Practical 2: Airlift pump
Team leader : Low Jian Hao Kerwin
Experimenter : Kevan Koh Jun Xi
Timekeeper and blogger : Lee JiaTian Jessica
C) Experiment Worksheet
Experiment 1
b = 10cm
a (cm) | X (cm) | Flowrate (ml/s) | Average Flowrate (ml/s) | ||
Run 1 | Run 2 | Run 3 | |||
2 | 14.5 | 9.29 | 10.19 | 8.80 | 9.43 |
4 | 12.5 | 6.68 | 6.19 | 6.92 | 6.60 |
6 | 10.5 | 4.83 | 4.86 | 4.64 | 4.78 |
8 | 8.5 | 2.19 | 2.17 | 2.29 | 2.22 |
10 | 6.5 | 0.75 | 0.76 | 0.76 | 0.76 |
Flowrate is volume of water collected/transferred divided by time taken
Experiment 2
a = 2cm
b (cm) | Y (cm) | Flowrate (ml/s) | Average Flowrate (ml/s) | ||
Run 1 | Run 2 | Run 3 | |||
10* | 16 | 9.29 | 10.19 | 8.80 | 9.43 |
12 | 14 | 4.68 | 4.34 | 4.77 | 4.60 |
14 | 12 | 2.50 | 2.62 | 2.30 | 2.47 |
16 | 10 | 0.00 | 0.00 | 0.00 | 0.00 |
18 | 8 | 0.00 | 0.00 | 0.00 | 0.00 |
20 | 6 | 0.00 | 0.00 | 0.00 | 0.00 |
Flowrate is volume of water collected/transferred divided by time taken
*This is the same setting as the first run in experiment1. You do not need to repeat it. Just record the results will do.
D) Questions & Tasks
1. 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.
Theres an increasing positive gradient, when the tube length X increases, the pump flow rate also increases.
2. 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.
There is an increasing positive gradient, when the tube length Y increases the pump flowrate also increases.
When Y is from 6cm to 10 cm, the value for the flowrate is 0.00ml/s.
3. Summarise the learning, observations and reflection in about 150 to 200 words.
Learning of how to use a pump is an enjoyable and wonderful experience. We had so much fun learning how to use the pump. During our experiment, we had trouble setting up the experiment. At the same time, we had problems with our experiment, where our pump seems to not work. However, through trial and error and perseverance, we managed to ensure that the pump is finally pumping water. During our runs, we found out that as you increase the length of a, it takes a longer time for water to be pumped out as the amount of water being pumped also decreases. Even increasing the length of B also took a longer time for water to be pumped out. Hence, the average flowrate decreases. We also realised that as length of X increases, the average flowrate also increases, this can also be seen from the length of Y. We continued to do the runs till where when b=16cm to 20cm, we could not record any flowrate, as we observed that no water is being pumped out. This means that the pump could be cavitated or it does not have the strength to pump the water.
4. Explain how you measure the volume of water accurately for the determination of the flowrate?
We use a 500ml jug to measure the volume of water and place the graduated cylinder on a flat surface and view the height of the liquid in the cylinder with the eyes directly level with the liquid.
5. How is the liquid flowrate of an air-lift pump related to the air flowrate? Explain your reasoning.
The liquid flowrate increases linearly with air flowrate. When the air flowrate increases, more liquid can be displaced by the air as more air can enter the U-shaped tube. However, when the air flowrate is too high, there is too much air entering the U-shaped tube and not enough liquid entering the tube to be displaced. When this happens, water is unable to flow out of the U-shaped tube. Thus, this means that there is an optimum value of air flowrate to obtain the fastest liquid flowrate.
6. Do you think pump cavitation can happen in an air-lift pump? Explain.
No. Cavitation will not occur in an air-lift pump. Cavitation will only occur to the pump that’s going to be used for added energy such as kinetic, potential or pressure /flow to fluids, enabling them to transfer these fluids from low to high pressures. It will cavitate when the vaporization of liquid occurs if the pressure of the liquid at the pump section is less than the vapour pressure, bubble of vapour form and move towards a region of high pressure inside the pump where they will collapse. The bubble will collapse on a metal surface and can surge the pressure high enough to loosen crystals of the pump metal which can corrode the impeller. But, an air-lift pump is used to compress the water into compressed air and supply the compressed air to the air pipelines so that the compressed air can mixed with water and carry the water up from lower reservoir to higher reservoir as compressed air is less dense than water. The compressed air will not collapse anything that in the pump.
7. What is the flow regime that is most suitable for lifting water in an air-lift pump? Explain.
Turbulent flow. This is because turbulent flow ensures high degree of mixing between water and compressed air. When there is high degree of mixing between water and compressed air, they will be higher density difference between the water and compressed air. As the main principle of an air-lift pump is the density difference between the water and compressed air, higher density difference ensures more compressed air carry the water up. The efficiency of the pump to transfer water from one vessel to another increase.
8. What is one assumption about the water level that has to be made? Explain.
We assume the water level in the barrel are the same throughout the experiment for each run, so that the flow rate of the water entering the air bubble tube is only a small change when performing each run with the same value to a and b. This is because, when the water level decreases in the barrel, the distance from air bubble tube to the distance from the surface water decreases, decreasing the flowrate of water.
Reflection:
During the practical, we learn about the basics behind an air lift pump. Two examples are it working mechanisms and how it can be applied.
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