This document describes the working principle and experimental setup for calibrating a venturimeter. A venturimeter consists of an inlet section followed by a converging section, cylindrical throat, and gradually diverging cone. It works by creating a pressure difference between the inlet and throat sections due to an increase in flow velocity at the throat. This pressure difference is measured to determine the flow rate. The experiment involves taking pressure and flow rate measurements at the inlet and throat sections using a manometer and collecting water over time. The data is then used to calculate discharge coefficients and Reynolds numbers to calibrate the venturimeter.

1. Venturimeter
It is a device, which is used for measuring the
rate of flow of fluid through a pipe.
It consists of an
• Inlet section followed by
• Convergent section
• A cylindrical throat and
• A gradually divergent cone.

2. Principle
The basic principle on which it works is that by reducing
the cross sectional area of the flow passage, a pressure
difference is created and the measurement of the pressure
difference enables the determination of the discharge
through the pipe.

3. OBJECT
1.
TO CALIBRATE THE VENTURIMETER.
2.
TO OBTAIN A GRAPH BETWEEN DISCHARGE
COEFFICIENT ‘K’ AND LOG10RE.

4. W
ORKING.
AS THE CROSS SECTION OF THE THROAT
IS SMALLER THAN THE CROSS
SECTIONAL AREA OF THE INLET SECTION,
THE VELOCITY OF FLOW AT THE THROAT
WILL BECOME GREATER THAN THAT AT
THE INLET SECTION, ACCORDING TO
CONTINUITY EQUATION.

5. THE INCREASE IN THE VELOCITY OF FLOW AT THE
THROAT RESULT IN DECREASE IN PRESSURE AT THIS
SECTION. AS SUCH A PRESSURE IS DEVELOPED
BETWEEN THE INLET SECTION AND THE THROAT OF
VENTURIMETER.
THIS PRESSURE DIFFERENCE CAN BE DETERMINED
EITHER BY CONNECTING DIFFERENTIAL
MANOMETER BETWEEN THE PRESSURE TAPS
PROVIDED AT THESE SECTIONS OR BY CONNECTING
THE SEPARATE PRESSURE GAUGE AT EACH OF THE
PRESSURE TAPS. THE MEASURE OF THE PRESSURE
DIFFERENCE BETWEEN THESE SECTIONS ENABLES
THE RATE OF FLOW OF FLUID TO BE CALCULATED .

6. THE CROSS SECTIONAL AREA OF THE THROAT
OF VENTURIMETER SHOULD NOT BE REDUCED
UNTO A CERTAIN LIMIT, OTHERWISE THE
PRESSURE AT THIS SECTION DROPS BELOW
THE VAPOR PRESSURE OF THE FLOWING
FLUID THAN THE FLOWING FLUID MAY
VAPORIZE AND THE VAPOR POCKETS MAY BE
FORMED IN THE LIQUID AT THIS SECTION.

7. THEORY
BY APPLYING BERNOULLI THEOREM
BETWEEN ENTRANCE AND THROAT
SECTIONS, THE RELATION FOR DISCHARGE
CAN BE DERIVED. A√2g √∆h
= K.C. √∆h
Q=K
√((D/d)4-1)
Here, ∆h is the difference of piezometric.

8. HEADS BETWEEN ENTRANCE AND THROAT SECTION AND
IS KNOWN AS “VENTURI HEAD” C IS CALLED CONSTANT OF
VENTURIMETER AND DEPENDS UPON GEOMETRIC
PARAMETERS OF GIVEN VENTURIMETER AND K IS CALLED
DISCHARGE COEFFICIENT.
IT TAKES ONTO ACCOUNT THE ENERGY LOSS BETWEEN
TWO SECTIONS AND DEPENDS ON THE RE. USUALLY K
VARIES FROM 0.96 TO 0.99 FOR RE>105. THE REYNOLDS NO
RE IS GIVEN AS U2 D/4= ‫ט‬Q/ΠD‫ט‬
‫ ט‬IS THE KINEMATIC VISCOSITY OF FLUID AND DEPENDS ON
THE TEMPERATURE.

9. EXPERIMENTAL SETUP
THE VENTURIMETER IS FITTED IN A PIPE
LINE, TO WHICH AN INLET VALVE IS
FITTED. THE PRESSURE TAPS ARE
PROVIDED AT ENTRANCE SECTION 1 AND
THROAT SECTION 2. A U-TUBE MERCURY
MANOMETER IS FITTED BETWEEN THESE
POINTS 1 AND 2. WATER TANK AND A
STOP WATCH IS USED TO MEASURE THE
DISCHARGE.

11. PROCEDURE
1.
REGULATE THE INLET VALVE TO ALLOW A STEADY
FLOW THROUGH VENTURIMETER
2.
COLLECT THE CERTAIN VOLUME OF WATER IN THE
TANK AND NOTE THE TIME T
3.
NOTE THE MANOMETER READING IN THE LEFT
LIMB (H1) AND RIGHT LIMB OF MANOMETER (H2).
THIS DIFFERENCE IS X.
4.
REPEAT THE STEPS 1 TO 3 FOR OTHER RATE OF
FLOW.
5.
TAKE SEVEN TO EIGHT SETS OF READINGS

12. CALCULATIONS
1.
THE VENTURIMETER CONSTANT C IS CALCULATED AS.
C = A√2G /√((D/D)4-1)
2.
THE DISCHARGE Q IS THEN CALCULATED BY VOLUMETRIC
METHOD
3.
THE DEFLECTION OF MERCURY MANOMETER X IS CONVERTED
INTO EQUIVALENT HEAD OF FLOWING LIQUID WATER)
H = X (SM/S - 1) = X (13.6/1 – 1 ) = 12.6XH
WHERE SM IS SPECIFIC GRAVITY OF MEASURING FLUID AND S
IS THE SPECIFIC GRAVITY OF WATER.
4.
NOW THE SQUARE ROOT OF H IS DETERMINED.
5.
THE DISCHARGE COEFFICIENT K IS CALCULATED.
K = Q/C√H
6.
FINALLY THE RE IS CALCULATED CORRESPONDING TO
DIFFERENT SET OF DISCHARGES.

13. FORMULA USED
1.
Q = K.HN
2.
K=
CD.A1.A2√2G
√(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= 0.5(APPR.)

14. OBSERVATION TABLES
TABLE 1
DISCHARGE MEASUREMENT TABLE
S.No.
Area
of
collecting
tank
Depth Of Water collected
Initia
Final
reading reading
Volume
of
water
collected
Time
of
collectio
n
Discharg
e
Q=
(A1∆h/t)
cumec
depth
Table 2
Dia of pipe D=
Dia of throat d=
S.NO.
Area of collecting tank = A
Manometer reading
I
Limb
II
Limb
Lab temperature = ,
Head
H cm
h½
K
Diff.
‘xcm
kinematic viscosity =
m2/sec
Re
LogRe

15. 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 =…..

16. PRECAUTIONS
1. DRIVE OUT ALL ENTRAPPED AIR FROM
DIFFERENTIAL MERCURY MANOMETER.
2. MAINTAIN A CONSTANT DISCHARGE
BEFORE TAKING ANY READING.

17. VIVA - VOICE
• WHAT IS THE PRINCIPLE AND USE OF VENTURIMETER? CAN IT
BE USED FOR LARGE PEN STOKES. HOW WILL PRESSURE
CORRECTIONS BE MADE THEN ?
• WHY IS THE LENGTH ON CONVERGING CONE SMALLER THEN
THE DIVERGING CONE OF VENTURIMETER?
• WHY IS THE PRESSURE DIFFERENCE BETWEEN ENTRANCE
AND THROAT SECTION INCREASED DUE TO FRICTION?
• IF THE DIRECTION OF FLOW IS REVERSED WHAT WILL BE THE
EFFECT ON THE VALUE OF ‘H’ (I) IF FRICTION IS NEGLECTED.
(II) FRICTION IS TAKEN INTO ACCOUNT?
• ACCURACY OF RESULT DEPENDS ON HOW GREAT IS THE
VALUE OF H. IF WE REDUCE ‘D’ FURTHER, THE VALUE OF H
INCREASES. CAN WE GO O REDUCING THROAT DIAMETER ‘D’
AS MUCH AS WE PLEASE?IF NOT WHAT IS THE FACTOR TO
LIMIT THE VALUED/D?
• JUST BY SEEING A SEPARATE VENTURIMETER, CAN YOU
ASCERTAIN THE DIRECTION OF FLOW, HOW?