Week 6

Overall equipment and setup for the practical:

Experiment 1

b = 10cm

Experiment 2

a = 2cm

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 tube length X increases, the pump flow rate 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 tube length Y increases, the pump flow rate also increases.

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

Throughout this experiment, we learned that the distance of where the air is being introduced into the bucket will affect the discharge of the flowrate of the water. The further the air is introduced into the system from the water surface, there will be an increase in flow rate being discharged.

During experiment 1, we had 5 different locations for a, intervals of 2, 5 times, while keeping the distance of b constant. After experiment 1, our observations are that when the distance of a increases, the flowrate of the water being discharged will decrease.

During experiment 2, we kept a constant, while changing the distance of b, we changed the distance of b, interval of 2, 5 times. After experiment 2, our observations are that when the distance b increases, the flowrate of the liquid being discharged decreases.

Overall, we learned that to increase the flowrate of the discharge, we must increase the distance between the surface liquid and the location of where the air is being introduced.

a- the distance of PVC tube in the U-shaped tube

b- the distance between the inlet of the U-shape tube and the base of the 5-liter jug.

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

1. Using a mass balance, obtain the mass of the container collecting the water in the experiment.

2. Upon collection of the water, obtain the mass of both the container and the water using the mass balance.

3. Obtain the mass of the water in the container by subtracting the mass found in 2 by the mass found in 1.

4. Using a thermometer, measure the temperature of the water.

5. Using the obtained temperature, calculate the density of the water at the temperature by using interpolation.

6. Use the formula Volume = Mass/Density to obtain the volume of water needed to determine the flowrate

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

The lower the air flowrate introduced by the pump, the lesser the liquid flowrate will be discharged. When the air flowrate being introduced into the U-shaped tube, it causes the density of the mixture of water and air to decrease, creating the liquid flowrate at the discharged. The higher the air flowrate, the mixture will be less dense, causing a high liquid flowrate. Therefore, by reducing the air flowrate, the liquid flowrate at discharge will drop as the mixture will be more dense.

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

Cavitation cannot occur in an air-lift pump. Cavitation is the result of vapourization of liquid that occurs when the pressure of the liquid at the pump section is less than the vapour pressure. As no liquid enters the air-lift pump, cavitation cannot occur.

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

In an air lift pump, the compressed air is mixed with water. As the water mixes with air, the density of water decreases because of the density of air and water mixture is less than the density of water. This density difference is the driving force pushing the liquid.

The flow regime that is most suitable for lifting water in the air-lift pump is the turbulence flow regime. During turbulent flow, the flow is not consistent, this will help to increase the amount of disturbance between the water and the air, creating a better water and air mixture. This will result in the mixture having a lower density and hence, more liquid flowrate will be discharged.

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

One assumption about the water level is that the height of the water level will be the same throughout the whole experiment. This means that the height of the water level is the constant variable while a is the change variable for experiment 1, and b is the changed variable for experiment 2. The height of the water level should be constant throughout the whole experiment because during the experiment there was some spillage of water causing a decrease in the water level. However, the drop in the water level is very minimal, therefore, we can assume that the change is 0.

By

Ted Chan Sheng