Thermos Project

The Goal: To create a thermos that holds 150mL of water at 100°C, maintains as much temperature as possible for 50 minutes, looks aesthetically pleasing, and costs $3 or less to make.

My Process

Testing:

1. I heated 150mL of water to 100°C using a hotplate.

2. I safely poured the water into the thermos using tongs.

3. I started a 50 minute timer and prepared a temperature probe.

4. I measured the final temperature with the probe after 50 minutes.

4. I measured the heat loss by comparing the final temperature to the initial temperature.

The Prototypes:

Thermos v1

Thermos v1 is a soup can with a threaded lip, that will eventually house a lid in following prototypes. Thermos v1 was a prototype that I expected to fail due to the lack of a lid and insulation, but I needed to do this test in order to compare how much the following prototypes improved.

Material Thermal Conductivity J/(kg-K) Amount Cost $
Aluminum (Canister) 921 1 0.15
Polylactic Acid (3 dimensionally printed threaded lip)
2137 52g 1.30
Total 1.45

Test Results

Thermos v1 started with water at a temperature of 90°C in it and ended with 47°C after only 20 minutes. This was a drop in 43°C/20 minutes or -2.15°C per minute. The main thing I noticed during this test was that lots of steam came out of the top and the outside of the thermos was also hot; signs of significant heat loss, which is what I expected. The next prototypes would be improved by adding a lid and insulation.

Thermos v2

Thermos v2 is a soup can with a threaded lip & lid, and insulating foam around the exterior. Thermos v2 was a prototype that I expected to do much better than Thermos v1 because of the added lid to stop convection, and the added insulation to stop conduction, but It still needed an outer chassis to prevent further conduction.

Material Thermal Conductivity J/(kg-K) Amount Cost $
Aluminum (Canister) 921 1 0.15
Polylactic Acid (3 dimensionally printed threaded lip)
2137 52g 1.30
Polylactic Acid (3 dimensionally printed threaded lid) 2137 52g 1.30
Polystyrene foam (outer insulation)
1131 6.5cm² 1.00
Total 3.75

Test Results

Thermos v2 started with water at a temperature of 99°C in it and ended with 50°C after 50 minutes. This was a drop in 49°C/50 minutes or -0.98°C per minute which is much better that Thermos v1. The main thing I noticed during this test was that some of the aluminum canister was still exposed and this let out enough heat that you could feel it. The last prototype would be improved by adding more insulation in the form of an outer chassis.

Thermos v3

Thermos v3 is a soup can with a threaded lip & lid, insulating foam, and an outer chassis. Thermos v3 was my third and final prototype, and I expected it to do much better than Thermos v2 because the added exterior chassis could help prevent heat loss due to conduction. Because I already went $0.75 over budget with the last prototype, I rationalized going even more over budget to add this exterior chassis to try to make it work as well as possible.

 

Material Thermal Conductivity J/(kg-K) Amount Cost $
Aluminum (Canister) 921 1 0.15
Polylactic Acid (3 dimensionally printed threaded lip)
2137 52g 1.30
Polylactic Acid (3 dimensionally printed threaded lid) 2137 52g 1.30
Polystyrene foam (outer insulation)
1131 6.5cm² 1.00
Polylactic Acid (3 dimensionally printed outer chassis) 2137 77g 1.93
Total
5.68

Test Results

Thermos v3 started with water at a temperature of 90°C in it and ended with 50°C after 50 minutes. This was a drop in 40°C/50 minutes or -0.8°C per minute which is much better that Thermos v2. The main thing I noticed during this test was that, compared to Thermos v2, the outside of the thermos was much cooler. This was probably due to the fact that the chassis provided more insulation, which prevented heat from conducting to the outside of the Thermos.

The Final Product

The final product ended up being Thermos v3 because it had all of the qualities a thermos needs to keep water warm: a reflective inner surface, threaded lip & lid, insulating foam, and an outer chassis. When I went about designing this thermos, I had to keep 3 things in mind: heat radiation, heat convection, and heat conduction. From my research, I found that to prevent heat radiation you need a reflective surface. To prevent heat from escaping through radiation, I used an aluminum canister for the inside of my thermos (since the interior is somewhat reflective). To prevent heat loss from convection, I figured that I would need to stop all fluids from escaping my thermos because these fluids, air or water, could bring heat with them out of my thermos. To stop heat loss from convection, I 3d printed a threaded lid and lip to contain all fluids in my thermos. Lastly, I needed  to prevent heat loss from conduction. In  my research, I found that to stop conduction you need to make sure that you have insulation or no air in between 2 walls, so that heat cannot conduct through the chassis of your thermos. Knowing that I wouldn’t be able to make a vacuum, I decided to go with insulation in the form of foam and an extra, non conductive chassis. With all of these features together, my thermos was able to only lose 0.8°C per minute. If I was to do this project again, I think I would try to make the thermos smaller so that the water has less surface area to conduct heat out from, and I would try to create a vacuum to stop further conduction.

Core Competencies