Student project: Build a refrigerator

[Svenvbin]

Hello all,

Just until the end of June, and my first year in University, studying Applied Physics, will be done. Until then however, we have one last big project.

The idea is that in groups of 4 people, you build a machine which can cool two litres of water down as much as possible, within 30 minutes. The only rules are as follows:
- Max 2x2x2 metres
- Has to be powered by one person. (So no electricity from the socket, but you can generate it yourself)
- All parts have to be at room temperature at the start of the 30 minutes.
- You may not use energy which has been buffered in any way before the 30 minutes start. (As in, chemicals that cool down when they mix with water etc)

My favorite so far is just vaporising a lot of water, but we also have to consider other alternatives. I personally think that building a 'real' refrigerator (Using the Joule-Thompson process) will be rather difficult, as we'd have to build the system pressure-proof and, of course, working :P

So, do you have any websites or advice on how to build a goodworking cooling machine? We've had the subject Thermodynamics, so I guess I understand a couple of things you'll say :) (Not everything, but hopefully most of it :P)

Thanks in advance!

[Brian_UK]

Peltier cooling plate powered from a bicycle driven generator?

[Svenvbin]

Thanks for answering, that was one of our possibilities.

What we remembered from our subject, and found on the internet (during a short search) was that Peltier Cooling is mainly used on a small scale (Cooling electrical components, chips etc). Were we wrong? :P

[Magoo]

Peltier bridge cooling has advanced to the stage of being applied to ice makers.
With your project you will of course take into account the food/ nutrician factor for the cycling operator and all the carbon miles/ chemical inclusion/ hospital care factors. Jet aircraft delivery and yardy yardy additives.
You would be safer staying in bed.

[Tesla]

First calculate or research how much work (energy) one person can gererate on a device like a bicycle, Then match that amount with a refrigeration system such as a vapour compression system (for maximum efficiency). Are you allowed to use refrigerants? or only natural refrigerants like air or water for the effct? I saw on this forum a refrigeration system which compresses air to 80degC with fan power then cools it and re-expands it for the refrigeration effect. Best of luck and let us know what you choose and how you go

[Svenvbin]

Asked some people, and according to my dad, you generate 200 (normal 'fast') to 300 W (Intensive) when biking. (At least, that's what the hometrainer at his physical therapy told him :P)
But I guess that goes down as soon as you want to use the energy for something :)

Did some more research on Peltiers and found out that they are indeed better than I thought. A small calculation showed me that a peltier with 100W Cooling power could cool down 2 liters by 21 degrees, in 30 minutes. (Ideal circumstances)

Here's where my question comes in: If I find a "100W" Peltier, what is its cooling power? I read somewhere that it will cool with 100W, and it needs the same amount to operate, so that you need to power it with 200 W. Is this true?

Thanks :)