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CONTENTS

Topic

ABSTRACT

1. INTRODUCTION.

2. HISTORY OF VENTURIMETER

3. DESIGN &TECHNOLOGICAL SPECIFICATIONS.

4. PARAMETERS TO CONTROL.

5. PARAMETERS TO BE EVALUATED.

6. BRIEF EXPLANATION.

7. CONCLUSION

8. REFERENCES


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ABSTRACT

IN connexion with an article on Early Hydraulio Engineering, in

which the work of Clemens Herschel (1842-1930) is referred to,

Engineering in its issue for August 2 reproduces a letter from Herschel to

the late Dr. Unwin describing his invention of the Venturi Meter. The

letter is dated June 5, 1888, and addressed from the hydraulic engineer's

office of the Holyoke Water Power Co., Mass. In his letter, Herschel says

ho tested a one-inch Venturi Meter, under 210 ft. head: I am now

satisfied that here is a new and pregnant principle to be applied to the art

of gauging fluids, inclusive of fluids such as compressed air, illuminating

or fuel gases, steam, etc. Further, that the shape of the meter should be

trumpet-shaped in both directions; such a meter will measure volumes

flowing in oither direction, which in certain localities becomes a useful

attribute. . . . And we are but in the beginning of the art of measuring

pressures, and differences of pressure. When these shall be delicatelymeasured, the Venturi Meter will have become as delicate in its lower

limits of capacity, as any other and it is on this score alone, that it is as

yet inferior to some of the volumetric meters. The letter was found

among the papers placed at the disposal of the Unwin Memorial

Committee by Miss Unwin

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1. INTRODUCTION

A venturimeter is a device which is used for measuring the rate of flow through a

pipe. As shown in Fig.1.1, a venturimeter consists of (1) inlet section followed by a

convergent cone, (2) the throat, and (3) a gradually divergent cone. Since the cross

sectional area of the throat section is smaller than the cross-sectional area of the inlet

section, the velocity of flow at the throat section will become greater than that at theinlet section, according to the continuity equation.

The increase in the velocity of flow at the throat section results in the decrease in the

pressure at this section. As such a pressure difference is developed between the inlet

and the throat sections of the venturimeter. The pressure difference between these

sections can be determined either by connecting a differential manometer between

the pressure tappings provided at these sections or by connecting a separate pressure

gauge at each of the pressure tappings.

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2. HISTORY OF VENTURIMETER

The Venturi effect is the reduction in fluid pressure that

results when a fluid flows through a constricted section of

pipe. The Venturi effect is named after Giovanni Battista

Venturi (17461822), an Italian physicist.

Background_______________________________________

The Venturi effect is a jet effect; as with a funnel the velocity of the fluid

increases as the cross sectional area decreases, with the static pressure

correspondingly decreasing. According to the laws governing fluid dynamics, a

fluid's velocity must increase as it passes through a constriction to satisfy the

principle of continuity, while its pressure must decrease to satisfy the principle of

conservation of mechanical energy. Thus any gain in kinetic energy a fluid may

accrue due to its increased velocity through a constriction is negated by a drop in

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pressure. An equation for the drop in pressure due to the Venturi effect may be

derived from a combination of Bernoulli's principle and the continuity equation.

The limiting case of the Venturi effect is when a fluid reaches the

state of choked flow, where the fluid velocity approaches the local

speed of sound. In choked flow the mass flow rate will not increase

with a further decrease in the downstream pressure environment.

3.TECHNOLOGICAL SPECIFICATIONS

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4. DESIGN OBJECTIVES

Size and Compute dimensions with the least loss of energy

Compute and manufacture critical dimensions based on pressure and

temperature. Minimize overall pressure loss using the Gibson method to design the recovery

cone

Streamline the flow through all sections to minimize overshoot and overall

pressure loss

Easily and timely add user inputs and requirements to module.

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5. PARAMETERS TO BE TAKEN CARE OF:

In viewing a Nozzle-Venturi three distinct sections are noted

The favorable pressure gradient entrance to the throat section.

The cylindrical throat region.

The adverse pressure gradient recovery cone region.

Each of these regions was designed using technical papers and a Computational

Fluid Dynamic (CFD) program. A CFD analysis being used to determine optimum

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design criteria for the inlet section, throat (or metering section), and to confirm the

Gibson (1961) recovery cone derivation.

Illustrated above are the resulting CFDs for the two basic designs.

S-Design: A cylindrical radius is the inlet geometry. The entrance to the PTC-6

throat section is critical to insure boundary layer development length is in

accordance with the PTC-6 theoretical extrapolation requirement (Keyser and

Murdock, 1990).

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Sdesign use an inlet geometry of the Standardized Torodial Throat Nozzle

(ASME/ANSI MFC-7M, 1990), extensive data and CFD studies show excellent

entrance to the throat results for this geometry.

T-Design: A Halmi double cone entrance with a unique cone angles and a throat

entrance developed based on test results in Holland (Miller 1989), with confirming

CFD studies. Recovery cone geometry for both S and T is designed in accordance

with the analysis developed

6. VENTURIMETER: Brief explanation

Basic principle:

When a venture meter is placed in apipe carrying the fluid whose flow rate is to be measured, a

pressure drop occurs between the entrance and throat of the venturimeter. This pressure drop is

measured using a differential pressure sensor and when calibrated this pressure drop becomes a

measure of flow rate.

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Construction of Venturi meter

The following are the main parts and areas of venture meter:

The entry of the venture is cylindrical in shape to match the size of the pipe through which fluid flows. This

enables the venture to be fitted to the pipe. After the entry, there is a converging conical section with an included

angle of 19 to 23.

Following the converging section, there is a cylindrical section with minimum area called as the throat.

After the throat, there is a diverging conical section with an included angle of 5 to 15.

Openings are provided at the entry and throat (at sections 1 and 2 in the diagram) of the venture meter for attaching

a differential pressure sensor (u-tube manometer, differential pressure gauge, etc) as shown in diagram.

Operation of venturi meter:

The fluid whose flow rate is to be measured enters the entry section of the venturi meter with apressure P1.

As the fluid from the entry section of venturi meter flows into the converging section, its pressure

keeps on reducing and attains a minimum value P2 when it enters the throat. That is, in the throat,

the fluid pressure P2 will be minimum.The differential pressure sensor attached between the entry

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and throat section of theventuri meter records the pressure difference(P1-P2) which becomes an

indication of the flow rate of the fluid through the pipe when calibrated.

The diverging section has been provided to enable the fluid to regain its pressure and hence its

kinetic energy. Lesser the angle of the diverging section, greater is the recovery.

Application:

It is used where high pressure recovery is required.

Can be used for measuring flow rates of water,gases,suspended solids, slurries

and dirty liquids.

Can be used to measure high flow rates in pipes having diameters in a few

meters.

Advantages of venturi meters

Less changes of getting clogged with sediments.

Coefficient of discharge is high.

Its behaviour can be predicted perfectly.

Can be installed vertically, horizontally or inclinded.

Limitations:

They are large in size and hence where space is limited, they cannot be used.

Expensive initial cost, installation and maintenance.

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Require long laying length. That is, the veturimeter has ti be proceeded by a

straight pipe which is free from fittings and misalignments to avoid

turbulence in flow, for satisfactory operation. Therefore, straightening vanes

are a must

.Cannot be used in pipes below 7.5cm diameter.

7.CONCLUSION:

The mechanical energy equation (or generalized Bernoullis

equation) is an expression of the energy balance equation for

steady flow and constant-density fluids.

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The mechanical energy equation can be applied with negligible

errorto almost all steady flows of liquids and for steady flows of

gases at low velocities.

A special case of the mechanical energy equation, the

Bernoullis equation, can be derived if we assume frictionless

flow and absenceof shaft work.A large number of devices for

the measurement of fluid velocity andflow rate are based on the

conservation of energy. The Bernoulliequation can be

conveniently used to make the appropriatecalculations.

REFERENCES

1. K. Openshaw, A review of Jatropha curcas:HYDRO-MECHANICS, 23 nov

2011.

2. A. Dufey, production, trade and International Institute for FLUIDS and (IIED),

London, UK, 23 nov 2011. .

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3. Y.D. Wang, T. Al-Shemmeri and P. Eames et al., An experimental investigation

of the performance and Hydro-Dynamics, Applied Thermal Engineering, 24

nov 2011.

4. K.L.KUMAR Hydraulic systems and machines 25 nov 2011.

5. Thans to wikipepia. www.wikipedia.com

6. Google for Various Diagrams and Pictures.

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