Improvements in or relating to solar stills

摘要

Solar distillation apparatus, suitable for the distillation of sea water, comprises a housing provided with a sloping, transparent upper cover and containing a sheet of capillary material such as a cloth which is disposed so as to be exposed to solar radiation passing through the cover of the housing, means for feeding distilland to the capillary sheet, means for collecting the condensate which forms on and runs down the inside surface of the cover, means for withdrawing residual undistilled liquid from the apparatus, and valvemeans for periodically rinsing the capillary sheet. A tank 10 (Fig. 2) or large area is connected by piping 22 to a plurality of distillation units 12 which extend lengthwise in an east-west direction. Sea water is pumped into the tank so as to maintain a depth of about 6 inches. The surface of the water is covered with a thin layer of dark petroleum oil or other heat-absorptive material 18. By these means the water in tank 10 is preheated by solar radiation. The flow of preheated water to the distillation units is controlled by valve 24. The housing of each distillation unit 12 is made of concrete or resistant wood; and has a low southerly (N-hemisphere) wall 32 (Fig. 3) and a high northerly wall 34. Sheets of a glass or of transparent plastic material 40 are supported on walls 32 and 34. A sheet of black cloth 42 made of cotton, muslin or canvas, impregnated with copper naphthenate to prevent fungus growth, is suspended between walls 32 and 34 by fasteners 44. Capillary wicks 46, such as loosely-twisted strands of cotton, rayon or linen, hang downwards from sheet 42 into troughs 48 which extend longitudinally through the bottom of the distillation unit. These troughs are kept filled with salt water by piping 22, and the wicks 46 raise the water to sheet 42, and keep it in a saturated condition. The water on the cloth is rapidly heated to 70-80 DEG F. by the sun's rays, thereby maintaining a high concentration of water vapour in the air present in unit 12. The vapour-laden air impinges on the under surface of sheet 40 which is relatively cool, and so the vapour condenses thereon. The distilled water drains by gravity into trough 50; and from thence via pipe 52 to tank 16. The troughs 48 slope gently to a common pipe 58 which discharges, via valve 60, into waste-brine tank 14. When, after a period of operation, cloth 42 is to be washed free of accumulated salts, valve 60 is closed and valve 24 is opened more fully to run in sufficient water to submerge the cloth 42, but not enough to flow into trough 50. After an adequate soaking time, valve 60 is opened to drain the rinsing water out of the unit. There is also described an embodiment wherein the evaporator-cloth is disposed in a nearly vertical position; and water is supplied, by wicks, to the upper end of the cloth.