Solar Water Purifier
The Solar Water Purifier is a rectangular shaped unit that contains an array of 32 shallow, square trays interconnected by a series of weaves. The trays are made from a black plastic sheet that is vacuum formed onto an aluminium pattern to reach the desired cell shapes.
The panel of cells is covered by a sheet of white-glass and sealed using the surface tensions of water vapour produced in the unit. The undersides of the black plastic trays have been thermally insulated to maximise heat absorption. The unit is framed by an aluminium mount for strength and to keep shadowing to a minimum. It is also fitted with folding legs, so that the entire system is inclined at 12.5 to the horizontal.
Polluted water is fed into the unit and cascades down, filling the trays. The sun's radiated heat shines through the glass onto the water. The sun rays are only partially absorbed by the water and then more completely by the black plastic lining of each cell which in turn heats the water more.
As the water is heated to 85, water vapour condenses on the inside surface of the glass and runs down into the purified water channel into a collection container. The unique design of the cells maximises heat absorption and condensation which increases the pure water output.
The ultra-violet radiation from the sun combined with prolonged exposure times prove to be extremely effective for killing commonly occurring bacteria and other water borne diseases.
Other pollutants do not evaporate and are flushed away in unpurified water into a chamber called the 'overflow channel'. Virtually none of the dissolved solid waste is collected in the trays. If the SWP is being used consistently there should be no build up at all. If solid impure material has been collected in the trays, the hardened deposit can be easily removed by using a diluted acid solution such as citric acid (or lemon juice).
The water output of the unit can be maximised when it is correctly positioned to the sun. John recommends rotating the unit every 30 mins or so throughout the day, so its shadow is underneath itself, effectively tracking the sun. This will increase the output by about 30%.
The cell geometry maximises the resultant condensation and high yields of pure water are obtained. Multiple units can be connected in a series to produce larger volumes of water.
The Solar Water Purifier can produce about 6 litres of pure water per square meter per day at 20C ambient and 9 litres at 35C. So an individual unit (which is 1/3 m) can produce up to 3 litres per day.
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