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As the topic already tells, I want to cool a glass or aluminium bottle down to roughly -60 to -70 °C for the sake of science. Additionally this setup should be portable for showcasing it at school.

I already looked around for options and found peltier modules, but they can only provide a maximum temperature difference of up to 70°, I need roughly 90° when I am in a normal room(20-25°C). Can I somehow "boost" this modules to give me the extra power I need. Large enough pc-0heatsinks(20W) for both sides are available to me if necessary.

A small styrofoam box will be necessary too, I guess.

What are your thoughts on this problem? Do you have any other solution than peltier modules?

Xenox
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You might want to read this question and associated answers. In particular - putting Peltier devices in series is horribly inefficient so you are limited in the temperature you can reach.

That said, since there are devices that will give you up to 70 K of temperature difference you need some way to run them in tandem. The problem is that the "colder" device in the tandem puts out a lot more heat (because it is inefficient), and that heat needs to be pumped by the hotter device.

So I propose a two stage solution: if you can make your heat sink for the first stage cold enough (a bath of ice) you just might get away with it. Run one Peltier for a day to make the ice bath, then turn on the second Peltier that takes heat from the bottle and pumps it to the ice. This allows you to get a 10:1 (or whatever) pumping ratio of heat that takes account of the inefficiencies in the system - the heat capacity of the ice (mostly the heat of fusion) becomes a "capacitor" for your system, giving you a burst of additional cooling capacity.

Alternatively you would need multiple second-stage devices - then the problem becomes how to get the heat from one stage to the other.

Usually when people want to get things cold, they get some liquid Nitrogen... works like a charm. Or dry ice - less dangerous, and cold enough for your experiment.

Floris
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    Wouldn't it be simpler to just get a big bag of ice from the supermarket to cool down the first stage rather than have a Peltier do all the work of cooling the water to a low enough temperature to make an ice bath for the second stage? That way only one Peltier is needed. The OP would still need to investigate whether his Peltier has enough cooling power to go from 0˚C to -70 ˚C since there will probably be significant heat leakage if he's planning on using a styrofoam box. Just using dry ice seems like the simplest solution. –  Sep 29 '17 at 23:56