PRACTICAL 2
This practical is indeed an interesting one we are going to have, since it is technically an in-campus challenge of pumps! But sadly, due to covid-19, we were not able to proceed with this practical yet. But yeah, the group has still decided to document it.
💨 What is an airlift pump?
An airlift pump is a type of pump that uses an air inlet supply as a medium to lift and circulate liquids from 1 place to another, through the pump tubing. Moreover, the pump is able to aerate and circulate large amounts of liquids at one go.
The pump works by submerging one end of the pump tubing into the liquid and feeding the air inlet supply from the same opening of the pump tubing. By doing so, air will be mixed together with the liquid to form a liquid-gas mixture and this changes the density of the fluid as air will be less dense than the liquid itself. Thus, this causes the combined fluid mixture to rise up through the tubing and out from the other end.
😁 Process of making this baby
Much effort has gone to prepare and make this pump, so before we start on this part, special thanks to Darius for tanking the preparations for the pump as we were unable to meet due to the unforeseen situation.
We have designed this making process like a manual so that anyone reading this will be able to follow it and create their own!
- Ideation of the pump
We had an idea and went ahead to do a rough sketch of the pump that we want to design and create. The picture below shows exactly that.
- Materials Needed & Used
So basically, there are the materials we used to construct the pump. It includes components of the pump and equipment.
Components of the pump:
- Clear air tubing
- Green U-tube
- Metallic air valve
- White plastic nozzles
- Black air pump
- Forceps
- Scissors
- Making a hole in the U-tube
Next, we will grab the green U-tube and a pair of scissors to pierce and create a hole on the straight end of the U-tube, as shown below.
- Attaching the nozzle into the hole
Then, we used one of the white plastic nozzle and attached it into the hole. Sadly, we forgot to take a picture for this part.
- Adding the air valve to the pump
We decided to install an air valve at the start of the white hose connected to the pump in order to start and stop the flow of air in the tube.
Firstly, we marked out where we should cut the white hose off to connect the valve. The picture blow shows exactly that and the part is pointed out using the blade of the scissors.
Next, we connected the air valve to the cut ends of the white hose and connected the shorter one to the pump and taped it.
- Modifications done to it
Next, we decided to improve it by trying to increase the pressure of the air inlet, causing more water to be pushed out from the U-tune at a faster rate.
Thus, we decided to cut the front end of the white hose, nearing to the pump, by 2 to 3 cm each and fit a nozzle in between them.
Our assumption was that by doing so, it induces a change in cross sectional area of the air inlet flow, causing pressure to increase instead, thus causing the air to flow faster.
- In operation
After assembling the pump, we decided to test it by running it in both low and high settings of the pump.
Low Settings:
High Settings:
💦 Testing of Pump
We decided to perform a test on the pump to get a rough gauge on how fast our pump works. Thus, we decided to record the amount of time taken for the pump to transfer 300mL of water.
Firstly, the set-up of the test is like what is shown below in the video. The pump and the U-tube is submerged in the red pail, which will pump water from the red pail into the measuring cup. After it reaches 300mL, the time will be taken.
After completing multiple runs for the test and recording all of the time taken, we took an average and calculated its average flowrate.
Time taken for run 1 = 85 seconds
Time taken for run 2 = 92 seconds
Time taken for run 3 = 88 seconds
Average time taken = 88 seconds
Liquid flowrate = 3.4mL per second
With all of these prepared, we are ready for the airlift pump challenge!!! And that is it for our practical 2 preparations 😸.
💦 Practical 2 (The experiment itself)
- Allocation of roles in the group
For this experiment, we were tasked to do it online with our groupmates through the video call function in Microsoft Teams as we were unable to carry out this experiment in campus due to the heightened measures.
We were given 4 different roles and we needed to assign each role to one member in the team. But since we only have 3 members, we decided that for this experiment, we will separate the role as a blogger and we will each blog about a section for this practical. This will not only lessen the load each member will have but it is also an opportunity for every member in the group to try to blog, so that we are all familiar with the applications we need to use for this module.
For the rest of the roles, we allocated each member as such,
Team leader: Zhi Yao
He will be the one facilitating the entire experiment, ensure all procedures are correct and preparations are done properly before we start. He is also the one who will brief the rest of the group about what to do and what we should expect during this practical. He ensures that the group is always communicating as communication is very important especially when we are doing a virtual experiment together for the first time as a team.
Experimenter: Darius
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 part of the experiment. We were rest assured that the experiment will run smoothly, we are able to collect all of the data required and finish the experiment quickly.
Timekeeper: Albie
He is able to divide the entire meeting duration to specific time slots with his strict time management so that the team has enough time to brief, carry out the experiment and discuss our observations and results collected after the experiment. He is capable of collecting all of the data neatly using the worksheet given and record down all of the observations made by the groupmates.
- The process
We recorded the entire experimental process, showing how the group actually conducted the experiment.
- Data collected
The results collected from the experiment is shown below.
- Answers for questions & tasks
Q1:
Plot tube length X versus pump flowrate. (X is the distance from the surface of the water to the tip of the air outlet tube). Draw at least one conclusion from the graph.
Answer for Q1:
From the graph, it shows that when the distance from the surface of water to the tip of the air outlet tube, X increases from 8cm to 16cm, the average pump flowrate of water increases from 3.544ml/s to 13.379ml/s. This concludes that the further the distance from the surface of water to the tip of the air outlet tube, the greater the pump flowrate.
Another conclusion that we can establish from the graph above is that the X value and the average pump flowrate exhibit a piecewise linear relationship, showing that the average pump flowrate increases almost linearly with the X value.
Q2:
Plot tube length Y versus pump flowrate. (Y is the distance from the surface of the water to the tip of the U-shape tube that is submerged in water). Draw at least one conclusion from the graph.
Answer for Q2:
From the graph, it shows that when the distance from the surface of the water to the tip of the U-shape tube that is submerged in water, Y increases from 8cm to 18cm, the average pump flowrate would gradually increase from 0ml/s to 13.379ml/s. This concludes that the larger the value of Y, the higher the average pump flowrate.
Another conclusion we can draw from the graph is that the average pump flowrate is 0ml/s once Y reaches 8cm. This means that Y needs to be at least above 8cm in order for the pump to pump water out. From it, we can conclude that the pump did not supply enough air to the system for the water to be pumped out when the distance from the surface of the water to the tip of the U-shape tube that is submerged in water is low.
Q3:
Summarize the learning, observations and reflection in about 150 to 200 words.
Answer for Q3:
Due to the extensive research we have done before the experiment, we came up with a hypothesis that the pump flowrate will increase as X or Y increases. The results we collected exactly matches with our hypothesis. Thus, through this experiment, we got to learn and brainstorm about how the distance can actually affect the pump flowrate itself 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.
This experiment was challenging due to the heightened measures implemented recently. We were unable to gather together for this experiment and it had to be done online. Communication was disrupted and it was harder to convey our ideas to one another since we could only meet and discuss virtually.
Furthermore, 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.
However, through this unique experiment, we managed to build a much more communicative relationship among group members and we realized the importance of effective communications.
Q4:
Explain how you measure the volume of water accurately for the determination of the flowrate?
Answer for Q4:
Due to the experiment being done at home, we are limited to the equipment that we have. After digging around, the best we could find is a measuring cup that is used for cooking purposes. The measuring cup can measure up to 500mL with intervals of 50mL. When taking the flowrate, we try our best to stop the pump when the volume of water in the measuring cup reaches 150mL. Then from there, we will record the time taken and find its flowrate.
However, the measuring cup 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.
Answer for Q5:
The liquid flowrate increases with increasing air flowrate. This is because when there is an increase in air flowrate, more amount of air is able to be supplied into the pump system, i.e. into the u-shape tube. The increase in air inlet will mean that more air will be mixed together with the water being supplied to the system. This will cause a greater decrease in the mixture's density and paired with the constant heavy flow of air, the mixture will be lifted and pushed out of the pump at a much faster flowrate. Therefore, a greater liquid flowrate will be achieved.
However, we believe that this will only be true to a certain extent. Once the air flowrate gets exceptionally high, the water entering the pump system will be limited due to the built-up pressure in the tubing from the air inlet supply, causing water to not be 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 for Q6:
Cavitation will happen in an airlift pump. Cavitation occurs when bubbles form within the fluid in the pump as the pressure in the pump falls below the fluid's vapor pressure. This can occur in a larger scale airlift pump as when the air inlet supply pressure used to lift the liquid in the pump is lower than the vapor pressure of the liquid. This is due to the increase in velocity of the air inlet supply. Thus, the liquid will start to form bubbles and cavitation will be induced in the pump, leading to damages in the system.
Q7:
What is the flow regime that is most suitable for lifting water in an air-lift pump? Explain.
Answer for Q7:
Q8:
What is one assumption about the water level that has to be made? Explain.
Answer for Q8:
We assumed that the water level in the pail remains the same throughout the entire experiment. When the experiment is ongoing, there will be displacements of water in and out from the pail to the pump tubing and into the measuring cup. In the process of it, water may be lost or entrained in equipment as tiny droplets. This will actually cause the water level in the pail to drop subsequently and gradually, leading to the water level having minute changes in between different runs. In order to reduce the hassle of needing to refill the pail and ensuring the set-up is exactly the same for every runs, water will be returned from the measuring cup into the pail. Thus, we assumed that the water level will remain constant throughout the entire experiment and loss or entrained water will be deemed as insignificant and thus neglected.
😟 End of practical 2.
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