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The Einstein-Szilard Refrigerator (2020) (si.edu)
92 points by Dracophoenix 10 months ago | hide | past | favorite | 48 comments



Did the article even read the patent?

The article goes on about an electromagnetic pump. A device never mentioned in the patent.

The patent describes(as best I can tell) an ordinary gas fired absorption refrigerator. of the type found in many RV's. A genius design to be sure. But not one that was suppressed or lost.

https://www.dometic.com/en-us/outdoor/rv-and-van/refrigerato...

My father, who worked for a gas company, used to tell me that Einstein invented the gas fired refrigerator. I always thought he was pulling my leg.


The absorption refrigerator already existed, but had room for refinement as seen in the patent cited.

Einstein's and Szilard's real innovation, maybe not seen there, was for a different, electric design with a moving part, sealed inside, that was moved back and forth by a varying magnetic field applied from outside. It is often described incorrectly as having no moving parts. (I used to think ammonia was itself diamagnetic or ferromagnetic, which would have been very cool, until I got a look at their design.) What was innovative was that it had no need for sealed bearings that might leak. Nowadays just the wires for the motor pierce the fluid chamber, less elegantly than a strictly magnetic coupling.

Absorption refrigerators are strictly better than the compressor designs used everywhere today, running continuously, silently, and efficiently. The main driver of the latter was that General Electric wanted people to use electric refrigerators, not gas-fired, and wanted them to buy electric motors. Mass production soon gave GE an insuperable economic advantage except in niche applications.

Modern institutional refrigeration systems often use ammonia as their working fluid, but nobody likes putting ammonia systems in houses or cars. The modern alternative to freon/"cfc" and "hfc" is liquid CO2 at very high pressure. Hfc that leaks traps heat more than 2000x as well as CO2, so there is a push on to replace it.


> Absorption refrigerators are strictly better than the compressor designs

That's not true! CoP of ammonia absorption refrigerators struggles to get past 1. You can easily get a CoP of 4-5 with a compression refrigerator.

Ammonia absorption fridges are useful when you have a source of waste heat, then it's basically "free" for you.


I am corrected. Compressor refrigeration benefits from decades of refinement. Just a few decades ago, 3 was considered good.


CoP isn't really about engineering refinement to eek out the best efficiency. In fact, we have known how to get really close to the Carnot limit for nearly 100 years. The Carnot limit for a fridge in room temperature is a CoP of ~20.

However, getting close to that limit requires huge evaporators and condensers, big pipes, large amounts of working fluid, and multi stage pumps. All of that costs money, and historically people didn't care much about efficiency if it means spending more money.


The Carnot limit for 26C -> 5C rerigeration is around: 1 / (T_high / T_low - 1) = 1/(300/278-1) = 13.

Industrial refrigerators can get to CoP of around 4 for this temperature delta. The overall system performance will typically be much lower, due to the need to run fans and other systems.

A couple of interesting technologies to watch in this area:

1. Acoustic refrigerators that use acoustic waves in helium. They theoretically can approach the Carnot limit.

2. Supercritical CO2 cycles. They can be used for larger deltas without losing efficiency.


It's worth noting that the Carnot limit really only applies to systems that return to thermal equilibrium much faster than the characteristic interaction and/or rely on thermal interactions to transmit energy.

Electrochemical, magnetohydrodynamic and various other systems are not properly characterized by the Carnot limit and can approach much higher efficiency limits.

I think the systems being discussed are appropriately characterized by the Carnot limit, but it is frequently mischaracterized as an absolute limit on systems that it is not relevant to and for example here it should probably not be considered the absolute limit of refrigeration efficiency.


> Electrochemical, magnetohydrodynamic and various other systems are not properly characterized by the Carnot limit and can approach much higher efficiency limits.

That usually is a distinction without difference. Other effects limit the efficiency at far lower levels than pure Carnot.

This can be intuitively understood like this: Carnot limits apply to gases, that are the simplest interacting systems. You can realistically model them as just a collection of individual independent particles interacting only via simple collisions.

Anything more complicated like electrons in semiconductors, and you have way more interactions and way more possibilities for your system to have inefficiencies.

Take, for example, solar panels. Sunlight has the optical temperature of around 6000K, so a Carnot engine that uses 6000K hot part and 300K cold part will theoretically have a 95% efficiency. And an infinite stack of solar panels with each layer tuned for a specific wavelength has the theoretically maximum 87% efficiency.


Meanwhile an infinite diameter conductor has a maximum efficiency of 100% with every part at whatever temperature you want.

Carnot characterizes classical heat engines and things that work a lot like them, it's not a universal limit of process efficiency and it's not even a good first approximation for many systems.

Your example of a meaningless distinction is a factor of over two in waste energy, in the favor of Carnot in this case, but distinct none-the-less.


It's worth noting that CO2 was also used in the early days of refrigeration alongside ammonia, when it was called "carbonic acid", and the relative nontoxicity of CO2 was a feature that made it popular for shipboard systems and a few other applications, but it fell out of use once other nontoxic refrigerants were invented because of the extremely high pressures involved that required far heavier equipment.

As an example, the Titanic had CO2 refrigeration.


Such a linear pump was invented by a Japanese guy, and is commonly used in ENGEL brand RV freezers.


They probably got it from Wikipedia [1], which the article appears to have been based on:

> One variant, the Einstein–Szilard electromagnetic refrigerator used a Einstein–Szilard electromagnetic pump to compress a working gas, pentane.

[1] https://en.wikipedia.org/wiki/Einstein_refrigerator


> Szilard and his team refined the prototype in their workshop at Germany’s General Electric Corporation in Berlin

Better known as Allgemeine Elektricitäts-Gesellschaft (AEG - https://en.wikipedia.org/wiki/AEG). Some names are better left untranslated. That's the same as writing "Allgemeine Motoren" instead of General Motors in a German article - nobody would know what you're talking about...


He says better known as and throws out this, "Allgemeine Elektricitäts-Gesellschaft". lol


Ok, the brand is (or was) known more under the acronym AEG (at least in Germany/Europe, probably not in the US), not sure if everyone was aware of what the acronym stood for however. I just mentioned the full name first because it explains how the author of the article arrived at the translation "General Electric Corporation"...


One of my parents were German. Such tortured pronunciation with German.


Here’s a much better article on the collaboration from 1990s Scientific American: https://www.physics.smu.edu/scalise/P3374fa17/EinsteinSzilar...


The patents having long expired, presumably there are practical reasons that this design is not competitive with modern compressor designs.. Would have been good if the article had said what these are


moving-parts-free ammonia-absorption refrigerators of the einstein-szilard type are in fact in wide use today, especially in camping trailers where the ability to run off propane without electricity is a big plus. i encountered one in a hotel room earlier this year. https://en.wikipedia.org/wiki/Absorption_refrigerator

vapor-compression types with midgley's cfcs, and derivatives like hcfcs and hfcs, are less likely to kill you if they leak, and i think they also have a higher coefficient of performance ('efficiency'); consequently they are in even wider use

einstein and szilard's no-moving-parts design does reduce the risk of leaks, but not to zero, as is obvious if you visit a junkyard to find spare parts for one of these


Leaks in modern fridges are mostly caused by humans using a knife to try to defrost them and puncturing the pipes...

And then 2nd most common cause is water leaks or dampness causing the pipes to corrode through.

If you run a fridge till it dies like most people, you will probably see a leak on about 15% of cases (other causes of failure are motor capacitor failure, thermostat failure).

With an ammonia based refrigerant, every single leak indoors would likely kill a few people, so such a fridge design still wouldn't be considered acceptable for use in the home today.


that depends on the speed of the leak and the amount of ammonia involved; as i said, ammonia-absorption refrigerators are in common use today, including in homes, and they do not have a high death toll (though large industrial ammonia-absorption systems do regularly kill people, about 20 people a year in all of prc, for example: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9318737/)

osha's idlh level is 300 ppm; in a typical small house of 200m³ that's 60 liters of gas, 2.5 moles at stp, about 40 grams of ammonia; this is a small enough amount of ammonia that you could definitely get it from a home refrigerator (https://www.dometic.com/assets/18/22/operating%20manual_5182... says it contains 226g of ammonia, which would be 1600 ppm in that houseful of air) but only if it's released quickly. lc50 for a one-hour exposure is in the 4000 to 11000 range https://www.cdc.gov/niosh/idlh/7664417.html which is several times more than the entire refrigerator's worth if diluted in a houseful of air

the odor threshold is about 5 ppm https://en.wikipedia.org/wiki/Ammonia#Safety so it's unlikely to go unnoticed


...and bingo! Thank you.


Szilard and Einstein would later collaborate on a letter that had a far greater effect on the world than their refrigerator did...


I have a question for the HN community. What exactly was Szilard's contribution to the Manhattan project, aside from the initial letter that started it all? I know that Szilard was the first to envision the idea of chain reaction, and got a (secret) patent for that, but at the time it was more or less idle speculation. When the project actually got going, I know he collaborated with Fermi on the Chicago pile reactor, but 99% of the accomplishment was due to Fermi, not to Szilard. After that, Szilard remain a towering figure inside the project, but did he actually contribute anything?


Anyone ever rig one of these things with a solar concentrator as the heat source? I feel like a fridge that runs colder as the sun gets hotter would be one of the more elegant systems.


Check out solar absorption chillers


There are refrigerators without any moving parts .. my VW camper has one which runs on either propane or 12V or utility power, and as a child we had one which ran on kerosene.


The phrase "Freon is a greenhouse gas that has depleted the earth’s ozone layer" annoys me. A lot of people don't get that the Ozone layer and climate change (the greenhouse effect) are different things. Freon is both a very powerful greenhouse gas, and it destroys the ozone layer.

Since Freon and other CFCs were banned, the Ozone layer has been mostly coming back, but climate change is still happening because of the other greenhouse gases.


Of course, the big question is efficiency, which is not addressed. Nice article otherwise.


My parents had an electric absorption refrigerator when I grew up. It was completely silent and lasted for more than 30 years. These days it seems they're only available in small gas fired models for RVs, not sure why.


Aside from other potential factors, who in their right mind would want [to sell] something that lasts 30 years these days /s


The article has a haunting picture. The caption reads:

Nazi storm troopers enforce a boycott of a Jewish-owned department store, Berlin, 1933. The sign reads, "Germans! Defend yourselves! Don’t buy from Jews!" Courtesy of the Bundesarchiv via Wikimedia

Advocates of hateful free speech should take note about the dangers of something taken too far.


Advocating a boycott of a store is free speech.

Enforcing it, by physically preventing people from entering the store, not so much.


Was the source of that sign in 1933 free speech? — or the effect of a central authority who controlled the media?

https://en.wikipedia.org/wiki/Censorship_in_Nazi_Germany

When you say “taken too far”, the outcome certainly was a fascist state with totalitarian control of media; how would staunchly defending freedom and decentralized control lead to that?


The people holding the signs are members of the SA - that is, members of the paramilitary wing of the Nazi Party, not state employees or members of the military. This was taken in April 1933, when Hitler had been chancellor for a little over 8 weeks, just one week after the 'Enabling Act' had been passed. What this picture shows is actually the very process of the shift from 'just a bunch of thuggish party supporters chanting slogans' (free speech) to 'the thugs who the cops won't stop are now indistinguishable from state authority' (fascism).

Not sure what it has to do with 'control of the media'. The person who took the photograph was likely part of the media.


> the thugs who the cops won't stop are now indistinguishable from state authority

Yeah! I remember when these thugs took mayor chunks of cities and fired some police stations and politicians refused to move a finger.


still the Nazi party was part of the political process in the Weimar Republic, prior to taking power. Back then there was no objection to their genocidal ideology, as it was regarded as 'free speech'.

Actually this historical precedent is the reason for the stricter rules on expression in the Germany of the present.


How do you suppose the central authority gained that control in the first place? They fomented this exact sort of "hate of the Other" to whip a certain kind of person into a fearful frenzy. Trump's doing the same thing today with MAGA. Trump-era USA is Germany during the late 20s and 30s.


Meds


Jfc, Trump is literally the one being prosecuted by a regime that took control through fear, force, and deceit. Yet somehow even though he is very visibly being subjected to a barrage of transparently meaningless political prosecutions you somehow still fear him as a fascist.

So who exactly has been "whipped into a frenzy here?"

Who are Trump supporters fearful of, other than the government that is actively attacking them?


Well, "migrant caravans at the southern border" for a start.

And if you're having a hard time figuring out who the proto-fascists are, look for the ones who don't respect free and fair election results, and look for the ones who try to make it harder for people to vote.


You know which famous fascist also got persecuted (and jail time) for a failed coup before he took power years later? You get 0 guesses.


Who are Trump supporters fearful of, other than the government that is actively attacking them?

People who aren't white, people who aren't straight, people who are transgender, people who aren't Christian extremists, people who don't think the government is a giant ball of evil incarnate, etc.

Trump literally tried to overthrow the government in 2020. This isn't debatable: it's a fact. In any sane, functioning democracy, he'd be jailed already. It's scary that such a large fraction of this country fears and hates everyone else so much, and this country so much, that they'd be willing to use violence to overthrow it and install a dictator.


A one day protest with only a protestor being shot and 1 building being entered really counts as an attempt to overthrow the government? Also where Trump tells everybody to go home and the he leaves office as scheduled?


He's being prosecuted for crimes, some of which preceded his time in office. I'm sure you have strong feelings about a certain laptop and prosecuting the alleged crimes attributed to it?

You need to at least be consistent with your complaints.


Poor, persecuted, POTUS? He led an attack on the capitol to try to overturn his loss in the election. The "meaningless political prosecutions" you refer to is the legal system failing to function at a basic level and throw him in jail for sedition, and yes, it is frustrating and scary for the rest of the free world.


I want to repeat the sibling comments claim that this doesn't show the pitfall of free speech, but the opposite as this was organized top-down state propaganda. In fact sadly the *lack of free* speech made it impossible to criticize this boycott and following ever tightening restrictions.

That said: The question if "calling for the genocide of Jews" violates Harvard's rules on bullying and harassment or is acceptable speech is still ongoing and left to the reader. /s


>> unlikely to do anybody any harm

Unlikely doesn't mean impossible.




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