Week 6 Practical 2

 

Objective

Originally, we were supposed to have an air-lift pump competition in school. Unfortunately, plans were changed, and we had to conduct this practical at home. The new results we were supposed to find are the relation between flowrate of the air-lift pump and the distance of the air pump tubing up the U-tube and the distance of the bottom of the U-tube to the container’s bottom.

Set-Up

For the experiment we used:

-        U-tube

-        Air pump

-        Measuring cylinders

-        Retort stand

-        Large container

-        Small container

-        Rubber tubing

We were fortunate enough to have things like a retort stand and measuring cylinders at home making the experiment a lot easier to conduct. Here is a photo of some of the set-up equipment.

The rest will be the worksheet we followed, the results, and the questions and answers.

A.               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) 

 

 

 

B.               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. 

 

 

C.               Experiment Worksheet 

 

Experiment 1 

b = 17cm 

a (cm)	X (cm)	Flowrate (ml/s)			Average Flowrate (ml/s)
		Run 1	Run 2	Run 3
2	12	3.76	3.75	3.53	3.68
4	10	2.60	2.67	2.73	2.64
6	8	1.60	1.70	1.67	1.66
8	6	0.93	0.83	0.90	0.89
10	4	0.70	0.77	0.74	0.74

Experiment 2 

a = 2cm 

b (cm)	Y (cm)	Flowrate (ml/s)			Average Flowrate (ml/s)
		Run 1	Run 2	Run 3
17*	12	4.26	4.17	4.20	4.21
19	10	1.43	1.47	1.53	1.48
21	8	0.167	0.153	0.167	0.16
23	6	-	-	-	-
25	4	-	-	-	-
27	2	-	-	-	-

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. 

 

As the length X increases, the pump flowrate 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.  

 

As the length Y increases, the pump flowrate also increases.

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

 

For Experiment 1, we observed that when increasing the length of the tubing in the U-shape tube (a), the flowrate of water from the outlet would decrease. For Experiment 2, we observed that when increasing the distance from the base of the pail to the U-tube, the flowrate also decreased. We learned to make do with what we have; the problem of each group member having each component, with one member having to replace each missing component and do the practical setup and process by himself. At first, our pump was too weak and was unable to pump out any water, which halted our progress severely, being unable to tabulate any data. Luckily, with the guidance of our teacher, we had a solution; to shorten the length of the U-tube. However, this only partially solved our problem as in Experiment 2, with only 3 sets of data being able to be tabulated. We concluded that it was due to the pump having insufficient pumping power to lift the water out the U-tube, and we were not able to do anything to resolve it. 

 

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

We used a measuring cup to collect the water that exits the U-Shaped tube. After collecting the water, we will look at the water levels at eye level to prevent parallax error. 

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

The higher the air-flowrate, the higher the liquid flowrate of an air-lift pump will be. As there is more air, more water will be pushed by the air through the U-tube causing a higher flowrate of liquid into the container. 

 

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

Cavitation will not occur in an air lift pump because cavitation will only occur when liquid in a pump turns into vapour at a low pressure. However, since the pump does not contain any liquid, cavitation will not occur. 

7.                What is the flow regime that is most suitable for lifting water in an air-lift pump? Explain.          Laminar flow for lifting water in an air-lift pump is the most suitable. Turbulence and transition flows will require a more powerful pump to turn the pressure into kinetic energy. This means that the air-lift pump may spoil due to overwork. Laminar flow exerts the least pressure among the 3 flow regimes.  Therefore, laminar flow will be the most suitable for an air-lift pump. 

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

No changes in water level due to evaporation of liquid. 

 

Discussion

Here’s our set-up.

Air gets pumped through a tubing going to the bottom of the U-tube which pushes the water out and into the small container.

We had our fair share of problems when conducting this experiment form home, one of which is that the pump we had bought was very weak with an air flowrate of 60L/h. This caused us to have lesser readings for our experiment 2 and we had to tweak the experiment a bit and cut the U-tube shorter.

Other than that, overall, the experiment went smoothly, and we had a lot of fun conducting the experiment.