmeters displayed flow rate can be changed to the correct value.

To obtain the correct flow, multiply the corrections factors for PC (Pressure Correction) and TC

(Temperature Correction) times the displayed flow to obtain the correct flow as depicted in the

below picture:




Flow Module Page 26


The above picture illustrates how to use the correction formulas to correct Gas and Vapor flows

from measured conditions to design flow conditions.

SUMMARY




Flow Module Page 27

Daniel Bernoul li determined that at any point in a closed pipe there were three types of

head pressure present:

1. Static Head Pressure due to elevation

2. Static Head Pressure due to applied pressure

3.

Velocity Head Pressure. Bernoull i Equation states that the sum of the heads of an enclosed flowing fluid is the

same at any two locations.

The Vena Contr acta is the point of lowest pressure and the highest velocity downstream

from a primary flow element. According to the Bernoull i Equation , the velocity

increases and the pressure decreases as fluid flows through the restriction.

Di ff erential Pressure Measurements: For turbulent flow, the flow rate is proportional to

the square root of the differential pressure.

F low measur ement is only accurate as long as the flowing conditions remain the same as

when the system was designed.

To obtain the correct flow , multiply the corrections factors for PC (Pressure Correction)

and TC (Temperature Correction) times the displayed flow to obtain the correct flow

DESCRIBE why locations for DIFFERENTIAL PRESSUREKEO 4.14.

CONNECTIONS of FLOWMETERS vary.

DIFFERENTIAL PRESSURE CONNECTIONS of FLOWMETERS vary as there are two

locations selected depending of the application. There are two different connections used to

measure the high pressure (Static Pressure in the pipe) and the low pressure (to measure the

reduced pressure developed by the flow through the flow element). Not all connection locations

are the same and are based on the type of flow element used and manufacture specifications.

Pitot Tubes vary from the standard Pitot Tube to the Averaging Pitot Tube. The standard Pitot

Tube uses two taps and the averaging Pitot Tube uses just one. When dealing with Orifice Tap

Locations, there are Flange Taps, Vena Contracta Taps, and Pipe Taps located at different

positions for measuring pressure drops.

Flange Taps are in the two flanges between the Orifice Plate. These tap connections requires thedistance to be 1 inch upstream of the Orifice Plate, and 1 inch downstream of the Orifice Plate.

Vena Contracta Taps are located at 1 pipe diameter upstream of the Orifice Plate and ½ the

pipe diameter downstream of the Orifice Plate.

Pipe Taps are located at 2 ½ times the pipe diameter upstream of the Orifice Plate and 8 times

the pipe diameter downstream of the Orifice Plate.




Flow Module Page 28

NOTE

Pipe Tap Locations are generally specified by the manufacture for Flow

Nozzles and Low-Loss Flow tubes, whereas pipe taps for Venturi Tubes aremanufactured with the tubes purchased.

The following picture illustrates Orifice Plate Tap Locations:


DESCRIBE how DIFFEENTIAL INSTRUMENT LOCATIONS areKEO 4.15.

determined for L iquid, Gas, and Steam flow applications.




Flow Module Page 29

When installing Differential Pressure Instruments/Transmitters, there are different requirements

for Liquid, Gas and Steam flow applications. The following picture illustrates how they are to be

connected to the process flow in order to accurately measure flow:


Location of a flow transmitter varies with the type of flowing fluid

Liquid Flow Transmitter location must be mounted below the elevation of the flow element,

and the impulse lines must be filled with the liquid being measured as depicted below:




Flow Module Page 30

Care must be exercised to ensure that no bubbles are trapped in the instrument or impulse lines.

This is accomplished via special valves for venting and releasing any air that may have entered

the transmitter or impulse lines.

A discuss later on will address how transmitter manifold assemblies can accomplish

this or the use of special vent release fittings on a transmitter.

The length of the transmitter impulse lines has no effect on the measurement accuracy as long as

the two impulse lines start and end at equal elevations as indicated in the above picture.

Gas Flow Transmitter location must be mounted above the elevation of the flow element and

the diameter of the impulse lines must be large enough and routed so that any liquids which may

condense in the impulse lines drain freely into the main piping as depicted below:




Flow Module Page 31

Steam Flow Transmitter location must be located below the elevation of the flow element even

though the fluid is a vapor. This is because steam condenses to water very easy, and mounting it

below the flow element allows the instrument and impulse lines to fill with condensate.




Flow Module Page 32

The steam condensate protects the instrument from coming in contact with the hot steam. The

best way to set up this transmitter is to manually backfill the impulse lines with water. The

following picture illustrates how to correctly locate the Steam Flow Transmitter:




Flow Module Page 33

SUMMARY

The standard Pitot Tube uses two taps and the averaging Pitot Tube uses just one.

When dealing with Orifice Tap Locations, there are Flange Taps, Vena Contracta

Taps, and Pipe Taps located at different positions for measuring pressure drops. Flange Taps are in the two flanges between the Orifice Plate. These tap connections

requires the distance to be 1 inch upstream of the Orifice Plate, and 1 inch downstream of

the Orifice Plate.

Vena Contracta Taps are located at 1 pipe diameter upstream of the Orifice Plate and ½

the pipe diameter downstream of the Orifice Plate.

Pipe Taps are located at 2 ½ times the pipe diameter upstream of the Orifice Plate and 8

times the pipe diameter downstream of the Orifice Plate.

Pipe Tap Locations are generally specified by the manufacture for Flow Nozzles and

Low-Loss Flow tubes, whereas pipe taps for Venturi Tubes are manufactured with the

tubes purchased.

When installing Differential Pressure Instruments/Transmitters, there are different

requirements for Liquid, Gas and Steam flow applications.

Liquid Flow Transmitter location must be mounted below the elevation of the flow

element, and the impulse lines must be filled with the liquid being measured.

Gas Flow Transmitter location must be mounted above the elevation of the flow

element and the diameter of the impulse lines must be large enough and routed so that

any liquids which may condense in the impulse lines drain freely into the main piping.

Steam Flow Transmitter location must be located below the elevation of the flow

element even though the fluid is a vapor. This is because steam condenses to water veryeasy, and mounting it below the flow element allows the instrument and impulse lines to

fill with condensate.

The steam condensate protects the instrument from coming in contact with the hot steam.

DESCRIBE how BLOCKING VALVES AND MANIFOLDS are used forKEO 4.16.

measuring differential measurements associated with flow.

A Blocking Valve is a valve used at the differential measuring instrument (transmitter, gauge, or

sensor) to provide a convenient location to isolate the instrument from the impulse, equalizing, or

venting lines and to provide a method to equalize the high and low pressure sides of the

differential instrument.




Flow Module Page 34

Equalizing instrument pressure is necessary so that the instrument can be periodically calibrated

and its zero status checked. Blocking valves may be connected with individual pipe fittings and

valves or can be part of a manifold assembly in one block that can be attached to a differential

pressure device.

Typical blocking valves are single-valve equalizers or three, four, or five valve manifolds. They

are essential in setting up and maintaining process flow instrumentation. The below picture

illustrates manifold valves:


The One-Valve is for equalizing pressure to perform a static test.

The Three-Valve is for equalizing, static testing, and isolating and is most commonly used.

The Five-Valve provides the Three-Valve function and adds the ability to vent and test.




Flow Module Page 35

The following picture depicts a typical Differential Pressure Transmitter configured to measure

flow with a three valve manifold and an Integral Orifice:

Picture page 188

DESCRIBE how VARIABLE-AREA FLOWMETERS maintain a constantKEO 4.17.

differential pressure and allows the flow area to change with flow rate.

VARIABLE-AREA FLOWMETERS maintain a constant differential pressure through the

flow of some type of flow restriction that repositions with changes in flow. This can be

accomplished by a fixed-size plug that moves in a tapered tube, a shaped plug that partially

blocks an orifice, or a restriction that moves up and down on a cone. The most common type of

Variable-Area Flowmeter is a ROTAMETER .

DESCRIBE how ROTAMETERS are used and how they measure flow.KEO 4.18.

A ROTAMETER is a tapered tube and a float with a fixed diameter. The float of the rotameter

changes its position in the tube to keep the forces acting on the float in equilibrium. One of

forces is gravity and the other force is produced by the velocity of the process fluid.




Flow Module Page 36

The following picture illustrates three types of floats depicting the fact that Rotameter floats have

different configurations for different fluids and applications and shows where on the float a

reading is taken:


As a rule, when reading floats, most floats have a sharp edge at the point where the reading

should be made on a scale.

The exception is a round float and the reading would be directly in the center. In the floats

pictured above, the general rule is the widest point on a float is where the reading reference

point is. There are also Guided Rod Glass Tube Rotameters.




Flow Module Page 37

There are Clear-Glass Tube Rotameters, Plastic Tube Rotameters, and Metal Tube Rotameters as

depicted below:


Glass Tube Rotameters are selected for fluids that are glass compatible. High temperatures

water with a high pH will actually soften glass. For non-glass compatible fluids, Plastic Tube

Rotameters are selected and are usually used with high temperatures, high pH, wet steam,

caustic soda, and hydrofluoric acid.

Metal-Tube tapered Rotameters consist of a metal tapered tube and a rod-guided float. A rod

is attached to the float passes through top and bottom guides in the tube. A magnet in the float is

coupled to a matching magnetic and indicator located outside the tube. Magnetic-Coupled

Rotameters cannot be used in areas where strong magnetic fields are generated.

Variations on Metal-Tube Rotameters include PVC Flanged Bodies and floats or with stainless

steel bodies and matching floats. Additionally, an indicating electrical transmitter is often

substituted for the visual indicator. Metal Tube Rotameters are selected for applications

involving fluids which obscure the float or those too hot, too corrosive, or involving high




Flow Module Page 38

pressures. A disadvantage to using magnetic coupled metal tube rotameters is that high

temperature can diminish the magnetic coupling effect.

SUMMARY

A Blocking Valve is a valve used at the differential measuring instrument (transmitter,

gauge, or sensor) to provide a convenient location to isolate the instrument from the

impulse, equalizing, or venting lines and to provide a method to equalize the high and

low pressure sides of the differential instrument.

Blocking valves may be connected with individual pipe fittings and valves or can be part

of a manifold assembly in one block that can be attached to a differential pressure device.

The One-Valve is for equalizing pressure to perform a static test.

The Three-Valve is for equalizing, static testing, and isolating and is most commonly

used.

The Five-Valve provides the Three-Valve function and adds the ability to vent and test.

VARIABLE-AREA FLOWMETERS maintain a constant differential pressure through

the flow of some type of flow restriction that repositions with changes in flow.

The most common type of Var iable-Area Flowmeter is a ROTAMETER .

A ROTAMETER is a tapered tube and a float with a fixed diameter. The float of the

rotameter changes its position in the tube to keep the forces acting on the float in

equilibrium. One of forces is gravity and the other force is produced by the velocity of

the process fluid.

As a rule , when reading floats, most floats have a sharp edge at the point where thereading should be made on a scale. The exception is a round float and the reading would

be directly in the center. The general r ule is the widest point on a float is where the

reading reference point is.

Glass Tube Rotameters are selected for fluids that are glass compatible. High

temperature water with a high pH will actually soften glass.

For non-glass compatible fluids, Plastic Tube Rotameters are selected and are usually

used with high temperatures, high pH, wet steam, caustic soda, and hydrofluoric acid.

Metal-Tube Rotameters consist of a metal tapered tube and a rod-guided float. A rod is

attached to the float passes through top and bottom guides in the tube. A magnet in the

float is coupled to a matching magnetic and indicator located outside the tube.




Flow Module Page 39

DESCRIBE how MODIFIED ROTAMETERS are used as PURGE ORKEO 4.19.

BYPASS METERS.

MODIFIED ROTAMETERS combine a standard rotameter with another device or the

rotameter itself is modified to achieve a specific function. Two common modified rotameters are

the Purge Meter and the Bypass Meter as depicted below:


A Purge Meter is a small metal or plastic rotameter with an adjustable valve at the inlet or outlet

of the meter to control the flow rate of the purge fluid. A Purge Meter is used for purging

applications such as regulating a small flow of nitrogen or air into an enclosure to prevent the

buildup of hazardous or noxious gases. Purge Meters are often used in a bubbler level

measuring system. A small bead or ball moves in the fluid stream to indicate the flow rate which

is accomplished by adjusting a small needle valve. Purge Meters also keep hazardous fumes and

fluids from entering the impulse lines or transmitting devices.




Flow Module Page 40

A Bypass Meter is a combination of a rotameter with an orifice plate used to measure flow rates

through large pipes. How this works is the differential pressure across the main pipe line is

matched to the differential pressure across the rotameter at the maximum flow rate. The

rotameter manufacture must provide a metering orifice plate at the inlet to the rotameter to

accomplish this matching of differential pressures.

DESCRIBE how METERING-CONE and SHAPTE-FLOAT & ORIFICEKEO 4.20.

VARIABLE-AREA METERS measure flow.

Other Variable-Area Meters use principles similar to those used in rotameters to measure flow

rate. Different from Rotameters, they consist of a straight tube meter body with other types of

movable parts. Two Common Other Variable-Area Meters are the Metering-Cone Meter, and

the Shaped-Float and Orifice Meter. The Metering Cone Meter is depicted below:


The Metering-Cone Meter is a flowmeter consisting of a straight tube and a tapered cone,

instead of a tapered tube, with an indicator that moves up and down the cone with changes in

flow. The variable area is the annular space between the flat and the tapered cone. The indicator

is often spring-loaded to allow the meter to be mounted at any angle. The indicator is often

spring loaded to allow the meter to be mounted at any angle.




Flow Module Page 41

A Shaped-Float and Orifice Meter is a flowmeter consisting of an orifice as part of the float

assembly that acts as a guide. Instead of a tapered tube, the float has a shaped profile that

provides more open flowing area as the float rises. The variable area is the annular space

between the float and the disk. The picture below depicts the Shaped-Float and Orifice Meter:


The Shaped-Float and Orifice Meter can provide external readouts as indicators or transmitters

with or without alarms.

SUMMARY

MODIFIED ROTAMETERS combine a standard rotameter with another device or the

rotameter itself is modified to achieve a specific function. Two common modified

rotameters are the Purge Meter and the Bypass Meter

A Purge Meter is a small metal or plastic rotameter with an adjustable valve at the inlet

or outlet of the meter to control the flow rate of the purge fluid.

A Purge Meter is used for purging applications such as regulating a small flow ofnitrogen or air into an enclosure to prevent the buildup of hazardous or noxious gases.

Purge Meters are often used in a bubbler level measuring systems.

A Bypass Meter is a combination of a rotameter with an orifice plate used to measure

flow rates through large pipes. How this works is the differential pressure across the main

pipe line is matched to the differential pressure across the rotameter at the maximum flow

rate.




Flow Module Page 42

The Metering-Cone Meter is a flowmeter consisting of a straight tube and a tapered

cone, instead of a tapered tube, with an indicator that moves up and down the cone with

changes in flow. The indicator is often spring loaded to allow the meter to be mounted at

any angle.

A Shaped-Float and Orifice Meter is a flowmeter consisting of an orifice as part of thefloat assembly that acts as a guide. Instead of a tapered tube, the float has a shaped profile

that provides more open flowing area as the float rises.

The Shaped-Float and Orifice Meter can provide external readouts as indicators or

transmitters with or without alarms

EXPLAIN operating principles associated with VARIABLE-AREAKEO 4.21.

FLOWMETERS.

The operating principles of a variable area flowmeters are different from the operating principles of a differential pressure flowmeter. A differential pressure flowmeter maintains a

constant flow area and measures the differential pressure. A variable area flowmeter maintains a

constant differential pressure and allows the area to change with the flow rate.

Rotameters can only provide correct flow rates for compressible gases and vapors when the

flowing conditions are the same as the design conditions. When flowing conditions have

changed, the pressure and temperature correction factors described for orifices are also valid for

rotameters.

DESCRIBE how MECHANICAL FLOWMETERS measure flow to includeKEO 4.22.

the following Posit ive-Displacement F lometers : Nutating Disc, Rotating-

Impeller, and Sliding Vane.

A MECHANICAL FLOWMETER is a flowmeter that uses the force of the flowing fluid,

usually liquid, to drive the meter. Positive Displacement Flowmeters include: Nutating Disc,

Rotating-Impeller, and Sliding Vane.

Positive Displacement Flowmeters separate the flowing stream into equal-volume segments

which are then mechanically counted. The velocity of the flowing material drives the propeller,turbine or paddle wheel and the rotational speed can be measured mechanically or electronically.

A Positive Displacement Flowmeter is a mechanical flowmeter that admits fluid into a chamber

of known volume and then discharges it. The number of times the chamber is filled during a

given interval is counted. These types of meters are commonly used for measuring total flow in

homes and factories. The chambers are arranged so that as one if filling, the other is being




Flow Module Page 43

emptied. This action is registered by a counting mechanism. The Total Flow is then determined

by reading the counters. The following picture illustrates how fluid flows through typical types

of Positive Displacement Flowmeters:





Flow Module Page 44

A Nutating Disc Meter is a positive displacement flowmeter for liquids where the liquid flows

through the chambers, causing a disk to rotate and wobble (nutate). This wobble momentarily

forms a filled chamber.

The rotation of the disc moves the chamber through the meter body. As the chamber is releasing

liquid, another chamber is being formed. A counter indicates the number the chamber has

released its volume of fluid. The rotation motion resembles that of a spinning coin just before it

stops. This type of meter us usually used as a domestic water meter.

A Rotating Impeller Meter is a positive displacement flowmeter for liquids where the liquid

flows into the chambers defined by the shape of the impellers. The impellers rotate, allowing

fluid to flow into the chambers. The fluid measurement chambers are created in the space

between the lobes and the housing. A counter indicates the number of times the fluid fills and

discharges the chambers.

A Sliding Vane Meter is a positive displacement flowmeter for liquids where the fluid fills a

chamber formed by sliding vanes mounted on a common hub rotated by the fluid. As the first

chamber fills, the hub rotates on a fixed cam, moving the chambers around the meter. One

revolution of the hub is equal to four times the chamber volume. A counter mechanism registers

each revolution.

NOTE

All Positive Displacement Flowmeters have chambers that alternately fill and

empty.

DESCRIBE how TURBINE METERS and PADDLE WHEEL METERSKEO 4.23.

measure flow.

A Turbine Meter is another example of a mechanical flowmeter. It consists of turbine blades

mounted on a wheel that measures the velocity of a liquid stream by counting pulses produced by

the blades as they pass an electromagnetic pickup.




Flow Module Page 45

The Turbine Wheel is suspended between bearings in a tubular body. The electromagnetic

pickup is threaded into the tube wall perpendicular to the wheel as illustrated below:


Flow straighteners are added before and after a turbine wheel to ensure that the velocity of steam

is the sole cause of its rotation. Turbine Meters are widely used in blending applications.

A Paddle Wheel Meter is another example of a mechanical flowmeter. It consists of a number

of paddles mounted on a shaft fastened in a housing, which can be inserted into a straight section

of piping. The housing is inserted so that only half of the paddles are exposed to the liquid

velocity. The following picture illustrates the Paddle Wheel Meter functionality below:





Flow Module Page 46

The paddles rotate in proportion to the liquid velocity like an old fashioned water wheel. This

rotation can then be detected by two methods. In one method, magnets are imbedded in the

tips of plastic paddles and are sensed by an electromagnetic coil housing . In the other

method, has a coil mounted in the housing that creates a magnetic field. The passage of the

metal tips disrupts the magnetic field. In both methods, the frequency generated by moving

paddles is linearly related to the liquid flow rate.

Paddle Wheel Meters are only used for measuring liquid flows and then only for the less critical

applications.

SUMMARY

A dif ferential pressure flowmeter maintains a constant flow area and measures the

differential pressure. A variable area flowmeter maintains a constant differential pressure

and allows the area to change with the flow rate. A MECHANICAL FLOWMETER is a flowmeter that uses the force of the flowing

fluid, usually liquid, to drive the meter.

Positive Di splacement F lowmeters separate the flowing stream into equal-volume

segments which are then mechanically counted.

A Positive Di splacement F lowmeter is a mechanical flowmeter that admits fluid into a

chamber of known volume and then discharges it. The number of times the chamber is

filled during a given interval is counted.

A Nutating Disc Meter is a positive displacement flowmeter for liquids where the liquid

flows through the chambers, causing a disk to rotate and wobble (nutate). This wobble momentarily forms a filled chamber.

A Rotating Impell er Meter is a positive displacement flowmeter for liquids where the

liquid flows into the chambers defined by the shape of the impellers. The impellers rotate,

allowing fluid to flow into the chambers.

A Sliding Vane Meter is a positive displacement flowmeter for liquids where the fluid

fills a chamber formed by sliding vanes mounted on a common hub rotated by the fluid.

As the first chamber fills, the hub rotates on a fixed cam, moving the chambers around

the meter. One revolution of the hub is equal to four times the chamber volume.

Al l Positi ve Displacement F lowmeters have chambers that alternately fill and empty.

A Tur bine Meter is another example of a mechanical flowmeter. It consists of turbine

blades mounted on a wheel that measures the velocity of a liquid stream by counting

pulses produced by the blades as they pass an electromagnetic pickup.

A Paddle Wheel Meter is another example of a mechanical flowmeter. It consists of a

number of paddles mounted on a shaft fastened in a housing. The paddles rotate in

proportion to the liquid velocity like an old fashioned water wheel.




Flow Module Page 47

DESCRIBE how MAGNETIC METERS measure flow.KEO 4.24.

Electrical Flowmeters are Magnetic Meters, Voretx Shedding Meters, and Ultrasonic

Flowmeters.

Magnetic Flowmeters are based on the electrical principle of voltage generation by a conductor

moving through a magnetic fluid. Magnetic Meters is commonly called a MAGMETER and is

an electromagnetic flowmeter consisting of a stainless steel tube lined with a non-conductive

material, with two coils mounted on the tube like a saddle.

Two Electrodes in contact with the electrically conductive fluid but insulated from the metal

tubes are located opposite one another and at right angles to the flow and magnetic field as

depicted below:


As the conductive fluid passes through the magnetic field created by the coils, a voltage is

induced into and detected by the electrodes. When the magnetic field strength, the position of the

electrodes, and the liquid’s conductivity remain constant, the generated voltage is linearly related

to the velocity of the liquid stream.




Flow Module Page 48

Magnetic Flowmeters (Magmeter) has no moving parts and now flow restricting components,

and they are not adversely affected by complicated piping configurations. They are used in many

water supply and waste water facilities and are somewhat immune to internal buildups.

DESCRIBE how MAGNETIC VORTEX SHEDDING METERS measureKEO 4.25.

flow.

A Vortex Shedding Meter is an electrical flowmeter consisting of a pipe section with

symmetrical vertical bluff body (a partial dam) across the flowing stream. A Vortex Shedding

Meter uses the formation of vortices as its principle of operation. A Vortex is a fluid moving in a

whirlpool or whirlwind motion. A Vortex Shedding Meter is depicted below:


A common way to describe how a Vortex Shedding Meter works is to look at a flag blowing in

the wind. The flag ripples faster when the wind is blowing because of the increase in vortices

formed along the flag.

A common Bluff Body shape is a triangular block with the broad surface facing upstream. As the

fluid in impeded by the bluff body, a vortex forms on one side of the body. It increases in size

until it becomes too large to remain attached to the bluff body and breaks away.




Flow Module Page 49

The information of a vortex on one side of the bluff body alters the flowing stream so that

another vortex is created on the other side of the bluff body and acts similarly. The alternating

vortices are formed and travel downstream at a frequency that is linearly proportional to the

speed of the flowing fluid and is inversely linearly proportional to the width of the body.

The frequency of release of the vortices can be measured using Temperature, Pressure,

Ultrasonic, Crystal, or Stain Gauge sensor. The Vortex Shedding Meter has been used

successfully to measure the flow of a wide variety of fluids such as Steam, Hot Oil, and

Liquefied gases such as Chlorine.

DESCRIBE how ULTRASONIC FLOWMETERS measure flow.KEO 4.26.

Ultrasonic Flowmeters are electronic flowmeters that uses the principle of sound transmission

in liquids to measure flow. They use either the change in frequency or a sound reflected from

moving elements or measure the change in the speed of sound in a moving liquid.

One major advantage of Ultrasonic Flowmeters is that nothing protrudes into the flowing liquid.

There are two types of Ultrasonic Flowmeters commonly used in industry. They are Doppler

Ultrasonic Meters and Transit Time Ultrasonic Meters.

A Doppler Ultrasonic Flowmeter is an electronic flowmeter that transmits an ultrasonic pulse

diagonally across the flow stream, which reflects off turbulence, bubbles, or suspended particles

and is detected by a receiving crystal.

The frequency of the reflected pulses, when compared to the transmitted pulses, results in a

Doppler Frequency shift that is proportional to the velocity of the flowing stream.

This is the same principle as radar used to measure the speed of vehicles on the highway, but

with different frequencies. Knowing the pipe size and velocity is sufficient to determine the

volumetric flow rate. The success of this meter is dependent on the presence of particles or

bubbles in the flowing liquid. Clear liquids or liquids with high solids entrapped cannot be

measured with a Doppler Meter.




Flow Module Page 50

A Doppler Ultrasonic Meter is depicted below:


A Transit Time Ultrasonic Flowmeter is an electronic meter consisting of two sets of

transmitting and receiving crystals, one set aimed diagonally upstream and the other aimed

diagonally downstream. The liquid velocity slows the upstream signal and increases the received

frequency while speeding up the downstream signal and decreasing the received frequency. The

difference in the measured frequencies is used to calculate the transit time of the ultrasonic

beams and thus the liquid velocity. A Transit Time Ultrasonic Flowmeter is depicted below:





Flow Module Page 51

The flowmeter circuitry is able to convert this information to a flow rate by multiplying the

velocity by the pipe area. This measurement method has been applied successfully to very large

pipes carrying clean, noncorrosive, bubble free liquids.

SUMMARY

Magnetic Flowmeters are based on the electrical principle of voltage generation by a

conductor moving through a magnetic fluid. Magnetic Meters is commonly called a

MAGMETER and is an electromagnetic flowmeter consisting of a stainless steel tube

lined with a non-conductive material, with two coils mounted on the tube like a saddle.

Magnetic Flowmeters (Magmeter) has no moving parts and now flow restricting

components, and they are not adversely affected by complicated piping configurations.

A Vortex Shedding Meter is an electrical flowmeter consisting of a pipe section with

symmetrical vertical bluff body (a partial dam) across the flowing stream.

A Vortex Shedding Meter uses the formation of vortices as its principle of operation. A

Vortex is a fluid moving in a whirlpool or whirlwind motion.

Ultrasonic Flowmeters are electronic flowmeters that uses the principle of sound

transmission in liquids to measure flow. They use either the change in frequency or a

sound reflected from moving elements or measure the change in the speed of sound in a

moving liquid.

A Doppler Ultrasonic Flowmeter is an electronic flowmeter that transmits an ultrasonic

pulse diagonally across the flow stream, which reflects off turbulence, bubbles, or

suspended particles and is detected by a receiving crystal.

A Transit Time Ultrasonic Flowmeter is an electronic meter consisting of two sets oftransmitting and receiving crystals, one set aimed diagonally upstream and the other

aimed diagonally downstream.

The liquid velocity in the Transit Time Flowmeter slows the upstream signal and

increases the received frequency while speeding up the downstream signal and

decreasing the received frequency. The difference in the measured frequencies is used to

calculate the transit time of the ultrasonic beams and thus the liquid velocity.




Flow Module Page 52

DESCRIBE how MASS FLOWMETERS measure flow to include aKEO 4.27.

CORIOLIS METER and a THERMAL MASS METER .

A MASS FLOWMETER is a flowmeter that measures the actual quality of mass of a flowing

fluid. Mass Flow measurement is a better way to determine the quantity of material than

volumetric flow measurement. Changes in pressure and temperature can affect density, which

then introduces errors into calculations that convert volumetric flow to actual quantity of

material. Two common types of mass flowmeters are the Coriolis Meter and the Thermal Mass

Meter.

A Coriolis Meter is a mass flowmeter consisting of specially formed tubing that is oscillated at a

right angle to the flowing mass of fluid. Coriolis Force is the force generated by the inertia of

fluid particles as the fluid moves toward or away from the axis of oscillation. The following

picture illustrates how Mass Flow through a meter causes a phase shift between the inlet and

outlet velocity sensors:





Flow Module Page 53

A Coriolis Mass Flowmeter uses the vibrations and twist of a tube to measure flow.

F low is divided and then passes through two tubes of equal length and shape. The tubes are

firmly attached to the meter body (a section of pipe). The two tube sections of tubing are made to

oscillate at their natural frequency in opposite directions from each other. The fluid accelerates

as it is vibrated and causes the tubing to twist back and forth while the tube oscillates.

Two detectors, one on the inlet and one on the outlet, consist of a magnet and a coil mounted on

each tubing section at the points of maximum motion. Each of these detectors develops a sine

wave current due to the opposite oscillations of the two sections of tubing as depicted in the

picture above.

The sine waves are in phase when there is no flow. When flow is present, the tubes twist in

opposite directions, resulting in the sine waves being out of phase. The degree of phase shift

varies with the mass flow through the meter. A Coriolis Mass Flowmeter accurately measures

the flow of either liquids or gasses and can also measure fluid density.

Thermal Mass Meter

A Thermal Mass Meter is a mass flowmeter consisting of two RTD (Resistance Temperature

Detector) probes and a heating element that measure the heat loss to the fluid mass. Thermal

Mass Meters are predominantly used for measuring gas flow .




Flow Module Page 54

The two RTD’s are immersed in the flow stream. One probe is in an assembly that includes an

adjacent heating element that is measured by the RDT. The other probe is spate and it measures

the temperature of the flowing fluid as depicted below:


The heated probe looses heat to the stream by convection. The electrical circuitry is designed

to maintain a constant difference in temperature between the two probes by varying the power to

the heating element. The power becomes the measured variable of the system and variations

in power are proportional to the variations in mass flow. Its circuitry includes corrections for

thermal conductivity, viscosity, and density.




Flow Module Page 55

Thermal Mass Meters are less accurate than many other types of flow metering devices,

but can be used to measure some low-pressure gases that are not dense enough for a

Coriolis Flow Meter.

DESCRIBE how ACCESSORY FLOW DEVICES function and how they areKEO 4.28.

used.

ACCESSORY FLOW DEVICES are instruments that do not actually measure flow, but use

flow principles to obtain information. Examples are devices that measure total flow and flow

switches that can be configured to trigger an alarm or a switch. An Accessory Flow Integrator is

depicted below:


An Integrator is a calculating device that totalizes the amount of flow during a specified time

period. Integrators are available for use with pulse output as produced by turbine flowmeters or

analog outputs (linear or square root) from orifice meters equipped with analog to digital

converters. When an Integrator is used for flow calculations, they can be either electronic or

pneumatic integrators to convert a differential pressure measurement to a flow rate.




Flow Module Page 56

The principle requirements for Integrators are: an accurate measurement of the differential

pressure, a conversion to flow rate, a constant time input, and an easy to read counter.

EXPLAIN how different FLOW SWITCHS function and how they are used toKEO 4.29.

include: DIFFERENTIAL PRESSURE SWITCHES, BLADE SWITCHES,

THEREMAL SWITCHES, and ROTAMETER SWITCHES.

FLOW SWITCHS are devices used to monitor flowing stream to provide a discrete electrical or

pneumatic output action at a predetermined flow rate. Flow rate switches are used to generate

alarms or shutdown signals for high or low flows. Flow switch functions are dependent on

measurement principles such as an orifice plate or a differential pressure switch as depicted

below:





Flow Module Page 57

A DIFFERENTIAL PRESSURE SWITCH is a flow switch consisting of a pair of pressure

sensing element and an adjustable spring that can be set at a specific value to operate an output

switch. The differential pressure switch measures the pressure drop across a primary flow

element.

A BLADE SWITCH is a flow switch consisting of a thin, flexible blade inserted into a pipeline.

The fluid flow develops a force which presses against the blade. The motion of the blade is

transferred through a sea and is opposed by an adjustable spring which establishes the trip point.

An electrical or pneumatic switch can sense the blade motion.

A THERMAL SWITCH is a flow switch consisting of a heated temperature sensor. The

flowing fluid carries away heat from the heated temperature sensor. The electronic circuits in the

switch can be set to trip at some predetermined flow rate.

A ROTAMETER SWITCH is a flow switch that consists of a shaped float, a fixed orifice, anda magnetic sensing switch outside the tube to activate a flow circuit at a predetermined flow rate.

SUMMARY

A Coriolis Meter is a mass flowmeter consisting of specially formed tubing that is

oscillated at a right angle to the flowing mass of fluid.

A Coriolis Mass Flowmeter uses the vibrations and twist of a tube to measure flow.

A Thermal Mass Meter is a mass flowmeter consisting of two RTD (Resistance

Temperature Detector) probes and a heating element that measure the heat loss to the

fluid mass. Thermal Mass Meters are predominantly used for measuring gas flow.

ACCESSORY FLOW DEVICES are instruments that do not actually measure flow, but

use flow principles to obtain information.

An Integrator is a calculating device that totalizes the amount of flow during a specified

time period.

The principle requirements for Integrators are: an accurate measurement of the

differential pressure, a conversion to flow rate, a constant time input, and an easy to read

counter.

FLOW SWITCHS are devices used to monitor flowing stream to provide a discrete

electrical or pneumatic output action at a predetermined flow rate.

A DIFFERENTIAL PRESSURE SWITCH is a flow switch consisting of a pair of

pressure sensing element and an adjustable spring that can be set at a specific value to

operate an output switch.

A BLADE SWITCH is a flow switch consisting of a thin, flexible blade inserted into a

pipeline.




Flow Module Page 58

A THERMAL SWITCH is a flow switch consisting of a heated temperature sensor. The

flowing fluid carries away heat from the heated temperature sensor.

A ROTAMETER SWITCH is a flow switch that consists of a shaped float, a fixed

orifice, and a magnetic sensing switch outside the tube to activate a flow circuit at a

predetermined flow rate

EXPLAIN how OPEN-CHANEL WEIRS and PARSHALL FLUME FLOWKEO 4.30.

MEASUREMTNS function and how they are used.

OPEN-CHANEL WEIRS use a restriction to create a head of liquid. A WEIR is an OPEN-

CHANEL device consisting of a flat plate that has a notch cut into the top edge as depicted

below:


The rate of flow is determined by measuring the height of liquid in the stilling basin upstream ofthe Weir. The crest is the bottom of the Weir. A Weir can be notched as a rectangular,

trapezoidal, or triangular and has a sharp upstream edge (similar to an orifice plate). The Weir is

installed in the outlet of a stilling basin. The flow is related to the height of the water above

the bottom of the Weir Notch measured at a point upstream of the Weir where the water has no

draw-down.




Flow Module Page 59

Weir Height Measurements are made a distance upstream equal to four times the height of

the water above the Crest.

A PARSHALL FLUME is a special form of an open-channel flow element that requires much

less channel elevation than a Weir. A PARSHALL FLUME has a horizontal configuration

similar to a Venturi Tube, with converging inlet walls, a parallel throat, and diverging outlet

walls as depicted below:


The bottom profile is specially designed to generate a hydraulic jump in the throat. Flow can be

calculated from a measurement of the elevation of the inlet water at a specific point.

PARSHALL FLUMES are much less subject to problems from dirt or other fouling factors than

a Weir and have the ability to measure much larger flows.




Flow Module Page 60

EXPLAIN how a BELT WEIGHING SYSTEM is used to measure a solidsKEO 4.31.

flow.

A BELT WEIGHING SYSTEM is used to measure the flow of solids like granular (bulk)

solids. Measuring solids is a different task because of the basic properties solids consist of. Bulk

solids vary greatly in flow properties. Some are sticky and do not flow well, and others are so

fine and slippery that they flow like liquids.

Bulk Solids are usually transported by a belt, screw, or a drag conveyor. The most successful

flow measurement is by the use of a BELT WEIGHING SYSTEM.

A BELT WEIGHING SYSTEM is a solids flow meter consisting of a specially constructed

belt conveyer and a section that is support by electronic weight cells as depicted below:


The conveyer belt is designed to minimize the transfer of the weight of the unmeasured section

of the conveyer. Solids are deposited on the conveyer and carried onto the weighing section.




Flow Module Page 61

The weight of the solids on the measured section divided by the length of the measured

section times the conveyer speed results is a pounds per unit time.

SUMMARY

OPEN-CHANEL WEIRS use a restriction to create a head of liquid.

The liquid head pressure is what is measured in Weirs.

A WEIR is an OPEN-CHANEL device consisting of a flat plate that has a notch cut into

the top edge.

Weir Height Measurements are made a distance upstream equal to four times the

height of the water above the Crest.

A PARSHALL FLUME is a special form of an open-channel flow element that requires

much less channel elevation than a Weir.

A PARSHALL FLUME has a horizontal configuration similar to a Venturi Tube, with

converging inlet walls, a parallel throat, and diverging outlet walls.

PARSHALL FLUMES are much less subject to problems from dirt or other fouling

factors than a Weir and have the ability to measure much larger flows.

A BELT WEIGHING SYSTEM is used to measure the flow of solids like granular

(bulk) solids.

A BELT WEIGHING SYSTEM is a solids flow meter consisting of a specially

constructed belt conveyer and a section that is support by electronic weight cells.

The weight of the solids on the measured section of a Belt Weighing System is divided

by the length of the measured section times the conveyer speed results is a pounds perunit time.




STEP TWO

Flow Measurement Course

Skill/Performance Objectives

Skill Knowledge Introduction:

Below are the skill knowledge objectives. How these objectives are performed depend on

equipment and laboratory resources available. With each skill objective it is assumed that a set

of standard test equipment and tools be provided.

For example, to be able to perform flow calibration tasks, the following tools and equipment will

be required:

1. A measuring device capable of measuring / indicating the output signal such as

meter or smart calibrator

2. Pressure sources to simulate head pressure generated for differential pressure

device/transmitter

3. An appropriate power supply to power the equipment being calibrated

Skill Terminal Objective (STO)

Given a Flow Measurement Task Checklist, under the direction of anSTO 4.1.

instructor, complete a series of tasks using calibration equipment, Flow

indicating devices, and Flow transmitting devices to demonstrate mastery of

both knowledge and skill objectives associated with the measurement ofFlow.

Documents

Module 10 Flow Measurement