Introduction
A flow meter measures the flow rate or quantity of a liquid or gas moving through a pipe. Flow meters have many different names such as flow indicators, flow gauges, liquid meters, among others depending on the industry in which they are used although the function of measuring the flow remains constant (Miller, 2013, p.17). The application of flow measurement is diverse, and every situation has its constraints as well as engineering requirements. Flow meters are used to provide correct monitoring and flow control. Some industrial applications need precise calculation of quantity like precision servo-valve development for the aerospace industry. On the contrary, an application to measure the flow of water to a vineyard may only need a measurement accuracy of 5 to 10 percent. It is important to understand some types of flow meters and their applications. Some of the common types of flow meters include differential pressure flow meters, velocity flow meters, positive displacement flow meters and mass flow meters.
In the differential pressure flow meter, the flow meter works based on the Bernoulli Equation whereby the pressure drops and the signal that is measured further is a function of the square flow speed. In the velocity flow meters, the flow is measured by establishing the speed in one or multiple points in the flow and integrating the speed of flow over the flow area (Beck and Pląskowski, 2017, p.24). Positive displacement flow meters measure the flow of fluids using precision-fitted rotors as flow measuring elements. Known as well as fixed volumes are displaced between the rotors. The rotation of the rotors is directly proportional to the volume of the fluid that is displaced. The rotations of the rotor are recorded using an integrated electronic pulse transmitter and translated to volume and flow rate. Lastly, a mass meter measures the mass flow rate directly. A prominent example of a mass flow meter is the thermal flow meter. The thermal mass flow meter works independently of variables such as density, viscosity, and pressure. They use a heated sensing element that is isolated from the path of the fluid flow whereby the flow stream conducts heat from the sensing element. The heat that is conducted is directly proportional to the rate of mass flow, and the difference in temperature is calculated to the mass flow (Arnold, 2016, p. 34). The thermal mass flow device accuracy depends on the reliability of the calibrations of the actual process as well as the variations in the pressure, temperature, heat capacity, flow rate and viscosity of the fluid.
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The reason for conducting this project is to learn how to produce as well as design a flow meter in the lab and establish how it works.
Theory
Flow meters are made up of a primary device, transducer and transmitter. The function of the transducer is to sense the fluid that passes through the primary device. The transmitter gives out a usable flow signal from the raw transducer signal (Yoshio, Miyaji and Hiroo, 2012, p. 43). The components are often combined and as a result, the actual flow meter may comprise of one or more of the physical devices. The mechanism of the flow meter to quantify the liquid is by having the liquid go by a small wheel found between the input and the output of the flow meter, creating resistance to the liquid. The liquid action makes the wheel to rotate according to the pressure of the liquid. The flow meter is connected to a circuit which that has a sensor which counts the numbers of rotations per second (Wright, 2015, p.17). Subsequently, the liquid volume is calculated using the number of rotations. When the fluid moves through the input in the flow meter, it moves the wheel then the electronic circuit counts the amount of the fluid until the fluid moves through the output and the wheel stops in a certain time. The methodology of calculating the output voltage for a flow meter with a given flow rate is as extrapolated below:
Vout = Vcc × F × R × C
Volume =π (0.5D) 2-π (0.5d) 2H- 8(W × L × H)
F= 2 × flow rate/volume
Rotational velocity = flow rate/volume × 60
Whereby
Vout = output voltage
F= frequency
Vcc = voltage from source (input voltage) = 9v
C = capacitance = 1.0*10ᴧ-8 F
R = Resistance = 1.0*10 ᴧ5 ohm
L = Length = 2.6 mm
H = height = 2.32 mm
W = width = 0.34 mm
D = External diameter = 11.8 mm
D = Internal diameter = 6.2 mm
Π = Pie = 3.14
Number of buckets = 8
Flow rate = ranging between 0 and 20 m/s
Risk assessment
The flow meter project had two distinct parts, that is, the mechanical and the electrical part. For safety purposes, it is critical for individuals to ensure that they wear their lab coats, protective glasses as well as leather boots. The purpose of the lab coat is to act as protection from burning in the event of fire. Before using the machines hand protective gear such as gloves ought to be worn to prevent hand injuries and burns (Slovic, 2016, p.71). Since the lab is contaminated to a certain extent with chemicals especially arising from stored gases, the hand protective gear ensures that the hands do not come into contact with undesirable substances that may be harmful to the skin. Likewise, gas masks were used to prevent the inhalation of hazardous gases. Additionally, special types of boots were worn to prevent injury to the feet by the heavy metals as well as pieces of broken metals or glasses in the lab. Also, the gloves, the lab coat and the goggles were worn to prevent shocks, sparks and burns resulting from soldering, flying wood and plastic and fumes from flux. During the whole experiment, there was a supervisor who ensured that everything was under control and according to plan. The supervisor would also be consulted especially on the use of particular equipment as well as when some adjustments needed to be done. Before the experiment commenced, the supervisor had everyone sign the risk assessment form which signified that the laid down guidelines would be observed.
Materials and methods
The first phase of the experiment was the electrical part. Every student at the beginning of the experiment was issued with components that would be used to build the electronic circuit for the flow meter. The materials that were issued included the following:
a. Green board
b. 7 Resistors
c. 2 Capacitors
d. Optical sensor (Reflective object sensor)
e. LED
f. Potentiometer
g. Black and red wires
h. Operational amplifier (opamp)
i. Battery
j. Battery clip
The first thing that the students did was to assemble the components on the green board, soldering them, and cutting the overload iron. After that, the voltage was measured from 0 to 9V at a current of 0.04A. Students had to ascertain that the LED worked at this stage. Lastly, students had to solder the optical sensor on the opposite side of the other components on the green board. Finally, the complete electric circuit was as shown in the image below
Results, discussion and analysis of results
After making the flow meter, various results were established using the following formula
Volume = π (0.5D) 2 – π (0.5d) 2 H – 8 (W × L × H)
Volume = 3.14 (0.5 × 11.8) 2 – 3.14 (0.5 × 6.2) – 8 (0.34 × 2.6 × 2.32) = 167.26 mm 3
V out = V cc × F × R × C
F = 2 × flow rate/volume
V out = V cc × 2 × flow rate/volume × R × C
The findings were then tabulated in the table below
| Flow rate | Volume | Frequency | Rotational velocity | Voltage output |
| Ml/s | Mm 3 | Hz | r/m | V |
| 0 | 167.26 | 0.00 | 0.00 | 0.00 |
| 1.00 | 167.26 | 11.96 | 358.72 | 0.11 |
| 2.00 | 167.26 | 23.91 | 717.45 | 0.22 |
| 3.00 | 167.26 | 35.87 | 1076.17 | 0.32 |
| 4.00 | 167.26 | 47.83 | 1434.89 | 0.43 |
| 5.00 | 167.26 | 59.79 | 1793.61 | 0.54 |
| 6.00 | 167.26 | 71.74 | 2152.34 | 0.65 |
| 7.00 | 167.26 | 83.70 | 2511.06 | 0.75 |
| 8.00 | 167.26 | 95.66 | 2869.78 | 0.86 |
| 9.00 | 167.26 | 107.62 | 3228.51 | 0.97 |
| 10.00 | 167.26 | 119.57 | 3587.23 | 1.08 |
| 11.00 | 167.26 | 131.53 | 3945.95 | 1.18 |
| 12.00 | 167.26 | 143.49 | 4304.68 | 1.29 |
| 13.00 | 167.26 | 155.45 | 4663.40 | 1.40 |
| 14.00 | 167.26 | 167.40 | 5022.12 | 1.51 |
| 15.00 | 167.26 | 179.36 | 5380.84 | 1.61 |
| 16.00 | 167.26 | 191.32 | 5739.57 | 1.72 |
| 17.00 | 167.26 | 203.28 | 6098.29 | 1.83 |
| 18.00 | 167.26 | 215.23 | 6457.01 | 1.94 |
| 19.00 | 167.26 | 227.19 | 6815.74 | 2.04 |
| 20.00 | 167.26 | 239.15 | 7174.46 | 2.15 |
The results in the table were used to plot graphs as presented below
Analysis
As deduced in the table as well as in the two graphs, there is a direct relationship between the rotational velocity and the flow rate. Also, the output voltage is directly proportional to the flow rate of the flow meter. After testing the flow meter, the output voltage was established to be 0.3V whereas the flow rate was found to be 320ml/m
Therefore,
Output voltage = 0.3V
Flow rate = 320 ml/ in one minute = 320/60 = 5. 33 ml per second
Volume out = V cc × 2 × (flow rate/volume) × R × C
0.3 = 9 × 2 × (flow rate/167.26 × 10 -3 ) × 1.0 × 10 5 × 1.0 × 10 -8
Flow rate = 4.65 ml/s
Percentage error = ((actual expected)/actual) × 100
Percentage error = ((5. 33 – 4.65)/5) × 100 = 9.18
Percentage error = 9.18%
Conclusion
The objective of the project was achieved because each student understood the process of designing a flow meter as well as understanding how it works. To test the practicality of the project, the flow rate of water was determined. The results were presented in a table and a better visual representation was shown using the two graphs. All the procedure was dully followed. For instance, it was a requirement that each student assembles the electric circuit before embarking on the mechanical part. The supervisor who was present ensured that everyone participated in the project to come up with his or her own results. After that, the findings were presented to the supervisor who counterchecked whether the results were consistent. As stated in the analysis section, it was established that there is a direct relationship between the rotational velocity and the flow rate. Likewise, the output voltage was directly proportional to the flow rate of the flow meter. Summarily, the project enabled students to acquire skills of making their own flow meters as well as use them.
References
Arnold, D.M., 2016. Measuring water flow rate.
Beck, M.S. and Pląskowski, A., 2017. Cross correlation flowmeters, their design and application . CRC Press.
In Kutz, M. (2015). Handbook of measurement in science and engineering: Volume 1 .
Miller, R.W., 2013. Flow measurement engineering handbook.
Slovic, P., 2016. Perception of risk. Science , 236 (4799), pp.280-285.
Stein, P. K. (1964). Measurement engineering . Phoenix: Stein Engineering Services.
Wright, B.M., 2015. A miniature Wright peak-flow meter. Br Med J , 2 (61
Yoshio, K., Miyaji, T. and Hiroo, Y., Yokogawa Electric Works Ltd, 2012. Current meter or flow meter . U.S. Patent 3,564,915.
