ACKNOWLEDGEMENT
I would like to thank to my for his tremendous support and
assistance in the complication of my project his support and guidance.
I also like to thank our Principal sir Dr.Sudipta Das for providing this wonderful
opportunity to work on this project & support and guidance in completing our project
I would like to take this opportunity to express & It was a great learning experience..
The project would not have been successful without their cooperation and insights
or inputs.
Introduction to Flow Measurement
Why Flow measurement is essential?
Flow meters are widely used to quantify the amount of fluid flowing
through pipe in combustion chamber, boiler, oil and gas, process and
Chemical industries, thermal power plant, milk and dairy. Flow
measurement of water in open canal and sewage flow is also essential
for preservation and storage of clean water. In every application,
different type of flow meters are used.
In Fluid mechanics, we learn basic fluid properties like density,
conservation of mass flow rate. How mass flow rate is determined that
should be known to every CFD engineer and process engineers in power
or chemical industries. Mass flow rate is an essential input for forced
flow CFD Modeling. Incorrect flow rate can lead to wrong results in
both experiment well as CFD analysis.
Flow Measurement is the experimental technique of measuring the
amount fluid flowing through duct or open channel
Laminar and turbulent Flow
The performance of most of flow measurement devices is also affected
by the Reynolds Number. It is a dimensionless number for ratio of
inertia to viscous forces.
For liquid flow, Reynolds number ccan an defined as the ratio of the inertial
forces to its viscous drag forces.It is useful to determine whether a flow
is laminar or turbulent.
Lamianr flow rate can be determined using velocity profile. But
turbulent flow rate can not determined easily. Turbulent flow is
visualized with higher number of vortices if dye or smoke is injected in
fluid flow.
For internal flow through duct, when the Reynolds number (ReD) is
lower than 2300. Turbulent flow is noted when the Reynolds number is
greater than 2300 for internal flow. The crictical Reynolds number for
open channel is 5,00,000. The critical Reynolds number depends on
velocity of fluid (V),
V), size of duct ((L),
), density (ρ) and viscosity (η) of
fluid, roughness of wall, external material (dirt particles) and practical
conditions.
A certain range around 2300 is considered the transition flow region
between laminar and turbulent flow.
Selection of Flow Measurement Devices
Flow measurement devices should be designed by following important factors
Devices should consider Fluctuations in fluid flow
Easy Integration with Piping System
High Accuracy of device is recommended to reduce errors in
measurements
High Turn-Down
Down Ratio of flow rate
Low capital and maintenance cost
Sensitivity to Dirt Particles should be minimum
Minimum Pressure Loss due to fitt fitting
ing of flow measurement devices
Low use of mechanical or moving Parts
Devices must be resistant to corrosion and Erosion
Essential Quantities for Flow Measurement
The volume flow rate (Q) is defined as the volume of fluid that flows
past a given cross sect
sectional area per unit time
Q = Cross sectional area*Average Velocity = A*V (m3/hr)
common volume units of volume flow rate: m3/s, m3/hr, Nm3/hr,
Gallons Per Minute (GPM), Standard Litre Per Minute (SLPM)
Mass flow rate is defined as
m = density * volume flow rate = ρ*Q =ρ*A*V (kg/hr)
Some devices both pressure and temperature along with volume flow
rate. Using these measured values, we can find out the density of fluid
using the property table or ideal gas eqequation
Coefficient of Discharge (Cd) is an important parameter for flow
meter to consider pressure loss. It is defined as the ratio of actual mass
flow rate to ideal (ρ*A*V
ρ*A*V ) mass flow rate. After measurement of actual
mass flow rate, the coefficient of di
discharge
scharge can be determined.
Units for Flow Measurement
SI Unit for volume flow rate (volume/time) : Cubic meters per
second (m3 /s)
Other common units for volume flow rate
Litre per minute LPM): 1L/s = 103 cm3 /s
Cubic centimetre per minute: 103 cm3 /s = 10-3 m3 /s
Gallons per minute (GPM): 1gal/s = 3.788 L/s
Cubic feet per minute: 1 cf/min = 4.719×10
4.719×10-4 m3 /s
Mass flow rate can be calculated by multiplying flow rate the density
(ρ) of measuring fluid
Classification of Flow measurement
devices
The list of commonly used flow meters in industry are given below
Mechanical Type Flow Meters
1. Piston Meters
2. Variable Area Meter
3. Turbine Flow Meter
4. Single Jet Meter
5. Woltmann Meter
6. Paddle Wheel Meter
7. Current Meter
8. Nutating Disc Meter
9. Pelton Meter
10. Oval Gear Meter
11. Inferential Meter
12. Thermal mass flow meter
13. Turbine Flow meter: turbine motion is used to calibrate flow rate
14. Electro-Magnetic: electro-magnetic field is related flow measurement
15. Coriolis flow meter
16. Positive Displacement
17. Vortex Flow meter
18. Ultrasonic Doppler Flow Tub
19. Reciprocating Piston
20. Rotary Vane Swirl
21. Target
22. Thermal Dispersion
23.Ultrasonic Transit Time
Differential Pressure Based Flow Meters
Orifice flow meter
Pitot Tube
Venturi Tube
Vortex Weir & Flume
Differential Pressure
Transmitters
Correlation Method
Elbow Tap – Elbow flow Meter
Flow Nozzles
Variable Area
Flow measurement techniques are further classified based on
closed duct (pipe) and open channel flow
Flow measurement can be carried out for volume flow rate (Q) and
mass flow rate (m). Majority of devices of mechanical and pressure
differential techniques measures volume flow flow rate after
determination of the velocity of fluid flow.
For determination of mass flow rate, the fluid to be isothermal or fluid
density needs to be known.
Direct Volume Flow Rate
Measurement
It needs a large device when the volume flow rate of fluid are high
For a smaller device, the measured values may not be accurate
During start or end of measurement, fluctuations in th
thee measuring
values are observed because of the disturbances in opening or closing of
valves
The measurement the mass (volume) flow of the fluid and the time may
not be consistent.
Venturi Flow Meter
The principle of Ventury effect is used to measure flow rate for ventury
flow meter
A reduction in fluid pressure occurs when a fluid flows through a
constricted section of pipe. Pressure decreases as flow velocity increases
across reduced cross section
The following formula derived from Bernoulli’s equation
A1 and A2 are cross sectional area at inlet and throat of venturi. ρ is the
mass density of fluid.
Actual flow rate measured by venturi meter
Where, H is the difference in static pressure head (P1– P2) measured across
the venturi meter, D1 is the diameter of upstream pipe and D2 is the diameter
in the throat section (lowest cross area),Cd is coefficient of discharge for the
venturi device
Orifice Flow Meter
The volume flow rate of liquid or gas is determined using the orifice
flow meter
This device creates a pressure drop across the orifice plate which
varies with the flow rate
The formula for orifice meter is similar to that used for Venturi flow
meter
Solenoid Valve Flow Meter
The amount of flow of a fluid through the solenoid valve is generally
calculated with the flow coefficient (Kv)
User has to note that for gases (like air, methane and oxygen etc.), the
formula is different with correction factor
The Kv-value presents the volume flow rate of fluid in m3/hour in a valve
with a specified pressure drop at ambient temperature (1 bar and 20°C).
If K-v volume flow rate is presented in m3/hour, then the kv-value can
be expressed in per unit time (l/min)
The volume flow rate (Q) is calculated using the volume coefficient (K-
v), the density of the fluid (ρ), and pressure difference between inlet and
outlet of pipe (ΔP = P1 -P2 )
The calculation of volume flow rate for liquid, gases, air and steam is
given below. In the following table, the variables are described as:
Q = volume flow rate of fluid (m3/h)
P1 = Inlet gauge pressure (bar)
P2 = Outlet gauge pressure (bar)
Qn = the normal flow rate (m3/h) for 20° temperature and 760 mmHg
of pressure
t = Inlet fluid temperature (°C)
V1 = Inlet specific volume of fluid (m3/Kg )
V2 = Outlet specific volume of fluid (m3/Kg ) for outlet pressure (P2) and
temperature (t)
G = mass flow rate for steam (Kg/h)
Pitot Tubes
The pitot tubes are widely used to measure
air velocity in many applications like air
ventilation and airplanes
The pitot tube is used to find the fluid
flow velocity by converting the kinetic
energy (dynamic pressure) to the potential
energy of the fluid
The use of the pitot tube is limited to point
measuring
It can be an annular or multi
multi-orifice
orifice type. The dynamic pressure
(1/ρ*V^2) is measured, and the annular is used to get the average
velocity.
The pitot tube is used to measure the air velocity around the aero plane.
It is mounted frontier of outer surface.
In conclusion, coriolis flow meter has the hi
highest
ghest accuracy, followed by the magnetic
flow meter, and last in the order is orifice flow meter. The objective of the experiment
which is to compare the accuracy of each flow meter as well as to study the
mechanism of the flow meters is achieved. The usag
usages
es of these flow meters are
different in the industry. The selection of flow meters is based on the specification
that can fulfill the requirement of the industry
industry.
References
Bela G. Liptak, Flow Measurement, 1st edition, CRC Press (1993)
Paul J. LaNasa, E. Loy Upp, Fluid Flow Measurement: A Practical Guide
to Accurate Flow Measurement
Measurement, 3rd edition, Butterworth-Heinemann
Butterworth
(2014)
David W. Spitzer, Industrial Flow Measurement, 3rd
edition, Instrument Society of America (2005)
