Ethylene carbonate solvent with a sodium iodide salt create a new refrigerator | Hacker News Reader

Ethylene carbonate solvent with a sodium iodide salt create a new refrigerator

techxplore.com

111 pointswglb47 comments

>Though technically, the salt does not melt the ice, its dark color attracts heat, allowing the ice below it to melt, which than allows the salt to mix with the water. And it does not refreeze because the salt dramatically lowers the freezing point of the water.

And this is why your northern car is covered in rust after a few years on the road... you're literally driving through liquid brine for a good 25% of the year.

I am surprised I have any car left to rust thinking of it that way.

Can rusted parts be recycled by reversing the process using energy ?

Yes, I don't know if it's done commercially but the general idea is to heat and melt the rusted parts in a reducing atmosphere.

What can be done commercially for rusted stuff (cars and such) is to apply rust converters that convert the iron oxide layer on the outside into a stable primer so it seals the outside of the metal from oxidizing further.

The problem with that is that there will probably be rust and moisture deeper down underneath the new paint that will continue the rust process, cracking the paint and allowing more water, salt and air in

Molar mass of Iron Fe =55.845 g/mol

Molar mass of Rust Fe2O3 =159.7 g/mol

Rust weighs in around 3x more than bare metal, so that makes this primer one expensive fuel guzzling choice.

That is why I always go to the toilet before driving

Once it’s been converted to primer it’s not rust anymore. Still probably heavier than the metal, but eh. Get a haircut.

More but not three times as much according to your molecular weights (there are two iron atoms in the rust molecules)

Yup. While I failed chemistry, I still remember most relevant stuff.

There are ways to turn rust back to iron, but what you get back is not the original strong steel piece, it is a spongy form of iron that immediately rusts in air.

Can it be smelted into proper iron?

I watch this YouTube channel "Watch Wes Work" which is a dude that runs his own auto repair service in the frozen wasteland that is Illinois. After seeing him work on older rusty vehicles, I have the desire to see one of them get driven into a large pool of Evapo-Rust and left for a week or two.

I'm in Iowa, and every car on the road has rust. Due to that.

I spent 2 months in Foster City during the lockdown at a gig, stuck in a hotel room, driving to a large empty building to do firmware porting on a bench.

One morning I walk out fiddling with my keys, went around the back of my truck and saw a pile of pipes behind it. Wha?

It was the pickup truck parked 2 stalls down from me. Burned during the night. Utterly consumed. No rubber on the rims; just naked metal. The seats were just springs. The license plate a melted blob. The engine on the ground. Broken in half, the cab tilted forward at a crazy angle, the bed tilted back.

Sucks to be that guy! I thought. Then turned to my truck. The left side was melted like a Dali painting, the mirror drooping down, the running boards spilling onto the pavement in strings and puddles. The lights were foamed-up weird sculptures sticking out like alien apendages.

Anyway 6 months later all the parts had arrived and it was repaired and I went back out to drive it home. My baby!

So now I drive a truck that's new on the left side, but a rusted Iowa clunker on the right side. Works for me; I get in the left side so I see that.

Still not feeling the love, California.

can they please ask whether it's silent? The major problem I have with refridgerators is that they are too loud and architects seem to have an obsession with designing single room apartments. It's getting harder and harder to find a cheap apartment that doesn't force you to put your fridge into the same room where you sleep.

This really sucks about Tokyo , nearly every apartment is similar, also heats the room

TECs are silent. Wildly inefficient, but silent.

If you're willing to deal with a chest-fridge built from a freezer it might be acceptable power consumption.

"Tech Ingredients" youtube channel built (https://www.youtube.com/watch?v=YWUhwmmZa7A) and then tested (https://www.youtube.com/watch?v=cw8ipUYodkE) such a thing.

Neat. Little bit frustrating that there was no input measurement. I strongly suspect you'd need very good insulation to make it viable.

Edit: Watched the freezer video. Performance is predictably bad, but not as awful as one would expect. Might actually be a viable daily driver with thick enough insulation or vacuum panels.

I've never had a loud refrigerator. However, my current refrigerator is an inverter refrigerator. It's particularly quiet, and seems to run 24/7 on a single lower power rather than on/off all the time.

The evaporation refrigerator, most commonly powered by natural gas or propane, most commonly seen in RVs and campers, is wholly silent and more reliable and efficient than the common electric compressor variety. It can of course work equally well driven electrically.

That we ended up with compressor refrigerators getting the lion's share of benefit of mass production is a tragic accident of history: General Electric drove refrigeration into homes, and wanted to build electric motors.

My understanding is that absorption refrigerators fell out of favor because compressor refrigerators typically offer five times greater coefficient of performance. They can make sense if you have a good source of waste heat, but electricity is generally cheap in the home

I think that is true - domestic absorption refrigerators were not uncommon in the early 20th century. The development of reliable hermetically sealed compressors, greatly reducing the risk of refrigerant leaks, may have tipped the balance in favor of compression refrigeration.

Interestingly, Albert Einstein and Leo Szilard made a foray into the field, patenting an electromagnetic refrigerator that was not commercially successful.

https://invention.si.edu/einstein-szilard-refrigerator

Update: from a quick look at the patent referenced here, it seems to be a rather conventional heat-driven absorption refrigerator - the plot thickens!

Update 2: The above article is conflating two different inventions. Einstein and Szilard also patented a compression refrigerator driven by a magneto-hydrodynamic pump of their invention, which used an internal liquid metal as its moving part and consequently required no seals to keep the refrigerant from leaking. It was far from being silent, however.

http://www.physics.smu.edu/scalise/P3374fa16/EinsteinSzilard...

> and more reliable and efficient than the common electric compressor variety

They are far less efficient than compressor refrigerators.

It feels like we’re breaking some laws of thermodynamics in that article.

The salts dark color draws in heat to melt ice? Also salt isn’t dark afaik.

How does this thing actually work?

> Their testing showed that their refrigerator was able to maintain a cool temperature and that it was approximately as efficient as refrigerators now on the market.

So apparently it uses the same amount of energy, so no breaking of thermodynamics.

And yeah salt is white or clear, dunno what's up with that statement.

It's not well edited. The dark color they are referring to is asphalt. Salt mixes with water once it melts and lowers the freezing point to prevent refreezing.

This refrigerator appears to use a similar premise of adding salt to (ethylene carbonate in this case) in order to drive an endothermic reaction and draw heat in from the environment. In order to remove the salt to reuse the loop, they are using electrodialysis, so thermodynamics is preserved - that's where energy goes into the system.

> Salt mixes with water once it melts

As I recall, ice has a thin layer on top that mixes with a little of the salt, which lowers the freezing temperature, causing more melting, and so on. You can throw white salt on white snow and it'll still work.

And in the dark of night, no less.

traps/retains heat might have been better

Removing the salt from the water requires energy to be added in externally. Adding the salt back in absorbs that energy back from the environment.

Road salt is often full of minerals or other impurities, making it gray or other colors.

That may be, but pure white salt on white ice will still cause melting.

According to the sources, the salt itself doesn't cause melting.

"When water is mixed with salt the freezing temperature of the solution is lower than 32 F. The salt impedes the ability of the water molecules to form solid ice crystals. It’s important to note that the salt must be in a solution with liquid water in order for this principle to be obeyed. Salt that’s dumped on top of ice relies on the sun or the friction of car tires driving over it to initially melt the ice to a slush that can mix with the salt and then won’t refreeze."

https://www.scientificamerican.com/article/salt-doesnt-melt-...

> The salts dark color draws in heat to melt ice? Also salt isn’t dark afaik.

Yeah, they're flat wrong on that claim. Science figured this one out long ago. You could throw white salt on white snow and it'll still cause it to start melting.

Ah, yes, we all forgot that salt doesn’t work at night.

The whole tie-in with road salt does a very poor job of explaining what is going on in the refrigeration cycle the work described - it's not totally unrelated, but the relationship is not particularly obvious.

The refrigeration cycle works by adding a salt (NaI, or sodium iodide to an ionic solvent, ethylene carbonate). This lowers the melting point of the salt below the temperature of the solvent, and the salt consequently absorbs heat from the solvent in order to overcome it energy of fusion, thus cooling the solvent. The the resulting temperature deficit relative to the environment can be transferred thermally to a cold reservoir. Subsequently, they use electro-dialysis to remove the salt from the "used" solvent, and recrystalize the salt, yielding fresh solvent and salt so the cycle can be repeated.

Relative to what happens with road salt, the salt in the refrigerator is playing the role of the road ice, and the solvent is playing the role of the liquid water with dissolved sodium chloride that forms on the ice when you salt the road. The reason that water forms is because the road salt, which is relatively dark due to impurities, absorbs solar energy melting a thin layer of water, or tire friction on the salt-ice combination does so, or because there is slushy liquid water already present.

Normal refrigeration work by turning a liquid into gas, and gas back into liquid. Doing so heats or cools the medium (one can imagine the molecules inside being more pressed together when in liquid, thus having more energy in a smaller volume of physical space, which translate as being hotter). When turned into a gas the opposite happens with fewer moving molecules in the volume of space.

Going from liquid to solid do not generally causes any changes in volume, but it does releases some energy as part of the conversion process, which if captured could contribute to make both the solid and liquid cooler (less energy among the molecules in the same volume).

With the use of a compressor and a vapor chamber in a fridge you can control when and where the liquid turn to a gas or back into a liquid. The hot place will be near a radiator, and the cold place in a vapor chamber next to the cooling area. With this system the salt would be near the radiator turning the solid into a liquid, heating the radiator. Then you would "remove the salt" in what would be similar to a vapor chamber, turning the medium cold.

The biggest issue I have with this concept is the efficiency. With a compressor you can make a gas really really hot by turning it into a liquid, and that heat will then have a large gradient difference when run through a radiator (which cools it down using ambient air). I am unsure how one would get a similar effect with solid to liquid.

> Also salt isn't dark AFAIK.

Table salt, no - manganese dioxide, yes.

Of course Manganese dioxide is not a salt.

Ah, that's odd - I mixed up with potassium permanganate.

Salt melts ice because of the effect they mention in the next sentence: "And it does not refreeze because the salt dramatically lowers the freezing point of the water." That's the reason it melts in the first place. It's something like: salt comes into contact with ice/snow and diffuses into it, causing it to melt, which then wets out more salt, accelerating the process.

This is because dark intercoolers perform better (not!)

https://www.youtube.com/watch?v=z_mmmXTbLP0

Modern refrigerators often use butane which is not particularly pollutive.

The real exciting thing here is if it can be done cheaply made solid state. Can it be done without moving solid crystals around?

Perhaps the salt crystals are still in the solution, but "suspension" is then moved quickly enough so that the majority of the dissolving process takes place in the area where we want the cooling to happen?

EDIT: the picture makes it look like they create two solutions: one with concentrated salt, and one with water ice sludge. Those are transported separately and then mixed in the cooling tank

I wonder what is the lifetime or how many cycles the electrodialysis part can last. More or less compared to right sized compressor?

So it's about as energy efficient as current refrigerators, but "They acknowledge that it does have one drawback—it takes quite a while for the mixed solution to cool."

Nothing in the available references to say how slow, but "quite a while" doesn't sound promising. Still, maybe a modification of the method could speed it up.

Quite a while might not be such a bad thing depending on the cooler design. Typical chest-style coolers are far more efficient than your standing refrigerator units, because cool air doesn't escape nearly as much when you open the lid since cool air tends to sink. If it needs time to recharge its cooling cycle, in such a cooler design, this may not be a concern because the cooler holds a lower temperature for longer.

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