7 ms·

Repost from four days ago: https://news.ycombinator.com/item?id=44060712 https://news.ycombinator.com/item?id=44060712 Also, they do a really good job of makin

Repost from four days ago: https://news.ycombinator.com/item?id=44060712 https://news.ycombinator.com/item?id=44060712 Also, they do a really good job of making it sound like it violates thermodynamics. Since it doesn't, and dehumidifiers already do a good job of getting water out of air for the energy price you have to pay, there has to be some other selling point. Right? But I'm not sure I see it.

bayindirh 1y ago
> there has to be some other selling point. Right? But I'm not sure I see it. Windtraps [0]. [0]: https://dune.fandom.com/wiki/Windtrap https://dune.fandom.com/wiki/Windtrap
- detourdog 1y ago
  or moisture vaporators https://starwars.fandom.com/wiki/Moisture_vaporator https://starwars.fandom.com/wiki/Moisture_vaporator
  - moffkalast 1y ago
    But moisture farming? Really? A man of your talents?
- simiones 1y ago
  Those exist, but, as the GP points out, they're called "dehumidifiers". Or sometimes clothes driers. The question was, what makes this new dehumidifier any better than existing dehumidifiers.
  - bayindirh 1y ago
    Windtraps are passive, like this material. They work solely on temperature differential and wind. I'm not aware of any passive, solid state dehumidifiers which are not chemical, which condense water to a chemically loaded solution, which what a Windtrap is not.
    - simiones 1y ago
      There is no way to make a passive, solid-state humidifier that doesn't involve some chemical reaction with water. Thermodynamics dictates that precipitating water from a non-saturated atmosphere must generate large amounts of heat (assuming pressure doesn't change) and so can't be a self-sustaining process. So, even though it may not be 100% clear how from their description, their device is nothing but a novel way of making a dehumidifier that needs some kind of active component - perhaps the AC that is keeping the temperature steady in their experiment (since water condensation generates large amounts of heat, it's likely that, without the AC, temperature would rise and their water droplets would evaporate right back).
      - bayindirh 1y ago
        > There is no way. No, there's a way without running afoul of thermodynamics. You need to bleed the heat to a cooler surface efficiently, and you can do it without any external power. You can use heat pipes to effectively wick away heat to a heat sink, like the Earth itself. Similar systems exists for cooling and heating, which uses buried pipes to extract or dump heat to the Earth's crust. You can sink the heat similarly without any external power (sans wind to push air through the material). In the Windtrap example, the other side of the opening is a deep well basically. Cooler than outside world. The rocks sink the heat probably, too. Sı it's possible to create self-sustaining process without external electricity. Yes, an heat-pipe is not solid-state per se, but it's insulated and works on the principle of heat difference only. > their device is nothing but a novel way of making a dehumidifier that needs some kind of active component... No, their paper say that they forced air through it and it worked on a temperature differential. Maybe a compressor or Peltier device can acclerate the process, sure, but sinking the heat to the earth and blowing air through it will work equally well. Have a friend who designs heat-pipes for space applications. That things are way faster than we see on computer applications, but equally more expensive.
        simiones 1y ago
        None of this matches the setup the paper describes, though of course you are right that bleeding heat into the Earth is a time-tested and known to function way to build such systems.
  - detourdog 1y ago
    This would be passive and solid state.
    - simiones 1y ago
      Except we know that is impossible from simple thermodynamics, so there's no point in contemplating this "what if".
      - detourdog 1y ago
        Have you done any work with this material?
        simiones 1y ago
        No, but I don't need to work on a perpetual motion machine to know that it doesn't work.
        detourdog 1y ago
        My question would be do you have enough experience to know that it is a perpetual motion machine. I read the article and nothing sounds like perpetual motion to me. The atmosphere is always dynamic and my reading of the article was that it is using 2 different changes to harness these changes. Surface tension and atmospheric pressure seem to be the mechanisms. I was trying to figure out if your comment was informed.
crazygringo 1y ago
> dehumidifiers already do a good job of getting water out of air for the energy price you have to pay They do a terrible job. Condensate dehumidifiers are as expensive to run as an AC, produce unwanted heat, and are noisy. Dessicant dehumidifiers are even less energy-efficient. If there's a way to extract moisture from the air with less energy and less noise, that would be huge.
- simiones 1y ago
  So, is this new method less noisy and/or more energy efficient? The article doesn't really say.
  - thfuran 1y ago
    >without the need for any external energy. That sure seems to imply that there's no need for a noisy and power hungry compressor.
    - vintermann 1y ago
      It also seems to imply that it violates thermodynamics. It takes energy to condense water, so where does it get it? If it isn't external, it runs out.
      - freeone3000 1y ago
        Condensation of water is exothermic. If you add a cold thing to the environment, ie, remove heat from the water, the water will condense all on its own. This reaches steady-state when the cold thing is warm and the water is condensed. No thermodynamics issue! They’re claiming they have a material that will do it at higher temperatures. Assuming such a material gets hotter as it works, there’s no thermodynamics problem here.
        nssnsjsjsjs 1y ago
        What about entropy? The reason you need to power AC for example is that if you didn't you could reduce entropy and generate power for free, and basically reverse time.
jcims 1y ago
It almost certainly doesn't violate our understanding of thermodynamics, but it's not clear that it would have to in order to condense ambient water vapor from the atmosphere. From the paper [1]: Remarkably, when these amphiphilic nanoporous PINFs are exposed to high yet subsaturating conditions [i.e., relative humidity (RH) < 100%], macroscopic water droplets appear spontaneously on the film surfaces without the need for cooling, as illustrated in Fig. 1C and shown in Fig. 1D. 1 - https://www.science.org/doi/10.1126/sciadv.adu8349 https://www.science.org/doi/10.1126/sciadv.adu8349
- BenjiWiebe 1y ago
  Well, when water changes from vapor to liquid, it releases heat. The heat has to go somewhere. Sorry, I don't know the correct physics lingo. Heat of enthalpy or formation or whatever.
  - chasd00 1y ago
    Tangent but this may solve a mystery of mine. When I make scrambled eggs I add a little bit of water to make them fluffy. When I turn off the heat there’s a puff of steam I can’t explain. Since it seems to me more heat is needed to produce that extra puff of steam. However, maybe the fast condensing of the water vapor that happens when I turn off the stove produces a. I start of extra heat and therefore the steam?
    - abracadaniel 1y ago
      Maybe the drop in temp stops a Leidenfrost effect that was reducing the surface area of the food that was contacting the pan.
    - jcims 1y ago
      Is it gas stovetop? If so, it could be that the water vapor coming from the eggs no longer mixing with the hot gases coming from the flame around the pan, allowing it to drop below the dew temp (?) and allowing it to condense right above the pan. IOW the water vapor is always there, you just can't see it until it is able to condense in lower ambient temps.
scotty79 1y ago
The idea here is that you don't need to cool down the air to get water. First you get water, and as a result material heats up a little bit, then it can cool down passively back to ambient.
dang 1y ago
> Repost from four days ago Thanks! there were a few comments there and we'll merge them hither.

bayindirh 1y ago

> there has to be some other selling point. Right? But I'm not sure I see it. Windtraps [0]. [0]: https://dune.fandom.com/wiki/Windtrap https://dune.fandom.com/wiki/Windtrap

detourdog 1y ago
or moisture vaporators https://starwars.fandom.com/wiki/Moisture_vaporator https://starwars.fandom.com/wiki/Moisture_vaporator
- moffkalast 1y ago
  But moisture farming? Really? A man of your talents?
simiones 1y ago
Those exist, but, as the GP points out, they're called "dehumidifiers". Or sometimes clothes driers. The question was, what makes this new dehumidifier any better than existing dehumidifiers.
- bayindirh 1y ago
  Windtraps are passive, like this material. They work solely on temperature differential and wind. I'm not aware of any passive, solid state dehumidifiers which are not chemical, which condense water to a chemically loaded solution, which what a Windtrap is not.
  - simiones 1y ago
    There is no way to make a passive, solid-state humidifier that doesn't involve some chemical reaction with water. Thermodynamics dictates that precipitating water from a non-saturated atmosphere must generate large amounts of heat (assuming pressure doesn't change) and so can't be a self-sustaining process. So, even though it may not be 100% clear how from their description, their device is nothing but a novel way of making a dehumidifier that needs some kind of active component - perhaps the AC that is keeping the temperature steady in their experiment (since water condensation generates large amounts of heat, it's likely that, without the AC, temperature would rise and their water droplets would evaporate right back).
    - bayindirh 1y ago
      > There is no way. No, there's a way without running afoul of thermodynamics. You need to bleed the heat to a cooler surface efficiently, and you can do it without any external power. You can use heat pipes to effectively wick away heat to a heat sink, like the Earth itself. Similar systems exists for cooling and heating, which uses buried pipes to extract or dump heat to the Earth's crust. You can sink the heat similarly without any external power (sans wind to push air through the material). In the Windtrap example, the other side of the opening is a deep well basically. Cooler than outside world. The rocks sink the heat probably, too. Sı it's possible to create self-sustaining process without external electricity. Yes, an heat-pipe is not solid-state per se, but it's insulated and works on the principle of heat difference only. > their device is nothing but a novel way of making a dehumidifier that needs some kind of active component... No, their paper say that they forced air through it and it worked on a temperature differential. Maybe a compressor or Peltier device can acclerate the process, sure, but sinking the heat to the earth and blowing air through it will work equally well. Have a friend who designs heat-pipes for space applications. That things are way faster than we see on computer applications, but equally more expensive.
      - simiones 1y ago
        None of this matches the setup the paper describes, though of course you are right that bleeding heat into the Earth is a time-tested and known to function way to build such systems.
- detourdog 1y ago
  This would be passive and solid state.
  - simiones 1y ago
    Except we know that is impossible from simple thermodynamics, so there's no point in contemplating this "what if".
    - detourdog 1y ago
      Have you done any work with this material?
      - simiones 1y ago
        No, but I don't need to work on a perpetual motion machine to know that it doesn't work.
        detourdog 1y ago
        My question would be do you have enough experience to know that it is a perpetual motion machine. I read the article and nothing sounds like perpetual motion to me. The atmosphere is always dynamic and my reading of the article was that it is using 2 different changes to harness these changes. Surface tension and atmospheric pressure seem to be the mechanisms. I was trying to figure out if your comment was informed.

crazygringo 1y ago

> dehumidifiers already do a good job of getting water out of air for the energy price you have to pay They do a terrible job. Condensate dehumidifiers are as expensive to run as an AC, produce unwanted heat, and are noisy. Dessicant dehumidifiers are even less energy-efficient. If there's a way to extract moisture from the air with less energy and less noise, that would be huge.

simiones 1y ago
So, is this new method less noisy and/or more energy efficient? The article doesn't really say.
- thfuran 1y ago
  >without the need for any external energy. That sure seems to imply that there's no need for a noisy and power hungry compressor.
  - vintermann 1y ago
    It also seems to imply that it violates thermodynamics. It takes energy to condense water, so where does it get it? If it isn't external, it runs out.
    - freeone3000 1y ago
      Condensation of water is exothermic. If you add a cold thing to the environment, ie, remove heat from the water, the water will condense all on its own. This reaches steady-state when the cold thing is warm and the water is condensed. No thermodynamics issue! They’re claiming they have a material that will do it at higher temperatures. Assuming such a material gets hotter as it works, there’s no thermodynamics problem here.
      - nssnsjsjsjs 1y ago
        What about entropy? The reason you need to power AC for example is that if you didn't you could reduce entropy and generate power for free, and basically reverse time.

jcims 1y ago

It almost certainly doesn't violate our understanding of thermodynamics, but it's not clear that it would have to in order to condense ambient water vapor from the atmosphere. From the paper [1]: Remarkably, when these amphiphilic nanoporous PINFs are exposed to high yet subsaturating conditions [i.e., relative humidity (RH) < 100%], macroscopic water droplets appear spontaneously on the film surfaces without the need for cooling, as illustrated in Fig. 1C and shown in Fig. 1D. 1 - https://www.science.org/doi/10.1126/sciadv.adu8349 https://www.science.org/doi/10.1126/sciadv.adu8349

BenjiWiebe 1y ago
Well, when water changes from vapor to liquid, it releases heat. The heat has to go somewhere. Sorry, I don't know the correct physics lingo. Heat of enthalpy or formation or whatever.
- chasd00 1y ago
  Tangent but this may solve a mystery of mine. When I make scrambled eggs I add a little bit of water to make them fluffy. When I turn off the heat there’s a puff of steam I can’t explain. Since it seems to me more heat is needed to produce that extra puff of steam. However, maybe the fast condensing of the water vapor that happens when I turn off the stove produces a. I start of extra heat and therefore the steam?
  - abracadaniel 1y ago
    Maybe the drop in temp stops a Leidenfrost effect that was reducing the surface area of the food that was contacting the pan.
  - jcims 1y ago
    Is it gas stovetop? If so, it could be that the water vapor coming from the eggs no longer mixing with the hot gases coming from the flame around the pan, allowing it to drop below the dew temp (?) and allowing it to condense right above the pan. IOW the water vapor is always there, you just can't see it until it is able to condense in lower ambient temps.

scotty79 1y ago

The idea here is that you don't need to cool down the air to get water. First you get water, and as a result material heats up a little bit, then it can cool down passively back to ambient.

dang 1y ago

> Repost from four days ago Thanks! there were a few comments there and we'll merge them hither.