WEEK 5 PRACTICAL 2

HELLO👋! welcome back to our blog. This week we got to do practical 2 at the comfort of our homes due to the tighter restrictions in phase 2 in Singapore. Don't worry we had taken videos and photos so that you can be on this journey with us as well😁.

PRACTICAL 2

This practical is about using an airlift pump to pump water from a 5L jug to another container. We used different measurements as identified in our lab manual to see which measurement would pump the same amount of water in a shorter amount of time. We used flowrates to determine which measurement is FASTEST💨. Higher the flowrate, the faster it takes to pump water from the jug to the other container.

Safety Precautions taken❗️: 1.Do not handle the electrical plugs when hands are wet 2.Clear the working area, i.e. do not put laptop within 1 m of the working area 3.Do not place the water containers near the edges of a table to prevent them from dropping off

Roles & Responsibilities	Name
Team Leader (Ensures all procedures are executed)	Kalyani
Executioner (Set up and carry out the hands-on part of the experiment)	Kalyani
TimeKeeper (Record the time, Tabulate the data and plot graphs)	Cui Han
Blogger (Consolidate and type the document in the blog)	Jolyn, Madelaine

What is an air-lift pump? 

Air-lift pump has a device that pumps air bubbles into the water medium. As gas is pumped into the water medium, many air bubbles are formed and float through a small plastic tubing connected to the air pump device. As the air bubbles floats up the small plastic tubing due to it being less dense than water. The air bubbles then occupy both plastic tubings in the water medium and carry the water up along with it. The air bubbles displace the water as it floats upwards and acts as a piston pushing the fluid upwards creating a buoyancy lift as the buoyant force is greater than the weight of water and gravitational forces.

Materials used for the air-lift pump:

1. Air pump device x 1

2. Small plastic tubing x 1

3. Large U-shaped plastic tubing x 1

4. Large container x 2

5. Plastic bottle x 1

6. Pyrex Measuring Cup x 1

7. Scissors x 1

8. Stapler x 1

9. Ruler x 1

10. Measuring tape x 1

11. Adhesive tape x 1

Procedures of making the air-lift pump

Steps on making the small segment hose:

Steps	Description
1	Using the scissors, cut out a strip of plastic from the plastic bottle.
2	Using a ruler, roll the strip of plastic into a cylinder with a diameter of about 25 mm.
3	Using the adhesive and tape to join the two ends of the plastic strip together to form the cylinder
Illustration  of Finished Product

Procedures for assembly of air-lift pump

Steps	Description
1	Connect one end of the small plastic tube to the air pump device. Insert the other end of the small plastic tube into the large U-shaped tube.
2	Fill the large container with water and insert the large U-shaped tube into it, ensuring that the small plastic tube connected is submerged into the water.
3	Adjust the length of both tubes submerged in water to get the required X and Y value.
4	When the set-up is ready, begin the experiment. Our pressure setting is set to high.
Illustration  of  final product

Video of operating the air-lift pump 

1. Experiment Worksheet

Experiment 1

b = 10cm

Amount of water collected: 100 ml

a (cm)	X (cm)	Flowrate (ml/s)			Average Flowrate (mL/s)
		Run 1	Run 2	Run 3
2	14.0	100mL/15s =6.67	100mL/12.4s =8.06	100mL/12.56=7.96	7.56
4	12.0	100mL/26.6s=3.75	100mL/21.1s=4.73	100mL/23.3s=4.28	4.25
6	10.0	100mL/93.1s=1.07	100mL/63.5s=1.57	100mL/61.2s=1.63	1.42
8	8.0	100mL/89.1s=1.12	100mL/150.11s=0.67	100mL/130.56=0.77	0.85
10	6.0	0	0	0	0.00

Flowrate is volume of water collected/transferred divided by time taken

Experiment 2

a = 2cm

Amount of water collected:: 100 ml

b (cm)	Y (cm)	Flowrate (mL/s)			Average Flowrate (mL/s)
		Run 1	Run 2	Run 3
10*	16.0	100ml/15s =6.67	100ml/12.4s =8.06	100ml/12.56=7.96	7.56
12	14.0	100ml/36.69s=2.73	100ml/22.33s=4.48	100ml/33.09=3.02	3.41
14	12.0	100ml/115s =0.87	100ml/93.7s =1.07	100ml/170.1s=0.59	0.84
16	10.0	0	0	0	0
18	8.0	0	0	0	0
20	6.0	0	0	0	0

Flowrate is volume of water collected/transferred divided by time taken

2. 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.

From the graph, it shows that as the length of tube X (cm) increases from 8cm to 14cm, the flowrate also increases gradually from 0.85 mL/s to 7.56 mL/s. This shows that the larger the length of X, the higher the flow rate.  In addition, the minimum length of tube X required for the pump to work successfully is around 7cm.

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. 

From the graph, it shows that as the length of tube Y increases from 10cm to 16cm, the average flow rate also increases from 0.84 mL/s to 7.56 mL/s. This shows that the larger the length of Y, the higher the flow rate. Additionally, the minimum length of tube Y required is around 11cm in order for the pump to transfer water to a jug properly.

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

Through this practical, we learnt that how an air-lift water pump used to pump water without any moving parts, it uses pressurised air to push the water up. As when air is mixed with water, the density of the water-air mixture is now lower, hence it is able to pump the water up the U tube. We also noticed that as the length of the PVC pipe submerged in water decreases, the flowrate also decreases, which is the same for the U-shape tube. During the practical, we faced some difficulties such as the water not coming out from the U-shape tube even when X is at the maximum value. After some discussion and we also seek help from our friends, we decided to change to a bigger pail. Then everything worked  well for us after we spent 30 mins figuring out the problem. We all enjoyed this practical as it was really fun even though it was regrettable that we did not have a chance to do it together.

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

A measuring cup was used, we chose to collect 100mL of water and we used a timer to take the time needed, then we will be able to calculate the flowrate using the volume of water (100mL) and divide the time taken for each run.

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

As air flow rate increases, liquid flow rate will also increase. because air has to be injected into the bottom of the pipe for the liquid to rise as air has a lower density than liquid. Hence the higher the air flow rate, the higher the liquid flow rate.

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

Yes. Cavitation is caused by air bubbles formed due to low pressure. In an air lift pump, air pressure must be high in order to ensure the air bubbles to overcome the vapor pressure of the water and push the water up. If the air pump device is at a low pressure setting and pressure of air is lower than vapor pressure of water, water will not be pushed up. Instead air bubbles will remain in the pump at low pressure causing cavitation.

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

The flow regime most suitable for lifting water in an air-lift pump is laminar flow. This can be determined by finding Reynold's number. The diameter of the large plastic tubing is determined to be 1.2 cm, converted to 0.012 m. We have chosen to use the flow rate of 7.56 ml/s as it's the highest. Density of water = 1000 kg/m3. Viscosity of water = 0.001 kg/m.s.

*Since 801.5<2100, the most suitable flow regime is a laminar flow.

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

The water level remains constant throughout for each run, hence the pressure acting on the tube is the same as time goes. As when we pour the water back into the large container after each run, there will be water residue left in the measuring cup which affects the water level.  As when water is pumping into the jug, the distance between the water surface and the tube decreases, since atmospheric pressure remains constant, water pressure = gh, hence when the distance decreases, the pressure decreases. Thus we assume there is negligible impact on the flowrate.