Practical 2
-Date:27/5/21-
Air Lift Pump Challenge - Practical 2
This practical was indeed one filled with twists and turns because we were supposed to carry out this practical during our practical session in school and we were given the materials in advance to hold onto. However, due to the worsening situation of COVID-19 in Singapore, there was a temporary Circuit breaker put in place where-by lessons shifted fully to Home-based learning mode. As such, we had to carry out this practical in our own homes. But how?
The ingenious and tenacious ICPD lecturers came up with modifications to the dynamics of the practical where a scenario of a team carrying out the practical would look like this:
He is in charge of facilitating the entire experiment, and would ensure all procedures are correct with the necessary preparations being done properly before we commence the practical. He is also in charge of briefing the rest of the group about what to do and what we should expect during this practical as he would be aware of the entire process thoroughly. He will ensure that the group is actively communicating as communication is very important especially when we are doing a virtual experiment together for the first time as a team in order for everyone to be aware of what is going on for there to be no hiccups in the experiment.
He has the best technical skills among all of us in the group, thus the group decided to entrust him with all of the equipment given to us to carry out this experiment. Thus, he will be the one who will set up and carry out the hands-on aspect of the experiment. He is also an effective communicator thus we were aware the coordination between him and the timekeeper would be seamless. Therefore, we were rest assured that the experiment will run smoothly, and that we will be able to collect all of the data required and finish the experiment quickly yet efficiently.
An airlift pump is a type of pump that uses an air inlet supply as a medium to lift and transport fluids from one place to another, through the pump tubing this is unlike a typical pump which also serves the same function of transporting fluids from one place to another but uses mechanical energy to do so. In addition, the airlift pump is able to aerate and transport large amounts of liquids in one run of operation.
The pump operates by first submerging one end of the pump tubing into the liquid and supplying the air in the inlet from the same opening of the pump tubing. This results in the air being mixed together with the liquid to form a liquid-gas mixture and thus changes the density of the fluid as air will be less dense than the liquid itself. Therefore, this causes the combined fluid mixture to rise up through the tubing and exit out from the other end.
Data Collection Table for Experiment 1
fixed b = 10cm
a (cm) | X (cm) | Flowrate (ml/s) | Average Flowrate (ml/s) | ||
Run 1 | Run 2 | Run 3 | |||
2 | 16 | 3.49 | 3.67 | 4.76 | 3.97 |
4 | 15 | 3.65 | 2.20 | 2.003 | 2.62 |
6 | 12 | 1.21 | 1.30 | 1.06 | 1.19 |
8 | 10.5 | 0.4773 | 0.642 | 0.482 | 0.534 |
10 | 8 | 0.296 | 0.377 | 0.266 | 0.313 |
Data collection Table for Experiment 2
fixed a = 2cm
b (cm) | Y (cm) | Flowrate (ml/s) | Average Flowrate (ml/s) | ||
Run 1 | Run 2 | Run 3 | |||
10 | 17.5 | 3.49 | 3.67 | 4.76 | 3.97 |
12 | 15.5 | 1.91 | 2.16 | 1.43 | 1.83 |
14 | 12.5 | 0.545 | 0.703 | 0.455 | 0.568 |
16 | 9.5 | 0.0459 | 0.0671 | 0.0732 | 0.0621 |
18 | 8.5 | 0 | 0 | 0 | 0 |
20 | 6.5 | 0 | 0 | 0 | 0 |
As we have learnt about the mechanism of the air-lift pump before the experiment, in Practical 1 and researched more about it to aid us in answering Question 2 in Practical 1, after discussing about what results we would expect, we concluded unanimously that the pump flowrate will increase as X or Y increases. After carrying out the experiment, the results obtained matches with our expectations.
Thus, through this experiment, we got to learn and brainstorm about how the distance can actually affect the pump flowrate and how they relate to each other. We also got to witness and observe how airlift pump actually works and the working mechanisms behind it. Compared to merely just learning about the theory of the similar mechanism of an air-lift pump in Practical 1 in the coffee machine whereby the vapour in the heated water+vapour mixture pushes the water upwards to contact with the coffee solubles, here in this experiment with some knowledge of the working mechanism of the air-lift pump we were more educated and aware of why water was able to flow upwards against gravity and put our knowledge into application.
In terms of carrying out this experiment, it was challenging due to the heightened measures implemented recently as we were unable to gather together for this experiment and it had to be done online thus communication was not as effective and it was harder to convey our ideas to one another since we could only meet and discuss virtually. Moreover only one person has the equipment and this means that he can only conduct the experiment physically. This means that the other groupmates actually lose out in the technical aspect as they are unable to conduct the experiment and can only view it through a screen rather than viewing it in person and able to have a better understanding of the experiment. We also faced the challenge of our given pump malfunctioning so we were struggling in understanding why it didnt work and we were all getting frustrated that we were lagging behind. However, we managed to pull through and find our way despite the difficulty.
Despite the revised dynamic of the practical, we found ourselves having more patience with one another and a mutual trust among group members especially since we had to rely solely on the experimenter for the practical aspect and especially on each other. But most importantly, we realized the importance of effective communication in a team.
Q4: Explain how you measure the volume of water accurately for the determination of the flowrate?
ANSWER:
We fixed the volume of water to measure (0.1L). To ensure that only 0.1L was pumped out each time, we referred to the markings on the 1.5L bottle for every 0.1L. It provides a close to accurate measurement of 0.1L with the limited resources we had. We then measured the time taken for that fixed volume of water to be reached. For example, throughout experiments 1 and 2, we measured the time taken for 100ml of water to be pumped out (we knew 100ml was pumped out when the water level dropped from the brim to the first 0.1L marking. We also run the same a and b values three times for every run and for each experiment and take the average for a more accurate reading of pump flowrate. However, the markings on the 1.5L bottle is not very accurate, and the volume of water may not be exact. This may cause calculated flowrate to deviate slightly from its actual flowrate. The deviation is unlikely to be very significant, thus the results we acquired will not be too far off its original and the flowrates calculated still match with the desired outcome, which was that when X or Y increases, the flowrate increases as well.
Q5: How is the liquid flowrate of an air-lift pump related to the air flowrate? Explain your reasoning.
When air flowrate increases, the liquid flowrate increases. This is because when there is an increase in air flowrate, more amount of air is pumped into the water and therefore occupying more space at the bottom of the U-tube . The increase in air inlet will mean that more air will be mixed together with the water being supplied to the system. This results in a greater decrease in the mixture's density together with the constant heavy flow of air, the mixture will rise and more air will push out more water from the U-tube at a much faster flowrate. Therefore, a greater liquid flowrate will be achieved. Hence liquid flowrate is directly proportional to air flowrate with a constant water level.
However, this is only true to a certain extent. This is because once the air flowrate gets increases extremely high, the water entering the pump system will decrease significantly due to the built-up pressure in the clear tube connected to the air inlet supply, which accounts for the water not being able to enter. Thus, it will cause the flowrate to drop due to the lack of water being displaced.
Q6: Do you think pump cavitation can happen in an air-lift pump? Explain.
ANSWER:
Pump cavitation will not happen in an air-lift pump. Cavitation occurs when air bubbles, or voids, form within a fluid because the pressure in the pump drops below the vapor pressure of the liquid. When the bubbles experience higher pressures they collapse, impinging on the pump. Since there is no fluid flowing through the pump, only air, it is not possible for cavitation to occur. Moreover, even though there is formation of bubbles in the pump but the bubbles form is used to lift up the water from the bottom of the pump to pump the water upwards which will not damage any parts of the pump. Therefore, cavitation will not happen in an airlift pump.
Q7: What is the flow regime that is most suitable for lifting water in an air-lift pump? Explain
ANSWER:
A turbulent flow regime will be the most suitable for lifting water in an air-lift pump. Turbulent flow occurs when there is a high degree of mixing between the adjacent layers in the fluid. This means that there will be substantial amount of mixing between fluids in the mixture and which is required in an air-lift pump to push up the water as air will need to be mixed substantially with the water in order to decrease its density and push it up. Having a turbulent flow will allow the air to have a greater contact surface area with the water and this will lead to the pump being able to displace higher volumes of water. Hence, it can be concluded that by using turbulent flow, the pump flowrate will increase.
Q8: What is one assumption about the water level that has to be made? Explain.
ANSWER:
The water level for each run is assumed to not affect the liquid flowrate. When the water level decreases, the pressure exerted by the water would be lesser hence causing the liquid flowrate to also decrease. Therefore, without a constant inlet of water to keep the water level constant, it has to be assumed that water level will not affect the liquid flowrate.
The water level in the 1.5L bottle is assumed to remain constant throughout the entire experiment. When the experiment is ongoing, there will be displacements of water in and out from the 1.5L bottle to the clear air tube and into the bowl. As this occurs, water may be lost or trapped in the equipment as tiny droplets. This will result in the water level in the 1.5L bottle to drop over time as the experiment occurs, leading to the water level having miniscule changes in between different runs. Therefore, in order to maintain the accuracy of the experiment with our already rather inaccurate equipment due to lack of resources as we do not have the luxury of laboratory apparatus to measure the volume of water accurately as well as to ensure the set-up is exactly the same for every run, water will be poured back from the bowl into the 1.5L bottle. Hence, we assumed that the water level will remain the same during the entire experiment and any loss or trapped water even in the form of miniscule water droplets will be deemed as insignificant and thus neglected.
- END-
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