1. VENTURIMETER Department of Chemical Engineering
By:
ACHARYA SHYAMAL R. ( )
Faculty: Krunal J. Suthar
Department of Chemical Engineering
Shroff S. R. Rotary Institute of Chemical Technology
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2. Active Learning Assignment SRICT/CE/FFO
Contain
Introduction
Principle
Construction
Working
Derivation
Advancement in using venturi meter
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3. Measurement of fluid flow
In the chemical process industry, it is desirable to know the amount of a fluid flowing to or form the process equipment.
Many different type of flow meter are used industrially to measure the rate at which a fluid is flowing through a pipe.
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4. Types of flow measuring instrument
Venturi meter
Orifice meter
Rota meter
Current meter
Positive displacement meter
Electromagnetic meter
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5. Active Learning Assignment SRICT/CE/FFO
History
his typical variation of fluid velocity and pressure by allowing it to flow through such a constricted convergent-divergent passage was first demonstrated by an Italian scientist Giovanni B.
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6. Venturi meter Introduction :
A venturi meter is a variable head meter which is used for measuring the flow rate of a fluid through a pipe.
In this meter, the fluid is gradually accelerated to a throat and then gradually retarded in a diverging section where the flow expand through the pipe size.
The large portion of kinetic energy is thus recovered.
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7. Principle :
The basic principle on which venturi meter work is that by reducing the cross section area of the flow passage.
The pressure difference is created and the measurement of the pressure difference enables the estimation of the discharge/flow through the pipe.
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8. Construction
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9. An inlet section followed by a convergent section.
The inlet section of the venturi meter is of the same diameter as that of pipe line in which it is installed which is followed by the short convergent section with a converging cone angle of the 15°-20°.
Its length is parallel to the axis is approximately equal to 2.7(D – DT).
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10. Where, D = diameter of pipe ; DT= diameter of throat.
A long diverging cone with a section angle of above 5° – 7° wherein the fluid is reacted and large portion of the kinetic energy is converted back into the pressure energy.
The convergent section is a short pipe that tapers from the original pipe size to that of the throat of the meter.
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11. Active Learning Assignment SRICT/CE/FFO
The divergent section of the venturi meter is gradually diverging pipe with the cross-sectional area gradually increasing from that of the throat to the original pipe size.
A piezometer ring is an annular chamber provided at the pressure taps with small holes drilled from the inside of the tube and is used for averaging out the individual pressures transmitted through the several small holes to a pressure measuring device.
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12. Working
A venturi meter of known coefficient is installed in the pipeline and the pressure taps are connected to a pressuring device.
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13. Air pockets, if any, are removed from connecting tubing after starting the flow of fluid through the pipeline in which is installed for flow measurement.
An increasing in the flow velocity at the throat results in a decrease in the pressure at the throat.
Due to this a pressure difference is developed between the inlet section and throat section which is measured by pressure gauge after the steady state is attained.
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14. This pressure difference is than related to the flow rate by a mathematical flow equation for the meter.
In the venturi meter, fluid is accelerated in the convergent cone from the inlet section to the throat section and in the divergent cone, it is retarded from the throat section to the end section of venturi meter.
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In order to avoid the possibility of flow separation and consequent energy loss, the divergent cone of a venturi meter is made long with a gradual divergence.
Since the separation of flow may occur in the divergent cone of a venturi meter, this portion is not used for measuring the flow rate.
Since the gradual reduction in the area of flow, where is no vena contracta and the flow area is minimum at the throat so that the coefficient of contraction is unity.
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16. Flow Equation or a Venturi Meter
Let P1, P2 and u1, u2 be the pressure and velocities at section 1 and 2, respectively .
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17. Let A1 and AT be the flow areas at stations and 2, respectively.
Section 1 is at the upstream side of the convergent cone(inlet section) and station 2 is the throat.
Assume that the flowing fluid is incompressible and there are no friction losses between station 1 and station 2.
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18. The Bernoulli's equation in terms of energy units (J/kg) between stations and 2 is
The venturi is connected in a horizontal pipe, so Z1 = Z2 = 0. So the above equation then reduces to
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19. From the equation of continuity, We have
Where and
In which D= pipe diameter &
DT= throat diameter
Let,
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20. So, above value is put in Bernoulli's Eq. Rearranging , we get
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21. Usually , α2/α1 =1
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22. Volumetric flow rate, Q = u2AT
This above equation is corrected by introducing an empirical factor CV as,
Where CV is the coefficient of venturi meter, or the coefficient of discharge of venturi meter.
Volumetric flow rate, Q = u2AT
Where AT = cross-section area of the throat
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23. Combining the equation
Where Q is the actual discharge / volumetric flow rate
The above gives the value of theoretical discharge through the venturi as it has been obtained by considering no frictional losses in the system.
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24. Active Learning Assignment SRICT/CE/FFO
For a well designed venturimeter, the coefficient of venturi, CV is about 0.98 for pipe diameter ranging from 50 to 200 mm and about 0.99 for larger sizes.
Δh is the manometer reading obtained in terms of meter of the manometric fluid, then pressure drop across the meter is given by,
(P1 – P2)= Δh( ρm – ρ) g
Where, ρm - density of manometric fluid in kg/m3
ρ - density of flowing fluid in kg/m3
g =9.81 m/S2
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25. So, Here, The above equation is for venturi meter.
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26. Advantages of venturi meter
It can be used for flow is compressible and incompressible fluid.
High reproducibility.
Less power loss.
High accuracy over wide flow ranges.
It can also be used where only a small pressure head is available.
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27. Disadvantages of venturi meter
It is expansive and bulky.
It occupies considerable space.
Relatively complex in construction.
Used only for permanent installations.
It cannot be altered once it is installed.
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28. Active Learning Assignment SRICT/CE/FFO
Orifice Meter
Venturi meter
Simple in construction
Relatively complex in construction
Low Space requirement
Occupies considerable space
Relatively cheap
Expensive
Pressure recovery is poor
Pressure recovery is high.
Coefficient of discharge is about 0.61
Coefficient of discharge is about 0.98
Larger power loss.
Smaller power loss
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29. Advancement in using venturi meter
Venturi and Orifice plates are widely used in industries to measure the flow rate of gases and liquids. The working principle is simple and flow is measured using the differential pressure principle. 
Even for a wind to blow, there has to be a low pressure and a high pressure.
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30. Active Learning Assignment SRICT/CE/FFO
If there is a flow (created naturally or artificially), there is a high pressure upstream and low pressure down stream. 
Can be used in any industrial, automotive, aeronautical, domestic or just about any field - which comes to imagination.
In aviation, the PITOT TUBE is a venturi meter that allows to measure the speed of the air around the airplane (its "Air speed"). 
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31. Active Learning Assignment SRICT/CE/FFO
Thank you
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