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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

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?

u320 4y ago
> 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.
arrosenberg 4y ago
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.
- rootusrootus 4y ago
  > 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.
  - greenbit 4y ago
    And in the dark of night, no less.
- selimthegrim 4y ago
  traps/retains heat might have been better
thehappypm 4y ago
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.
gcanyon 4y ago
Road salt is often full of minerals or other impurities, making it gray or other colors.
- happyopossum 4y ago
  That may be, but pure white salt on white ice will still cause melting.
  - gcanyon 4y ago
    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-ice-heres-how-it-makes-winter-streets-safer/ https://www.scientificamerican.com/article/salt-doesnt-melt-...
rootusrootus 4y ago
> 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.
- semireg 4y ago
  Ah, yes, we all forgot that salt doesn’t work at night.
walnutclosefarm 4y ago
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.
belorn 4y ago
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.
e12e 4y ago
> Also salt isn't dark AFAIK. Table salt, no - manganese dioxide, yes.
- zafka 4y ago
  Of course Manganese dioxide is not a salt.
  - e12e 4y ago
    Ah, that's odd - I mixed up with potassium permanganate.
kazinator 4y ago
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.
1970-01-01 4y ago
This is because dark intercoolers perform better (not!) https://www.youtube.com/watch?v=z_mmmXTbLP0 https://www.youtube.com/watch?v=z_mmmXTbLP0

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?

u320 4y ago

> 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.

arrosenberg 4y ago

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.

rootusrootus 4y ago
> 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.
- greenbit 4y ago
  And in the dark of night, no less.
selimthegrim 4y ago
traps/retains heat might have been better

thehappypm 4y ago

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.

gcanyon 4y ago

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

happyopossum 4y ago
That may be, but pure white salt on white ice will still cause melting.
- gcanyon 4y ago
  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-ice-heres-how-it-makes-winter-streets-safer/ https://www.scientificamerican.com/article/salt-doesnt-melt-...

rootusrootus 4y ago

> 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.

semireg 4y ago
Ah, yes, we all forgot that salt doesn’t work at night.

walnutclosefarm 4y ago

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.

belorn 4y ago

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.

e12e 4y ago

> Also salt isn't dark AFAIK. Table salt, no - manganese dioxide, yes.

zafka 4y ago
Of course Manganese dioxide is not a salt.
- e12e 4y ago
  Ah, that's odd - I mixed up with potassium permanganate.

kazinator 4y ago

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.

1970-01-01 4y ago

This is because dark intercoolers perform better (not!) https://www.youtube.com/watch?v=z_mmmXTbLP0 https://www.youtube.com/watch?v=z_mmmXTbLP0