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A recent Eco News article says:

The “reverse microwave” is already a reality: it works without electricity and will revolutionize our life

[...]

Imagine a reverse microwave to cool food instead of heating it. It has just been invented, and it works without electricity and does not emit polluting gases. It’s clear: it’s going to revolutionize our kitchens.

[...]

The reverse microwave was something we’ve been asking for for years, but this one also works without electricity and is 100% sustainable.

They're describing an electrocaloric cooling effect recently discovered by researchers at the Luxembourg Institute of Science and Technology (LIST). However...

The electrocaloric cooling system developed by LIST consists of electrocaloric capacitors and liquid coolant which make rapid heat transfer. Heating of the fluid in the capacitors, causes cooling of the system via application of electric field.

Doesn't that require electricity?

LIST's paper 'High cooling performance in a double-loop electrocaloric heat pump' begins...

Electrocaloric materials pump heat out of a system through a phase transition driven by changing an electric field.

That sounds an awful lot like it needs alternating current electricity.

We present an electrocaloric cooler with a maximum temperature span of 20.9 kelvin and a maximum cooling power of 4.2 watts under the moderate applied electric field of 10 volts per micrometer without any observed breakdown.

Seems like it uses electricity.

Can LIST's new electrocaloric cooling effect ("reverse microwave") cool without electricity and is it 100% sustainable?

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    To whether it's notable, it managed to make it into my Google News feed. :shrug: I'm fairly certain the answer is "No". The paper summary mentions "the material does not break down under repeated field cycling" which I'm guessing is where the "100% sustainable" claim comes from.
    – Schwern
    Mar 25 at 2:33
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    @Schwern: I was going to close because EcoNews appears to be just one dude, and their Facebook and Instagram feeds have barely any viewership. On Twitter, though, they have a big viewership (Should I be suspicious about bots?). If it made it into your feed, that is a sign that they have reach.
    – Oddthinking
    Mar 25 at 3:34
  • @Oddthinking I just earned "Notable Question", 4000 views, it seems you were right.
    – Schwern
    Mar 25 at 17:44
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    I find it interesting that "ten volts per micrometer" is described as a "moderate electric field".
    – Mark
    Mar 25 at 21:22
  • @Mark I'm inclined to agree, especially after shifting units to 10 kiloVolts / mm or 10 MegaVolts / meter. Mar 25 at 23:14

2 Answers 2

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The claim, to no-one's surprise, is false.

Electrocaloric heat-pumping requires energy to be supplied (e.g. by electricity). The alternative would be to break the Second Law of Thermodynamics.

The Econews article appears to be a confused report about November 2023 announcements of a recent paper in Science, High cooling performance in a double-loop electrocaloric heat pump.

The Science article doesn't claim that no electricity is required, but talks about its potential efficiency:

Moreover, the maximum coefficient of performance, even taking into account energy expended on fluid pumping, reaches 64% of Carnot’s efficiency as long as energy is properly recovered.

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    Regardless of power needs, could one actually use this process to build a reverse microawave that cools food?
    – quarague
    Mar 25 at 8:41
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    I had a conjecture: That this article was originally written in Spanish and translated to English, and the errors were introduced during the translation phase, but I am unable to find a corresponding article on their Spanish page.
    – Oddthinking
    Mar 25 at 12:16
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    @quarague every heat pump is both a heater and a cooler. It just depends on which side you use and which side you expose to the environment. So yes, it could be used as a refrigerator. Mar 25 at 20:56
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    @LarsH a microwave oven is not a heat pump.
    – vsfDawg
    Mar 26 at 15:51
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    @AlexMeiburg this answer is about “electrocaloric heat-pumping” which is, no surprise, a kind of heat pumping. Maybe someone should have said explicitly that there is no such thing as a “reverse microwave”, but what the article linked in the question calls “reverse microwave” is electrocaloric heat-pumping which is not even remotely something like a “reverse microwave”.
    – Holger
    Mar 26 at 16:42
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There is a good answer here already, but it doesn't really address the appropriateness of the "reverse microwave" description. I would argue that it is an inappropriate description, even though it is not completely indefensible. The Science paper describes a refrigeration method that uses a special material along with a varying electric field. The changing field causes one side of the material to get hotter and the other side to get colder, and you can use the cold side for refrigeration purposes. This is like a regular refrigerator, except that there are no moving parts.

Here is why the "reverse microwave" description is inappropriate (misleading may be a better word): Microwave ovens heat things quickly, using EM waves that directly get inside the food and shake the water molecules. The method in the paper is just another way to cool a refrigerator. Things won't get cold any faster. There is no kind of radiation that can slow down the water molecules, and so no way to cool food faster than heat can be conducted through the food.

Here is the sense in which it is defensible: Like a microwave oven, it uses a varying electromagnetic field to change the temperature of something, and so it doesn't have moving parts. But it does this by moving heat from one side of it to another, not magically creating coldness, and only works for a specially tuned material. I only call it "defensible" here because I suspect there are well-meaning people who use that description and I want to convey what I think they mean. It's really not a good description.

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    1) "There is no kind of radiation that can slow down the water molecules" There is! Laser cooling. Not practical for the home kitchen. 2) The microwave analogy is even more strained. A microwave works by heating water, whereas the heat pump the article describes works by moving heat. 3) Maybe they got it from the "reverse microwave oven" rapid drink cooler.
    – Schwern
    Mar 28 at 2:37
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    A standard refrigerator also uses a varying electromagnetic field to change the temperature of something (presumably reducing), so by your logic is also defensibly a "reverse microwave". So is a room with a ceiling fan, assuming the contents are damp. It's a more comprehensible analogy than describing it as "inflatable penicillin" or somesuch, but the ways it misleads are more numerous and salient than the ways it reveals.
    – Jay McEh
    Mar 28 at 12:47

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