FLOW MEASUREMENT PART I

ER. FARUK BIN POYEN, Asst. ProfessorDEPT. OF AEIE, UIT, BU, BURDWAN, WB, INDIAfaruk.poyen@gmail.com

FLOW M

EASUREMENT PART I Er FARUK BIN POYEN

2Contents: 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

FLOW M

EASUREMENT PART I Er FARUK BIN POYEN

3Definition 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.

FLOW M

EASUREMENT PART I Er FARUK BIN POYEN

4Reynolds 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. RD = Reynolds number V = average velocity D = inside pipe diameter ρ = density of flowing fluid μ = absolute viscosity

FLOW M

EASUREMENT PART I Er FARUK BIN POYEN

5Units 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.

FLOW M

EASUREMENT PART I Er FARUK BIN POYEN

6Types 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.

FLOW M

EASUREMENT PART I Er FARUK BIN POYEN

7Bernoulli'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.

FLOW M

EASUREMENT PART I Er FARUK BIN POYEN

8Basic 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

FLOW M

EASUREMENT PART I Er FARUK BIN POYEN

9Factor affecting Flow meter Performance

Process Media – Gas/Liquid Temperature Velocity Viscosity Pressure Density

FLOWMETER TYPES

Differential Pressure Positive Displacement Velocity Mass Open-Channel

Orifice PlateVenturi Tube

Flow TubeFlow NozzlePitot TubeElbow Tap

TargetVariable-Area (Rotameter)

Reciprocating PistonOval Gear

Nutating DiskRotary Vane

TurbineVortex Shedding

SwirlConada

Effect & Momentum Exchange

ElectromagneticUltrasonic, Doppler

Ultrasonic, Transit-Time

CoriolisThermal

WeirFlume

FLOW M

EASUREMENT PART I Er FARUK BIN POYEN

10

FlowmeterVolumetric

Mass

FLOW M

EASUREMENT PART I Er FARUK BIN POYEN

11Selection 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

FLOW M

EASUREMENT PART I Er FARUK BIN POYEN

12Definitions 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

FLOW M

EASUREMENT PART I Er FARUK BIN POYEN

13Calibration 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

FLOW M

EASUREMENT PART I Er FARUK BIN POYEN

14Calibration 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.

FLOW M

EASUREMENT PART I Er FARUK BIN POYEN

15Coanda 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.

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.

FLOW M

EASUREMENT PART I Er FARUK BIN POYEN

16Coriolis 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.

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.

FLOW M

EASUREMENT PART I Er FARUK BIN POYEN

17References: 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.