[ChuckMcM]

Does hydroelectric power violate the second law of thermodynamics in your opinion? I mean

1. Drops fall from the sky

2. They collect and flow down a river

3. We use that river to generate hydroelectric power to get free energy!

Water vapor, in air, has both thermal and potential energy that under the right conditions can be converted into a more useful form. We agree on that yes?

[cyberax]

No, we don't.

In case of hydroelectric power, there's a temperature gradient, driven by the Sun. Water evaporates in higher temperatures, radiates the heat into space, and falls out as rain.

[ChuckMcM]

This:

"Water evaporates in higher temperatures, radiates the heat into space, and falls out as rain."

The paper says, "Water vapor in the nano-pores radiates its heat into the material and comes out to the surface as liquid water."

So you don't believe that the researchers experiment did what they say it did?

That's fine, typically in science you go and see if you can reproduce it.

So you don't believe that the researchers correctly described what was going on when it did what it did?

That's fine, typically in science you go and propose a way to falsify their hypothesis and test that.

My point was simply, if the researchers were presumptively accurate in their understanding (that's the principle of giving them the benefit of the doubt), then it would imply their material would pull liquid water out of the air below the temperature and conditions in which it would normally precipitate out.

They go to some length in their exposition to describe how they think it does that and where the energy comes from and where it goes. But if you don't believe them, then sure.

[cyberax]

> "Water vapor in the nano-pores radiates its heat into the material and comes out to the surface as liquid water."

Then the _material_ is a store of energy. Once it's exhausted, the condensation will stop.

> So you don't believe that the researchers correctly described what was going on when it did what it did?

The article is very low-quality. They must understand that their work implies the conservation law violations, so there must be some unaccounted source of energy. But they have not attempted to find it.

And it can be as simple as energy from the moving air. Or maybe an electrostatic charge, or something similar.

Once the energy source is identified, they should have calculated the efficiency of their setup, compared to regular dehumidifiers.

[ChuckMcM]

Awesome, that is very helpful.

> Then the _material_ is a store of energy. Once it's exhausted, the condensation will stop.

The paper points out that the sample was surface that maintains a particular temperature (20 degrees C in this case). The water condenses, the material heats up, the thing its sitting on removes that excess heat to maintain the temperature. No violation of CoE or TD.

Without that temperature controller, the material would presumably continue to store the heat, which would make it hotter than the ambient temperature. By how much is, as you point out, something to be characterized.

Thermodynamics says that the heat will equalize, so that excess heat will conduct to the air around it (it's not in a vacuum so it doesn't have to radiate it). That will lower the temperature of the material which will then condense more water and heat up again. My original thought was you could enhance that conduction by putting a heatsink on one side of the material.

The paper states that inside the pores they have managed to create a space that changes the parameters around the vapor carrying capacity of the air which results in the water condensing even though it would not have condensed outside those pores. Then they go on to describe how the effects of hydrophillic and hydrophobic materials, used in conjunction, create spaces near the molecular limit of water molecules and how the forces acting on that water might result in it condensing. When the vapor does condense, the heat goes somewhere, and they assume its going into the material (reasonable assumption in my opinion) and that their temperature controlled platform is then removing it. I found the description of how that water expresses to the surface a bit more "hand wavy" but that they observed liquid water on the surface, and that it is somehow coming from the material they created, seems reasonably well supported.

I think for the purposes of this discussion we're done. I really do appreciate that you are skeptical and feel that some of the more well tested laws of physics are being violated :-). Since we can only go on what they wrote up, I did make the presumption that they too know the laws of physics and have a good faith belief that they are not being violated either. It is one of the things I look for in papers that talk about things like this. Also the journal where they published their paper, Science Advances, is a refereed journal so I would presume that the reviewers were also satisfied they weren't violating any well known laws of physics. Doesn't mean that you should believe what they say, just that it's not obviously wrong.

[gus_massa]

From the research paper:

> When water droplets reach a certain size, the system reaches a steady state. As the volume of voids decreases with increasing ϕPE, the growth and coalescence of water droplets are slowed down.

That does not break the current laws of physics.

Form the press release:

> these films could be integrated into passive water harvesting devices for arid regions

I asume "harvesting" mean we can collect the water and drink it or use to irrigation or something interesting. Not just absorbing it like silica, even if the unusable water is visible.

Passive as using the day-night temperature different to collect water: It has been done.

Passive as a continue stream of running water: It breaks the second law of thermodynamics.