Air Lift Pump Challenge

Emily Tang
May 28, 2021
4 min read

Synopsis

We are tasked to design and build an air-lift pump to transfer 500ml of water from one vessel to another. Due to the resurgence of COVID-19 in Singapore, the originally planned air-lift pump challenge has to be carried out at Alex's home.

Roles

Team leader - Syufyan

Experimenter - Alex

Timekeeper - Iman

Blogger - Emily

How does the air-lift pump work?

In the air-lift pump, the compressed air is mixed with water. The density of water is higher than the density of air.

By buoyancy, the air which has a lower density than the liquid rises quickly.

By fluid pressure, the liquid is taken in the ascendant air flow and moves in the same direction as the air.

Therefore, Air is fed into the bottom of the U-shape tube where it is combined with the fluid. This changes the density of the fluid, causing the combined medium to rise up through the U-shape tube.

Materials:

Green U-shape tube
Silicon tubing
Air pump
Big bucket
30cm ruler
Measuring cup
Syringe
Stopwatch

Setting-up

All group members meet up in MS team.
Laptop, camera and power socket extension set up away from experiment.
Make sure that the bucket is tall enough to run the experiment (more than 20cm water level).
Check if the air pump is functioning properly.

Video of us doing the experiment

Experiment 1

When the tube length inside the U-shape tube increases, the distance from the surface of the water to the tip of the air outlet tube (Y) decreases, hence the pump flowrate decreases.

Experiment 2

When a = 2cm

flowrate decreases when the U-shape tube is further away from the base of the pail.

when b=18cm, barely any water flowing any water out

When the distance between the tip of the U-shape tube that is submerged in water and the bottom of the bucket increases , the distance from the surface of the water to the tip of the U-shape tube that is submerged in water (X) decreases, hence the pump flowrate decreases.

Difficulties

Finding the perfect height of the bucket.
Making sure that the U-shape tube is at the correct height at all time.
Making sure that the silicon tubing stays inside the U-shape tube without changing its length.

How do we overcome it?

Find a substitute bucket in the house that is big enough to be able to run Experiment 2. The bucket needs to be the correct height (in between the maximum and minimum height of the U-shape tube, a and b height).
The U-shape tube is tied and secured to a ruler with a rubber band and measured the depth. It was hold on to prevent it from toppling left and right.
The silicon tubing was tied and secure to the U-shape tube using a black wire.

Questions and Answers

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

In this experiment, we have to find out how different heights of a and b affects the flowrate of the pump. a is the height which is the length of the tubing inside the U-shape tube. b is the height which is the distance between the tip of the U-shape tube submerged in water and the base of the bucket. These different a and b values affect the X and Y values which are the distance from the surface of the water to the tip of the air outlet tube and the distance from the surface of the water to the tip of the U-shape tube that is submerged in water respectively.

When height of b = 10cm and height of a changes

Flowrate decreases when the length of the air tube increases in the U-shape tube.

When a = 2cm and height of b changes

Flowrate decreases when the tip of the U-shape tube that is submerged in water is further away from the base of the bucket.

When b = 18cm, barely any water flowing any water out.

The flowrate is better when the U-shape tube is submerged near the base of the bucket and the tube connected is at minimum.

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

The water level is constant or the same for every run. After every run, water is poured back into the bucket that has been pumped off. This minimises any small changes in the change in height and hence can be assumed as constant height.

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

Assuming all variables are constant and the only difference is the air flowrate. The pressure of the low setting of the air-lift pump is lower than the high setting of the air-lift pump. This means that low setting has lesser energy being output to push the water as compared to the high setting. This means that the low setting of the air-lift pump required more time to output the same amount of energy as compared to the high setting of the air-lift pump. Hence, the low setting would output lesser energy, hence flowrate will be lower as compared to the high setting. This can be represented by the formula, Q=V/T.

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

Pump cavitation will not happen in an air-lift pump. Cavitation in pumps occurs when pockets of air are formed and implode in a liquid. Causing a shockwave that damages the pump itself. In the case of the air-lift pump, there is no liquid in the pump to form air bubbles since it is already filled with air. Therefore, no pockets of air will implode and cause cavitation.

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

Slug flow. In slug flow, the lighter, faster moving continuous fluid containing gas bubbles, pushes along dispersed gas bubbles. The gas bubbles, known as slugs will have different variations of pressure, with the variation of pressure, the liquid flow may also vary. The turbulence in the U-tube increases as it transitions to slug flow regime and the water surface fluctuates rapidly. As transiting from annular flow regime to slug flow regime, the large bubbles alternate with the slugs that contain increasing amounts of small bubbles as flow rate increases.

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