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Some background regarding my question:

I'm thinking if making some sort of TEC-based ice cream maker. Considering the combined specific heat capacities, I calculated (possibly incorrectly) the value in watt hours to be slightly less than 8wh to cool 600 grams of ice cream mix (would be 1 batch) 14 degrees from (a refrigerator-cooled) 4 degrees celsius to -10 degrees celsius.

So the TEC needs to be able to reach that low temperature, and for time's sake it (or the combined set of them) needs to pump heat energy at around 24 watts so it won't take more than 20 minutes to reach a solid-ish ice cream.

I bought once (for a different purpose) a couple of cheap TEC from a Chinese vendor and they seemed to perform lousily and were of inconsistent quality, so I tried looking for offerings from known TEC manufacturers.

The spec sheet of one of them is, for example, Qmax @ Th of 13.0W @ 27 degrees celsius, while the maximal current and voltage are 5.6A and 3.6V.

Are these specs saying something different? Because how can a TEC running at 20.16 watts pump heat at 13 watts, which would mean an efficiency of ~64.5% (even if only at the specific most efficient temperature), when I read their efficiencies are perhaps 8%?

Thanks in advance.

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    $\begingroup$ A heat pump can pump more heat than the work input, certainly when the difference in temperature is small. Maybe this helps: physics.stackexchange.com/questions/489467/… $\endgroup$
    – user137289
    Aug 23, 2020 at 23:08
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    $\begingroup$ @Pieter Regarding that point, when I read about it in the past I still didn't understand why a heat pump can have a COP of 4, even. If it is 4 it means for each 1 watt of put into running the heat pump, it moved 4 watts of heat energy? In a simplified scenario, if I compress a gas using 100 watts and that raises its temperature by 100 watts (is that exact?), let it equalize temperatures with one space and then decompress it at another space to its original volume, won't it now be (possibly up to) -100 watts colder than it had started? So it would just equalize with the other space to original? $\endgroup$
    – TLSO
    Aug 24, 2020 at 7:00
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    $\begingroup$ @Pieter So regarding such a cycle, I'd like to know where does more energy moved than inserted occurs. And regarding TEC, when I read they are <10% efficient, does that not translate into "moving less than 10% energy in heat compared to electrical energy put into the system"? The possibility of some sorts of heat pumps being more than 100% efficient (in essence) being disregard. $\endgroup$
    – TLSO
    Aug 24, 2020 at 7:05

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