Final report in Calibration of Venturi and Orificemeter CheLab1

1. 1
1. INTRODUCTION
The objective of this experiment is to calibrate the venturi and orifice meter. This also
includes comparing the two apparatus by plotting their coefficient of discharge with Reynolds
number. These devices estimate the fluid flow velocity by the use of pressure drop principle. The
coefficient of discharge is measured using the pressure drop. This allows the students to compare
the obtained data from that of the standard. The experiment assumes the fluid to be incompressible.
In industry, when controlling the production rate, flow rates must be measured. If not,
turbulent flow rates may cause unfinished mixing or laminar flows may slow the production.
Venturi and orifice both provides ease of reading of these kinds of factor.
2. THEORITICAL BACKGROUND
Venturi Meter
A venturi meter is a device that is usually used to measure the flow of a fluid in the pipe.
A Venturi meter may also be used to increase the velocity of any type fluid in a pipe at any
particular point. It basically works on the principle of Bernoulli's Theorem. The pressure in a fluid
moving through a small cross section drops suddenly leading to an increase in velocity of the flow.
The fluid of the characteristics of high pressure and low velocity gets converted to the low pressure
and high velocity at a particular point and again reaches to high pressure and low velocity. The
point where the characteristics become low pressure and high velocity is the place where the
venturi flow meter is used.

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The Venturi meter is constructed as shown in Figure 1.1. It has a constriction within itself.
The pressure difference between the upstream and the downstream flow, Δh, can be found as a
function of the flow rate. Applying Bernoulli’s equation to points 1 and 2 of the Venturi meter and
relating the pressure difference to the flow rate yields. The discharge coefficient of a Venturi meter
is typically 0.985 but may be even higher if the convergent section is machined.
Figure 1.1
The Orifice Meter
The orifice meter consists of a throttling device (an orifice plate) inserted in the flow. This
orifice plate creates a measurable pressure difference between its upstream and downstream sides.
This pressure is then related to the flow rate. Like the Venturi meter, the pressure difference varies
directly with the flow rate. Figure 1.2 describes the basic components of an Orifice meter.

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Figure 1.2
Bernoulli’s Principle
Both devices are based on Bernoulli’s Principle
Assuming a horizontal flow (neglecting the minor elevation difference between the
measuring points) the Bernoulli Equation can be modified to:
p1 + 1/2 ρ v1
2
= p2 + 1/2 ρ v2
2
Equation (1)
Assuming uniform velocity profiles in the upstream and downstream flow - the Continuity
Equation can be expressed as
q = v1 A1 = v2 A2
Equation (2)
Combining (1) and (2), assuming A2 < A1, gives the "ideal" equation:

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q = A2 [ 2(p1 - p2) / ρ(1 - (A2 / A1)2
) ]1/2
Equation (3)
For a given geometry (A), the flow rate can be determined by measuring the pressure
difference p1 - p2.
Equation (3) can be modified with diameters to:
q = cd (π / 4) D2
2
[ 2 (p1 - p2) / ρ (1 - d4
) ]1/2
Equation (4)
where
D2 = orifice, venturi or nozzle inside diameter (m, in)
D1 = upstream and downstream pipe diameter (m, in)
d = D2 / D1 diameter ratio
The coefficient of discharge, Cv (for venturi) and Co (for orifice), can be calculated using
the following equation
C = Qactual/ Qtheoritica
(Equation 5)

5. 5
When measuring the mass flow in gases, its necessary to considerate the pressure reduction
and change in density of the fluid. The formula above can be used with limitations for applications
with relatively small changes in pressure and density.
Although both uses the same principles, there are some differences of these apparatus:
• A venturi meter can be used to measure the flow rates of all incompressible
fluids (gases with low pressure variations, as wells as liquids), whereas an
orifice meter is generally used for measuring the flow rate of liquid.
• Venturi meters are only installed in pipelines, and the accelerated flow through
the apparatus is subsequently decelerated to the original velocity at the outlet
of the venturi meter. The flow continues through the pipe line. In the orifice
meter, the entire potential energy of the fluid is converted into kinetic energy,
and the jet discharges freely into the open atmosphere.
C. Because venturi is theoretically has lesser pressure loss, then it is assumed to have
a greater coefficient of discharge than that of the orifice.

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3. MATERIALS AND METHODS
3.1 Materials
Hydraulic Bench Apparatus
Orifice meter, Venturi meter
Stopwatch
Water
Caliper
Manometer
3.1.1 Specifications for the apparatus
Orifice meter – D1- 26.6mm D2 – 13.0mm
Venturi meter – D1 – 26.6mm D2- 20mm
3.2 Methods
Materials and apparatus were checked and prepared before the experiment started
and were also cleaned appropriately. For the calibration of venture meter/ orifice meter
apparatus, the venturi or orifice meter apparatus was set up. The diameter of both apparatus
was recorded for the purpose of computation. The pump was started and the main
regulating flow valve was opened to fix the water flow rate. The tubes from the venture or
orifice pressure tapping points to the manometer (mouth or inlet tap point and throat tap
point) were connected. It was ensured that there is no trapped air in the connecting lines.
Ample time was allowed to stabilize the flow before readings were taken. The upstream

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and downstream of the manometer were read and recorded. The theoretical volumetric flow
rate was computed. For any reading of the manometer, the volume discharged was
collected at the outlet and the time to collect the volume discharged at the outlet was
measured using a graduated cylinder. The volume collected and the time was recorded. The
actual volumetric flow rate from the volume collected divided by the time obtained was
computed. A total of ten (10) trials were taken by adjusting the main flow regulating valve.
All the data were recorded and the coefficient of discharge of the Venturi and Orifice
apparatus and their Reynolds Number were computed respectively

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4. RESULTS AND DISCUSSION
4.1 Results
A. Orifice meter
Figure 4.1.1 Coefficient of discharge vs. Reynolds number for orifice meter
B. Venturi meter
Figure 4.1.2 Coefficient of discharge vs. Reynolds number for orifice meter
y = 80571x - 38286
0
5000
10000
15000
20000
25000
30000
0.69 0.7 0.71 0.72 0.73 0.74 0.75 0.76 0.77 0.78 0.79 0.8
ReynoldsNo.
C
0
2000
4000
6000
8000
10000
12000
14000
16000
0 0.1 0.2 0.3 0.4 0.5
REynoldsNo.
C

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4.2 Discussion
In orifice meters, the C and Reynolds number is direct proportional as shown in
figure 4.1. On the other hand, the relationship of C and Reynolds number is inversely
proportional, as shown in Figure 4.2
From the tables 4.1.1 and 4.1.2 (appendix) it is confirmed that the pressure drop in orifice
meter is greater than that of the venturi meter.
As observed also, the flow of the water in the venturi and orifice meter are turbulent. This
is because the equipment needed more speed to avoid bubbles from getting into the tubes.
Also it is observed that Reynolds number of smaller compared to that of orifice because
venturi meter provide smooth flow than that of orifice.

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5. CONCLUSION
In orifice meters, the C and Reynolds number is direct proportional. On the other hand, the
relationship of C and Reynolds number is inversely proportional. The tables also show a greater
discharge as the pressure drop increases. This supports the Bernoulli’s principle but however there
are errors in the experiment. The errors of the experiment may lie on the flow rates. The flow is
not very consistent. This causes the graph to be distorted a little. Overall the objectives of the
experiment were met and the students learned the characteristics of both apparatus. The experiment
gives knowledge to the student since both apparatus is commonly used in the industry.
6. RECOMMENDATION
In manipulating both devices, it is recommended to let the flow of water to above 70 cm to
avoid bubbles from getting in the tube. For ease, valves must be labeled according to the beginners’
view to avoid confusion. Also, the diameter of the pipe must be shown in the specification.

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7. APPENDICES
Trial Manometer Reading Rm(cm) Volumetric
flowrate Q
(x10-5
m3/s)
Coefficient
of discharge
Reynolds
NumberUpstream
(cm)
Downstream
(cm)
1 71.75 73.5 1.75 5.65 0.703784643
17913.35385
2 73 75 2 6.0 0.72268771
18525.45246
3 77.25 79.5 2.25 6.3 0.715424333
19649.20959
4 74 76.5 2.5 6.25 0.673324519
20712.08551
5 81.5 84.4 2.9 7.12 0.712189246
22307.59879
6 80.5 83.5 3.0 7.0 0.688417385
22688.95289
7 79.5 82.5 3 7.5 0.737590055
22688.95289
8 87 90 3 7.79 0.766110204
22688.95289
9 88.4 92 3.6 8.0 0.718212821
24854.50261
10 93.6 97.4 3.8 9.0 0.786439155
25535.57399
Table 4.1.1: Data from Orifice Meter

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Trial Manometer Reading Rm(cm) Volumetric
flowrate Q
(x10-5
m3/s)
Coefficient
of
discharge
Reynolds
number
Upstream Downstream
1 72 71.8 0.2 4.5
0.59612302 7131.102413
2 88 88.3 0.3 6.6
0.7138742 8733.781108
3 72.4 72.4 0.4 4.6
0.4308898 10084.90175
4 88.5 88.9 0.4 6.5
0.60886602 10084.90175
5 72.4 72.8 0.5 4
0.33513005 11275.26293
6 84.5 85 0.5 5.88
0.49264117 11275.26293
7 67 67.5 0.5 3.4
0.28486054 11275.26293
8 62 62.5 0.5 3.9
0.3267518 11275.26293
9 84.5 85 0.5 5.7
0.47756032 11275.26293
10 63 63.7 0.7 3.22
0.22800545 13341.07101
Table 4.1.2: Data from venturi Meter

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8. REFERENCES
https://www.quora.com/What-is-the-difference-between-venturimeter-and-orificemeter
https://www.mecholic.com/2016/11/venturi-meter-construction-working-equation-application-
advantages.html
http://www.thermopedia.com/content/1241/
https://www.slideshare.net/HirizzaJunkoYamamoto/calibration-of-venturi-and-orifice-meters
https://www.slideshare.net/HirizzaJunkoYamamoto/calibration-of-venturi-and-orifice-meters
https://www.engineeringtoolbox.com/orifice-nozzle-venturi-d_590.html