HELLOOOOO Welcome Back!
Holidays have ended so back to school hais 😅
In this blog, I will document my learning for Week 11 and 12. Let's begin with Week 11.
In Week 11, Dr Noel covered Topic 5: Materials for design. To summarise what I've learnt in class, I'll list some main points:
1. Importance of selecting the right material
- The material have to exibit properties that satisfy the functional requirements, as well as optimise performance objectives
2. Characteristics of materials
- Mechanical properties (eg: tensile strength, Young's Modulus)
- Thermal properties (eg: thermal conductivity, thermal expansion coefficient)
- Magentic properties
- Fabrication properties (eg: machinability)
- Environmental properties (eg: toxoc effects, polluting effect)
With all the knowledge, we proceeded to select a suitable material for the inner layer and cover of a thermoflask, using COWS. COWS stand for:
C - Criteria
O - Options
W - Weightage
S - Score
(A) Choosing material for cover Listing material requirements for design
Functions | Contain and prevent liquid from spilling out |
Constraints | Water resistant Corrosion resistant Chemical resistant Not reactive with food ingredients (inert) Withstand high/low temperatures Low thermal conductivity |
Objectives | Minimise thermal conductivity so that the cover will not burn mouth when hot liquid is stored |
After we listed down all the constraints, we moved on to selecting and evaluating suitable candidates.
Selection and Evaluation of suitable materials
Here's the criteria, weightages and the explanation for the allocated weightage
Criteria | Weightage (%) | Explanation |
Resistance to corrosion by water | 20 | Cover should be resistant to corrosion by water so that when it comes into contact with water, it will not corrode and still remain usable. Thus, it is placed at 15% as it is relatively important that the thermos flask be reusable and safe to use |
Resistance to chemicals | 20 | Cover should be resistant to chemicals so that when it comes into contact with chemicals during washing, it will not corrode and still remain usable. Thus, it is placed at 15% as it is relatively important that the thermos flask be reusable and safe to use |
Density | 5 | Cover should be light so that it is easier to carry around, however since the stainless steel outer cover of thermos flasks already contribute to most of the bottle’s weight, it is not as important as the other criterias. |
Melting Point | 25 | Material should be able to contain liquids at high temperatures without melting and contaminating the liquid, thus it is important that the cover does not melt when it comes into contact with hot liquids. |
Thermal conductivity | 15 | The cover should have low thermal conductivity so that there is a lower rate of heat transfer from the hot water to the cover, so as to prevent the cover from being too hot and burning the consumer’s mouth. Thus it is less important as fewer people drink straight from the thermos flask opening |
Food grade | 15 | The cover should be able to store foods that may be acidic (coffee/coke) and prevent the transfer of non-food chemicals into the liquid, which may be hazardous to the human body. Thus it is relatively important that the user does not get any food–poisoning |
After we are done with the above, we went on to find our best friend - Google, for information about the respective materials. We then rank the materials with scores 1, 2, and 3. 1 being the poorest and 3 being the best.
|
| Options |
Criteria (Units) | Weightage (%) | Polypropylene (PP) | Polyethylene terephthalate (PTE) | Polyether ether Ketone (PEEK) | Polyphenylene sulfide (PPS) |
Resistance to corrosion by water | 20 | Excellent Score: 3 | Excellent Score: 3 | Excellent Score: 3 | Excellent Score: 3 |
Resistance to chemicals | 20 | Excellent Score: 3 | Excellent Score: 3 | Excellent Score: 3 | Excellent Score: 3 |
Low Density (g/cm3) | 5 | 0.91 Score: 3 | 1.38 Score: 1 | 1.3-1.35 Score: 2 | 1.35 Score: 2 |
Low Thermal conductivity (W/m.K) | 15 | 0.1 - 0.2 Score: 3 | 0.15 - 0.24 Score: 2 | 0.25-0.29 Score: 1 | 0.29 - 0.32 Score: 1 |
High Melting Point (0c) | 25 | 130 Score: 1 | 260 Score: 2 | 340-345 Score: 3 | 280 Score: 2 |
Food Grade | 15 | Food-safe Score: 3 | Food safe Score: 3 | Food safe Score: 3 | Food safe Score: 3 |
Score | 100 | 250 | 250 | 265 | 240 |
Choosing the most economical material
Finally, we went on to choose the most economical material. The material has to be cost effficient because:
1. No one will buy a product that they cannot afford. The product has to have a customer base in order for it to be successful, therefore it has to be affordable for the masses
2. No company will want to use a material that is expensive, it will only increase the production price of the product. Additionally, if the product has to be made affordable, it reduces their profit.
|
| Options |
Criteria (Units) | Weightage (%) | Polypropylene (PP) | Polyethylene terephthalate (PET) | PolyetheretherKetone (PEEK) | Polyphenylene sulfide (PPS) |
Cost of material | 60 | Excellent Score: 3 Sgd $1.13/kg | Excellent Score: 3 Sgd $1.01/kg | Poor Score: 1 Sgd $450/kg | Average Score: 2 Sgd $10.18/kg |
Ease of handling/ manufacturing | 40 | Excellent Score: 3 | Average Score: 2 | Poor Score: 1 | Excellent Score: 3 |
Total score | 100 | 300 | 260 | 100 | 240 |
And with that, we are done with the evaluation of all the candidates for cover. Considering cost and the material requirements above, our group decided on polypropylene.
(B) Choosing material for inner layer
We applied the same steps for the material selection of the inner layer. Here are all the COWS matrix.
Step 1: Listing of material requirements
Functions | Contain hot/cold liquid and reduce temperature change |
Constraints | Water resistant Not reactive with food ingredients (inert) Withstand high/low temperatures Low thermal conductivity Low thermal expansion coefficient Corrosion resistant Chemical resistant High machinability |
Objectives | Minimise thermal conductivity to reduce as much heat loss as possible |
Step 2: Selection and Evaluation of candidates
Criteria | Weightage (%) | Explanation |
Resistance to corrosion by water | 15 | Inner layer should be resistant to corrosion by water so that when it comes into contact with water, it will not corrode and still remain usable. Thus, it is placed at 20% as it is relatively important that the thermos flask be reusable and safe to use |
Resistance to chemicals | 15 | Inner should be resistant to chemicals so that when it comes into contact with chemicals during washing, it will not corrode and still remain usable. Thus, it is placed at 20% as it is relatively important that the thermos flask be reusable and safe to use |
Melting Point | 20 | Material should be able to contain liquids at high temperatures without melting, thus it is important that the inner layer does not melt when it comes into contact with hot liquids. |
Thermal conductivity | 25 | It is very important that the inner layer has low thermal conductivity. Since the main function of a thermoflask is to maintain the temperature of the liquid contained, a material of low thermal conductivity should be preferred as it reduce the rate of heat transfer from the liquid to the surroundings |
Thermal Expansion Coefficient | 15 | It is relatively important that the inner layer does not expand too much when it comes into contact with hot liquids and vice versa for cold liquid to prevent thermal shock. |
Food grade | 10 | The inner layer will be constantly in contact with various types of liquids and possibly food, hence the material should be of decent food grade to ensure the quality of the food, which ensures the health of the user. Thus it is least important as most of the materials for inner layers are of acceptable food grade |
|
| Options |
Criteria (Units) | Weightage | Borosilicate Glass | PolyetheretherKetone (PEEK) | Fibreglass | Polytetrafluoro ethylene (PTFE) |
Resistance to corrosion by water | 15 | Excellent Score: 3 | Excellent Score: 3 | Excellent Score: 3
| Excellent Score: 3 |
Resistance to chemicals | 15 | Excellent Score: 3 | Excellent Score: 3 | Excellent Score: 3 | Good Score: 2 |
High Melting Point (0c) | 20 | 1252 Score: 3 | 340 - 345 Score: 1 | 1135 Score: 3 | 327 Score: 1 |
Low Thermal Conductivity (W/m·K) | 25 | 1.15 Score: 1 | 0.25-0.29 Score: 2 | 0.04 Score: 3 | 0.220 - 0.320 Score: 2 |
Thermal Expansion Coefficient (m/0c) | 15 | 3.2 x 10-6 Score: 2 | 4.5-5.5 x 10-7 Score: 3 | 5.4 x 10-4 Score: 1
| 1.2 - 1.7 x 10-4 Score: 1 |
Food Grade | 10 | Food Safe Score: 3 | Food safe Score: 3 | Food safe Score: 3 | Food safe Score: 3 |
Score | 100 | 235 | 235 | 270 | 190 |
Step 3: Choosing the most economical material
|
| Options |
Criteria (Units) | Weightage (%) | Borosilicate Glass | PolyetheretherKetone (PEEK) | Fibreglass | Polytetrafluoro ethylene (PTFE) |
Cost of material | 60 | Excellent Score: 3 Sgd $8/kg | Poor Score: 1 Sgd $450/kg | Excellent Score: 3 Sgd $0.96/kg | Average Score: 2 Sgd $34.84/kg |
Ease of handling/ manufacturing | 40 | Average Score: 2 | Poor Score: 1 | Excellent Score: 3 | Poor Score: 1 |
Total score | 100 | 260 | 100 | 300 | 160 |
Considering the cost and the properties of the material, we decided on fibreglass as the material for the inner layer.
Now let's vroom vroom to Week 12 - Topic 6: Design for Materials.
Topic 6 started with Dr Noel giving us a briefing. Then he let us explore the materials in the library for us to select one, so that this material could be:
1. used as a replacement to a material in an existing product, keeping its original design
2. enhance the functionality of another product through some changes in the design
After exploring the library, we decided on Netlon, which is a type of plastic. We then proceeded to discuss possible ways that Netlon could be used. After intense discussion and our braincells dying, we decied on this:
This concludes Week 11 and Week 12, yay. These two weeks brings back memories from CP5091: Materials for Design. In addition to the fun I had exploring the materials, I also learnt more about designing and materials in general. Before ICPD started this sem, I really hated designing and I always thought of it as a very troublesome thing, having to brainstorm again and again just for one idea that has so many uncertainties. After Week 11 and 12, I realised that there is much more when it comes to designing. I wouldn't say I really enjoy the process of design, but I could say I don't dread it as much anymore. 😊
Armed with the theoretical knowledge, we went on to Practical 3 in Week 13, which allowed us to explore more about material properties. For practical 3, I was grouped with Joelle, Jun Ying, Ethan and Wayne, and we were tasked to find out more about surface tension.
The moment I heard surface tension, I was like WHATTT WHYY. Firstly, I wasn't very familiar with surface tension and secondly, I did not really understand the experiment. Well, I guess this is life, you have to get used to circumstances and not the other way round. I decided to change my thinking a little, instead of viewing this as a difficulty, why not take it as a learning opportunity for me to learn more about surface tension. Let's get started with what went on during Practical 3.
Firstly, we allocated roles.
Joelle and Ethan did the slides
Jun Ying and Wayne carried out the experiment
I was in charge of data recording and documentation
Then, we proceeded with the experiment, this was our set up
So, how did we carry out the experiment? We did the experiment using the Du Nuoy's method and these are the steps:
Firstly, prepare the balance setup and the beaker of test liquid
Secondly, submerge the ring into the test liquid at a point where it is 1-2mm beneath the liquid surface.
Thirdly, add staples or pebbles 1 by 1 gradually until the meniscus tears from the ring
Next, remove the load from the apparatus to be weighed and recorded. This load recorded is the load used to tear the meniscus and is directly proportional to the surface tension of the liquid
Next, repeat the test 8 times for the 100ml of water and take the average mass of the load used
Next, add 1 drop of detergent to the solution of 100ml of water
Lastly, repeat the steps 1 to 4 to record the weight load used for the run and take the average mass of the load used.
Here's a video for better visualisation:
This video shows one of the runs with 100ml of water plus 1 drop of detergent, in the video, you can see the meniscus tearing with the load is put on the weighing boat :)
This was the data we collected:
Run | Mass of load usage (g) |
| 100ml of water | 100ml of water, 1 Drop of detergent |
1 | 3.71 | 2.87 |
2 | 3.22 | 2.85 |
3 | 3.17 | 2.85 |
4 | 3.17 | 2.80 |
5 | 3.18 | 2.86 |
6 | 3.25 | 2.85 |
7 | 3.21 | 2.77 |
8 | 3.28 | 2.87 |
| 100ml of Water | 100ml of water, 1 Drop of detergent |
Average (g) | 3.27 | 2.84 |
With the data, we proceeded with calculating the surface tension.
Weight Range to tear meniscus from the ring (100ml Water + 1 drop of detergent) = 2.77-2.87g
Weight Range to tear meniscus from the ring (100ml Water) = 3.17-3.71g
Average Load used for 100ml of Water = 0.00327kg 9.81Nkg
= 0.03208N
Average Load used for 100ml of Water + 1 drop of detergent = 0.00284kg 9.81Nkg
= 0.02786N
Surface Tension of 100ml Water = F/2(pi)D
= 0.032082/2pi(0.017)
= 0.300N/m
Surface Tension of 100ml Water + 1 drop of detergent = F/2(pi)D
= 0.027862/2pi(0.017)
= 0.261N/m
We concluded that the solution with 100ml of water + 1 drop of detergent was of lower surface tension, as it required less weight to tear the meniscus as compared to only 100ml of water.
From the practical, I learnt more about surface tension, and the Du Nuoy's method. Here are some of my learning points:
1. Surface tension is commonly measured in dyn/cm
2. The Du Nuoy's method requires the ring to be horizontal
3. Platinum is preferred for the Du Nuoy's method
4. As temperature decreases, surface tension increases
Other than learning about surface tension, the sharing session by other groups allowed me to learn more about Young's modulus, thermal conductivity as well as viscosity. It provided a recap for Materials for Design, a module in Year 1 Semester 1, it also provided me with more knowledge that would benefit me in the future😎
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