Good Thinking

New solar still uses a rotating cylinder to produce more potable water

New solar still uses a rotatin...
Research engineer Alharbawi Naseer Tawfiq Alwan works with the prototype solar still
Research engineer Alharbawi Naseer Tawfiq Alwan works with the prototype solar still
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Research engineer Alharbawi Naseer Tawfiq Alwan works with the prototype solar still
Research engineer Alharbawi Naseer Tawfiq Alwan works with the prototype solar still

In many arid regions, people use devices known as solar stills to extract drinkable water from seawater or tainted water. A new type of solar still is claimed to be much more effective than others, by incorporating a rotating cylinder.

In its most basic form, a conventional solar still consists of a basin of undrinkable water that is set beneath a transparent cover. The water evaporates as it's heated by the sun, condensing on the inside surface of the cover. That condensation – which is pure, clean water – trickles down the cover and is collected in a separate receptacle for drinking.

It's a clever setup, but it also takes some time to produce significant amounts of potable water. In an effort to speed the process up, scientists at Russia's Ural Federal University have developed an experimental new solar still that incorporates a rectangular basin (with a hinged transparent cover), inside of which is a horizontally oriented black steel cylinder.

The basin is filled with undrinkable water, and the cylinder is slowly rotated by a solar-powered DC motor. As the hollow cylinder turns, a thin film of water is continuously formed on its surface. Because that film is so thin, the water that composes it heats up and evaporates much quicker than it would if it were just sitting in the deeper and cooler basin.

As with a traditional solar still, the resulting condensation subsequently runs down the inside of the cover into an aluminum trough, which in turn channels it into a separate vessel.

Because the cylinder does shade the tainted water in the basin, that water is continuously circulated through an external solar collector by a solar-powered pump. This helps keep the water hot, so that it more readily evaporates.

A prototype was tested on a rooftop in the Russian city of Ekaterinburg from June through October of 2019, with its cylinder turning at a rate of 0.5 rpm. As compared to a conventional solar still, the device was found to be 280 percent more effective at producing drinking water during the warmer months of June, July and August, and 300 to 400 percent more effective in September and October.

The scientists are now working on making the technology even more effective, and on minimizing its production costs.

A paper on the study, which also involved researchers from Iraq's Northern Technical University, was recently published in the journal Case Studies in Thermal Engineering.

Source: Ural Federal University

Heating a small amount of water to evaporation makes a lot of sense. The cylinder seems a bulky way to do it and at least half of it is unusable all the time, since the back is not in the sun.

Maybe some kind of pan the size of the cylinder cross section mounted on a hinge that oscillated between immersion in the water and perpendicular to the sun would perform even better. It could be driven with a windshield wiper motor, cheap and available everywhere in the world.

In any case this looks like a great idea.
Excellent use of existing technology. No microprocessors to program just 90s technology. Hope to see this commercialized soon.
Bill Fortune
ThorCon's molten salt reactor produces a lot of high temperature heat which coupled with other technologies can produce a lot of potable water. The MSR uses spent nuclear fuel so the fuel is almost free.
It seems that people make the systems more complicated than needs be. They have installed an electric motor to turn a large drum as well as a water pump.

there are numerous ways to improve this and in fact get rid of the rotating drum that would make it far cheaper to manufacture, setup and improve efficiency much further.

I am always surprised how people ignore Object-Oriented approached to engineering solutions as well as the well-known TRIZ methodology.
It would be interesting to know how the device copes with the build-up of salts and/or other contaminants which must inevitably occur.
What isn't said is 4x not much is still not much. Run it though sand then living biomass and the output will be 50x more at less cost. Add a little chlorine, etc and you are ready to drink.