The Einstein-Szilard Refrigerator (2020) | Hacker News Reader

The Einstein-Szilard Refrigerator (2020)

invention.si.edu

109 pointsEndXA55 comments

It's a very clever trick: a refrigerator without a compressor which uses heat as the energy source. It could run on either a gas flame or an electric heating element.

There are three working fluids (butane, water and ammonia) and it works by exploiting differences in partial pressure (that is, the pressure contributed by each component of a gas mixture). Instead of using a compressor to change the overall pressure, it changes the composition of the mixture.

The cycle basically works by adding and removing ammonia at different points to make the butane refrigerant evaporate and condense in the appropriate places.

On the "condenser" side of things, water is used to remove the ammonia from the gas mixture by absorption. Because the total pressure is approximately the same throughout the system, removing ammonia increases the butane mole fraction and therefore its partial pressure, causing the butane to condense. This is the heat rejection side.

On the evaporator side, ammonia is added again. This lowers the butane partial pressure, shifting the equilibrium and causing the liquid butane to evaporate. That's where the cooling effect occurs.

The other part of the cycle is regenerating the ammonia by separating it from the water again. That's where heat is added, and that heat input is what ultimately drives the process.

USSR made compact fridges like that, called Морозко. They are still made. No moving parts, very quiet.

Man WTH? Now I want one. I hate how loud my fridge is!

They're not energy efficient so I'm not sure that type of fridge is available to buy now.

Energy efficiency is secondary, that can be mitigated by solar power plus some thermal mass inside. That is actually most efficient use of solar from my pow.

Their bane is hydrogen partial pressure dropping due to it leaking through the metal of the tubes. That .. is problematic. OTOH it'll last for like 20 years before you'd need to replenish.

The Einstein-Szilard device doesn't use hydrogen, did the USSR device use it ?

in the US you can still buy hydrogen/ammonia/water gas absorption refrigerators such as "EZ Freeze". Propane/Natural Gas refrigerators use this cycle. I'm sure you can get them all over the world, the cycle is older than the one in the article.

You can buy them almost anywhere where there is a need to keep food cold without electricity.

Get one with an inverter compressor, they are very quiet. They have a compressor that can be run at varying power levels, so instead of having one that goes of noisy at 100%, then sits off for a while, you have one that runs for example at 10% most of the time.

Interesting. Is this better or worse for compressor life span?

From what I know it's better for the life span. Less load, fewer start-stop cycles, less vibration.

Usually that means either a fan or compressor pump is making a metal panel resonate; the pump itself is usually pretty quiet, and the fan is pretty much the same as a PC fan. You can usually add a sticky foam panel to the metal backpanel to eliminate the vibration.

Thank you. I can't believe the main article doesn't bother explaining how it works

Is the other way possible - a heat pump which heat and similar to this setup? If so you attach a solar thermal panel to such pump and store the heat in thermal battery to be used by Einstein-Szilard Refrigerator for constant cooling.

What is the electromagnetic component?

It sounds like the article completely mixed together two different inventions of theirs and the one you described was the much more important one.

My parents had a completely noiseless refrigerator similar to this. It did not have a compressor and had an electric heating element instead. It was very durable and worked for many decades until the plastic and door hinges etc was too damaged for it to be used any more.

I actually found a picture of the exact model from a museum

https://digitaltmuseum.no/011014769284/evalet-kjoleskap/

I looked at bit more and it seems the original article is quite misleading. It seems the Einstein-Szilard refrigerator is a type of absorption fridge and a major reason they did not come to market was a related absorption fridge, the Platen-Munters absorption refrigerator made by Electrolux and Evalet. The Einstein-Szilard refrigerator was not completely unique, but an attempt at improving this design with other gases.

This post reminded me of the movie “The Mosquito Coast” from 1986 starring Harrison Ford, who set out to build a refrigerator in the jungle to produce ice from heat. He used the Platen-Munters principle, which is similar to the Einstein -Szilard principle.

Both machines use heat instead of a mechanical compressor, both can operate with essentially no moving mechanical parts, and both exploit partial pressure so a refrigerant can evaporate at a low temperature. The crucial difference is which fluid does which job.

The conventional diffusion-absorption refrigerator, developed by Platen and Munters in the 1920s, uses ammonia as the refrigerant. Hydrogen occupies the evaporator and lowers ammonia’s partial pressure, allowing liquid ammonia to evaporate at a low temperature. The ammonia vapor is subsequently absorbed into water. This is the basic technology that became familiar in gas-powered and RV refrigerators.

From the specific standpoint of a field-built jungle refrigerator, the Einstein–Szilard working-fluid combination arguably makes the better plot device. The Platen–Munters choice has the advantage of commercial precedent, but the hydrogen charge is decidedly the awkward ingredient. Even though once the system is charged the constituent chemicals stay put, I would rather schlep through the jungle with butane in a canister than the requisite amount of hydrogen.

“The Mosquito Coast” is an interesting movie.

I was lucky enough to be compelled to read the book before the movie came out, and I quite recommend it. The movie did a pretty good job of hewing to it IIRC.

Since I haven't seen anyone bring up the viability of this method yet, here are a few additional bits of info I dug up:

> the total mass of the completed apparatus is around 400 kg with 20 kg of alcohol in the refrigeration cycle

> The group, led by Malcolm McCulloch noted that the design was still "nowhere near commercialised", but might allow the efficiency of the original Einstein–Szilárd design to be quadrupled.

It would be great if someone could improve this tech to where there's a breakeven point of ownership (preferably less than 20 years) when it becomes a better deal than other modern refrigerators.

The efficiency of most existing heat-driven refrigerator and heat-pump designs is kind of disappointing. This isn't a fundamental thermodynamic issue; the Carnot efficiency for a gas burner at 2000 C running a refrigerator offering a 40 C temperature drop is close to the electric efficiency. In principle, it could be a more efficient way to use stored hydrogen than a fuel cell. In practice, it isn't. Maybe actually taking advantage of such high temperature differences requires very good refractory alloys. I would be curious to know the absolute efficiency proposed here rather than just a rough estimate of relative efficiency.

> It would be great if someone could improve this tech to where there's a breakeven point of ownership (preferably less than 20 years) when it becomes a better deal than other modern refrigerators.

Given that absorption chillers have a COP of 0.7 to 1.2 vs a vapor-compression chiller with a COP of 4-6, it’s likely impossible to create an absorption chiller/refrigerator that equals or exceeds a vapor-compression chiller/refrigerator due to physics/thermodynamics. This isn’t much of a downside for absorption chillers powered by waste heat since the energy would otherwise be lost.

Someone smarter than I am will have to explain why, all I know is that vapor-compression refrigeration is 4-6x more efficient than absorption refrigeration.

Thank you, that's the sort of response I was hoping for, actually analyzing the efficiency of the thing. Waste heat is something I think we can get a lot more juice out of in the future.

I'd happily pay for a silent fridge with much less than a 20 year breakeven point.

Silent and ostensibly failure free to boot.

Reading your and others comment I wonder what sort of refrigerators and freezers you have. Mine are about 10 years old now, Bosch, full height and whatever the best energy class was available at the time.

I'm very sound sensitive but rarely do I hear any noise from them unless I recently opened them for an extended period. Do we just have quieter appliances in Scandinavia than the rest of the world or something?

My refrigerator is a Whirlpool purchased new in 1995 at Best Buy.

It is the exact model pictured: https://bids.fowlerauction.com/auctions/38959/lot/5830641-wh...

It works perfectly (except for the hum which has been there unchanged on and off as the compressor cycles for 31 years). I'm kind of used to it by now....

For lulz I checked and you can buy working models of this fridge at estate sales for $50-$110: the one pictured sold at a 2024 estate sale auction in Alabama/Tennessee/Georgia for $110.

> Einstein and Szilard eliminated the risk of leakage by jettisoning the mechanical pump

Einstein–Szilard refrigerator: https://en.wikipedia.org/wiki/Einstein_refrigerator :

> The three working fluids in this design are water, ammonia, and butane. [1] The Einstein refrigerator (co-invented with Leó Szilárd) was actually a modification of an earlier three-fluid absorption design created by Swedish engineers Baltzar von Platen and Carl Munters

Szilard is an underrated genius. Also was an early formulator of the nuclear chain reaction concept, to tap into nuclear energy, but did not zero in uranium right at the outset as the element to make it feasible.

This is the fridge that is used in the book and movie 'The Mosquito Coast'.

The infamous Worm Tub! It always bothered me that that character (nor the author) ever gave credit to Einstein.

And because of that omission, Einstein drifted into obscurity...

On a related note, there is a reasonably well known commentary on an adjacent technology by Ruth Schwartz Cowan (1985) titled "How The Refrigerator Got Its Hum". It describes a 1930s market battle between heat-driven ad/absorption chiller technology ("Kelvinator") and work-driven compressor chiller technology ("GE"). Tl;DR GE won.

The ab-chiller is likely best known these days as the "propane fridge" in RVs.

Sadly, the only online resources for Cowan's work I can find are either Scribd paywalled [1], the entire book in which Cowan's piece is a chapter on the Internet Archive [2] or a pointer-to-a-pointer from a piece in the Guardian [3] to a boingboing piece [4] that seems to be offline.

(Background: I work in Direct-Use geothermal. Such ad/absorption chillers are one major tool in the toolbox for low-T cases where it is uneconomical to turn geothermal heat into electrical energy -- mostly due to Carnot's Law considerations.)

[1] https://www.scribd.com/document/527479452/Cowan-How-the-refr...

[2] https://archive.org/details/socialshapingoft0000unse_g5b0

[3] https://www.theguardian.com/science/political-science/2014/f...

[4] https://boingboing.net/2012/08/20/how-the-refrigerator-got-i...

These sort of refrigerators are common in RVs and campers as they usually have a propane tank, as well as commercial/industrial installations that have waste heat and cooling needs (absorption chillers).

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

Technically, those are Platen-Munters Cycle. Different fluids.

Also, the propane part makes them nasty fire hazards. I much prefer 12 VDC fridges, and these days even a small solar panel is enough to run such a fridge, so no need to use propane for that.

a great book or documentary idea would be a different angle on Einstein regarding all his amazing partnerships

I found his partnership with Satyendra Nath Bose one of the most fascinating, when Bose couldn't get his paper published Einstein took it upon himself personally to translate it and get it published for him

(Bose was BRILLIANT, he discovered the Boson particles by mathematical statistics!

https://en.wikipedia.org/wiki/Satyendra_Nath_Bose#Bose%E2%80... )

I linked to this same article a few years ago, although the original URL is now broken.

https://news.ycombinator.com/item?id=38616289

Hmm. Would a refrigerator built like this be silent?

There is no compressor. No moving parts. The only thing that I personally heard was heater relay clicking (that was 70s tech) and some intermittent bubbling.

Then maybe I'd pay a small premium for this tech.

... and I'd love if hotels did.

History can be so weird (and funny).

Was there also an Oppenheimer-Bohr outdoor grill?

I can't pop outside to check, I'm too busy filling Russel's Teapot from this von Neumann Kettle.

I love learning that the “Einstein-Szilard Letter”, perhaps the most important letter written in the history of the world, was predated by the Einstein-Szilard Refrigerator.

I didn’t know that they had had a long relationship before that.

I believe these types of refrigerators are used on RVs and camper vans

they use either a propane flame and/or an electric heating element.

Many Amish/Anabaptists use them, too: no electricity needed.

Seems a bit hypocritical though: Yes, operating one does not need electricity, but I don't see how you'd build one (or just produce the required quantities of butane and ammonia) without modern industrial equipment and electricity.

Many Amish will ride in your car if you’re going into town, as one example. Similar to Sabbath-keeping Jews are allowed to have Gentiles do $TASK (not recalling offhand what that might be). Regardless, to think it hypocritical is to perhaps misunderstand the reasoning, in the case of the Amish. As I understand it, it’s not avoidance of technology, but avoidance of relying on technology. Thus opportunistic car rides in the neighbor’s car, or using a fridge someone else built as long as it runs on propane (which isn’t extracted with horses and buggies, either).

Anyway, I don’t speak for any Amish, but I have lived around them and take that FWIW.

Now imagine now this being used in a liquid-cooled computer with no moving parts. Any takers?

The only moving part right now is the fan. That's needed because even a small amount of forced air flow greatly reduces the size of radiating fins needed to transfer heat from the system to the outside. Any compact fridge also needs a fan.

The computer needs to be cooled, but not below ambient temperature. The latter is where refrigeration enters the picture.

Any compact fridge also needs a fan.

I seem to recall that the absorption fridge in our old VW camper had a fan w/thermostat on the heat sink on the back of the fridge. A common mod was to put a bigger fan on it to improve efficiency. (W/o looking it up, it might not have had an OEM fan, and the mod was to add one, details are fuzzy.)

So, depending on circumstances, the fridge might not be completely silent.

(2020)

"It isn’t possible to know what Einstein and Szilard might have accomplished, had their professional and personal lives not been interrupted."

Is it just me?

I am a bot, so says Cloudflare. What does the article say?

Perhaps this archive.org snapshot will work for ye?

https://web.archive.org/web/20250329043544/https://invention...

Interestingly all of the snapshots newer than this one appear to be blocked by cloudflare as well :P

That's not a good sign. Have you checked that you're not a robot?

I liked this short movie on the theme: https://www.youtube.com/watch?v=4VrLQXR7mKU

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