Speaks about the different aspects of flow measurement i.e. flow types, fluid types, its units, selection parameters; definition of common terms, coanda effect coriolis effect . it also speaks about the factors affecting flow measurement.

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

2. Contents:
 Definition
 Fluid Type
 Reynolds Number
 Unit of Flow
 Types of Flow
 Bernoulli's Equation
 Basic Requirements for Flow Measurement
 Factor affecting Flow meter Performance:
 Selection of Flow Meters
 Definitions of Quantities to be measured
 Calibration Methods for Flow meters (Liquid & Gas)
 Coanda effect
 Coriolis Effect
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3. Definition of Flow & Fluid Types
 Flow is the motion characteristics of constrained fluids (liquids or gases). It deals with two
things: how much (total) and how fast (rate)
 Viscosity: Dynamic or absolute viscosity (η) is measure of the resistance to a fluid to
deformation under shear stress, or an internal property of a fluid that offers resistance to
flow.
 Fluids may generally be divided into two types: Newtonian and Non-Newtonian fluids.
 When held at a constant temperature, the viscosity of a Newtonian fluid will not change
regardless of the size of the shear force.
 When held at a constant temperature, the viscosity of a Non-Newtonian fluid will change
with relation to the size of the shear force, or will change over time under a constant shear
force.
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4. Reynolds Number
 The Reynolds number is the ratio of inertial forces to viscous forces of fluid flow
within a pipe and is used to determine whether a flow will be laminar or turbulent.
 𝑅 𝐷 =
𝑉𝐷𝜌
𝜇
 RD = Reynolds number
 V = average velocity
 D = inside pipe diameter
 ρ = density of flowing fluid
 μ = absolute viscosity
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5. Units of Flow
 The units used to describe the flow measured can be of several types depending on
how the specific process needs the information.
 Solids: Normally expressed in weight rate like Tonnes/hour, Kg/minute etc.
 Liquids: Expressed both in weight rate and in volume rate.
Examples: Tonnes/hour, Kg/minute, litres/hour, litres/minute, m3/hour etc.
 Gases: Expressed in volume rate at NTP or STP like Std m3/hour, Nm3/hour etc.
 Steam: Expressed in weight rate like Tonnes/hour, Kg/minutes etc. Steam density at
different temperatures and pressures vary.
 Hence the measurement is converted into weight rate of water which is used to produce
steam at the point of measurement.
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6. Types of Flow
 Laminar Flow occurs at low Reynolds numbers, typically Re < 2000, where viscous
forces are dominant. Laminar flow is characterized by layers of flow traveling at
different speeds with virtually no mixing between layers. The velocity of the flow is
highest in the center of the pipe and lowest at the walls of the pipe.
 Turbulent Flow occurs at high Reynolds numbers, typically Re > 4000, where inertial
forces are dominant. Turbulent flow is characterized by irregular movement of the fluid
in the pipe. There are no definite layers and the velocity of the fluid is nearly uniform
through the cross section of the pipe. The flow is turbulent.
 Transitional Flow typically occurs at Reynolds numbers between 2000 and 4000.
Flow in this region may be laminar, it may be turbulent or it may exhibit characteristics
of both.
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7. Bernoulli's Equation
 Bernoulli's principle says that a rise (fall) in pressure in a flowing fluid must always be
accompanied by a decrease (increase) in the speed, and conversely, i.e. an increase
(decrease) in the speed of the fluid results in a decrease (increase) in the pressure.
𝑝 +
1
2
𝜌𝑉2
+ 𝜌𝑔ℎ = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
𝜕
𝜕𝑠
𝑣2
2
+
𝑝
𝜌
+ 𝑔. ℎ = 0
𝑣2
2
+
𝑝
𝜌
+ 𝑔. ℎ = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
𝑣2
2𝑔
+
𝑝
𝛾
+ ℎ = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡, 𝑤ℎ𝑒𝑟𝑒 𝛾 = 𝜌. 𝑔
𝜌𝑣2
2
+ 𝑝 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
𝜌𝑣1
2
2
+ 𝑝1 =
𝜌𝑣2
2
2
+ 𝑝2 = 𝑐𝑜𝑛𝑠𝑡𝑎𝑛𝑡
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8. Basic Requirements for Flow Measurement
 Ability to calibrate
 Ability to integrate flow fluctuations
 Easy integration with piping system
 High accuracy
 High turn-down ratio
 Low cost
 Low sensitivity to dirt particles
 Low pressure loss
 No moving parts
 Resistant to corrosion and erosion
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9. Factor affecting Flow meter Performance
 Process Media – Gas/Liquid
 Temperature
 Velocity
 Viscosity
 Pressure
 Density
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10. FLOWMETER TYPES
Differential Pressure Positive Displacement Velocity Mass Open-
Channel
Orifice Plate
Venturi Tube
Flow Tube
Flow Nozzle
Pitot Tube
Elbow Tap
Target
Variable-Area
(Rotameter)
Reciprocating Piston
Oval Gear
Nutating Disk
Rotary Vane
Turbine
Vortex Shedding
Swirl
Conada Effect & Momentum
Exchange
Electromagnetic
Ultrasonic, Doppler
Ultrasonic, Transit-Time
Coriolis
Thermal
Weir
Flume
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Flowmeter
Volumetric
Mass

11. Selection of Flow Meters
 Measuring media – Fluid/ Gas/ Vapour/ Slurry
 Application – Control/ Monitor/ Supply
 Operating Condition – Temperature/ Pressure loss/ Range ability
 Installation Condition – Bore/Upstream/ Downstream/ Piping work/ Explosion Proof
 Performance – Accuracy/ Velocity range.
 The parameters which are to be kept in mind while choosing a flow meter for a
particular type of flow are as follows
 Accuracy
 Safety
 Installation
 Cost
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12. Definitions of Quantities to be measured
 Volume Flow Rate: The volume of the fluid that flows past a given cross sectional
area per second.
 V = Av (m3/h),
where V = Volume Flow rate, A = Cross Sectional Area, v = velocity of fluid.
 Mass Flow Rate: The number of kilograms of mass that flows past a given cross
sectional area per second.
 m = ρV = ρAv (kg/hr),
m = Mass Flow rate, V = Volume Flow rate, ρ = specific density, A = cross sectional area,
v = velocity of fluid
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13. Calibration Methods for Liquids
 In – Situ Calibration Methods
 Insertion Point Velocity Method
 Dilution Gauging / Tracer Method
 Laboratory Calibration Methods
 Master Meter Method
 Volumetric Method
 Gravimetric Method
 Pipe Prover Method
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14. Calibration Methods for Gases
 In – Situ Calibration Methods
 Insertion Point Velocity Method
 Dilution Gauging / Tracer Method
 Laboratory Calibration Methods
 Soap-Film Burette Method
 Water Displacement Method
 Gravimetric Method
 Insertion Point Velocity Method: It utilizes point – velocity measuring devices where
calibration device chosen is positioned in the flow stream adjacent to the flow meter being
calibrated and such that mean flow velocity can be measured.
 Dilution Gauging / Tracer Method: It finds application in both open – channel and closed
– pipe flow meter calibration. A chemical or radioactive tracer is injected at an accurately
measured constant rate and samples are taken from the flow stream at a point downstream
of the injection point where complete mixing of the injected water will have taken place.
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15. Coanda Effect
 Coanda Effect is the phenomena in which a jet flow attaches itself to a nearby surface
and remains attached even when the surface curves away from the initial jet direction.
In free surroundings, a jet of fluid entrains and mixes with its surroundings as it flows
away from a nozzle.
 Coanda Effect: A moving stream of fluid in contact with a curved surface will tend to
follow the curvature of the surface rather than continue traveling in a straight line.
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This diagram shows that increasing the
angle of attack increases how much the air
is deflected downwards. If the angle of
attack is too high, the air flow will no
longer follow the curve of the wing
(Coanda effect is losing the power). As
shown in the bottom of the diagram, this
creates a small vacuum just behind the
wing. We can say that wing is stalled. As
the air rushes in to fill this space, called
cavitation’, it causes heavy vibrations on
the wing and greatly decreases the
efficiency of the wing.

16. Coriolis Effect
 Coriolis Effect is a deflection of moving objects when the motion is described relative
to a rotating reference frame. In a reference frame with clockwise rotation, the
deflection is to the left of the motion of the object; in one with counter-clockwise
rotation, the deflection is to the right.
𝐹𝑐 = −2𝑚𝛺 ∗ 𝑣
Coriolis force Fc = - 2 (mass of the relevant object m) (angular velocity Ω) (velocity in
rotating frame v)
 The Coriolis Effect is caused by the rotation of the earth and the inertia of the mass
experiencing the effect. Newton's laws of motion govern the motion of an object in a
(non-accelerating) inertial frame of reference.
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17. 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.
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