Experimental study of a solar water desalinizer with displacement-storage elements

On our planet, despite the fact that 70 % of the Earth's surface is covered with water, fresh water accounts for only 2,5 % of the total water volume, while 97,5 % is composed of mineralized seawater. While it is not possible to directly use seawater for drinking, agricultural, or industrial purposes, there are numerous countries that rely on seawater after the desalination process as a source of drinking water. The global average daily production of drinking water through traditional desalination processes is estimated to be 23 · 10⁶ m³. This process requires a large amount of fossil fuel. It is estimated that it takes about 10 million tons of oil to produce 1 million cubic meters of drinking water per day, which leads to additional carbonization of the atmosphere and contributes to the greenhouse effect and subsequent climate change.

The energy and desalination systems of the future must be economical, reliable and safe, ensuring maximum continuity of energy supply to consumers in all regions, especially in remote and rural areas. This can be achieved by developing energy systems based on renewable, primarily solar energy sources.

Currently, the most widespread, mass type of solar desalination plants in developing countries remain single-sloped solar desalination plants with direct heating of water by sunlight, which have the greatest availability due to the minimum cost of construction.

However, the freshwater production of traditional evaporative solar desalination systems is low, and even in countries with high levels of solar insolation, it does not exceed 2-3 liters per square meter per day, which is largely due to the high transparency of water (low blackbody coefficient) for photons in the solar spectrum.

In order to improve the efficiency of solar desalination systems, scientific research and engineering development of new principles and designs for solar desalination plants based on the use of heat carriers with nanoparticle additives, reverse osmosis systems, solar orientation systems, rotational and film methods for intensifying evaporation, and the use of hybrid systems, including those using heat generated by nuclear reactors, are being conducted. It is clear that such improvements and increased productivity of solar desalination plants lead to a significant increase in their cost and reduce the availability of desalinated water for millions of people in Africa and the Middle East.

This study proposes a method for increasing the productivity of a solar distiller for producing fresh water by converting the optical interaction of sunlight photons with the evaporating water into increased photon energy assimilation and increased "effective blackness" of the evaporation basin by placing black Ural stones (dunite) in it as photon energy absorbers and accumulators, which can significantly increase the temperature and evaporation rate of the water without significantly increasing the cost of the installation.

In the same climatic conditions, three solar desalination systems were studied: a traditional single-sloped solar distiller (TSD), a distiller with 10 kg of stones added (TSD-10), and a distiller with 20 kg of stones added (TSD-20). With a constant water level, adding stones reduced the mass of water in the pool and increased the «effective blackness» of the evaporation pool, significantly increasing the desalination capacity. The total daily volume of desalinated water was 3 L/m² for a traditional single-sloped solar distiller (TSD), 6 L/m² for a distiller with 10 kg of stones (TSDK-10), and 12 L/m² for a distiller with 20 kg of stones (TSDK-20).

 Reducing the volume of water and increasing the «effective blackness» of the evaporation basin significantly improves the efficiency of the solar distiller with minimal design changes and increased installation costs.

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