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Ive been wondering about how small of a cooler you can build.

Although this probably is just really low-level engineering, i have a rather particular question.

For my idea, the cooler has to be as small as possible, rather efficient and not use a chemical compound or reaction that is not locally reversible. It has to be an fully working circle that, theoretically, keeps working, solely relying on electricity for power.

While I understand how certain cooling systems work, I could not find a satisfying example, since mobile phones, tablets and other handheld devices rely on, if any, air cooling.

However, what I'm searching for woul'd be a small cooler that can reach slightly lower temperatures than the surrounding area, lets say about 5 °C, maybe less or even more, if it just gets below average surrounding temperatures (room-temperatures).

Would this be achievable in a watch-like size? And how efficient woul'd that be, running on electrical reloading only?

EDIT: The heat would, as far as i understand thermodynamics, not be a big problem. A short-range "relocation" (idk the term) about a few centimeters to a small vent would be enough.

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closed as too broad by Wasabi, Fred, wwarriner, hazzey, Dave Tweed Jul 24 '16 at 15:38

Please edit the question to limit it to a specific problem with enough detail to identify an adequate answer. Avoid asking multiple distinct questions at once. See the How to Ask page for help clarifying this question. If this question can be reworded to fit the rules in the help center, please edit the question.

  • $\begingroup$ Where do you want the heat to go? $\endgroup$ – Dave Tweed Jul 24 '16 at 15:38
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A Peltier cooler would fit the requirements you set out. They can be compact enough to fit the 'wristwatch sized' requirement and use electrical power to achieve the cooling effect.

You do still need some way of shedding heat from the hot side of the cooler and this may require either a passive heat exchange, heat pipe etc depending on the application.

The performance will depend not just on the temperature difference you want to achieve but also on the heat flux required.

The most common comparison would be with the coolers used in laptops which tend to be heat pipe based. Typically a modern CPU would generate up to about 100W of heat, depending on load and performance and look to limit internal temperatures on the hot side to about 40-50 deg C. This isn't exactly the same as the refrigeration you require but should give you some sense of what is possible.

If you have a bit more space to play with water cooling is now pretty mainstream for high performance PCs although most most units are substantially bigger than wristwatch size they will give substantially better performance than a laptop heat spreader.

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