Blog 5 + practical 3
WWEEHHEE, we're finally reaching step 4 of 4. It's definitely a tough process but hey we are now reaching the end.
Just a quick recap on the 4 stages:
- needs identification- which is to identify what our consumer need
- ideation
- selection
- prototyping & process development🤚(hii we're here now)
Now we are learning all about MATERIALS as it is very important to choose the right material for the product and by getting the material right the first time, it could save a lot of money for the company.
There are a few types of material properties:
- mechanical properties - strength, young's modulus, etc
- thermal properties - thermal conductivity, specific heat capacity and thermal expansion coefficient
- magnetic properties
- fabrication properties - ease of machining, casting, etc
- environmental properties -corrosion properties, toxic effect, etc
3 important steps for material selections are
- define material requirement for the design(includes talking about the function of the product, constraints and objective)
- select and evaluate candidate materials by using COWS (and not 🐮)
- choose the most economical material by using COWS💸(because we aint want the cost to be soooo HIGH where when we sell it, no one wants it)
We also kickstarted our CA2, as part of our CA 2 part 1, my group was tasked to choose the material for the inner body of the thermo flask and also the material for the cap of the thermo flask.
Here's the link for the selection of materials for our thermo flask
1. Inner layer of thermo flask
For the body, we decided to go between 3 materials which is aluminium, stainless steel and also borosilicate glass.
By using COWS, we eliminated the use of aluminium as it has high thermal conductivity which is unsuitable for the inner of the thermo flask which has to have minimal thermal conductivity. Since aluminium has the lowest score, we have narrowed it down to borosilicate glass and stainless steel.
Through the COWS for economic viability, although borosilicate glass is harder to handle, however the cost is much cheaper than stainless steel hence borosilicate glass is more suitable.
2. Cap of thermo flask
By using COWS, we eliminated the use of polyethylene terephthalate(PETE) as it has high thermal conductivity which is unsuitable for the cap of the thermo flask which has to have minimal thermal conductivity as it will burn the user as he's drinking. Since polyethylene terephthalate(PETE) has the lowest score, we have narrowed it down to silicon and high density polyethylene (HDPE).
Through the COWS for economic viability, although HDPE is harder to manufacture, the cost is much cheaper than silicon hence HDPE is more suitable for the cap of the thermo flask.
Topic 6 lesson, we learnt about design for material. This is different than material for design such that for material for design, we choose the design and see its function and choose the material. However, for design for material, we choose an interesting material first then change the design of the product.
Here's the link to our design for material document
We chosen Lunabrite (shine bright like a diamond💠) to replace the cover of the table lamp. Lunabrite is a high performance photoluminescent material that illuminates fully when places in the darkness. When the user uses it during the night for minimally 5 minutes, it will glow after the light is turned off. This can help the user to save electricity and also prevent risk of fire as the light source wouldn't be turned on the entire night.
This idea is great for children and people who needs light to sleep during the night. Users could use it during the night before they sleep for just 5 minutes, Lunabrite material will absorb the light ray and illuminates once the night light is turned off.
For our chemical device which is a sweat powered watch, we decided to change the normal TPE which is non biodegradable to a material called Tefabloc TPE. This material contain up to 50% renewable raw material.
More details about our prototype can be found here
Practical 3
Back in Year 1 Semester 2, we did this module called "materials for design". Its about how to choose a material such as for a cooking pot🥘, it has to transfer heat fast so it can cook the food hence it should have high thermal conductivity.
Speaking about thermal conductivity, our group was assigned to test the thermal conductivity of a material. Besides thermal conductivity, there were also other properties such as
- surface tension of liquid
- young's modulus
- viscosity of liquid
To test for the thermal conductivity, we recorded the time the ice took to melt and performed some calculations.
The materials needed are:
- Retort stand
- 2 small beaker(one to catch the condensed steam and another to catch the melted ice.
- 1 plastic container with a layer of material(about 2.2mm thickness) at the bottom and a weighted ice(around 20g)
- Steam generator with the tube connected to the test bed
- Infrared thermometer
Here is an overview of how the set up should look like.
time for some magiiicccc 🧙🏻♀️🪄 ABRAcadabra
Step 1: Boil water
This is so that to reduce the time the steam generator takes to turn the liquid to steam and since we aint have no time to waste, we should boil the water while preparing the set up.
You know what's so cool about this boiler, it can cook hotpot. Yes, you read correctly, HOTPOT🍲. yummmm ok where were we?
Step 2: Assembly
As we are waiting for the water to boil, lets assemble according to the set up shown above.
A point to remember is that the test bed has to be tilted so the liquid can flow through to the hole and down to the tube into the beaker.
Step 3: Add boiled water to steam generator
Add the boiled water from kettle to the steam generator until the rusty line and start the steam generator. TAKE NOT!!!! 📢Frequently check to see if there is enough water and wear thermal gloves as it may get pretty hot. 📢
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Step 4: Wait for steady temperature
Let the waiting game begin. It took about 20 min to get to a stable temperature of 70℃.
Step 5: Getting the sample
After a steady temperature was reached, head over to the freezer (it's freezing cold🥶) and get the sample. Remove the duct tape that was used to cover the hole on the plastic and place it on the test bed and start the timer.
*the hole is used to let the melted ice to flow out
Step 6: Wait for the ice to melt
tik tok tik tok (NOT tiktok but tik tok uukk? the time with the bird uuwwuu)
It's a waiting game isn't it. For our sample, we waited around 30 minutes for the whole ice to melt.
Step 7: Always clean up after yourselves.
🧮📝✏️
Here are our data collected. Mass of ice(kg) | 0.02006 |
Diameter of test specimen(mm) | 34.5 |
Surface area of specimen(m) | 0.0009348 |
Thickness of test specimen(mm) | 2.2 |
Latent heat of fusion of ice(KJ/Kg) | 333.5 |
Time taken to melt the ice completely(s) | 30min |
Reflection
During this practical, I've learnt about the method for calculating the thermal conductivity of a material. Through our calculations, we actually have the wrong concept of calculating it and after Dr. Noel guided us how to do, we managed to get the right answer.
There are some factors that we assume negligible such as the heat transfer of the thin metal on the test bed.
Here is our final calculations
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