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Flow Measurement

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Title: Flow Measurement


1
Flow Measurement(basics)
  • Ashvani Shukla
  • CI
  • Reliance

2
INTRODUCTION
  • In the physical world, mechanical engineers are
    frequently required to monitor or control the
    flow of various fluids through pipes, ducts and
    assorted vessels. This fluid can range from thick
    oils to light gasses. While some techniques work
    better with some groups of fluids, and less well
    with others, some are not at all suitable for
    some applications. In this primer on fluid flow
    instrumentation we will look at a wide variety of
    flow transducers and their application in the
    physical world.

3
Fluid flow measurement
  • Fluid flow measurement can encompass a wide
    variety of fluids and applications. To meet this
    wide variety of applications the instrumentation
    industry has, over many years, developed a wide
    variety of instruments. The earliest known uses
    for flow come as early as the first recorded
    history. The ancient Sumerian cities of UR and
    Kish, near the Tigris and Euphrates rivers
    (around 5000 B.C.) used water flow measurement to
    manage the flow of water through the aqueducts
    feeding their cities. In this age the a simple
    obstruction was placed in the water flow, and by
    measuring the height of the water flowing over
    the top of the obstruction, these early engineers
    could determine how much water was flowing. In
    1450 the Italian art architect Battista Alberti
    invented the first mechanical anemometer. It
    consisted of a disk placed perpendicular to the
    wind, and the force of the wind caused it to
    rotate. The angle of inclination of the disk
    would then indicate the wind velocity. This was
    the first recorded instrument to measure wind
    speed. An English inventor, Robert Hooke
    reinvented this device in 1709, along with the
    Mayan Indians around that same period of time.
    Today we would look down our noses at these crude
    methods of flow measurement, but as you will see,
    these crude methods are still in use today.

4
TYPE OF FLOW
  • There are in general three types of fluid flow in
    pipes
  • laminar
  • turbulent
  • transient
  • Laminar flow
  • Laminar flow generally happens when dealing with
    small pipes and low flow velocities. Laminar flow
    can be regarded as a series of liquid cylinders
    in the pipe, where the innermost parts flow the
    fastest, and the cylinder touching the pipe isn't
    moving at all.
  • Shear stress in a laminar flow depends almost
    only on viscosity - µ - and is independent
    of density - ?.
  • Turbulent flow
  • In turbulent flow vortices, eddies and wakes make
    the flow unpredictable. Turbulent flow happens in
    general at high flow rates and with larger pipes.
  • Shear stress in a turbulent flow is a function
    of density - ?.
  • Transitional flow

5
CONTINUE..
  • Transitional flow is a mixture of laminar and
    turbulent flow, with turbulence in the center of
    the pipe, and laminar flow near the edges. Each
    of these flows behave in different manners in
    terms of their frictional energy loss while
    flowing and have different equations that predict
    their behavior.
  • Turbulent or laminar flow is determined by the
    dimensionless Reynolds Number.
  • Reynolds Number
  • The Reynolds number is important in analyzing any
    type of flow when there is substantial velocity
    gradient (i.e. shear.) It indicates the relative
    significance of the viscous effect compared to
    the inertia effect. The Reynolds number is
    proportional to inertial force divided by viscous
    force.
  • The flow is
  • laminar when Re lt 2300
  • transient when 2300 lt Re lt 4000
  • turbulent when 4000 lt Re

6
TYPE OF FLOW
  • Uniform Flow, Steady Flow
  • It is possible - and useful - to classify the
    type of flow which is being examined into small
    number of groups. If we look at a fluid flowing
    under normal circumstances - a river for example
    - the conditions at one point will vary from
    those at another point (e.g. different velocity)
    we have non-uniform flow. If the conditions at
    one point vary as time passes then we have
    unsteady flow. Under some circumstances the flow
    will not be as changeable as this. He following
    terms describe the states which are used to
    classify fluid flow
  • uniform flow If the flow velocity is the same
    magnitude and direction at every point in the
    fluid it is said to be uniform.
  • non-uniform If at a given instant, the velocity
    is not the same at every point the flow is
    non-uniform. (In practice, by this definition,
    every fluid that flows near a solid boundary will
    be non-uniform - as the fluid at the boundary
    must take the speed of the boundary, usually
    zero. However if the size and shape of the of the
    cross-section of the stream of fluid is constant
    the flow is considered uniform.)
  • steady A steady flow is one in which the
    conditions (velocity, pressure and cross-section)
    may differ from point to point but DO NOT change
    with time. unsteady If at any point in the
    fluid, the conditions change with time, the flow
    is described as unsteady. (In practice there is
    always slight variations in velocity and
    pressure, but if the average values are constant,
    the flow is considered steady.

7
CONTINUOUS
  • Combining the above we can classify any flow in
    to one of four type
  • 1. Steady uniform flow. Conditions do not change
    with position in the stream or with time. An
    example is the flow of water in a pipe of
    constant diameter at constant velocity. Fluid
    Mechanics Fluid Dynamics The Momentum and
    Bernoulli Equations.
  • 2. Steady non-uniform flow. Conditions change
    from point to point in the stream but do not
    change with time. An example is flow in a
    tapering pipe with constant velocity at the inlet
    - velocity will change as you move along the
    length of the pipe toward the exit.
  • 3. Unsteady uniform flow. At a given instant in
    time the conditions at every point are the same,
    but will change with time. An example is a pipe
    of constant diameter connected to a pump pumping
    at a constant rate which is then switched off.
  • 4. Unsteady non-uniform flow. Every condition of
    the flow may change from point to point and with
    time at every point. For example waves in a
    channel.

8
CONTINUOUS
  • Compressible or Incompressible All fluids are
    compressible - even water - their density will
    change as pressure changes. Under steady
    conditions, and provided that the changes in
    pressure are small, it is usually possible to
    simplify analysis of the flow by assuming it is
    incompressible and has constant density. As you
    will appreciate, liquids are quite difficult to
    compress - so under most steady conditions they
    are treated as incompressible. In some unsteady
    conditions very high pressure differences can
    occur and it is necessary to take these into
    account - even for liquids. Gasses, on the
    contrary, are very easily compressed, it is
    essential in most cases to treat these as
    compressible, taking changes in pressure into
    account.

9
continuous
  • Three-dimensional flow Although in general all
    fluids flow three-dimensionally, with pressures
    and velocities and other flow properties varying
    in all directions, in many cases the greatest
    changes only occur in two directions or even only
    in one. In these cases changes in the other
    direction can be effectively ignored making
    analysis much more simple. Flow is one
    dimensional if the flow parameters (such as
    velocity, pressure, depth etc.) at a given
    instant in time only vary in the direction of
    flow and not across the cross-section. The flow
    may be unsteady, in this case the parameter vary
    in time but still not across the cross-section.
    An example of one-dimensional flow is the flow in
    a pipe. Note that since flow must be zero at the
    pipe wall - yet non-zero in the Centre - there is
    a difference of parameters across the
    cross-section. Should this be treated as
    two-dimensional flow? Possibly - but it is only
    necessary if very high accuracy is required. A
    correction factor is then usually applied.

10
continuous
  • Flow is two-dimensional if it can be assumed that
    the flow parameters vary in the direction of flow
    and in one direction at right angles to this
    direction. Streamlines in two-dimensional flow
    are curved lines on a plane and are the same on
    all parallel planes. An example is flow over a
    weir foe which typical streamlines can be seen in
    the figure below. Over the majority of the length
    of the weir the flow is the same - only at the
    two ends does it change slightly. Here correction
    factors may be applied.

One dimensional flow
11
Two dimensional flow
12
Flow rate.
  • Mass flow rate If we want to measure the rate at
    which water is flowing along a pipe. A very
    simple way of doing this is to catch all the
    water coming out of the pipe in a bucket over a
    fixed time period. Measuring the weight of the
    water in the bucket and dividing this by the time
    taken to collect this water gives a rate of
    accumulation of mass. This is know as the mass
    flow rate.
  • Volume flow rate - Discharge. More commonly we
    need to know the volume flow rate - this is more
    commonly know as discharge. (It is also commonly,
    but inaccurately, simply called flow rate). The
    symbol normally used for discharge is Q. The
    discharge is the volume of fluid flowing per unit
    time. Multiplying this by the density of the
    fluid gives us the mass flow rate.

13
Type of flow measurement
  • The most common principals for fluid flow
    metering are
  • Differential Pressure Flow meters
  • Velocity Flow meters
  • Positive Displacement Flow meters
  • Mass Flow meters
  • Open Channel Flow meters

14
1.Differential Pressure Flow meters
  • In a differential pressure drop device the flow
    is calculated by measuring the pressure drop over
    an obstructions inserted in the flow. The
    differential pressure flow meter is based on
    the Bernoulli's Equation, where the pressure drop
    and the further measured signal is a function of
    the square flow speed.

15
  • Common types of differential pressure flow meters
    are
  • Orifice Plates
  • Flow Nozzles
  • Venturi Tubes
  • Variable Area - Rota meters
  • Orifice Plate
  • An orifice plate is a device used for measuring
    flow rate, for reducing pressure or for
    restricting flow (in the latter two cases it is
    often called a restriction plate). Either a
    volumetric or mass flow rate may be determined,
    depending on the calculation associated with the
    orifice plate.With an orifice plate, the fluid
    flow is measured through the difference in
    pressure from the upstream side to the downstream
    side of a partially obstructed pipe. The plate
    obstructing the flow offers a precisely measured
    obstruction that narrows the pipe and forces the
    flowing fluid to constrict.

16
continuous
  • Orifice Plate is the heart of the Orifice Meter.
    It restricts the flow and develops the
    Differential Pressure which is proportional to
    the square of the flow rate. The flow measuring
    accuracy entirely depends upon the quality of
    Orifice plate, its installation and maintains.
  • When measuring wet gas or saturated steam a weep
    hole is drilled in a concentrically bored orifice
    plate. This is a small hole drilled on the
    orifice plate such that its location is exactly
    on ID of the main pipe.

17
  • The Orifice plates are manufactured as per ISA /
    AGA/ API / ANSI standards and in various
    materials
  • such as SS304 /SS316 / SS316L /Hestoly C / Monel
    / PTFE coated.
  • Various bores are used for various applications.
  • Orifice Plate is categories in two types -
    Paddle Type Universal Palate.
  • Paddle Type Orifice Plate
  • This plate is sandwiched between two Orifice
    Flanges. Tag Plate of orifice plate projects out
    from Orifice flanges and it indicates the
    existence of Orifice plate. Details such as Tag
    NO /Orifice ID / Pipe ID / Plate Material are
    stamped on one side of the tag plate which faces
    upstream side of the pipe line. Outside diameter
    of the orifice plate equals to PCD-1 Bolt Dia.
    This ensures the concentricity with the main pipe
    line. The other method to maintain the
    concentricity is by using sleeves on the bolts or
    by providing dowel pins on the Orifice Flanges.
  • Universal Orifice Plate
  • This is a circular plate designed to fit in the
    Orifice fittings / Plate holders / carrier rings
    / Ring Type Joints(RTJ).

18
Technical Specification
1.Size for Integral Design 15, 20, 25, 40 mm
2.Size for Flanged Design 25, 40, 50, 65, 80,
100, 150 ...250 mm 3.Material- Flanges
Carrier Ring A105 / SS304/ SS316 / SS316L / CS
Other materials on request. 4.Orifice
Plate SS304, SS316, SS316L, Hast C, Monel, PP,
PVC,PTFE, Coated or Clad with PP / HDPE / PTFE.
5.Gasket CAF / SS Spiral Wound CAF / PTFE /
PVC / Rubber, Other materials as per special
request. 6.Stud / Nut ASTM A193 Gr B/ASTM
A194 CI 2H A193 B16/A194 C14 7.Standards
Applicable Design - ISA RP 3.2 / DN 1952 / BS
1042 - 1981-84 8.Bore Calculation ISO 5167 /
BS 1042 / RW Miller / L. K. SPIN / AGE - 3.7
9.Flanges ANSI B-16-36 / or Equivalent
10.Types Square edge concentric, Quadrant
edges, Conical entrance, Eccentric.
11.Pressure Toppings For 1" to 16" - Flange
Taps / Corner Taps. Above 16" - D x D/2
19
Type Orifice Plate
  • Paddle Type Orifice Plate
  • Concentric Beveled Bore
  • Application  This Most Common Bore Used In The
    Industries. This Is The Only Type Generally
    Accepted For Use In Custody Transfer Measurement,
    Since Adequate Data Is Not Available For Other
    Bores. Used Primarily For Clean Homogeneous
    Liquids, Gases, Non Viscous Fluids. The Bevel Is
    Matched At 45 Angle To The Desired Throat
    Thickness.

20
2) Restriction BoreApplication This Type Is
Not Used For Flow Measurement But For Dropping
The Pressure Considerably And Reducing The Flow
Accordingly. The Bore Is Not Beveled But Kept
Straight. The Beta Ratio Has No Limit As Accuracy
Is Not The Goal
21
Eccentric Bore
  • Application  Used For Measurement Of Flow For
    Fluids Containing Solids And Slurries. It Is Also
    Used For Vapors And Gases Where Condensation Is
    Present. The Eccentric Bore Is Offset To Where
    The Bore Edge Is Inscribed In A Circle That Is
    98 The Line Id.

22
4) Segmenta Bore
  • Application
  • The Segmental Bore Is Located In The Same Way
    That The Eccentric Bore Is. This Type Is Used
    Primarily For Slurries Or Extremely Dirty Gases
    Where The Flow May Contain Impurities Heavier
    Than The Fluid.

23
Quadrant Bore
  • Application  Used For High Viscous Fluids Such
    As Heavy Crude, Syrups  And Slurries. It Is
    Always Recommended For Flow Where Reynolds Number
    Is Less Than 10,000.The Inlet Is Quarter Of A
    Circle And The Plate Thickness Must Be At Least
    Radius Of The Inlet.

24
6) Ring Type Joint Integral
  • Application
  • These Are Available In Oval Or Octal Shapes.
    Orifice Plate Is A Part Of RTJ Gasket.

25
Ring Type Joint- Separate
  • Application  These Are Available In Oval Or
    Octal Shapes. The  Orifice Plate Is Universal
    Type And Snap Fitted On The RTJ Gasket By Screws.

26
Universal Orifice Plates
Application  This Is A Circular Plate Designed
To Fit In The Orifice Fittings / Plate Holders /
Carrier Rings / Ring Type Joints(RTJ).
27
Various Orifice Assemblies
WNRF - Flange Taps
WNRF - Corner Taps
28
Orifice working principle
  • Working
  • The orifice plate, being fixed at a section of
    the pipe, creates an obstruction to the flow by
    providing an opening in the form of an orifice to
    the flow passage.

When an orifice plate is placed in a pipe
carrying the fluid whose rate of flow is to be
measured, the orifice plate causes a pressure
drop which varies with the flow rate. This
pressure drop is measured using a differential
pressure sensor and when calibrated this pressure
drop becomes a measure flow rate. The flow rate
is given by.
29
Where, Qa flow rateCd Discharge
coefficientA1 Cross sectional area of pipeA2
Cross sectional area of orificeP1, P2 Static
Pressures
  • The main parts of an orifice flow meter are as
    followsA stainless steel orifice plate which
    is held between flanges of a pipe carrying the
    fluid whose flow rate is being measured.
  • It should be noted that for a certain distance
    before and after the orifice plate fitted between
    the flanges, the pipe carrying the fliud should
    be straight in order to maintain laminar flow
    conditions.
  • Openings are provided at two places 1 and 2 for
    attaching a differential pressure sensor (U-tube
    manometer, differential pressure gauge etc) as
    shown in the diagram.

30
Operation of Orifice Meter
  • The detail of the fluid movement inside the pipe
    and orifice plate has to be understood.
  • The fluid having uniform cross section of flow
    converges into the orifice plates opening in its
    upstream. When the fluid comes out of the orifice
    plates opening, its cross section is minimum and
    uniform for a particular distance and then the
    cross section of the fluid starts diverging in
    the down stream.
  • At the upstream of the orifice, before the
    converging of the fluid takes place, the pressure
    of he fluid (P1) is maximum. As the fluid starts
    converging, to enter the orifice opening its
    pressure drops. When the fluid comes out of the
    orifice opening, its pressure is minimum (p2) and
    this minimum pressure remains constant in the
    minimum cross section area of fluid flow at the
    downstream.
  • This minimum cross sectional area of the fluid
    obtained at downstream from the orifice edge is
    called VENA-CONTRACTA.
  • The differential pressure sensor attached between
    points 1 and 2 records the pressure difference
    (P1 P2) between these two points which becomes
    an indication of the flow rate of the fluid
    through the pipe when calibrated.

31
  • Applications of Orifice Meter
  • The concentric orifice plate is used to measure
    flow rates of pure fluids and has a wide
    applicability as it has been standardized.
  • The eccentric and segmental orifice plates are
    used to measure flow rates of fluids containing
    suspended materials such as solids, oil mixed
    with water and wet steam.
  • Advantages of Orifice Meter
  • It is very cheap and easy method to measure flow
    rate.
  • It has predictable characteristics and occupies
    less space.
  • Can be use to measure flow rates in large pipes.
  • Limitations of Orifice Meter
  • The vena-contracta length depends on the
    roughness of the inner wall of the pipe and
    sharpness of the orifice plate. In certain cases
    it becomes difficult to tap the minimum pressure
    (P2) due to the above factor.
  • Pressure recovery at downstream is poor, that is,
    overall loss varies from 40 to 90 of the
    differential pressure.
  • In the upstream straightening vanes are a must to
    obtain laminar flow conditions.
  • Gets clogged when the suspended fluids flow.
  • The orifice plate gets corroded and due to this
    after sometime, inaccuracy occurs. Moreover the
    orifice plate has low physical strength.
  • The coefficient of discharge is low.

32
Venturi Tube
  • Due to simplicity and dependability, the Venturi
    tube flowmeter is often used in applications
    where it's necessary with higher TurnDown Rates,
    or lower pressure drops, than the orifice plate
    can provide.
  • In the Venturi Tube the fluid flow rate is
    measured by reducing the cross sectional flow
    area in the flow path, generating a pressure
    difference. After the constricted area, the fluid
    is passes through a pressure recovery exit
    section, where up to 80 of the differential
    pressure generated at the constricted area, is
    recovered. With proper instrumentation and flow
    calibrating, the Venturi Tube flowrate can be
    reduced to about 10 of its full scale range with
    proper accuracy. This provides a TurnDown
    Rate 101.

33
Venturi tube
34
Flow Nozzles
  • Flow nozzles are often used as measuring elements
    for air and gas flow in industrial applications

35
  • The flow nozzle is relative simple and cheap, and
    available for many applications in many
    materials.
  • The Turndown Rate and accuracy can be compared
    with the orifice plate.
  • The Sonic Nozzle - Critical (Choked) Flow Nozzle
  • When a gas accelerates through a nozzle, the
    velocity increase and the pressure and the gas
    density decrease. The maximum velocity is
    achieved at the throat, the minimum area, where
    it breaks Mach 1 or sonic. At this point it's not
    possible to increase the flow by lowering the
    downstream pressure. The flow is choked.
  • This situation is used in many control systems to
    maintain fixed, accurate, repeatable gas flow
    rates unaffected by the downstream pressure.

36
Recovery of Pressure Drop in Orifices, Nozzles
and Venturi Meters
  • After the pressure difference has been generated
    in the differential pressure flow meter, the
    fluid pass through the pressure recovery exit
    section, where the differential pressure
    generated at the constricted area is partly
    recovered. As we can see, the pressure drop in
    orifice plates are significant higher than in the
    venturi tubes.

37
Variable Area Flow meter or Rota meter
  • The Rota meter consists of a vertically oriented
    glass (or plastic) tube with a larger end at the
    top, and a metering float which is free to move
    within the tube. Fluid flow causes the float to
    rise in the tube as the upward pressure
    differential and buoyancy of the fluid overcome
    the effect of gravity.

38
continuous
  • The float rises until the annular area between
    the float and tube increases sufficiently to
    allow a state of dynamic equilibrium between the
    upward differential pressure and buoyancy
    factors, and downward gravity factors.
  • The height of the float is an indication of the
    flow rate. The tube can be calibrated and
    graduated in appropriate flow units.
  • The rotameter meter typically have a TurnDown
    Ratio up to 121. The accuracy may be as good as
    1 of full scale rating.
  • Magnetic floats can be used for alarm and signal
    transmission functions.

39
Velocity Flow meters
  • In a velocity flow meter the flow is calculated
    by measuring the speed in one or more points in
    the flow, and integrating the flow speed over the
    flow area

40
Pitot Tubes
  • The pitot tube are one the most used (and
    cheapest) ways to measure fluid flow, especially
    in air applications like ventilation and HVAC
    systems, even used in airplanes for speed
    measurent. The pitot tube measures the fluid flow
    velocity by converting the kinetic energy of the
    flow into potential energy.
  • The use of the pitot tube is restricted to point
    measuring. With the "annubar", or multi-orifice
    pitot probe, the dynamic pressure can be measured
    across the velocity profile, and the annubar
    obtains an averaging effect.

41
Calorimetric Flow meter
  • The calorimetric principle for fluid flow
    measurement is based on two temperature sensors
    in close contact with the fluid but thermal
    insulated from each other.

42
One of the two sensors is constantly heated and
the cooling effect of the flowing fluid is used
to monitor the flow rate. In a stationary (no
flow) fluid condition there is a constant
temperature difference between the two
temperature sensors. When the fluid flow
increases, heat energy is drawn from the heated
sensor and the temperature difference between the
sensors are reduced. The reduction is
proportional to the flow rate of the
fluid. Response times will vary due the thermal
conductivity of the fluid. In general lower
thermal conductivity require higher velocity for
proper measurement. The calorimetric flow meter
can achieve relatively high accuracy at low flow
rates
Vortex Flow Meter An obstruction in a fluid flow
creates vortices in a downstream flow. Every
obstruction has a critical fluid flow speed at
which vortex shedding occurs. Vortex shedding is
the instance where alternating low pressure zones
are generated in the downstream.
43
  • Electromagnetic Flowmeter
  • An electromagnetic flowmeter operate on Faraday's
    law of electromagnetic induction that states that
    a voltage will be induced when a conductor moves
    through a magnetic field. The liquid serves as
    the conductor and the magnetic field is created
    by energized coils outside the flow tube.
  • The voltage produced is directly proportional to
    the flow rate. Two electrodes mounted in the pipe
    wall detect the voltage which is measured by a
    secondary element.
  • Electromagnetic flowmeters can measure difficult
    and corrosive liquids and slurries, and they can
    measure flow in both directions with equal
    accuracy.
  • Electromagnetic flowmeters have a relatively high
    power consumption and can only be used for
    electrical conductive fluids as water.
  • The Electromagnetic Flowmeter Principle - An
    introduction to the electromagnetic flowmeter
    principle

44
Ultrasonic Doppler Flow meter
  • The effect of motion of a sound source and its
    effect on the frequency of the sound was observed
    and described by Christian Johann Doppler.
  • The frequency of the reflected signal is modified
    by the velocity and direction of the fluid flow
  • If a fluid is moving towards a transducer, the
    frequency of the returning signal will increase.
    As fluid moves away from a transducer, the
    frequency of the returning signal decrease.
  • The frequency difference is equal to the
    reflected frequency minus the originating
    frequency and can be use to calculate the fluid
    flow speed.
  • The Ultrasonic Doppler and Time of Flight Flow
    meter

45
Positive Displacement Flowmeter
  • The positive displacement flow meter measures
    process fluid flow by precision-fitted rotors as
    flow measuring elements. Known and fixed volumes
    are displaced between the rotors. The rotation of
    the rotors are proportional to the volume of the
    fluid being displaced.
  • The number of rotations of the rotor is counted
    by an integral electronic pulse transmitter and
    converted to volume and flow rate.
  • The positive displacement rotor construction can
    be done in several ways
  • Reciprocating piston meters are of single and
    multiple-piston types.
  • Oval-gear meters have two rotating, oval-shaped
    gears with synchronized, close fitting teeth. A
    fixed quantity of liquid passes through the meter
    for each revolution. Shaft rotation can be
    monitored to obtain specific flow rates.
  • Notating disk meters have movable disks mounted
    on a concentric sphere located in spherical
    side-walled chambers. The pressure of the liquid
    passing through the measuring chamber causes the
    disk to rock in a circulating path without
    rotating about its own axis. It is the only
    moving part in the measuring chamber.
  • Rotary vane meters consists of equally divided,
    rotating impellers, two or more compartments,
    inside the meter's housings. The impellers are in
    continuous contact with the casing. A fixed
    volume of liquid is swept to the meter's outlet
    from each compartment as the impeller rotates.
    The revolutions of the impeller are counted and
    registered in volumetric units.
  • The positive displacement flowmeter may be used
    for all relatively nonabrasive fluids such as
    heating oils, lubrication oils, polymer
    additives, animal and vegetable fat, printing
    ink, Dichlorodifluoromethane R-12, and many more.
  • Accuracy may be up to 0.1 of full rate with a
    TurnDown of 701 or more.

46
Mass Flow meters
  • Mass meters measure the mass flow rate directly.
  • Thermal Flow meter
  • The thermal mass flowmeter operates independent
    of density, pressure, and viscosity. Thermal
    meters use a heated sensing element isolated from
    the fluid flow path where the flow stream
    conducts heat from the sensing element. The
    conducted heat is directly proportional to the
    mass flow rate and the temperature difference is
    calculated to mass flow.
  • The accuracy of the thermal mass flow device
    depends on the calibrations reliability of the
    actual process and variations in the temperature,
    pressure, flow rate, heat capacity and viscosity
    of the fluid.
  • Coriolis Flow meter
  • Direct mass measurement sets Coriolis flowmeters
    apart from other technologies. Mass measurement
    is not sensitive to changes in pressure,
    temperature, viscosity and density. With the
    ability to measure liquids, slurries and gases,
    Coriolis flowmeters are universal meters.
  • Coriolis Mass Flowmeter uses the Coriolis effect
    to measure the amount of mass moving through the
    element. The fluid to be measured runs through a
    U-shaped tube that is caused to vibrate in an
    angular harmonic oscillation. Due to the Coriolis
    forces, the tubes will deform and an additional
    vibration component will be added to the
    oscillation. This additional component causes a
    phase shift on some places of the tubes which can
    be measured with sensors.
  • The Coriolis flow meters are in general very
    accurate, better than /-0,1 with an turndown
    rate more than 1001. The Coriolis meter can also
    be used to measure the fluids density.

47
Open Channel Flow meters
  • A common method of measuring flow through an open
    channel is to measure the height of the liquid as
    it passes over an obstruction as a flume or weir
    in the channel.
  • Common used is the Sharp-Crested Weir, the
    V-Notch Weir, the Cipolletti weir, the
    Rectangular-Notch Weir, the Parshall Flume or
    Venturi Flume.
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