About that Global Shortage of Drinking Water

[an seanduine]

Chunlei Guo´s lab at the University of Rochester has come up with a novel use for aluminum plates to cheaply purify water with solar energy.
https://www.nature.com/articles/s41893- ... 6-x#citeas
More about Chunlei Guo here: http://www2.optics.rochester.edu/workgr ... about.html

While cheap drinking water is important, this may also lead to cheaper solar hot water.

Bob

[Nanohedron]

Got anything about it couched in layman's terms?

[an seanduine]

They took aluminum plates : https://images.dailykos.com/images/8319 ... 1594791427
Then they micro-etched them with bursts of green laser energy (similar to Lasix Surgery Lasers) : https://images.dailykos.com/images/8319 ... 1594791097
This produced microgrooves with rough interiors that act as open capillaries: https://images.dailykos.com/images/8319 ... 1594792928
These capillaries wick water up themselves very quickly. How fast? Very fast: https://images.dailykos.com/images/8319 ... 1594793459
This etching turns the bright aluminum into a jet-black super absorber of light energy across a broad spectra of radiant energy: https://images.dailykos.com/images/8319 ... 1594793632
This is a schematic of such a plate turning wicked polluted water into steam, to be condensed into essentially drinkable water:
https://images.dailykos.com/images/8319 ... 1594794961

This is the ´speed´ version in a nutshell.

Bob

[an seanduine]

The ´Nature´ abstract details further astounding findings with copious formulae, calculations, and numbers. The ´Speed´ version of this is roughly as follows:
The Aluminum plate is transformed into a remarkably efficient radiant energy absorber. First they measured the capacity of the plate to wick water, and then essentially evaporate water molecules at ambient (room) temperature. Fairly efficient. . .much better than expected. Then they measured the plate´s ability to evaporate water when radiant energy was applied. Extremely surprising. A side effect of the micro-capillary wicking was that water was evaporated as clusters of water molecules, not just single molecules.
They then measured the efficiency of their setup against heat losses from the plate which would result in heating up the polluted water. It didn´t heat up. Nearly all the radiant energy was used to evaporate the wicked water. Because the angle of the plate has no effect on the wicking action, the plate can be oriented to track the sun and give extremely long hours of effective service at extreme latitudes.
The evaporation effectively separated water from heavy metals, dyes, and various petrochemicals. The end result is potable water.
An added benefit was found that the capillary grooves, being ´open capillaries´ did not clog as ´closed micro-capillaries´ have done in earlier tests. This very much reduces maintenance and is extremely important in Third-World applications.

Bob

[david_h]

It seems to be a big increase in efficiency.

But - and sorry for the negative tone - is it enough move solar stills from 'survival aids' to being a practical, cost-effective source of clean water for people in the developing world? In round numbers we are talking about 3 litres/person/day just to sustain life. Minimum targets for clean water, for basic hygiene as well as drinking, start at about 15 litres/person/day. It has to cost less than a walk to a clean source. In many places people's own labour is cheap, what they don't have is money.

[an seanduine]

It seems to be a big increase in efficiency.

But - and sorry for the negative tone - is it enough move solar stills from 'survival aids' to being a practical, cost-effective source of clean water for people in the developing world? In round numbers we are talking about 3 litres/person/day just to sustain life. Minimum targets for clean water, for basic hygiene as well as drinking, start at about 15 litres/person/day. It has to cost less than a walk to a clean source. In many places people's own labour is cheap, what they don't have is money.

It is good to be critical, but. . .

Several points:

The test apparatus closely tracks the efficiency of a a theoretically perfect system. The test apparatus produced 5-7 ml purified water over a 7 hour period using a surface 20mm square. Scaling this up does not introduce loss of efficiency (one of the remarkable things about this setup).

This infrastructure has very little maintenance cost. After initial cost, you have a source of clean water, free of biological and chemical contaminants. You can recycle both black and grey water.

In many parts of the Sub-Sahara it takes between 2 to 4 man hours per day to procure potable water for a family of 4. This is a tremendous drain on productivity. Maintenance of a system scaled to provide the same amount of water would take between 15 minutes to one half hour per day. Rinsing away accumulated salts in the wicking capillaries.

The test apparatus demonstrates efficiency well beyond that of solar electric systems. Granted electricity is not water, but this speaks well for its place in a third world economy. Further, this technology doesn´t appear to have degradation over time that solar cells have, making the ROI very favorable.

Just as a side note, not only is the manpower saved to procure water, but the purity and healthy nature of the water from this source is assured.

I´m looking forward to the development of this novel technology.

Bob

[PB+J]

Fantastic if it actually works as described. I'm skeptical about the clogging, but it looks like a great idea

[Nanohedron]

Just as a side note, not only is the manpower saved to procure water, but the purity and healthy nature of the water from this source is assured.

Does this include eliminating toxic elements like arsenic?

[an seanduine]

To expand on several points, in non-technical language. This method shows several results that have to be explained. The rate of evaporation is massively greater than that of simple surface evaporation. A square meter of water surface receiving a known quantity of solar radiation has a predictable rate of evaporation. This system greatly exceeds that. There are several theoretical explanations. If you look at the detail photo of the nano-capillaries, their interior is pitted and quite irregular, greatly increasing the surface available for evaporation. Looking at one of the videos, that is steam coming off that 20mm square plate.
The ´blackness´ of the etched plate allows the absorption of radiant spectra well outside the absorption range of a simple water surface. Yet, the surface temperature of the plate isn´t elevated.

Bob

[Nanohedron]

Sorcery.

[an seanduine]

Just as a side note, not only is the manpower saved to procure water, but the purity and healthy nature of the water from this source is assured.

Does this include eliminating toxic elements like arsenic?

Yes.

Bob

[an seanduine]

Sorcery.

I´m reminded of the film ¨The Gods Must Be Crazy!.

Bob

[Nanohedron]

Just as a side note, not only is the manpower saved to procure water, but the purity and healthy nature of the water from this source is assured.

Does this include eliminating toxic elements like arsenic?

Yes.

It's looking compellingly good, isn't it. What, if any, are the projected production and application cost estimates should this thing get rolling?

[an seanduine]

Nano: Quote ¨What, if any are the projected. . .costs?¨

¨Once the rockets are up, who cares where they come down. That´s not my department,¨ says Werner von Braun.

Bob

[Nanohedron]

Nano: Quote ¨What, if any are the projected. . .costs?¨

¨Once the rockets are up, who cares where they come down. That´s not my department,¨ says Werner von Braun.

Bob

I guess what I'm saying is that if third world populations can readily get this technology at an exchange rate that doesn't pose a hardship (I have no idea if it's a realistic or even viable example, but on a sliding scale let's say that in an impoverished community, a comparatively well-off household could spare a couple of chickens to get started), this would be an ideal scenario on the humanitarian end. On the business end, though, someone still has to get their beak wet. It's the tension between the two that I'm wondering about, because this could prove a real boon for humankind IF it's affordable to all in some way.

But it further occurs to me that pure water, if it's essentially the same as distilled, isn't good either. We still require some mineral content in our drinking water, because IIRC distilled water pulls essential minerals out of our bodies, and this can pose health problems if continued long-term.

This isn't to knock down the idea, because it's a really important one if it succeeds. But there's going to have to be more to it than having the purified water as-is, if what's used for drinking is to be truly beneficial to life.