this section speaks about the quantity flow meter and its different types i.e. positive displacement flow meter and metering pump, it comprises discussion on mass flow meter, coriolis flow meter, variable reluctance tacho generator and linear resistance element flow meter.

1. FLOW MEASUREMENT
PART IV
ER. FARUK BIN POYEN, Asst. Professor
DEPT. OF AEIE, UIT, BU, BURDWAN, WB, INDIA
faruk.poyen@gmail.com

2. Contents:
Quantity Flow Meter
 Positive Displacement Meter
 Metering Pump
Mass Flow Meter
 Coriolis Mass Flow Meter
Miscellaneous Flow Meter
 Variable Reluctance Tacho generator
 Linear Resistance Element Flow Meter
2

3. Quantity Flow Meter
Quantity flow meter are of two types
1) Positive Displacement Meters and 2) Metering Pumps
Positive Displacement Meters have further sub divisions
 Nutating Disk
 Oscillating Piston
 Rotating Vane
 Lobed Impeller
 Oval Gear
 Reciprocating Piston
Metering Pumps come in these three types
 Reciprocating Piston
 Peristaltic Piston
 Diaphragm Pump
3

4. Positive Displacement Flow Meters
 Itis the only flow measurement technology that directly measures the volume of the
fluid passing through the flow meter.
 This is achieved by repeatedly entrapping fluid in order to measure its flow. This
process can be thought of as repeatedly filling a bucket with fluid before dumping the
contents downstream.
 The number of times that the bucket is filled and emptied is indicative of the flow
through the flow meter.
 The rate at which it is passed is the volumetric flow rate.
 As because they pass a known quantity, they are ideal for certain fluid batch, blending
and custody transfer applications.
 They give very accurate information and are generally used for production and
accounting purposes.
4

5. Positive Displacement Flow Meters
 Advantages:
- Low to medium initial set up cost
- Can be used in viscous liquid flow
 Disadvantages
- Higher maintenance cost than other non-obstructive flow meters
- High pressure drop due to its total obstruction on the flow path
- Not suitable for low flow rate
- Very low tolerance to suspension in flow (particles larger than 100 µm
need to be filtered before the liquid enters the flow meter)
- Gas (bubbles) in liquid could significantly decrease the accuracy
5

6. Nutating Disk Meter
 It has a moveable disk mounted on a concentric sphere located in a spherical side-walled
chamber.
 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.
 A pin extending perpendicularly from the disk is connected to a mechanical counter that
monitors the disk's rocking motions.
 Each cycle is proportional to a specific quantity of flow.
 As is true with all positive-displacement meters, viscosity variations below a given threshold
will affect measuring accuracies.
6

7. Nutating Disk Meter
 Advantages:
Relatively low cost
Applicable to automatic liquid batching system
Make use of moderate pressure loss
Construction available in several material
 Disadvantages
Limited to pipe size and capacity
Accuracy average
Not suitable for slurries
7

8. Oscillating Piston
 It is similar to that of a nutating disc except that the measurement device
is a split ring oscillating in only one plain.
 It comprises a slotted cylinder oscillating about a dividing bridge which
separates the inlet and outlet ports.
 Initially the piston rests at the neutral position.
 As fluid enters the section, the ring starts rotating from left to right until
the fluid is escorted to the outlet.
 The rotation of piston is transmitted through a diaphragm to the gear
train and register.
 This type is suitable for viscous and corrosive liquids. Accuracy is ±
1%.
8

9. Oscillating Piston
 Advantages
Good accuracy at low flow rates
Good repeatability
Easy installation
Moderate cost
 Disadvantages
Only small sizes are available
Limited power capacity
Fluid should be clean
9

10. Rotating Vane Meter
 Spring loaded vanes slide in and out of a channel in a rotor so that they
make constant contact with the eccentric cylinder wall.
 When the rotor turns, a known volume of fluid is trapped between the
two vanes and the outer wall.
 The flow rate is based on volume per revolution.
 The piston type is suitable for accurately measuring small volumes and
is not affected by viscosity.
 Limitations with this device are due to leakage and pressure loss.
10

11. Rotating Vane Meter
 Advantages
- Reasonable accuracy of 0.1%.
- Suitable for high temperature service, up to 180°C
- Pressures up to 7 Mpa
- Maximum flow rate that it can support is 17500 gpm
 Disadvantages
- Suitable for clean liquids only
- High cost
11

12. Lobed Impeller
 This type of meter uses two lobed impellers, which are geared and
meshed to rotate at opposite directions within the enclosure.
 A known volume of fluid is transferred for each revolution.
12

13. Lobed Impeller
 Advantages
- High operating pressures, up to 8Mpa.
- High temperatures, up to 200°C.
- Accuracy ± 0.1 % to ± 0.5 %
 Disadvantages
- Poor accuracy at low flow rates.
- Bulky and heavy.
- Expensive
13

14. Oval Gear
 Two oval gears are intermeshed and trap fluid between themselves and the outer walls
of the device.
 The oval gears rotate due to the pressure from the fluid and a count of revolutions
determines the volume of fluid moving through the device.
 The viscosity of the fluid can affect the leakage, or slip flow.
 If the meter is calibrated on a particular fluid, it will read marginally higher should the
viscosity rise.
 Newer designs of this type of meter use servomotors to drive the gears.
 This eliminates the pressure drop across the meter and also the force required to drive
the gear.
 This eliminates the force, which causes the slip flow. This mainly applies to smaller
sized meters and significantly increases the accuracy at low flows.
14

15. Oval Gear
 Advantages
- High accuracy of 0.25%
- High operating pressures, up to 10MPa
- High temperatures, up to 300°C
- Wide range of materials of construction
 Disadvantages
- Pulsations caused by alternate drive action
15

16. Reciprocating Piston Meter
 This type is mainly used for heavy chemical and manufacturing fluids.
 It employs a piston with inlet and outlet check valves with the piston moving in a
reciprocating manner.
 Check valves prevent back flow.
 As piston retracts from cylinder, fluid is filled in. as piston re-enters, the fluid is
forcefully discharged out of the cylinder.
 It has a very high temperature sustenance capability of 540 ° C and can handle 100000
psig pressure.
 Accuracy ranges between ± 0.5 % and 1 %.
16

17. Reciprocating Piston Meter 17

18. Metering Pump
 A metering pump is a positive displacement pump which is used to provide a
predictable and accurate rate of process fluid flow.
 Any positive displacement pump may be used as a metering pump due to its
volumetric mode of fluid transfer.
 Only those pumps which have very little internal or external leakage are used for as
metering pumps.
 Metering Pumps are of three types
 1) Reciprocating piston Pump
 2) Peristaltic Pump
 3) Diaphragm Pump
18

19. Reciprocating Piston Pump
 It is mainly used in heavy chemical and manufacturing industry employing a piston or
a plunger having inlet and outlet check valves and a piston moving with a reciprocating
motion in the chamber. Check valves prevent back flow.
19

20. Peristaltic Pump
 It is a type of positive displacement pump used for pumping a variety of fluids. The
fluid is contained within a flexible tube fitted inside a circular pump casing (though
linear peristaltic pumps have been made).
 A rotor with a number of "rollers", "shoes", "wipers", or "lobes" attached to the
external circumference of the rotor compresses the flexible tube. As the rotor turns, the
part of the tube under compression is pinched closed (or "occludes") thus forcing the
fluid to be pumped to move through the tube.
 Additionally, as the tube opens to its natural state after the passing of the cam
("restitution" or "resilience") fluid flow is induced to the pump. This process is called
peristalsis.
 There will be two or more rollers, or wipers, occluding the tube, trapping between
them a body of fluid.
 The body of fluid is then transported, at ambient pressure, toward the pump outlet.
Peristaltic pumps may run continuously, or they may be indexed through partial
revolutions to deliver smaller amounts of fluid.
20

21. Peristaltic Pump 21

22. Diaphragm Pump
 A diaphragm pump (also known as a Membrane pump, Air Operated Double
Diaphragm Pump (AODD) or Pneumatic Diaphragm Pump) is a positive displacement
pump that uses a combination of the reciprocating action of a rubber, thermoplastic or
teflon diaphragm and suitable valves on either side of the diaphragm (check valve,
butterfly valves, flap valves, or any other form of shut-off valves) to pump a fluid.
 When the volume of a chamber of either type of pump is increased (the diaphragm
moving up), the pressure decreases, and fluid is drawn into the chamber.
 When the chamber pressure later increases from decreased volume (the diaphragm
moving down), the fluid previously drawn in is forced out.
 Finally, the diaphragm moving up once again draws fluid into the chamber, completing
the cycle.
22

23. Diaphragm Pump 23

24. Mass Flow Meter
 Coriolis Mass Flow meter: The basis of the Coriolis meter is Newtons’ Second Law of
Motion, where:
 Force = Mass x Acceleration
 The conventional way to measure the mass of an object is to weigh it. In weighing, the
force is measured with a known acceleration (9.81m/sec^2).
 This type of measuring principle is not easy or possible with fluids in motion,
particularly in a pipe.
 It is possible to manipulate the above formula and apply a known force and measure,
instead, the acceleration to determine the mass.
 The Coriolis Effect causes a retarding force on a rotating section of pipe when flow is
moving outward, conversely producing an advance on the section of pipe for flow
moving towards the axis of rotation.
 When the full section of pipe is moved about its axis in an oscillatory motion, the
outgoing section of pipe is retarded (or decelerated) and the return section is advanced
(or accelerated), producing a twist in the pipe.
24

25. Coriolis Meter
 The force is applied to oscillate the flow pipes and the Coriolis Effect is the principle
used to determine the acceleration due to the torque (the amount of twisting).
 Sensors are used to measure the amount of twist in the flow tubes within the meter as a
result of the flow tube vibration and deflection due to the mass flow.
 The amount of twist measured is proportional to the mass flow rate and is measured by
magnetic sensors mounted on the tubes.
 Developments on the looped pipe Coriolis meter were made to keep to the pipes
straight.
 This is done by making the pipes straight and parallel.
 The force is applied by oscillating the pipes at the resonant frequency.
 This has the advantage of reducing pressure loss in the pipeline.
25

26. Coriolis Meter 26

27. Coriolis Meter
 Advantages
- Direct, in-line mass flow measurement.
- Independent of temperature, pressure, density, conductivity and viscosity.
- Sensor capable of transmitting mass flow, density and temperature information.
- High density capability.
- Conductivity independent.
- Suitable for hydrocarbon measurements.
- Suitable for density measurement.
 Disadvantages
- Cost.
- Affected by vibration.
- Installation costs.
- Adjustment of zero point.
27

28. Miscellaneous Type Flow Meters:
Variable Reluctance Tachogenerator
 It is used for measurement of linear and angular velocity measurement.
 Magnetomotive force (mmf) is the force that causes flux to be established and it is
analogous to the electromotive force for electric circuits.
 SI unit of mmf is Ampere and it only refers to one turn of a coil.
 The opposition to the establishment of magnetic flus is reluctance.
 𝑹𝒆𝒍𝒖𝒄𝒕𝒂𝒏𝒄𝒆 𝑹 =
𝒎𝒎𝒇
∅
∴ 𝒎𝒎𝒇 = 𝑹 ∗ ∅
 Where mmf is in Ampere turns and ϕ (flux) is in Weber.
28

29. Variable Reluctance Tachogenerator
 If the time – varying flux ϕ is linked by a single trun of coil, then the back emf
developed in the coil can be expressed as 𝒆 = −
𝒅∅
𝒅𝒕
 The permanent magnet is extended by a soft iron pole piece. The teeth of the wheel
move is close proximity to the pole piece. Therefore, the flux linked by the coil
changes with time and voltage is developed across the coil. The total flux (ϕ T) linked
by the coil of m turn is expressed as ∅ 𝑻 = 𝒎∅ = 𝒎
𝒎𝒎𝒇
𝑹
 Again it is known, with reluctance being minimum, flux becomes maximum and vice
versa. The variation of ϕ T with angular position θ is expressed as
 ∅ 𝑻 𝜽 = 𝜶 + 𝜷𝐜𝐨𝐬(𝒏𝜽)
 α = mean flux, β = time – varying flux’s amplitude, n = no. of teeth of the wheel.

29

30. Variable Reluctance Tachogenerator
 The induced emf is expressed as
 𝒆 = −
𝒅∅ 𝑻
𝒅𝒕
= −
𝒅∅ 𝑻
𝒅𝜽
𝒅𝜽
𝒅𝒕
 Again
𝑑∅ 𝑇
𝑑𝜃
= −𝛽𝑛𝑠𝑖𝑛 𝑛𝜃 and 𝜃 = 𝜔𝑡
 ∴
𝑑𝜃
𝑑𝑡
= 𝜔, 𝑤ℎ𝑒𝑟𝑒 𝜔 = 𝑟𝑜𝑡𝑎𝑡𝑖𝑜𝑛𝑎𝑙 𝑣𝑒𝑙𝑜𝑐𝑖𝑡𝑦 𝑜𝑓 𝑤ℎ𝑒𝑒𝑙
 ∴ 𝒆 = 𝜷𝒏𝝎𝐬𝐢𝐧(𝒏𝝎𝒕)
30

31. Miscellaneous Type Flow Meters:
Linear Resistance Element Flow Meter
 For a small flow rate or for highly viscous flows the linear resistance element flow
meter (also called capillary flow meter) is effectively suitable.
 It is a constant head loss type and its principle of operation is based on Hagen –
Poiseulle equation for laminar flow in tubes.
 𝑸 =
𝝅𝑫 𝟒
𝟏𝟐𝟖𝝁𝑳
(𝒑 𝟏 − 𝒑 𝟐)
 Q = flow rate
 D = inside diameter
 L = length of tube
 μ = viscous coefficient
 (p1 – p2) = pressure drop along tube length
31

32. Linear Resistance Element Flow Meter
 The total metered fluid is guided by means of flow straighteners to the metering element in
the shape of a bundle of capillary tubes in honeycomb configuration.
 Due to high viscosity, small flow rate and small size of diameter tube, the Reynold’s
number is small and is in the laminar range of flow.
 The primary advantage of this flow meter is that flow rate is directly proportional to the
pressure drop and that is why it is termed as linear resistance element flow meter.
 Advantages
 Accurate average measurement
 Good damping ability
 Reverse flow is measurable
 Disadvantages
 Subject to plugging for slurries fluid
 High pressure loss involved
 Expensive
32

33. References:
 Chapter 11: Flow Measurement, “Industrial Instrumentation and
Control” by S K Singh. Tata McGraw Hill, 3rd Edition. 2009, New
Delhi. ISBN-13: 978-0-07-026222-5.
 Chapter 12: Flow Measurement, “Instrumentation, Measurement and
Analysis”. 2nd Edition, B C Nakra, K K Chaudhry, Tata McGraw-Hill,
New Delhi, 2005. ISBN: 0-07-048296-9.
 Chapter 7: Flowmeter, “Fundamentals of Industrial Instrumentation”,
1st Edition, Alok Barua, Wiley India Pvt. Ltd. New Delhi, 2011. ISBN:
978-81-265-2882-0.
 Chapter 5: Flow Measurement, “Principles of Industrial
Instrumentation”, 2nd Edition. D. Patranabis, Tata McGaw-Hill, New
Delhi, 2004. ISBN: 0-07-462334-6.
33