Practical 2

 Practical 2 (Air Lift Pump Challenge) 


Assigned Roles

Roles

Responsibilities

Member

Team Leader

Ensure all the procedures are executed accurately and assistant any member which requires help.

Lau Jun Foong Wayne

Experimental

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

Wong Kea Tzer

Timekeeper

Record the time, tabulate data and plot graphs.

Kee Soon Heng Cavell

Blogger

Consolidate and type the documentation in the blog.

Rong Yiren


Experiment 1

b = 10cm

a (cm)

X (cm)

Flowrate (ml/s)

Average Flowrate (ml/s)

Run 1

Run 2

Run 3

2

12

 7.58

7.80 

7.60 

7.66 

4

10 

 5.55

5.15 

5.40

5.37

6

8

 4.82

5.16 

4.79 

4.92 

8

6

 4.06

4.40 

3.98

4.15

10

4

 2.58

2.46 

2.32 

2.45

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*

 14

7.58 

7.80 

6.54 

 7.31

12

 12

 1.83

1.99 

2.11 

 1.98

14

 10

 1.54

1.49 

1.47 

 1.50

16

 8

 -

 -

 -

- 

18

 6

 -

 -

 -

- 

20

 4

 -

 -

 -

- 

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.


When y>=16cm, there is no water flowing out of the u tube. The pressure gradient between the water pressure and atmospheric pressure is too small, thus no water is flowed out of the u tube.

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.


            ANS:

Figure 1: Flowrate vs X


 

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.

            ANS: 

Figure 2: Flowrate vs Y





When y>=16cm, there is no water flowing out of the u tube. The pressure gradient between the water pressure and atmospheric pressure is too small, thus no water is flowed out of the u tube. 


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

            ANS: 

Water flowrate is the fastest when the utube and airlift pump outlet is nearer to the bottom of the tank. This can be proven with experiment 1 and 2. As length of “a” increases from 2cm to 10cm, the water flowrate decreases. As length of “b” increases from 10cm to 20cm, water flowrate also decreases. When length of “a” and “b” is nearer to the bottom of the tank, there is a larger pressure gradient. The nearer towards the bottom of the tank, the higher the water pressure. Pressure gradient is the difference between the water pressure and the atmospheric pressure. Water flows from high pressure to low pressure. Since there is higher pressure at the bottom of the tank, water flowrate will be the fastest nearer the bottom of the tank. Fluid flow requires a pressure gradient between 2 points such that the flow is directly proportional to the pressure difference. A higher pressure difference will create greater driving force which will increase the flow rate.  

 


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

  ANS: 

To accurately measure the volume of water in order to determine the flowrate, we used a measuring cup with markings every 50ml to obtain the time it takes to reach the 50ml mark. We made sure that the measuring cup is directly below the tube outlet in order to minimise the amount of water lost due to it splashing out of the cup. This is because the tube outlet is a lot higher than the measuring cup as we did not want to physically lift the cup up as this will make reading the water level harder as our hands may not be steady when holding the cup. We also made sure to read the water level in the cup at eye level and read the water at its meniscus in order to prevent parallax error. After each run, we also poured the water in the cup back into the bottle before starting the next run, in order to make the water level the same for all runs. To collect the amount of water accurately in the measuring cup, we empty the cup to prevent any errors in reading from affecting subsequent runs as the starting point of 0mL will affect our flowrate. 


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

           ANS: 

When the air flowrate increases, the liquid flowrate also increases as it results in a larger pressure gradient in the u tube, causing the water to flow faster due to the increase in pressure gradient. Using Bernoulli’s Equation when the pressure increases, more energy is gained by the liquid, thus increasing the liquid flowrate. 


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

            ANS:

No, cavitation will not happen in an air-lift pump. Cavitation refers to the formation and collapse of vapor bubbles in the pump. These vapor bubbles will only be formed if the pressure of the liquid at the pump suction is less than the vapor pressure. In an air-lift pump, there is no loss of energy for the liquid when air is discharged from the air-lift pump. Liquid will not vaporised and cause cavitation. Moreover, there is no spinning blades which will ruin the pump as air is used to transport this liquid instead.


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

            ANS:

Churn turbulent flow regime is most suitable for lifting water in an air- lift pump   

Churn turbulent flow is a two-phase gas/liquid flow regime characterized by a highly-agitated flow where gas bubbles are sufficient in numbers to both interact with each other and, while interacting, coalesce to form larger distorted bubbles with unique shapes and behaviors in the system. When these bubbles become bigger, more liquid can be transported as more liquid can be carried by the bubble. The larger gas bubbles become unstable and collapse, resulting in a highly turbulent flow pattern with both phases dispersed. 


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

            ANS:

One assumption that has to made about the water level is that it remains constant throughout the entire experiment. This means that no water is lost throughout the experiment be it from natural factors such as evaporation and experimental factors such as water spillage and not all the water being able to be returned to the bottle as some of it will remain in the cup. 



Experiment Set-Up

Height on water in water bottle: 24cm


Experiment 1:


Experiment 2:


Extra Questions:

Qn: What is an air-lift pump and how does it work?

ANS: The air-lift pump carries the water using the air produced by the air-pump. The air will ‘carry’ and transport the water into the plastic tubing which then transfers the water upwards. After the air carries the water to the top of the u tube, the water will slowly drip into our measuring cup.


Qn: Making on an air-lift pump.

ANS: Inserting the tube of the air-pump into the bottom of the u tube. Place this setup inside the water.


Qn: Materials used

ANS: air-pump, u tube, air-pump tube, 1.5litres water bottle, 500mL measuring cup, phone stopwatch


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