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7/23/2019 venturimeter-140116003452-phpapp02

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Venturimeter

It is a device, which is used for measuring therate of flow of fluid through a pipe.

It consists of anInlet section followed byConvergent sectionA cylindrical throat andA gradually divergent cone.


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Principle

The basic principle on which it works is that by reducingthe cross sectional area of the flow passage, a pressuredifference is created and the measurement of the pressuredifference enables the determination of the discharge

through the pipe.


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OBJECT1. TO CALIBRATE THE VENTURIMETER.

2. TO OBTAIN A GRAPH BETWEEN DISCHARGECOEFFICIENT K AND LOG10RE.


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WORKING.

AS THE CROSS SECTION OF THE THROAT

IS SMALLER THAN THE CROSS SECTIONALAREA OF THE INLET SECTION, THE

VELOCITY OF FLOW AT THE THROAT WILL

BECOME GREATER THAN THAT AT THE

INLET SECTION, ACCORDING TO

CONTINUITY EQUATION.


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THE INCREASE IN THE VELOCITY OF FLOW AT THE THROATRESULT IN DECREASE IN PRESSURE AT THIS SECTION. ASSUCH A PRESSURE IS DEVELOPED BETWEEN THE INLET

SECTION AND THE THROAT OF VENTURIMETER.THIS PRESSURE DIFFERENCE CAN BE DETERMINED EITHERBY CONNECTING DIFFERENTIAL MANOMETER BETWEEN THEPRESSURE TAPS PROVIDED AT THESE SECTIONS OR BYCONNECTING THE SEPARATE PRESSURE GAUGE AT EACH OFTHE PRESSURE TAPS. THE MEASURE OF THE PRESSUREDIFFERENCE BETWEEN THESE SECTIONS ENABLES THERATE OF FLOW OF FLUID TO BE CALCULATED.


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THE CROSS SECTIONAL AREA OF THE THROAT OF

VENTURIMETER SHOULD NOT BE REDUCED UNTO

A CERTAIN LIMIT, OTHERWISE THE PRESSURE ATTHIS SECTION DROPS BELOW THE VAPOR

PRESSURE OF THE FLOWING FLUID THAN THE

FLOWING FLUID MAY VAPORIE AND THE VAPOR

POCKETS MAY BE FORMED IN THE LIQUID AT THIS

SECTION.


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THEORY

BY APPLYING BERNOULLI THEOREM

BETWEEN ENTRANCE AND THROATSECTIONS, THE RELATION FOR DISCHARGE

CAN BE DERIVED. ! " A#$g #%h

#&&'(d)*+)! ".C. #%h

Here, %h is the difference of pie-ometric.


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HEADS BETWEEN ENTRANCE AND THROAT SECTION AND ISKNOWN AS !VENTURI HEAD" C IS CALLED CONSTANT OFVENTURIMETER AND DEPENDS UPON GEOMETRICPARAMETERS OF GIVEN VENTURIMETER AND K IS CALLEDDISCHARGE COEFFICIENT.

IT TAKES ONTO ACCOUNT THE ENERGY LOSS BETWEEN TWOSECTIONS AND DEPENDS ON THE RE. USUALLY K VARIESFROM 0.#$ TO 0.## FOR RE%10&. THE REYNOLDS NO RE IS

GIVEN AS U2 D'=4

Q'(D

IS THE KINEMATIC VISCOSITY OF FLUID AND DEPENDS ONTHE TEMPERATURE.


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E)PERIMENTAL SETUPE)PERIMENTAL SETUP

THE VENTURIMETER IS FITTED IN A PIPE LINE,

TO WHICH AN INLET VALVE IS FITTED. THEPRESSURE TAPS ARE PROVIDED AT ENTRANCE

SECTION 1 AND THROAT SECTION 2. A U*

TUBE MERCURY MANOMETER IS FITTED

BETWEEN THESE POINTS 1 AND 2. WATERTANK AND A STOP WATCH IS USED TO

MEASURE THE DISCHARGE.


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PROCEDURE

1. REGULATE THE INLET VALVE TO ALLOW A STEADYFLOW THROUGH VENTURIMETER

2. COLLECT THE CERTAIN VOLUME OF WATER IN THETANK AND NOTE THE TIME T

+. NOTE THE MANOMETER READING IN THE LEFT LIMBH1- AND RIGHT LIMB OF MANOMETER H2-. THISDIFFERENCE IS ).

. REPEAT THE STEPS 1 TO + FOR OTHER RATE OF FLOW.

&. TAKE SEVEN TO EIGHT SETS OF READINGS


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CALCULATIONSCALCULATIONS

1. THE VENTURIMETER CONSTANT C IS CALCULATED AS.

C / A2G 'D'D-*1-

2. THE DISCHARGE Q IS THEN CALCULATED BY VOLUMETRICMETHOD

+. THE DEFLECTION OF MERCURY MANOMETER ) IS CONVERTED

INTO EQUIVALENT HEAD OF FLOWING LIQUID WATER-

H / ) SM'S * 1- / ) 1+.$'1 1 - / 12.$)H

WHERE SM IS SPECIFIC GRAVITY OF MEASURING FLUID AND S ISTHE SPECIFIC GRAVITY OF WATER.

. NOW THE SQUARE ROOT OF H IS DETERMINED.

&. THE DISCHARGE COEFFICIENT K IS CALCULATED.

K / Q'CH

$. FINALLY THE RE IS CALCULATED CORRESPONDING TODIFFERENT SET OF DISCHARGES.


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FORMULA USED

1. Q / K.HN

2. K / CD.A1.A22G

A12*A22-

WHERE ,

Q/ DISCHARGE RATE OF FLOW-

K/ CONSTANT

H/ DIFFERENTIAL HEAD

CD/ COEFFICIENT OF DISCHARGE

A1/ AREA OF INLET SECTION

A2/ AREA OF THROAT SECTION

G/ GRAVITATIONAL ACCELERATION

N/ 0.&APPR.-


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OBSERVATION TABLESTABLE 1

DISCHARGE MEASUREMENT TABLES.No. Area

of

collecting

tank

Depth Of Water collected Volume

of

water

collected

Time

of

collection

Discharge

Q =A!"h#t$

cumec

Initia

reading

Final

reading

depth

S.NO. %anometer reading &ead& cm

h' ( )e *og)e

ILimb

IILimb

Diff.xcm

Table $Dia of pipe D=

Dia of throat d=Area of collecting tank = A

Lab temperature = , kinematic viscosity = m2/sec


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PRESENTATION OF RESULT

PLOT A GRAPH BETWEEN Q AND H ON AN ORDINARY

GRAPH. IT WILL BE A STRAIGHT LINE PASSING

THROUGH THE ORIGIN

PLOT ANOTHER GRAPH BETWEEN K AND RE ON A

SEMI LOGARTHMIC GRAPH SHEET

AVERAGE VALUE OF K /..


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PRECAUTIONS

1. DRIVE OUT ALL ENTRAPPED AIR FROM

DIFFERENTIAL MERCURY MANOMETER.2. MAINTAIN A CONSTANT DISCHARGE

BEFORE TAKING ANY READING.


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VIVA * VOICE WHAT IS THE PRINCIPLE AND USE OF VENTURIMETER3 CAN IT BE

USED FOR LARGE PEN STOKES. HOW WILL PRESSURECORRECTIONS BE MADE THEN 3

WHY IS THE LENGTH ON CONVERGING CONE SMALLER THEN

THE DIVERGING CONE OF VENTURIMETER3 WHY IS THE PRESSURE DIFFERENCE BETWEEN ENTRANCE ANDTHROAT SECTION INCREASED DUE TO FRICTION3

IF THE DIRECTION OF FLOW IS REVERSED WHAT WILL BE THEEFFECT ON THE VALUE OF H I- IF FRICTION IS NEGLECTED. II-FRICTION IS TAKEN INTO ACCOUNT3

ACCURACY OF RESULT DEPENDS ON HOW GREAT IS THE VALUEOF H. IF WE REDUCE D FURTHER, THE VALUE OF H INCREASES.CAN WE GO O REDUCING THROAT DIAMETER D AS MUCH ASWE PLEASE3IF NOT WHAT IS THE FACTOR TO LIMIT THEVALUED'D3

4UST BY SEEING A SEPARATE VENTURIMETER, CAN YOUASCERTAIN THE DIRECTION OF FLOW, HOW3

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