[ChuckMcM]

Okay I think we're saying the same thing, but let me check that..

> This can be done by storing energy in the material itself (that's how desiccants work)

This is exactly where the energy goes. From the paper (in it's Materials and Methods section) -- All measurements were performed at 20° ± 0.2°C maintained by an air circulation system unless otherwise noted. The temperature of the films was controlled using a heating/cooling unit (THMS350V, Linkam Scientific Instruments, Salfords, UK) when necessary.

So the hypothesis is that the heat in the water vapor goes into the nano-pore material, which in their experiment they were actively maintaining at 20 degrees C. So yes, they are actively removing the heat created by the phase change.

One difference with desiccants is that once they are saturated you have to restore them through heating them up, but this stuff doesn't have that property. And while it may sound like nonsense it was reproduced in another lab[1].

Apparently capillary condensation is a thing, its the popping out of the liquid water that was unexpected.

[1] With a material that could potentially defy the laws of physics on their hands, Lee and Patel sent their design off to a collaborator to see if their results were replicable.

[gus_massa]

>>>> consider a 'cube' of fins of this stuff sitting in shade with a collection bucket underneath it.

There is no cube. The droplet's are attached strongly to the surface.

If the droplets drop to a cube, you can replace the cube with a cotton mat and let the water evaporate and get a low temperature mat. And then use the difference of temperature to generate electricity https://en.wikipedia.org/wiki/Thermoelectric_generator and turn on a lamp. And now you are breaking the second law of thermodynamics.

Consider a typical unplugged dehumidifier with Calcium Chloride. It generates water that drops to a cube, but it's salt water that evaporates less than fresh water, so you can't do the trick.

If you use silica gel, the water is trapped inside the material, so there is no cube.

With this new material the droplets are on the surface, but they refuse to fall down.

With an AC you get a cube full fresh water, but it obviously work only while plugged, so there is no magic.

> And while it may sound like nonsense it was reproduced in another lab [1].

They reproduced the visible droplets in the surface of the material. In neither lab they had a cube filing process. The sentence you quoted in [1] is very misleading.

[ChuckMcM]

Okay, I see where we diverge. The 'cube' was something I was thinking about not in the paper. I'll see if I can describe what I was thinking and you can tell me it breaks the rules :-).

You coat a piece of aluminum with nano-pore material and hang it vertically. Air flows over it and droplets appear on its surface (based on the paper). You also hang a frame of vertical wires (unenergized just small diameter wires, kind of like a screen but without the horizontal members) in front of the sheet by 1/2 the droplet's diameter. The wires don't touch the surface, they are suspended 1/2 droplet away.

Now when a droplet forms, it grows and intersects the wire (which is not hydrophobic) Surface tension puts the droplet around the wire and it slides down to the bottom of the wire frame, impacting any other droplets that had formed below it.

The resulting liquid water drops off the bottom of the wire frame into a catch pan below.

If one of these assemblies generates net water production from RH 70% air then an array of then would generate more water.

What am I missing?

[cyberax]

The second law of thermodynamics. It's now trivially easy to create a free energy:

1. Have the drops fall on some surface and let them evaporate. This can happen because the relative humidity is below 100%.

2. This surface will get cooled by the evaporation.

3. Now use that temperature gradient to get free energy!

[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.

[gus_massa]

I agree, but let's try to explain the microdetails of the scenario.

The new material is very hydrophilic, so the water prefer to be attached to it than been vapor.

If the wire is even more hydrophilic then the droplets will jump and collect around the wires, but they will be so attached that they will not fall down from the lower extreme of the wires.

If the wires are not so hydrophilic, the water will prefer to keep attached to the surface, or even the droplets will be smaller to avoid the wires and the collection will stop earlier.

Tweaking smartly the hydrophilic values and separations between the wires and the separation with the surface you may get interesting capillarity effect, but the water will be trapped again.

Anyway, it's difficult to look at all the details, but at the end of the day "The second law of thermodynamics. It's now trivially easy to create a free energy:"

[cyberax]

To add to this, there is a well-known "free energy" device design: have wicks moving water from a lower reservoir to a higher reservoir. Then use it to drive a water wheel.

It sounds good on paper because everybody knows that water can travel up a wick. But of course, if the end of the wick in the upper reservoir is submerged in the water, then water will just as happily travel _down_ the wick. And if the end of the wick is in free air, then water will not drip from it because the same capillary forces prevent it.