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
