Practical 2

 CP5065 Introduction to Chemical Product Design

Practical 2 – Air Lift Pump Challenge

Due to the resurgence of COVID-19 in Singapore, the originally planned air-lift pump challenge has to be changed. This practical has to be carried out at the home of one of the team members.

For this hands-on activity, the roles and responsibilities of each member must be designed and listed down. Discuss and appoint members to the following roles:

1. Team leader: Ensure all the procedures are executed

2. Experimenter: Set up and carry out the hands-on part of the experiment

3. Timekeeper: Record the time, tabulate data and plot graphs

4. Blogger: Consolidate and type the documentation in the blog (1 to 2 members)

All members are to jointly work on the discussion

1. Experimental Setup

The experimenter will set up the apparatus as per Figure 1 below.

Figure 1: Experimental Setup

For the small segment of hose, you can make one yourself (see photo instructions below)

 

2. Experiment Details

Experiment 1

Referring to the Figure 2 below, find a way to fix the U-shape tube to be 10cm from the base of the jug (i.e. b = 10cm). You can also ask your family members to hold the tube for you. Prepare an accurate way to measure the volume of water for the determination of the flowrate.

Adjust the length of the tubing inside the U-shape tube. Such that a is 2cm.  Slide the hose segment (refer to Figure 1) up or down so that the PVC tube does not dislodge from the U-shape tube and does not have any kink.

Turn on the air pump and determine the pump flowrate rate. Repeat the test 3 times and average the timing

Repeat the experiment with different values of a from 2 to 10 cm. Tabulate your findings using the worksheet enclosed

Figure 2 Positioning of the tube

Experiment 2

Referring to Figure 2 again, with a fixed at 2 cm, adjust b to 12 cm. Measure the pump flowrate. Repeat the experiment with different values of b from 12 to 20 cm. Tabulate your findings using the worksheet enclosed.

For the experiment, have someone to video record a segment of the experiment. The video should capture the laptop screen with members with camera switched on MS Teams. The picture below explains the requirement better.

3. Experiment Worksheet

Experiment 1

b = 10cm

a (cm)	X (cm)	Flowrate (ml/s)			Average Flowrate (ml/s)
		Run 1	Run 2	Run 3
2	17	18.86	18.52	19.42	18.93
4	15	12.99	18.18	17.70	16.29
6	13	13.33	13.07	13.07	13.16
8	11	8.23	8.23	8.26	8.24
10	9	5.97	5.19	6.23	5.46

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	19	18.86	18.52	19.42	18.93
12	17	8.97	8.33	8.26	8.52
14	15	6.23	6.17	6.49	6.30
16	13	3.85	3.98	3.34	3.72
18	11**	0.95	0.71	0.83	0.83
20	9**	0.0	0.0	0.0	0.0

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.

**100ml

4. 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.

Tube length X is proportional to the pump flowrate.

Tube length X is almost linearly proportional to pump flowrate.

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. 

Tube length Y is proportional to the pump flowrate.

As the tube length Y increases, rate of change of the pump flowrate decreases.

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

Our group had to do the experiment twice since the jug we initially used was not deep enough to carry out the experiment for all of the values. Through this we learnt the importance of planning and how the experiment will go with our plan. When things do go wrong we need to be able to step back, reflect, and figure out how to fix unforeseen difficulties during the experiment. During the experiment, even though we got frustrated by the flowrate, we were able to take a breath and figure out how to fix the problems such as why the flow was slowing down. We finally figured out we needed to place the U-tube deeper into the jug so that our X was large enough and so we needed a deeper jug. 

The water flowrate was very dependent on the column of water in the U-tube for the air to lift. The water we collected had a lot of bubbles from the air compressor.

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

We used a measuring cup used for baking to measure 200ml of water and timed how long it took for 200ml of water to be collected.

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

The liquid flow rate is dependent on the air flow rate since the force pushing the water over the U-tube was the air bubbles pushing the liquid. The faster the air flow rate, the faster the liquid is pushed through the U-tube by the faster air.

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

No it may not happen. This is due to cavitation being caused by vaporization of water that creates bubbles. In the case of an air-lift pump, there is no water flowing, air itself is already in gaseous form thus cannot vaporise.

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

Slug Flow regime, this is due to the gas forming large enough bubbles to fit the diameter of the passage or pipe to lift the water. This ensures that liquid is being lifted through the pipe at a constant and uniform state compared to other vertical flow patterns. The churn flow which is not uniform thus unable to be used to measure flow rate.  Bubble flow gas flow rate is too low and the bubbles too small to transport water. Whereas in annular and mist flow, the gas flow rate is too high that liquid is transported as droplets.

source: https://www.sciencedirect.com/topics/engineering/flow-regime#:~:text=A%20flow%20regime%20(or%20flow,phase%20relative%20to%20the%20other. 

Reynolds (a=2,b=10)= 85122 (Turbulent)

Reynolds (a=2, b=18) = 3732.24 (Laminar)

The preferable flow regime is turbulent flow. Since, there is more air in relation to water in the fluid, therefore the overall density of the fluid is lower thus results in the water being more easily lifted.

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

The assumption is that everytime the experiment is repeated for another run, the starting water level will be the same as the previous run. This is due to the possibility that the water in the measuring container may not totally be poured back into the pail, thus affecting Y value. Some water may be left behind in the measuring container or evaporated, it is also not easy to measure the water left behind in the measuring cup or evaporated and is thus considered negligible.