Solar stills made with tubes for sea water desalting Original Research Article

The report concerns basic technological features of simple solar stills utilizing tubes for sea water desalting. The evaporation section comprises horizontal transparent thin-walled plastic or glass tubes, of ~0.10–0.25 m inner diameter, half-filled with sea water which absorbs solar radiation. The condensation section is physically separated from the evaporation section, in a shaded space below it, and comprises horizontal plastic or metal tubes of ~0.01 m inner diameter. The wall thickness of condenser plastic tubes is rather small, ~50 μm. Water vapour released by solar radiation in evaporator tubes flows into condenser tubes to be condensed into produced fresh water by delivering condensation latent heat to atmospheric air. Heat transfer by air convection may be helped by surface winds, often available in coastal areas. Enhanced fresh water productivity is expected with respect to conventional solar stills in which sea water evaporation and water vapour condensation occur in one confined space. Technological features of the proposed solar stills are analysed in some detail and specific experimental work is suggested on prototype solar stills in view of clarifying relevant aspects concerning transparent and opaque construction materials, assembling procedures, and the role of the The use of solar energy in thermal desalination processes is one of the most promising applications of the renewable energies. Solar desalination can either be direct; use solar energy to produce distillate directly in the solar collector, or indirect; combining conventional desalination techniques, such as multistage flash desalination (MSF), vapor compression (VC), reverse osmosis (RO), membrane distillation (MD) and electrodialysis, with solar collectors for heat generation. Direct solar desalination compared with the indirect technologies requires large land areas and has a relatively low productivity. It is however competitive to the indirect desalination plants in small-scale production due to its relatively low cost and simplicity. This paper describes several desalination technologies in commercial and pilot stages of development. The primary focus is on those technologies suitable for use in remote areas, especially those which could be integrated into solar thermal energy systems. operative parameters vis-à-vis energy efficiency and fresh water productivity.