Week 4

 Week 4 (13/5/2021)

 

Group has been tasked to select materials for the body and cover of a thermoflask.

 

Main focus:

·         Material for the inner layer that comes into contact with hot fluid.

·         Cover (black colour part shown in the image above)

Material Requirements:

To be a thermoflask, it must be able to retain heat and prevent heat loss to the surrounding. At the same time, it must be able to resist the corrosion of fluid that might be filled in it, including tea, coffee, and carbonated drinks.

Material Selection:

For the inner layer that comes into contact with hot fluid, we decided to use metals. The following are some of the shortlisted metals we have decided on:

• ·         Stainless Steel 304
• ·         Stainless Steel 316
• ·         Aluminium

For the cover we decided to use polymers. The following are some of the polymers we have shortlisted and decided on.

• ·         Polytetrafluorethylene
• ·         Polyimide
• ·         Polystyrene
• ·         Polypropylene

                                    Table 1: Criteria Selection for the inner layer of Thermoflask

Criteria	Materials
	Stainless Steel 304	Stainless Steel 316	Aluminium
Thermal conductivity (W/m-k)	16.2	16.2	210
Density (g/cm3)	8.00	7.99	2.7
Corrosion Resistance	Excellent	Excellent	Excellent

We chose thermal conductivity as we felt that the thermoflask must be able to conduct heat away slower such that the fluid inside can retain its warmth for a longer period of time.

We chose density as the next criteria as we felt that the thermoflask needs to be lightweight and not too heavy so that it still remains portable.

We chose corrosion resistance as the last criteria as we felt that having it is an indication of whether the vessel is suitable to hold the drinks as users are the receiving end of this Thermoflask, if our vessel is not suitable to hold simple drinks such as water, it is not acceptable.

Table 2: COWS Decision matrix for the inner layer of Thermoflask.

Criteria	Weightage	Materials
		Stainless Steel 304	Stainless Steel 316	Aluminium
Thermal Conductivity (W/m-K)	40%	3	3	1
Density (g/cm3)	30%	2	2	3
Corrosion Resistance	30%	3	3	3
Total	100%	270	270	220

Thermal conductivity was given the highest weightage, 40%, among the 3 criteria chosen as the group felt that this criterion is the indicating factor whether our Thermoflask is suitable for keeping fluids warm/cold.

As for Density and Corrosion resistance, the group felt that it was equally important thus it is being given a weightage of 30% each.

 *Rating Scale from 1 to 3, 1 being the poorest and 3 being the best.*

For the the inner layer, we have decided to use aluminum as it has the highest score of 280 among all the other materials. 

 Table 3: Criteria Selection for cover of Themoflask

Criteria	Polytetrafluorethylene	Polystyrene	Polypropylene
Low Thermal Conductivity (W/m.K)	0.25	0.12-0.17	0.17-0.33
High Melting point (oC)	325	270	130-170
High Corrosion Resistance (Water, distilled)	Excellent	Fair	Excellent

Table 4: COWs matrix for the cover of Thermoflask 

Criteria	Weightage	Polytetrafluorethylene	Polystyrene	Polypropylene
Thermal Conductivity	40	1	3	2
Melting point	30	3	2	1
Corrosion Resistance	30	3	1	3
Total	100%	220	190	200

 

*Rating Scale from 1 to 3, 1 being the poorest and 3 being the best.*

 

For the cover, we have decided to use Polytetrafluorethylene as it has the highest score of all the three materials at 220.

Reflection:

After completing the assignment, the group was able to refresh the knowledge learned from MFD and apply it to this assignment itself, and it helped us to finish the assignment with ease.