Flow Sensors

Prepared By : Saralah Alizadeh Arand
Supervisor : Dr B.Rashidian
Sharif University of Technology
1

 Fluid Basics
 Flow Basics
 Flow Sensors
 Different Types
 Principles
 Basic Specs
 Comparison
 Products
 Prices
 Trends
 Conclusions
2

 What is the Fluid?
 Under shear force :
 Solid is Elastic
 Fluid deforms continusely
3
Fluid Basics Flow Basics Flow Sensors Different Types Principles Basic Specs
Comparison Products Prices Trends Conclusions

 Newtonian vs non-Newtonian fluids
 Newtonian : In a newtonian fluid shear stress
relates to velocity gradient linearly:
 Non-Newtonian : In some fluids like honey
and blood the above equation doesn’t satisfy
4
u: velocity
µ: Dynamic Viscosity

 Measurement & Units
 Compressible & Incompressible
 Steady & unsteady flow
 Viscous & inviscid flow
 General Equations of Flow
 Bernoulli’s Equation
 No-slip condition & Boundary layer
 Reynolds number
 Laminar & Turbulent
5

 Flow can be measured in terms of :
 Quantity: how many liters of gas did I use and how
much will it cost me?
 Liquid : gallons, barrels or liters
 Gas : cubic feet (ft3), cubic meters (m3)
 Vapour (steam) : lbs, kg
 Rate : you must keep the water flowing at 10 gallons
per minute to fill up the pool by lunch time.
 Liquid : gallons per minute (gpm) or liters per min.
 Gas : cubic feet/hr (ft3/hr), cubic meters/hr (m3/hr)
 Vapour (steam) : lbs/hr, kg/hr
6

 For all flows, The Continuty Equation states that:
 In an incompressible flow the mass density is constant
Thus divergence of velocity is zero.
 If the velocity of the flow is low enough:
7

 A flow is considered to be a compressible flow if the
change in density of the flow is non-zero.
 This is the case where the Mach Number in part or all
of the flow exceeds 0.3.
M > 0.3
 Mach Number:
M=
8

 In a Steady flow characteristics of flow
(pressure, velocity, temprature) don’t change
with respect to time.
9

 Flow is essentially viscous, i.e. Friction
between layers is present.
 For simplificatin purposes it is ideally assumed
that viscous phenomenon is negligible
(inviscid).
10

 All newtonian Fluids satisfies the “Navier-
Stokes” momentum Equations set
 Relates velocity vector with pressure function
in flow domain
 3 PDE momentum equations in x,y, and z
directions
 Nonlinear without a general Analytical
solution
 Analytical solution in special cases By
Simplification assumption
 Computational fluid Dynimaics (CFD)
11

 Steady
 Incompressible
 Inviscid
 Between 2 points of a
streamline
 Very benefitial in piping
and hydraulics
12
constvhgPorvhgPvhgP  2
2
12
22
1
22
2
12
1
11 

 At a solid boundary, the fluid will have zero velocity
relative to the boundary.
 Bounadary Layer:
 Established by Prantel in 1931
 Narrow region surrounding the fluid
boundaries
 It’s develpoing in flow direction
 In Boundary region viscous effects should be considered
 Outside of BL flow is inviscid; i.e. Bernoulli Equation is valid
13

 Established by Osborne Reynolds in 1883
 Reynolds number is a dimentionless parameter.
 Ratio of inertial force to viscous force
 Directly exhibits flow speed in same
experiments.
 Describe the velocity profile of flowing fluids.
14
In the case of flow through a pipe:
Re < 2000 Laminar
Re > 3000 Turbulent

 Flow can be considered laminar ,turbulent or a
combination of both.
 At low flow rates, fluids have a laminar flow characteristic.
 At high flow rate the laminar break up and becomes
turbulent.
15
Laminar
Turbulent

 The fluid that have contact with constraining
walls will produce zero velocity.
 In the center of the flow, the liquid particles
have the maximum velocity
16

17

 Our interest in the measurement of air and
water flow is timeless.
 In the Sumerian cities of Ur, Kish, and Mari near the
Tigris and Euphrates Rivers around 5,000 B.C.
 Is a critical need in many industrial plants:
 It can make the difference between making a profit or
taking a loss.
 Inaccurate flow measurements can cause serious (or
even disastrous) results.
18

 Differential Pressure
 Orifice Plate
 Venturi Tube
 Flow Tube
 Flow Nozzle
 Pitot Tube
 Elbow Tap
 Target
 Variable-Area(Rotameter)
 Open-Channel
 Weir
 Flume
 MFC
 Mass
 Coriolis
 Thermal
19
Fluid Basics Flow Basic Flow Sensors Different Types Principles Basic Specs

 Velocity
 Turbine
 Vortex Shedding
 Swirl
 Conada Effect & Momentum Exchange
 Electromagnetic
 Ultrasonic, Doppler
 Ultrasonic, Transit-Time
 Positive Displacement
 Reciprocating Piston
 Oval Gear
 Nutating Disk
 Rotary Vane
 MEMS
20

 Differential Pressure
 MFC
 Mass
 Velocity
 MEMS
21

 The most common units in use today.
 Over 50 percent of all liquid flow measurement
applications use this type
 Calculation of fluid flow rate by reading the pressure loss
across a pipe restriction
 As a fluid passes through a restriction, it accelerates, and
the energy for this acceleration is obtained from the fluid's
static pressure.
22

 The relationship is determined by the Bernoulli
equation.
23
PKCQ
Q
Q
C
PKQ
PP
A
A
A
vAQ
A
Av
PP
V
A
A
VVAVAQ
dactual
ideal
actual
d 












)(
2
)(1
)(1
2
)(
21
2
1
2
2
22
2
1
2
2
2
21
2
1
2
12211


K :Constant of flow obstruction device

 Most commonly used flow sensor
 An orifice is a flat piece of metal with a specific-
sized hole
 Pressure taps on either side of the plate are
used to detect the difference
24

 Have no moving parts
 Low cost
 Liquids with suspended solids can also be
metered
 Low precision
 High pressure loss
25

 Consist of a tapered tube and a float
 Float have a density higher than that of the fluid
 When there is no flow:
 The float rests at the bottom of the tube.
 As liquid enters :
 The float begins to rise.
26

 Its position
 The point where the differential balance the weight of the float
 No secondary flow-reading
devices are necessary
 Rotameter tubes are
manufactured from glass,
metal, or plastic.
27

 Accurate measurement and control of a mass
flow of gas
 4 main components:
 A bypass
 A sensor
 An electronics board
 A regulating valve
28

 Measurement side (a Mass Flow Meter):
 The bypass
 The sensor
 One part of the electronics board
 Controlling side:
 The regulating valve
 The other part of the electronics board
29

 The sensor can only measure small flow
 The bypass :
 Control greater amounts of flow
 Sensor :
 Uses the thermal properties of a gas(specific heat)
 Directly measure the mass flow rate
 Adds heat to a gas and monitoring
the change in temperature
30

 The electronics board:
 amplifies and linearizes the sensor signal
 compares the sensor’s output to the desired set point
 error signal that
 A piezoelectric actuator
31

 Coriolis
 Thermal
32

 Coriolis effect:
 Particle (dm) travels at a velocity (V) inside a tube
 The tube is rotating about a fixed point
 The particle moves with angular velocity (w)
under two components of acceleration
 A centripetal acceleration
 A coriolis acceleration acting at right angles to ar
at (Coriolis) = 2wv
33

 A force of at (dm) has to generated by the tube
 If the process fluid has density D and is flowing at
constant speed inside a rotating tube of cross-sectional
area A, a segment of the tube of length x will experience a
Coriolis force of magnitude:
Fc = 2wvDAx
so:
Mass Flow = Fc/(2wx)
34
at (Coriolis) = 2wv
Fc = at(dm) = 2wv(dm)

 Rotating a tube is not practical when building a
commercial flowmeter
 Oscillating or vibrating the tube can achieve the same
effect.
 The tube is anchored at two points and
vibrated between these anchors.
 Drivers vibrate the tubes
 Drivers consist of a coil connected to
one tube and a magnet connected
to the other
35

 When there is no flow:
 identical displacements at
the two sensing points
 When flow is present:
 Coriolis forces act to produce
a secondary twisting vibration
 Small phase difference in the
relative motions
36

 Include :
 Two temperature sensors
 An electric heater
 1. Introducing a known amount of
heat into the flowing stream and
measuring an associated temperature
change
 2. Maintaining a probe at a constant
temperature and measuring the
energy required to do so
 The heater can protrude into the fluid
or can be external to the pipe
37

 Velocity
 Turbine
 Vortex Shedding
 Swirl
 Conada Effect & Momentum Exchange
 Electromagnetic
 Ultrasonic, Doppler
 Ultrasonic, Transit-Time
38

 Operate linearly with respect to the volume flow
rate
 No square-root relationship (as with differential
pressure devices)
 Minimum sensitivity to viscosity changes
39

 Invented by Reinhard Woltman in the 18th century
 Has found widespread use for accurate liquid
measurement applications
 It consists of a multi-bladed rotor mounted at right
angles to the flow
 The rotor spins as the liquid
passes through the blades
40

 The rotational speed can be sensed by magnetic
pick-up, photoelectric cell, or gears
 The number of electrical pulses counted for a given
period of time is directly proportional to flow
volume.
41

 Make use of a natural phenomenon that occurs when
a liquid flows around a bluff object.
 Discovered by Theodor von Karman
 Eddies or vortices are shed alternately downstream
of the object
 The frequency of the
vortex shedding is
directly proportional
to the velocity of the
liquid
42

 A sensor detect the presence of the vortex and generate
an electrical impulse.
 shedding frequency is independent of fluid properties such
as density, viscosity, conductivity, etc.
 The relationship between vortex frequency and fluid
velocity is:
St = f(d/V)
St is the Strouhal number
Q = AV = (A f d B)/St
B is the blockage factor
Q = fK
43

 The operation is based on Faraday's law of
electromagnetic induction:
E = BLV
 Ideal for any dirty liquid which is conductive.
 Ideal for applications where low pressure drop
and low maintenance are required.
44

 Consists of :
 A non-magnetic pipe lined with an insulating material.
 A pair of magnetic coils
 A pair of electrodes penetrates the pipe.
45

 Doppler effect established by Johann Doppler in
1842
 The frequencies of received sound waves:
 Depended on the motion of the source or observer relative to
the propagating medium.
46

 Transmitted wave hits particles in the liquid and
reflect back.
 The velocity of the fluid creates a frequency shift.
47

 Two transducers are
required
 It takes less time to go
upstream than downstream
 Flow is a function of the
difference in time
48

 Good for clear liquids or gases
 Better accuracy than Doppler
 Difficult to align
49

 Reciprocating Piston
 Oval Gear
 Nutating Disk
 Rotary Vane
50

 High accuracy
 Separate liquids into accurately measured
increments
 Each segment is counted by a connecting register
 Popular for automatic batching and accounting
applications
51

 The most common PD meter
 Used as water meter
 Function:
 Water flows through the metering chamber
 It causes a disc to wobble (nutate), turning a spindle,
which rotates a magnet.
 The meter housing is
usually made of bronze
52

 Two rotating, oval-shaped gears
 A fixed quantity of liquid
passes through the meter
for each revolution
53

 Thermal transfer
 Pressure distribution
 Based on Drag Force
 Based on von Karman Vortex Shedding
 Based on Flow Turbine
 Artiﬁcial Haircell (AHC)
 …
54

 An optical MEMS flow sensor based on drag force
 consists of:
 A tall, wide cantilever beam or wall hinged at the bottom
 Silicon tension spring
 Optical fiber
55

56
 The drag force of fluid force provides a clockwise torque
 Result a tilt angle of θ
 The deflection of the beam will be sensed by a optical fiber
 The light reflects from an Au mirror on the beam back into
the fiber.
 If the beam is deflected, less light
will be reflected back

 Relation between fiberoptic intensity loss and
beam offset
57
Relative beam offset theta/theta0
Intensityloss

 Consists of:
 A silicon cantilever beam
(cilium)
 Silicon piezo-resistive
strain gauge
58

 Flow passing through the cilium introduces a bending
moment
59

 The resistance of The piezoresist varies under
strain
 The output voltage is corresponding to the
strain
60

61
 We can use an array of AHSs to achieve an
accurate flow measurement.

 Typical Accuracy
 In percent of full scale
 Pressure loss
 Pipe sizes
 Flow Rate
 Cost
 Liquid
 Steam
 Natural Gas
 Fuel Oil
 Water
 Pressure
 Temperature
 Viscosity
62

 Which type of flow sensors should be used?
63

Flowmeter element Recommended Service Range Pressure loss Typical Accuracy, % L (Dia.) Cost
1.Orifice Clean, dirty liquids;
some slurries
4 to 1 Medium ±2 to ±4 of full scale 10 to 30 Low
Venturi tube Clean, dirty and viscous liquids; 4 to 1 Low ±1 of full scale 5 to 20 Medium
Flow nozzle Clean and dirty liquids 4 to 1 Medium ±1 to ±2 of full scale 10 to 30 Medium
Pitot tube Clean liquids 3 to 1 Very low ±3 to ±5 of full scale 20 to 30 Low
Elbow meter Clean, dirty liquids; some slurries 3 to 1 Very low ±5 to ±10 of full scale 30 Low
Variable area Clean, dirty viscous liquids 10 to 1 Medium ±1 to ±10 of full scale None Low
6.Positive Displacement Clean, viscous liquids 10 to 1 High ±0.5 of rate None Medium
3.Turbine Clean, viscous liquids 20 to 1 High ±0.25 of rate 5 to 10 High
7.Vortex CLean, dirty liquids 10 to 1 Medium ±1 of rate 10 to 20 High
4.Electromagnetic Clean, dirty viscous conductive
liquids& slurries
40 to 1 None ±0.5 of rate 5 High
Ultrasonic (Doppler) Dirty, viscous liquids and slurries 10 to 1 None ±5 of full scale 5 to 30 High
Ultrasonic(Travel Time) Clean, viscous liquids 20 to 1 None ±1 to ±5 of full scale 5 to 30 High
5.Mass (Coriolis) Clean, dirty viscous liquids; some
slurries
10 to 1 Low ±0.4 of rate None High
2.Mass (Thermal) Clean, dirty viscous liquids; some
slurries
10 to 1 Low ±1 of full scale None High
Weir (V-notch) Clean, dirty liquids 100 to 1 Very low ±2 to ±5 of full scale None Medium
Flume (Parshall) Clean, dirty liquids 50 to 1 Very low ±2 to ±5 of full scale None Medium
64
Rangeability is the ratio of full span to smallest flow that can be measured with sufficient accuracy.

 Orifice Plate
65

66

 Vortex
67

 Electromagnetic
68

69

 Wide range of prices
 Rotameters are usually the least expensive
 For some small-sized units : less than $100
 Mass flowmeters cost the most
 Prices start at about $3500
 Installation, operation, and maintenance costs
are important economic factors
70

71
FDT103
Ultrasonic Flowmeter
Omega Engineering
$2,120.00
FMG-403H-T
Magnetic Flow meter
Omega Engineering
$2,600.00
M100L
MASS FLOW METER
Davis Instruments
$1,150.00

72
810C-DR
MFC
Davis Instruments
$1,045.00
VORTEX
5755 SCFH
VORTEX FLOWMETER
Cole-Parmer Instrument
$2,390.00
OVAL GEAR GM007R2R21
OVAL GEAR
Davis Instruments
$1,257.00
P16B4-BA0A
ROTAMETER
Davis Instruments
$136.00

73

 There is a trend in:
 Ultrasonic
 Magnetic
 Mass
 MEMs
 …
74

 Over 75 percent of the flowmeters installed in
industry are not performing satisfactorily
 Improper selection accounts for 90 percent of these
problems
 Flowmeter selection is no job for amateurs!
 What is the instrument supposed to do?
75

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