Fluid Mechanic Lab - Venturi Meter

Soran University
Faculty of Engineering
Department of Petroleum Engineering
Fluid Mechanic
Title: Venturi Meter
Experiment No.: 5
Name: Muhammad Sulaimon Rasul
Group: A1
Date: 14/11/2019
Supervisors: Mr. Shahab, Mr. Sarkar, Mrs. Marriam, Mr. Balen

Contents
Aim………………………………………………………………………………………….…….1
Theory…………………………………………………………………………………….…….…1
Apparatus…………………………………………………………...…………………………..…3
Procedure………………………………………………………………………………………….4
Calculation………………………………………………………………………………...………5
Result and Discussion……………………………………………………………………………..6
Conclusion………………………………………………………………………………………...7
References…………………………………………………………………………………………8
List of Figures
Figure 1 Venturi Meter………….…………….………………………….....….….……….….…2
Figure 2 Graph between flow rate and pressure loss …………………….....….….……….….…6
List of Tables
Table 1 Theorical Results……………………………………………..…………………………..5
Table 2 Experimental and Theorical Results……………………………….……………………..5

Aim
This experiment tends to obtain both compressible and incompressible fluids in a pipe line, and
graph between flow rate and pressure loss.
Theory
A Venturi Meter is basically used to measure the volumetric flow rate of a fluid. Sometimes an
amount of pressure drop occurs in pipelines due to the reduction in flow passage, which depends
on geometrical parameters such convergent cone angle, divergent cone angle, diameter ratio and
throat length of Venture and properties of the fluid. In industries like chemical, papers, minerals
processing, oil and gas, etc., which they require an accurate flow measurement and controlling it.
A Venturi-Meter is used because of its accuracy of measuring fluid flow rate using a Bernoulli’s
principle work which illustrate that the velocity of a fluid increases with decreasing the pressure.
However, the device has studied by researchers for different purpose. (Elperin et al, 2002).
Inside the Venturi-Meter a pressure difference is created by changing the flow passage cross
sectional area, while the pressure difference helps in determination of the discharge flow rate
through the pipe line. The throat pass area of the Venturi meter is smaller than the inlet cross
sectional area of the Venturi. When a fluid passes through a Venturi mere, will cause the flow to
pressure drop between the inlet and cylindrical throat of Venturi Meter. The pressure drop can be
measured using a differential pressure measuring instrument. The differential pressure instrument
can be configured in order to exhibit and display the flow rate instead of differential pressure
(Herschel, 1888).
A Venturi mainly has three parts, an inlet section followed by converging cone. A circular throat,
a diverging cone followed by an outlet section. Normally the diameter of the inlet section and
outlet section are the same (Modi et al, 2009). The following equations can be used to determine
the theorical flow rate in the Venturi:
…………..…………………………..…………………………………(1)
Qactual = LxWxH/t …………………………………………………………………………………(2)
1

Cd = Qactual/Qtheory ………………………………………………………………..…………(3)
Pressure Loss = ϒh ……………………………………………………………………………..(4)
Where:
AD: Cross sectional area of the smallest part of venturi.
AA: Cross sectional area of hA in venturi.
g: Gravity acceleration (9.81m/s2).
hA: High of h in m.
hD: High of h in smallest cross-sectional area.
L: Length of storage (0.73m).
W: Width of storage (0.3m).
H: High of water in storage.
t: Time in seconds.
Cd: Discharge coefficient.
ϒ: Specific weight
h: Hight of manometer.
2

Apparatus and Materials
Apparatus
• Venturi meter apparatus: Is a device used to measure flow rate. Shown in Figure 1.
Materials
• Water.
Figure 1 Venturi Meter Apparatus
3

Procedure
1. The apparatus was leveled by opening both the Bench Supply valve and the control valve
downstream of the meter to allow water to flow and clear air pockets from the supply hose.
This was achieved by connecting the apparatus to a power supply.
2. The control valve was then gradually closed causing water to rise up in the tubes of the
manometer thereby compressing the air contained in the manifold.
3. When the water level had risen to a convenient height, the bench valve was also closed
gradually so that as both valves are finally shut off, the meter was left containing static
water at moderate pressure.
4. The adjustable screws were operated to give identical reading for all of the tubes across the
whole width of the manometer board. To establish the meter coefficient measurements of
a set of differential heads (h1-h2) and flow rate Q were made.
5. The first reading was taken with the maximum possible value when (h2 – h1) i.e. with h1
close to the top of the scale and h2 near to the bottom. This was obtained by gradually
opening both the bench valve and the control valve in turn.
6. Successive opening of either valve increased both the flow and the difference between h1
and h2. The rate of flow was found by timing the collection of a known amount of water
in the weighing tank, in the meantime valves h1 and h2 was read from the manometer.
Similarly, readings were then taken over a series of reducing values of h1 – h2 roughly
equally spread over the available range from 250mm to zero. About ten readings sufficed.
4

Result and Discussion
Table 1 Experimental Results
Table 2 Theorical and Experimental Results
Figure 2 Graph between flow rate and pressure loss
Regarding to the Table 1, the flow rate has been changed 4 times with opening and closing the
discharge valve and the high of “H” recorded in each flow rate. The cross-sectional areas are
No AD(m2) AA(m2)
H (Q1)
(cm)
H (Q2)
(cm)
H (Q3)
(cm)
H (Q4)
(cm)
H (Q5)
(cm)
H (Q6)
(cm)
H (Q7)
(cm)
1 2.01x10-4
5.3x10-4
31.5 31 30.8 25.5 28 29.5 30
2 2.01x10-4
5.3x10-4
28 27 25 13 18.5 21 22
3 2.01x10-4
5.3x10-4
25.5 24.5 23 9.5 16 19 19.5
4 2.01x10-4
5.3x10-4
24 23.5 21.5 7 14.5 17 17.5
No
Qactual
(m3
/s)
Qtheory
(m3
/s)
Cd R% Cd avg
Pressure
Loss (Pa)
1 1.53x10-4
2.35x10-4
0.652 75
0.624
75
2 2.19x10-4
3.725x10-4
0.588 60 60
3 2.49x10-4
3.847x10-4
0.649 62.5 62.5
4 2.41x10-4
3.96x10-4
0.607 61.76 61.76
6

known for each high (H) on Venturi meter. After recording the first train, the discharge valve will
be opened more and another time the heights will be recorded for 3 more trains which showed a
decay of heights due to reduction of pressure and increase in velocity. Figure 2 shows a differential
height for 4 trains according to their pressure loss. In Table 2 the theorical flow rate has been
calculated one time using the Equ.1 for each train, and actual flow rate has been calculated one
time using the Equ.2 for each test. At last the discharge coefficient (Cd) has been calculated using
Equ.3 for each test. And the average was taken in order to compare with the device’s Cd which its
0.8-0.9. Since, the results show that there is an error in calculating flowrates that may due to the
pressure loss from a safety valve in a manometer and bubbles that inserted to the manometer tubes
due to the low efficiency of motor pump. And the pressure loss has been recorded via the Equ.4
for each test which shows a high difference between first and second test which maybe pressure
loss occurred in safety valve addition to discharge valve.
Conclusion
This experiment can conclude that, A Venturi meter can be used to determine the flow rate in the
pipelines and the pressure loss that occurring in order to control the discharge fluid addition to the
discharge coefficient of a Venturi meter.
7

References
Dr. P.N. Modi and Dr. S.M. Seth, (2009): Hydraulics and Fluid Mechanics Including Hydraulic
Machines (In SI Units), Fifth Edition, Rajsons Publications PVT. LTD., Delhi-110006.
Herschel, (1888): Apparatus for Measuring the Quantity of Water Flowing in a Pipe, U.S. patent
number US381.
T. Elperin, A. Fominykh, M. Klochko, (2002): Performance of a Venturi meter in gas–liquid flow in
the presence of dissolved gases. Flow Measurement and Instrumentation. Pp 13–16.
Figure Reference
Fraser, D.M., R. Pillay, L. Tjatindi, and J.M. Case, (2007): “Enhancing the Learning of fluid
Mechanics using Computer Simulations,” Journal of Engineering Education, Vol. 96, No. 4.
8

Fluid Mechanic Lab - Venturi Meter

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