Practical 2

1. What is an air lift pump? How does it work?

An air lift pump is a pump that has low suction and moderate discharge of liquid and entrained solids. The pump injects compressed air at the bottom of the discharge pipe which is immersed in the liquid. The compressed air mixes with the liquid causing the air-water mixture to be less dense than the rest of the liquid around it and therefore is displaced upwards through the discharge pipe by the surrounding liquid of higher density.

2. Making of air lift pump:

2.1 Material Used

(Photo 1: Materials needed to make air lift pump)

2.2 Making of hole

Before we start to make a hole, we need some materials in order to making the hole on the tube such as one part of chopstick, screwdriver and a pair of scissors.

(Photo 2: Materials needed in order to make a hole on the tube.)

(Photo 3: Making of hole using a pair of scissors)

(Photo 4: Enlarge the hole using chopstick)

2.3 Attaching the connector

(Photo 5: Connector being attached to the tube)

2.3 Air Lift Pump in Operation

3.0 Testing

We actually put into a test whether it can obtain 500ml of water in a short time and also calculated its molar flow rate.

(Photo 6: Set up of the air lift pump to obtain 500ml of water.)

(Photo 7: 500ml of water in the bottle)

After few times of testing, we calculated its molar flow rate:

500ml= 500/(1000×1000)= 5×10^-4 m³

Testing No.	Time taken to obtain 500ml of water (s)	Molar flow rate (m³/s)
1	117	4.27×10^-6
2	144	3.47×10^-6
3	113	4.42×10^-6

(Table 1: Data collected and its molar flow rate)

Average molar flow rate:

= (4.27×10^-6 + 3.47×10^-6 + 4.42×10^-6) / 3

= 4.053×10^-6 m³/s

Now it’s time to carry out the real experiment! (Practical 2- Air-Lift Pump Challenge)

1. Allocation of duties to team members:

We discuss among each other to decide a respective role which are team leader for this practical, experimenter, timekeeper and blogger so that our experiment can be done smoothly.

a.   Team leader: Joshua Lee (Ensure all the procedures are executed.)

b.   Experimenter: Ambrose (Set up and carry out the hands-on part of the experiment.)

c.   Timekeeper: Edmund (Record the time, tabulate data and plot graphs.)

d.   Blogger: Ambrose and Yongjie (Consolidate and type the documentation in    the blog.) 

Due to the current COVID-19 situation in Singapore, all the equipment and tools are with Ambrose himself. Therefore, due to the insufficient of manpower needed, Ambrose was the only person to carry out this experiment alone and he had to record down the results as well😭😭😭...

After distributing roles to each other, we proceed to carry out this experiment!!!

2. The process:

By the way, we recorded the video of ourselves carrying out this experiment.

3. Data collection:

Here are the results that we collected after carrying out 2 experiments.

Experiment 1

b = 10cm

a (cm)	X (cm)	Flowrate (ml/s)			Average Flowrate (ml/s)
		Run 1	Run 2	Run 3
2	10.1	4.170	3.830	3.800	3.933
4	8.1	1.667	1.667	1.500	1.611
6	6.9	1.500	1.333	1.333	1.389
8	4.7	0.833	0.583	0.500	0.639
10	3.7	0.133	0.150	0.133	0.139

Experiment 2

a = 2cm

b (cm)	Y (cm)	Flowrate (ml/s)			Average Flowrate (ml/s)
		Run 1	Run 2	Run 3
10*	12.1	4.170	3.830	3.800	3.933
12	10.1	1.333	1.250	1.000	1.194
14	8.2	0.667	0.667	0.667	0.667
16	6.9	0.417	0.417	0.333	0.389
18	4.7	0.250	0.250	0.250	0.250
20	4.0	0.000	0.000	0.000	0.000

4. Questions and 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.

Answer:

Conclusion:

As the length of X, which is the distance from the surface of the water to the tip of the air outlet tube increases, the water flow rate will increase.

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.

Answer:

Conclusion:

As the length of Y, which is the distance from the surface of the water to the tip of the U-shape tube that is submerged in water increases, the pump flow rate will also increase.

3. Summarise the learning, observations and reflection in about 150 to 200 words.

Answer:

This experiment demonstrates the working principles of the air lift pump which as a concept was previously introduced in the previous practical by the coffee machine. The air lift pump is a pump with no moving parts that transports fluids upwards by injecting compressed air to decrease the density of the air-liquid mixture.

In this practical, we observed how changing various parameters affects the flowrate of the pump. Increasing the length of the tubing inside of the U-shaped tube decreases flowrate, as does reducing the length of tube below the water surface.

This is because these factors affect the difference in pressure, which decreases the velocity of the water exiting the tube and thus, the flowrate.

With these classroom concepts that were taught in our DCHE modules, such as fluid flow and dynamics, we can see their use when they are in play and their actual applications. For example in this Air-Lift Pump application.

4. Explain how you measure the volume of water accurately for the determination of the flowrate?

Answer:

The method we used for the determination of the flowrate, was to measure the volume of water that was pumped in a fixed time interval of 60 seconds. The volume of water in the collecting container divided by 60 seconds gives the flowrate.

The container used to collect the water pumped had volume markings. Measuring the water volume was done by reading off the volume from the water level.

5. How is the liquid flowrate of an air-lift pump related to the air flowrate? Explain your reasoning.

Answer:

The liquid flowrate rises as the air flowrate rises since the air flowrate increases, more air is fed into the pump system. As the air inlet increased, more air will be able to lift the water and displaced from the pump by decreasing the density of the air and water mixture followed by the constant heavy flow of air.

6.  Do you think pump cavitation can happen in an air-lift pump? Explain.

Answer:

I believe that pump cavitation can happen in an air-lift pump. Cavitation occurs because of the formation of bubbles within the fluid in the pump as the pressure in the pump falls below the fluid’s vapour pressure. When the air intake supply pressure used to raise the liquid in the pump is lower than the liquid's vapor pressure, this can happen in a larger size airlift pump. This is due to an increase in the air input supply's velocity causing cavitation in an air-lift pump.

7. What is the flow regime that is most suitable for lifting water in an air-lift pump? Explain.

Answer:

The flow regime that is most suitable for lifting water in an air-lift pump is turbulent flow. Water undergoes irregular mixing between the layers and cause turbulent flow to occur. Furthermore, turbulent flow occurs because of the speed of the water changes in both direction and magnitude, causes the water to lift up, contact with the wall of the U-tube, and water is being transferred into the U-tube. When there is more turbulent flow, more water will be pumped out.

8. What is one assumption about the water level that has to be made? Explain.

Answer:

One assumption about the water level that can be made is we assume the water level in the water jug remains the same throughout the entire experiment. For example, since the water is drawn out and pumped out into the displacement cup by the rubber tubing and the U-tube, there may be water droplets attached to them. As the water is poured back into the water jug after every run, there will also have water droplets in the cup as well. These factors cause the water level slightly decreases in every run. Because of that, the loss of the water level by the droplets can assumed to be negligible.