Molded plastic solar still

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Drawing sheet — no readable text.

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In summary, this invention has as its objective an improved cellent heat insulation to reduce thermal losses to a minimum. In fact, it has been found that the productivity rate of the apparatus for vaporizing liquids or for condensing vapors.or preferred solar still of this specification exceeds that of com both, utilizing radiant or solar energy and using the environ parable solar stills of conventional construction and materials ment such as air as the coolant to effect condensation, Major by 60 to 100 percent improvements over the prior artresults from the use of molda operating conditions.when The tested simultaneously under equal materials of construction as con ble materials of construction that also provide for good ther mal insulation, so as to reduce the manufacturing cost and to ceived in this invention, viz foamed plastic having high ther mal insulating properties, constitutes a significant improve enhance thermal efficiencies, of vaporization and to increase ment over the prior art. A second significant improvement the distillate productivity rates. This specification will be 10 directed mainly to the production of potable water from saline over the prior art results from the mode of construction, viz by moulding the frame for supporting the transparent sheet. For water but wider application is anticipated and is implied. instance, the cost of materials and of construction of a unit of The art of producing potable water from brackish water or the sea water by means of solar distillation is well known and is 15 halfpreferred solar still of this specification can be less than quite suitable for rural domestic use or for small villages, par and constructionawhen the cost-of comparable still of conventional materials both are produced in quantities in ex ticularly in coastal areas. Several designs of solar stills, are cess of 500.

known including rectangular and round based horizontal stills The shape and size of the molded plastic solar still of this and tilted tray stills. Conventional materials of construction specification are not confined to the preferred embodiments are wood, plastic, metal or concrete frames supporting a 20 shown and described; this material and method of construc slanted glass or transparent plastic cover sheet over a pool or tion can be utilized in unlimited shapes and sizes. The mode of pools of the brine; the transparent sheet allows radiant heat to construction and materials of construction of this specifica pass through it and thus enter the still and to provide heat to tion are applicable to all forms of solar stills known in the art. vaporize the distilland. Vapor thus produced condenses, on The lightweight material used for construction, readily contact with the lower side of the sloping transparent sheet 5 adaptable to mass production by molding, and the dimen that is cooled by the atmospheric air outside the still. Heat of sional rigidity of the molded form condensation of the vapor is thus passed to the atmosphere capability of being made in units orofmodules this material, and the of any desired through the transparent sheet and the condensate adhering to shape and size represent a major advance in the art. the lower side of the sloping sheet is collected by gravity flow The unitized mode of construction of this specification and is piped out of the still for use. The distilland consisting of 30 readily allows for the replacement of defective units brackish water is replenished either intermittently or by con tiunit solar still without interrupting the operation ofinremain a mul stant flow through the base area of the still. Solar energy is sing units.

thus captured in the still, is utilized to provide heat of When the bottom (base) of the still is omitted, it can be vaporization of unpotable water and is passed to the at used mosphereupon condensation of the vapor into potable distil 35 damptomaterials, produce potable water from vapors released from late water. The driving force, solar heat, is free but the econo ground. This can for instance by placing the frame on the be of vital importance, under, desert condi my and productivity of a solar still can be greatly enhanced by tions. Similarly, potable water can be produced from vegeta improved thermal efficiency and by reducing the cost of con ble matter or another source struction and of materials. This specification provides for such mud or moist earth, especiallyofatdampness, for example, from night when heat stored in the improvements over the prior art. 40 earth produced vapor that condenses readily on the cover The thermal efficiency of a solar still is greatly improved by glass that is in contact with the cool night air, a condition this invention comprising the use of moldable foamed plastics, particularly expanded foamed plastics; for instance, expanded somewhat comparable to dew formation. In addition, a per forated base for instance of sponge-like material can be in polystyrene, or a similar material, having superior heatinsulat serted in the still or can replace its bottom and can be soaked ing properties; and this represents a major advantage over the 45 with non-potable water, for instance when used for survival at prior art. The structural strength of such molded forms and Sea, the light weight of such materials provide for improved materials economy, and the ease of manufacturing and the low tionAnother advantage of this mode and material of construc is that it allows assembly of survival kits, for example, at unit cost of molding a multiplicity of the required frames or shapes constitute substantial improvements over the prior art. 50 sea be where the buoyancy of the material allows it to float and to easily recovered for instance after being dropped from a

The following is a description of the preferred embodiments

FIG.I is a perspective side view section of a preferred form ofg invention and of their operation, with reference to the of the Molded Plastic Solar Still. 55 FIGS.

FIG.II is a side view section of a Molded Plastic Solar Still. FIG. 1 shows a perspective section view of a molded foamed FIG.III is a side view section of a Molded Plastic Solar Still plastic solar still comprising a rectangular-based molded for use on damp soil or for placing over damp material con frame having generally vertical sides 1 supporting a slanted

FIG. IV is a side view section of a generally rectangular 60 glass cover 2 for transmitting solar radiation into the body of the still. The top edge of the molded side walls of the still are

Molded Plastic Solar Still that is tilted when in operation. shaped to receive the glass cover 2, for instance standard win DESCRIPTION OF PREFERREDEMBODIMENTS dow pane of suitable dimensions, and to form a good seal therewith. This seal may be improved by applying any suitable

The rate of distillate production of a solar still depends glazing compound or sealant to seal or secure the glass 2 to the : mainly upon the rate, of absorption of solar heat, the dif 65 frame 1. The inclination or slant of the cover glass 2 is such as ference in temperature between the surface of the brine to allow passage of a maximum of solar radiation and to per sheated by solar radiation and the condensing surface, and the mit condensate to collect and drain from it as a thin film in surface areas at which mass or heat transfer takes place. Since contact with the lower (inside) surface of the cover glass 2. the solar heat received for a given location and shape and size This condensate is collected in a horizontal trough 3 that may of solar still is fixed, the productivity, rate can be enhanced 70 be molded into the base frame 1 along its lower side wall but most significantly by reducing thermal losses so that a max being separated from the main liquid reservoir 4 in the still, for imum of the captured heat is used for evaporation and is instance, by a suitable molded divider wall having a top edge passed to the atmosphere by condensation of the vapor on the spaced from the cover glass 2. Condensates collected in the lower side of the air-cooled transparent sheet. A major ad trough 3 can be removed from the still by means of a suitable vantage of the still of this invention is that it provides for ex 75 conduit, for instance, a pipe 5 communicating with the trough

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and extending through the wall of the still. The main liquid walls of the still, thus increasing the radiant heat absorption at reservoir 4 can be molded as an integral part of the frame and this surface and enhancing the evaporation rate of the distil provides for a shallow pool of distilland that can be land. In the preferred embodiment of the molded foamed replenished as required, for instance, through an inlet conduit plastic solar still of the tilted tray type shown, the side walls 22 6 at the back side of FIG. I. A similar outlet conduit located a 5 are relatively low, thus providing for the relatively close prox distance from the inlet conduit 6 may be provided to allow imity of the evaporating surface and the condensing surface, continuous or intermittent drainage of concentrated residual for instance, a gap of about one-half inch between these sur distilland from the still, faces is adequate in most cases. The base 23 can have an in FIG. 11 shows a side view section of a molded plastic solar tegrally molded saw-tooth pattern 24 on its inside surface so as

still, the base and sides 7 of which are made preferably from to provide for parallel troughs or pools of distilland and for expanded or foamed plastic, for instance, expanded cascading of the distilland under gravity flow from one trough polystyrene, polyurethane or another suitable moldable to the next. Alternately, a zig-zag flow path can be provided material having good thermal insulating characteristics. A for by arranging the distilland inflow and outflow for succes transparent cover sheet, for instance, glass of window pane sive troughs to be at opposite ends thereof through the series type 8, fits over or on the sides or into a slot or depression 9 15 of troughs. This provides for an elongated, zig-zag flow path of formed by molding so as to provide a good fit between the the distilland through each still and it enhances the evaporat glass surface and the body (sides) of the still. A trough 10 for ing coefficient or rate. The cover glass 25 or another suitable collecting the condensate and a conduit 11 to communicate heat-transparent sheet can be supported loosely on a shoulder with the trough 10 to allow withdrawal of the product from the 20 provided by molding the top edge of the side walls 22. A distil still can be provided by molding. The main base area 12 of the late or condensate collecting trough 26 can be provided by still provides a reservoir for the distilland and an area for col molding it into the side wall as shown. Distilland inlet 27 and lecting solar heat to effect vaporization of the distilland. The base area 12 should preferably be of a dark or black color to outlet 28 conduits and a condensate outlet 29 can be provided by molding suitable holes and by inserting suitable tubular enhance absorption of solar or radiant heat. Alternatively, this 25 conduits as shown, for instance, short lengths of plastic pipe inside surface may be painted with a dark material, or a dark inserted through the side walls 22 at suitable locations. A surfaced material, for instance, a sheet of tar paper 13 or a suitable seal at 30 between the cover glass 25 and the side layer of dirt or dark sand may be placed in the base to increase walls 22 may be obtained by proper molding and by relying on the rate of absorption of solar heat. A rough surface is also a liquid seal provided by condensate seeping into and sealing helpful. For example, small stones 14 can be placed in the 30 the gap at 30 or it may be obtained by applying a glazing com base area or on the tar paper to hold it down while at the same pound, a plastic sealant, glue or by sticky tape applied over or time providing additional heat transfer surface area, and for in the joint at 30.

dissipation of heat to the distilland by creating convection cur Additional shapes, sizes or modules of molded foamed rents in the layer of distilland close to these surfaces. Alterna plastic solar stills or sectional parts thereof can be utilized tively, a rough surface pattern and/or a dark surface can be 35 singly or in multiple series operation without departing from provided by molding or by a placing a preformed grid or mat this specification; for instance, rounded rather than angular on the base 12. The distilland can be replenished intermit shapes and pre-molded sections fitted or joined together. In tently as needed, or continuously for instance by by passing it addition, the separate uses or functions of vaporization and into the base area of the still through a suitable conduit 15. condensations according to this invention are anticipated and Residual distilland or brine can be withdrawn or can overflow 40 covered by this specification. The embodiments shown and from the still through a suitable conduit 16. A sealant may the applications described are intended as examples and this used to improve the seal formed between the cover glass 8 and invention is not to be limited to or by these examples. For in the body 7 of the still or one can rely on a liquid seal provided stance, these same principles can be utilized to heat water, to by the condensate filling the gap between these surfaces. The make or recover salt from brine, to produce distilled water for inclination of the transparent sheet or cover glass 8 is suffi 45 medical or pharmaceutical or photographic or industrial or cient to ensure that the condensates collected on its lower (in domestic uses, for instance, for batteries and steam irons. Dif side) surface drains towards the collection trough 10 and to ferent types of foamed or foamable plastic materials can be provide for a maximum transmission of solar heat into the still. used, for instance, polyurethane, polystyrene, styrofoam, FIG. 111 shows a side view section of a molded plastic solar pelafoam, etc. and different modes of molding can be utilized still that has an open base. This provides that it may be placed 50 to produce components of the molded, foamed plastic solar on damp soil or over another suitable source of moisture, for still without departing from the scope of this specification. instance, plant material from which potable water may be ob The invention claimed is:

tained by vaporization and by condensation of the vapor. A 1. A dimensionally rigid solar distillation apparatus includ condensate collection trough 17 having an outlet conduit con 55 ing a frame comprising a generally flat base and a plurality of nected therewith can be molded into one side of the still and generally upright wall members extending upwardly for a the transparent cover sheet or glass plate 18 may be sealed to short distince and completely around the entire periphery of the upper surface of the molded sides 19. A detachable base said base, an enclosing, bottomless and topless housing com 20 of any suitable material, shape or size, for instance molded prising a similar plurality of upright wall members of equal plastic, may be provided. Provision is also made for placing a 60 number but greater height than those of the base and sloping sponge or gridlike mat 21 or other suitable wetable material to from its highest to its lowest opposite wall, said housing seat hold water while it is being partially vaporized, for instance, ing on the base within its relatively short upright wall mem when the solar still is used on shipboard, a sponge-like insert bers, said lowest opposite wall having a channel in its upper as a precaution against sloshing of the distilland is of im portance. Sloshing of condensate in the trough 17 may be 65 aedge for collecting condensate drippings from the cover sheet, slanted transparent cover sheet capable of transmitting radi prevented similarly by placing a sponge-like material in it. ant heat and providing an inner surface for condensation of FIG. IV shows a side view section of a molded plastic solar evaporated liquid, said sheet being spaced from said base by still that is supported in a tilted orientation at a suitable angle said upright members of said housing to provide a chamber during operation. One advantage of the tilted tray still is that adapted to retain a body of vaporizable, brackish water in the vapor path of flow from the distilland surface to the con 70 direct connect with the base and wall members of said frame, densate surface is short. Another is that the material required conduit means in said frame for introducing and removing for the wall structure to support a unit surface of glass is brackish water and recovering liquid condensate, said ap reduced as compared to other types of solar stills. The tilted paratus consisting essentially of molded, foamed plastic tray still also allows for increased evaporating surface area and material and said base having means disposed thereon for for a reduction of shading of the base surface area by the side 75 preventing sloshing of the liquid within said frame.

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2. Apparatus as in claim 1 wherein said means on said base comprises spongealike means to prevent sloshing of said liquid tilted orientation at a suitable angle. 4. Apparatus as in claim 1, further including provision for with said frame.

3. Apparatus as in claim 1, wherein said molded foamed placing a preformed gridlike mat within said frame to enhance plastic base provides a multiplicity of parallel distilland pools the rate of heat transfer to said distilland and to prevent slosh within said frame, the water containing portion of said base ing of liquid within said frame. being generally parallel to said sheet for transmitting radient 5. Apparatus in accordance with claim 1 wherein said heat and spaced therefrom by about 1 inch, said base having a foamed plastic material is selected from expanded polyu saw-tooth profile that provides for said parallel pools of distil rethane and polystyrene.

land in series flow connection by supporting the apparatus in a 10 xk k + k sk