Cooling water using only work provided by a person

[paulwiersma]

I have received an assignment which requires me to build a device that can cool two liters of water (at room temperature) as much as possible. The only source of energy is me; I can drive the device in whatever way I can. I am allowed to run the device for 30 minutes, and the lowest temperature reached counts. The device can't be bigger than 2x2x2 metres and all of it has to be at room temperature at the beginning. Also, it can't cost more than €100 in materials.

I have some ideas for it, and was wondering if anyone has criticisms or other ideas.

1. use the Joule-Thompson cycle to cool the water. I would drive the compressor with my legs (so like a bicycle).
2. use a fridge-like system, with a phase change. Again, I would drive the compressor.
3. use a piston. If liquid water is forced to be in a low perssure environment, it will want to evaporate. This costs energy which is taken out of the remaining water, which would freeze. This can be done with several liquids, each being cooled in advance by the previous one.
Then a very cold liquid can be dropped in the water which will cool the water.

These are my ideas. Any suggestions or criticisms would be much appreciated.

 

[Valkarie]

You could also try using a heat exchanger. This would involve having a closed loop of liquid flowing through one side, and the water you want to cool on the other side. Heat will be transferred from the water to the liquid in the closed loop, which you can cool using whatever method you choose (such as a fan or a Joule-Thompson cycle). You could also look into evaporative cooling. If you have access to a fan, you can set up a system to blow air across the surface of the water, causing some of it to evaporate and take away the heat in the process. Finally, you could use ice to cool the water. You would just need to buy some ice cubes and place them in the water for 30 minutes, then remove them before they completely melt.