MXPA99003542A - Solar stills for producing fresh water - Google Patents

Abstract

The apparatus has a long cylindrical shape (10), inflated with air under slight excess pressure, comprising:an evaporating chamber (12), a first condensing chamber (14) and a second condensing chamber (30);the evaporating chamber (12) is provided with a thermal insulating transparent cover (46b) and its external wall is made up of a black impermeable membrane, internally coated with a hydrophile lap;the first condensing chamber (14) has an impermeable wall and is separated from the evaporating chamber (12) by a dividing partition (16), coated with a hydrophile lap of this chamber (12);the second condensing chamber (30) communicates with the two preceding ones and its wall which comprises an impermeable membrane and an external hydrophile lap, exposed to the open air and kept wet by a permanent supply of water;a ventilating fan (28) blows air in close circuit in the three chambers and associated means (54-56) maintain excess pressure therein;the fresh water is collected at a lower point (64) of the second condensation chamber (30) and the brine at a lower point (66) of the evaporation chamber (12). The invention is useful for economical production of fresh water in dry regions.

Description

SOLAR ALAMBIQUES TO PRODUCE SWEET WATER This invention relates to solar stills for producing fresh water, in other words domestic equipment units or industrial plants that use energy alone to produce demineralized water from natural, non-potable water. When this non-potable water is sea water, these stills could also, as a useful collateral product, produce brine. The problems that arise, both economic and technical, water desalination facilities of different types (distillation and filtration), have been presented in detail in an article written by Andy Coghlan, entitled "Fresh water from the sea", published in the pages from 37 to 40 of the British magazine New Scientist of August 31, 1991. In this article, we are reminded of how vital it is to develop faster and faster techniques that are both effective and inexpensive to desalinate sea water , in order to satisfy the exponential requirements of fresh water in dry areas of the earth. To address this problem, numerous solutions have been proposed to distill seawater that use the relatively intense and cheap energy of the sun, as a replacement for the expensive energy produced by fossil fuels. The solutions have been the subject of numerous patents and articles of which two are of special interest, and are taken as reference in view of their particular relevance. European Patent 0 612,691 published in 199 filed by Mitsubishi, describes a solar unit for producing fresh water of the conventional type, in which a container having a black base, containing sea water, is installed below a transparent space which has a sloping roof. Two gutters, designed to recover the fresh water that falls through the vertical walls of the space, are placed at the foot of these walls. In order to prevent the drops of fresh water, condensed in the inner space of the roof and which, in addition, reflect a portion of the solar radiation, fall back into the container, this surface is provided with a wettable cover, which e transparent or at least translucent, which prevents s from forming the drops. Additionally, in order to reduce the temperature of the ceiling of the space and thus improve the condensation of steam, water is constantly sprayed on this roof. In this way, it improves the performance of this installation. However, at least two disadvantages are preserved: (1) an excessive amount of water is constantly heated by the sun, which decreases the maximum temperature of the water mass in the container and reduces the degree of evaporation achieved and (2) loses all the latent heat of condensation of water vapor.

The New Scientist magazine article cited above leads, on page 39, to a brief description of a piece of domestic equipment to produce fresh water that is original, has a high yield, and uses solar energy. This equipment, developed by P. Le Goff, has, underneath a transparent plastic membrane, an adjustable mirror that reflects the solar energy towards the frontal black surface of a first aluminum plate, arranged vertically. The back surface of this first plate is covered with gauze, which is supplied with seawater under gravity. Several identical plates provided with this same hydrophilic cover are arranged in cascade with a distance of a few centimeters between them. Solar energy heats the first plate to about 94 ° C, the effect of which is to evaporate a relatively large amount of water that circulates in the cover that lines the back surface. The water vapor produced in this manner in the space separating the first and second plates condenses on the front surface of this second plate; The effect of this is to make it hot, leading, in turn, to the evaporation of a larger amount of salt water circulating on the rear surface. This continues until the sixth plate, which is heated up to 45 ° C. The condensed fresh water on the front surface of each plate starting from the second, is collected by a collector. Another collector, which is not shown, collects the brine that appears at the bottom of each lining. The manufacturer announces a daily production of twenty liters of fresh water per square meter of a plate exposed to the sun. This high yield is the result of recovery, on the second to the sixth plates, of the latent heat of the condensation of the water vapor produced by the hot lining, and which are kept constantly moistened, from the first to the fifth plates. In agreement with the author of the article, this result is advantageously compared with the results (2 to 3 liters per day and per square meter) of the solar water distillation equipment of the conventional type. This device is effective and convenient for domestic equipment but is relatively expensive to build due to some of its components (the heliostat and the aluminum plate) that it includes. In the text that follows, we will take the performance of a solar still to produce fresh water as it means the proportion between, on the one hand, the quantity of dulc water produced effectively per hour of the light of the average sun and per square meter of water. the surface that absorbs the solar radiation and, on the other hand, the amount of water (Q), theoretically evaporated by the heat of the sun, absorbed by this unit of surface area during this unit of time (dand Q = 1.5 kg / h. m2 of an average level of sunlight of u kilowatt / m, in dry areas).

The first object of the invention is to construct improved solar stills to produce fresh water. The second object of the invention is to build this stills that have a yield that is as high as possible, while at the same time requiring a relatively low initial investment and maintenance operation costs that are particularly low. The third object of the invention is to provide solar stills to produce fresh water in which the latent heat of condensation of the vapor is recovered as much as possible. The fourth object of the invention is to provide solar stills that are easily adaptable to the particular conditions of their implementation. The fifth object of the invention is to provide these solar stills to produce fresh water, which adapt well to permanent strong winds. The sixth object of the invention refers to the solar industrial plant that produces fresh water by distillation of seawater and that comprises a relatively large number of identical solar stills. The seventh object of the invention refers to an industrial plant that combines a solar plant to produce fresh water by distillation of sea water and a salt marism supplied by the brine provided by this plant. The eighth object of the invention relates to a novel composite product, especially adapted for the construction of improved solar stills to produce sweet water according to the invention. According to the broadest formulation of the invention, a solar still is provided to produce sweet water comprising: a device, adapted to absorb solar radiation and to contain the water to be distilled; a condensation surface on which steam, produced by heating the water of the device, can be condensed; an element to collect the fresh water that drips a little on the condensing surface; characterized in that: the device comprises a waterproof membrane, which is flexible, remains stretched, is dark in color, exposed to the sun and, accommodated in the shade and forming a cover for the membrane, a hydrophilic sheet, fed with water by capillarity and severity; an element to recover brine is accommodated in the lower part of the nappa. It will be immediately noticed that the more less hydrophilic nature of the material is measured by the degrees of capillarity that it has with respect to the capacity of the liquids to wet it. Under these conditions, a wettable but relatively little hydrophilic nap will be fed by gravity, pouring on it the water that is to be distilled. In contrast, a more hydrophilic web will be fed by simple capillarity, by immersing one of its edges in the water. After this, the same capillarity, however small, of the nappa, and the gravel forces will ensure the dispersion, retention and flow of this water as it travels downward through the nappa. For a very hydrophilic layer, the production, per unit of submerged anchors, of the water thus pumped, decreases as the maximum height of the layer above the water level increases. Thanks to the arrangements according to the invention presented above, solar stills are obtained to produce fresh water which avoid several of the disadvantages of traditional solar units for distilling seawater. In effect, the mass of water heated by the sun is here reduced to a minimum value, since it is limited to a constantly small volume of water retained in the water. / every moment in the hydrophilic layer. Under these conditions, the maximum temperature that this water can adopt is greater than that reached in the conventional solar still, and the effect of this is to increase significantly the pressure of the saturated vapors in the immediate vicinity of the hydrophilic layer and, thus, , the intensity of the evaporation reached. Additionally, since the time of the momentary stop of the seawater in the installation is short (when much, some minutes), the development of algae and molds on this layer is excluded a priori, even after several months of continuous operation. And this also because the wet layer receives very little solar radiation, because it is shaded by the dark colored membrane. According to a first particular embodiment of this still, the membrane constitutes the wall of an evaporation chamber which is relatively long, and is installed po below a transparent shelter element, the transparent shelter element is a closed space, relatively well sealed, the inner surface of the wall of the same constitutes the condensing surface; A blower is associated with the apparatus to produce a flow of air in the closed circuit between the evaporation chamber and a condensation chamber, constituted by the volume of the external space of the evaporation chamber. this solar still: "the dark membrane constitutes the external wall of a evaporation chamber that is relatively long, installed under a transparent thermally insulating cover, - the condensing surface is the impermeable inner side of the waterproof wall of a condensation chamber , accommodated below the evaporation chamber and separated therefrom by a common longitudinal dividing wall, the two chambers communicating with each other by means of openings formed above the transverse partition walls separating the lower parts from their adjacent ends, - the outer wall of the condensation chamber has a hydrophilic cover that is maintained humid mediant any convenient element and at least partially exposed to the air; a blower is associated with the apparatus for making a closed circuit air flow from one chamber to another; convenient elements are associated with blowing to allow the two chambers to be inflated to maintain a slight excess of pressure inside them. According to a third particular modality of this solar still: the dark membrane constitutes the external wall of a evaporation chamber which is relatively long, installed under a transparent thermally insulating cover; the condensing surface is the inner side of the impermeable wall of a well-fitted condensing chamber, without a common wall, near the vaporization chamber, the two chambers communicating with each other by means of openings formed above the walls. transverse divider separating the lower parts of their adjacent ends, - the outer wall of the condensation chamber includes a hydrophilic cover, which is protected from the sun and kept moist by any convenient means and is at least partially exposed to air; a blower is associated with the apparatus to cause a closed-loop air flow inside the two chambers; Suitable elements are associated with blowing to allow both chambers to inflate and to maintain a slight excessive pressure inside them. In the three particular embodiments of the invention presented above, the circulation of air in a closed circuit inside the evaporation and condensation chambers considerably improves the conditions of transport of water vapor, produced in the evaporation chamber, to the condensation surface. In the first described particle mode, the drops of condensed water falling from the closed space roof are not lost since they find the impermeable membrane before reaching the fresh water collection element provided for this purpose. Additionally, in the other two embodiments of the invention described above, we will point out the value of the presence of a transparent thermally insulating cover installed above the portion of the wall of the evaporation chamber exposed to the sun. This cover prevents the formation of condensed water droplets and forms a screen to the solar radiation, thus allowing this portion of the wall to receive a greater amount of heat at each moment and consequently increase the intensity of the evaporation of the water contained in it. the hydrophilic nappa. To this increased amount of heat, a lower temperature of the condensation surface can be added, which here depends on the temperature of the wet cover, exposed to air, of this surface, and consequent on the temperature of the dew point and of the dew point. the relative humidity of the outside air. As an example, this transparent cover will be a thin sheet of plastic, with edge glued to the dark colored membrane, trapping a layer of dry air a few centimeters thick or, again, a relatively thick plastic sheet. that have low thermal conductivity. Additionally it will be noted that a part of the condensation of the steam, achieved in the condensation chamber d of the second embodiment of the invention, is produced with the recovery of the latent heat in the dividing wall that separates this chamber from the evaporation chamber.; this allows this second embodiment of the invention to benefit from a slightly higher yield per unit. To conclude on this point, it will be recognized that the second and third modalities of the invention can be easily installed in any place (on land, in a terrace or a water blanket) and that its ability to withstand high winds is excellent. Thanks to the relatively high tension in the external wall "of the evaporation and condensation chambers that remain under pressure slightly in excess, another advantage of the particular device to retain the water to be distilled, which includes a solar alambiqu according to the with the invention, it refers to the brine Indeed, it will be noted that, as soon as the seawater product, distributed by the hydrophilic layer on the impermeable membrane heated by the sun, is sufficiently high, no deposit can be formed This production varied with the maximum intensity of the solar radiation of the place, determined by the ratio between the water production of ma and brine, which ede be less than eight, and for example it can be four. These figures are the result of values, the salt concentration of seawater, which is generally about 30 grams per liter and the concentration of salt in the brine, in which salt crystals may appear, which It is approximately 24 grams per liter. If these conditions are respected, all the salt contained in the sea water circulating in the hydrophilic nap is evacuated in the recovered brine, and no salt deposit can be formed in this layer. According to a general formulation of the optimum form for the implementation of the present invention by means of a solar still to produce fresh water, it is characterized because: it comprises an evaporation chamber, a first condensation chamber and a second condensation chamber, - the chamber of evaporation has a flexible wall formed by a dark external waterproof membrane provided with an internal hydrophilic cover, this chamber being relatively long, exposed to the sun and installed under a transparent thermally insulating cover, - a duct fed with water that is goes to distillate is adapted to moisten, by capillarity or gravity, the hydrophilic layers that cover the evaporation chamber; The first condensation chamber has flexible walls formed by impermeable membranes and when one of these membranes is located, it is provided with an external hydrophilic coating fed with water by gravity capillarity, which constitutes the dividing wall that separates the first condensation chamber from the evaporation chamber. , - the downstream end of the evaporation chamber communicates with the inlet of the first condensation chamber by means of an opening adapted to prevent and passage of the water to be distilled; the downstream end of the first condensing chamber discharges into the second condensation chamber, the outer wall of this second chamber being provided with a hydrophilic cover exposed to the air, protected from the sun kept moist by a permanent water supply, the second chamber of condensation communicates with the evaporation chamber through an aperture adapted to prevent any passage of the water to be distilled, - an electric blower is associated with the apparatus to produce a flow of air in a closed circuit inside the chamber of evaporation and then inside the first condensation chamber and the second condensation chamber; A convenient element is associated with the blowing to allow them. three chambers are inflated and to maintain a slight excessive pressure inside them, - a brine removal tube ends at a low point in the evaporation chamber; A tube to remove sweet distilled water ends in a low point in the second condensation chamber. According to a supplementary feature, the geometrical shape of the first condensing chamber of the evaporation chamber depends on one another and is adapted to minimize the heat exchange between this first chamber the outer part, and to maximize heat exchange. between these two cameras.

According to another characteristic, the first second condensing chambers communicate with each other mediated links adapted to maximize the heat exchange between the air flow leaving the first chamber and the inner side of the external wall of the second condensation chamber . According to a first optimum particulate mode of the solar still to produce fresh water according to the invention, the still takes the form of an elongated cylinder having a circular cross section, inside which the three chambers and the common dividing wall are installed. What separates the evaporation chamber from the first condensation chamber forms two planes arranged in a V-shape. According to a second particular optima mode, the solar still for producing fresh water is a type of large pneumatic mattress formed of a plurality of cells. of distillation; each distillation cell includes, arranged in series, an evaporation chamber and two condensing chambers, a first one and, respectively, a second one; the second condensing chamber of a cell being the preliminary chamber for the evaporation chamber of the next cell, when the cells are arranged in series, - a single blower, installed externally to the cover formed by the distillation cells, to cause the air circulate in a closed circuit, in all the chambers of the cells of the distillation apparatus; symmetrical oblique common dividing walls attached to the two surfaces of the apparatus, which separate the evaporation chambers from the first condensation chambers and which give these chambers cross sections in the form of narrow circular sectors; a single thermally insulating transparent cover that covers the portion of the surface of the apparatus exposed to the sun, formed by hot contiguous zones of the evaporation chambers. Thanks to these novel configurations, this solar stills to produce - sweet water, improved according to the optimal modalities of the invention, are suitable for distilling sea water and most natural non-potable water, with a particularly high yield This is due primarily to the particular characteristics of the invention already presented, which will not be discussed again. As against this, we will notice what is stated later. Inside the evaporation chamber, the temperature of the moist hydrophilic cover of the hot zone exposed to the sun is relatively high and clearly greater than that of the cover of the common dividing walls that are in the shade. The temperature of the hot humid air leaving the evaporation chamber to then enter the first condensation chamber is between these two temperatures. Thanks to the particular cross-sectional shape of the common dividing walls separating the evaporation chambers from the first condensing chambers of the different distillation cells described above, the area is relative surface of these dividing walls co with respect to the surface area of the dark colored walls exposed to the sun is relatively large. And, in the case of the solar still containing several distillation cells, in the total surface area of the common dividing walls that form the less hot walls of the evaporation chamber may also be several times as high as those in the relatively hot zone. exposed to the sun Under these conditions, the exchanges of heat between the two chambers considered are significant and the condensation of the steam is greatly enhanced, as will be explained in detail below. In the case of a still having a first condensation chamber that is thermally insulated from the outside, the common dividing walls that separate this chamber from the evaporation chamber form a set of relatively cold zones that find the flow of hot humid air that comes out of the evaporation chamber. Immediately, significant condensation of the water vapor transported by this air flow occurs, by diffusion in these partition walls having a relatively large total surface area. The extension of this condensation decreases progressively as the air stream, which is becoming less hot and humid, advances towards the first condensation chamber. Throughout this first chamber, a significant portion of the latent heat of the condensation of the vapor is immediately recovered by the impermeable surface of these dividing walls, and is continuously recycled in order to participate in the evaporation of the distributed water. by the hydrophilic layer that covers the external surface of these tubes. It will be noted that an identical result is obtained, or even better, when the first condensation chamber is completely surrounded by the evaporation chamber. "The wall of the second condensation chamber is relatively cold, and since the temperature of the latter constantly steers towards that of the dew point of the ambient air (which is particularly low in desert regions due to the presence, around the second camera, an external damp cover that is exposed to the air and protected from the sun.In addition, the links between the first and second condensation chambers are arranged so that the air flows out of the first condensation chamber achieve better Sweeping of the internal surface of the external wall of this second chamber For each still design, the relative length of this second condensation chamber is determined following routine tests, in order to optimize the temperature of the air flow that exits. The passage through the second condensation chamber is a last step in the production of sweet water during a cycle of air circulation. and inside a still distillation according to the invention. Under these conditions, the air entering the evaporation chamber of a distillation cell is relatively dry and relatively cold. And this, as will be seen below, particularly favors the effective performance of the dual function that this air will perform inside the evaporation chamber, specifically (1) becoming progressively hot and thus being charged with a maximum amount of water vapor during its passage and (2) allow the effective recycling of latent heat of the steam which will condense in the first condensation chamber. With reference to this, it will be noted that the presence of this second condensation chamber is a necessary condition for the possibility of more or less complete recycling of the latent heat of the steam, made through the common dividing walls that separate the first condensation chamber. of the evaporation chamber. In the second condensation chamber the significant cooling of the air flow, achieved before its return to the evaporation chamber, is the phenomenon that constitutes the necessary condition to transfer the latent heat through the common dividing walls. E effect, thanks to this final cooling of the air flow before its return to the evaporation chamber, do positive temperature differences, necessary for this transfer, are permanently set at a high level, on each side and over the entire length of The common dividing walls. The first of these positive differences is between T ^, the decreasing temperature of the air, which is initially hot and humid at the outlet of the evaporation chamber, during its journey through the tubes of the first condensation chamber and Q, The temperature, which is also decreasing, of the impermeable walls of the common dividing walls, from the right entrance to the exit of the first condensation chamber. In all the common dividing walls, from the entrance to the exit of the first condensation chamber, the relation Ti >is fulfilled; Tc. The second of these positive differences is between Te, and temperature increase of the moist hydrophilic cover over the entire length of the common dividing walls from the right entrance towards the outlet of the evaporation chamber, T2, the temperature, which is also increasing , of the moving air layers that sweep these wet covers during their passage from the evaporation chamber. On the entire length of the common dividing walls, from the entrance to the exit of the evaporation chamber, the ratio T > T2. Consequently, this phenomenon is the real one that established the necessary conditions for the recycling of high amplitude of the latent heat of the transported vapor, during a period d circulation of the air in the distillation cell. The effect of this phenomenon is remarkably to increase the yield of solar still to produce fresh water according to the invention, up to a value well above unity. You will notice that this performance increases with the value of the proportion between the area of the total surface of the common dividing walls on which the latent heat of steam condensation is recycled, and the surface area of the hot zone of the chamber. evaporation. From the above, it turns out that the different stages of the air circulation cycle in the three successive chambers of a distillation cell of a solar still for producing fresh water according to the invention are optimized. This made a considerable contribution to improve the performance of this still. Additionally, this improved solar still can easily adapt to the external installation and the implementation conditions imposed on it (either on land or in a stretch of water) and is capable of withstanding strong winds. The reason for this will be seen in the tension in the walls of the chamber and in its suitably inflated insulating cover that is greater than the pressure exerted by the normal strong winds while a second reason lies in the effective elements used to secure the apparatus which are simple to install and to implement. These advantages are particularly apparent for a solar still having multiple distillation cells, since, for a large absorbent surface area, the volume occupied is reduced, as well as its relative height. These features and advantages of the invention will become clearer from the following description of the embodiments of the invention, provided by way of non-limiting example, with reference to the accompanying drawings in which: Figure 1 is a side view diagrammatic of a solar still to produce fresh water according to a first particular embodiment of the invention; Figure 2 is a cross section of the unit in Figure 1, shown in a cradle installed in the ground, - Figure 3 is a cross section of this unit installed in a stretch of water; Figure 4 is a perspective view of a solar still to produce fresh water, according to a second optimum embodiment of the invention; Figure 5 is a sectional view of a useful modality of a solar still to produce fresh water according to the invention. Figure 1 is a longitudinal view of an optimal implementation of a solar still to produce sweet water according to the invention. It comprises a housing 10, having flexible walls, adapted to be inflated with air in order to give it a certain degree of rigidity and cause it to take the form of a long cylinder with a circular transverse section. In Figure 1, the right end 10a and the left end 10b of this housing 10 are closed by glued lines respectively running in the plane of the figure perpendicular to it. Under these conditions, the end edges of the cylindrical housing with circular cross-section, relatively rigid 10, form "projecting" horns such as 10c, 10d at the right extremity. As an example, this unit 10 will have a length of 10 meters with a diameter of one meter. Referring to Figures 1 and 2, inside this housing 10, there is provided the evaporation chamber 1 exposed to the sun and a first condensation chamber 14 accommodated in the shade, and the two chambers 12 and 14 are separated by a dividing wall common longitudinal 16, which forms two symmetrical planes 16a, 16b which are substantially orthogonal. The evaporation chamber 12 includes two transverse end partitions 18 and 20. The left partition 18 d the evaporation chamber 12 is impermeable and includes, in its upper portion, a broad opening 22 in the form of a circular segment, and in its portion , central, its edges are glued to the external wall of the evaporation chamber 12. In this lower portion, this partition 18 is stuck to the left edges of the two planes 16a and 16b of the common divider 16, and the line of The union of these planes is stuck to the base line of. the first condensation chamber 14. Due to this, ~ the first condensation chamber 14 comprises two tubes 14a and 14b having a circular cross-section in the form of symmetrical circular segments. The two openings upstream of the first condensation chamber 14 discharge at the left end 10 of the housing 10. This end 10 constitutes an intermediate part 24 having a flexible waterproof black wall, which provides communication between the outlet of the chamber of evaporation 12 the entrance to the first condensation chamber 14. The partition of the right end 20 of the evaporation chamber 12 includes, in its upper portion, a circular aperture 26 in which the electric blower 28 is installed.

Additionally, the edges of the partition 20 are welded to the circular wall of the evaporation chamber 12 and to the right edges of the planes 16a and 16b of the common divider wall 16. The downstream ends of the two condensation tubes 14a, 4b discharge at the right end 10a of the unit 10, via two sleeves 14c, 14b extending from this tubes. This end 10a constitutes an intermediate portion 3 that provides communication between the outlet of the first communication chamber 14 and the entrance of the evaporation chamber 12. The wall portion exposed to the sun of the evaporation chamber 12 is constituted by an outer membrane 36 which is waterproof and dark in color (a sheet of black polyethylene, 50 to 100 microns thick for example), and an internal hydrophilic nap 38a (a relatively thick woven cellulose, for example), fixed to each other with adhesive suitable. The two planes 16a, 16b of the common divider walls 16 in the same way carry a hydrophilic web 38b on the side closest to the evaporation chamber 12, and a waterproof web 36b (of an approved type for food packaging), in the side of the two tubes 14a, 14b, having symmetrical circular segment cross sections, constituting the first condensation chamber 14. Inside the evaporation chamber 12, along the upper generating line thereof, a conduct 40 is installed, fed with the water to be distilled, and adapted to moisten, by capillarity and gravity, the hydrophilic nap 38a. The conduit 40 is provided with a connector 42a at one end thereof and an end retainer 44 at the other end. One embodiment of this conduit 40 will be described later in detail. A tube 42b connects the connector 42 with another connector 42c secured to the apex of the "horn" 10 at the end 10a of the unit. The outer wall, common to the two tubes 14a, 14b of the first condensing chamber 14, comprises, internally, an impermeable membrane 36c (identical to the membrane 36b) and, externally, a relatively long thermally insulating sheet 46a accommodated as a cover , at least in the left portion of the external base of the first condensation chamber 14. If appropriate, a humid hydrophilic layer 38c, partially exposed to air, is accommodated in the right portion of the external base of the first condensation chamber. 14. The utility of the presence of the insulating cover 46 as well as the respective length, and possible separation, of the hydrophilic cover 38c, and of the insulating cover 46a, will be determined experimentally. The wall of the intermediate part 30, located at the right end 10a of the alembic 10, includes an internal waterproof membrane 36d (identical to the membranes 36b, 36c) an external hydrophilic cover 38d, exposed to air, protected from the sun by a screen against the sun (n shown) and kept moist by a permanent feed of water, as will be explained later. Under these conditions, the intermediate part 30 similarly constitutes a second condensing chamber and a chamber preceding the evaporation chamber 12. In order to ensure that the hydrophilic layers 38a, 38b, 38c, 38d retain as much as possible. Possible of initial capillarity and flexibility, the adhesive used to fix these webs to the waterproof membranes 36a, 36b, 36c, 36d will only be slightly fluid and their fine consistency will be plastic. The wall of the evaporation chamber 12, exposed to sun, is located below a transparent thermally insulating inflatable cover, which traps a thin layer. (for example with a thickness of 3 centimeters) of hot air.

The edges of the cover 46d are glued to the unit 10, together with the joining line of the common dividing walls 1 and the walls of the two chambers 14 and 12. The inflation of the cover 46d is achieved by any suitable element. U connector 48 is provided for this purpose and this will close as soon as inflation is achieved. The volume of air layer trapped under cover 46b will increase with temperature, but its pressure will hardly vary. The right end 10a of the still 10 is rigidly secured to the mast 50, along the length of which four tubes 52, 54, 56 and 58 are fixed respectively handling the seawater feed to the conduit 40 and the outer hydrophilic covers 38c, 38d, and finally, the evacuation of the distilled water and the brine. A funnel 60 s associated with the water feeding tube 52 to the unit 1 which is provided with a constant flow of water of ma contained in a container 62, placed at a higher level, exposed to the open air, fed by a pump electrical d constant production which is not shown. The column of agu of variable height, contained in the vertical tubes 52, made it possible to maintain a constant inflow rate to still 10, despite the variations in pressure (from 10 to 50 hPa for example) and due to the radiation from the sun The vertical tube 54 for evacuating the distilled water that has accumulated in the portions 14a, 14b "of the first condensation chamber 14 and in the second condensation chamber 30, is connected to a connector 64 mounted on the apex of the" horn ". "lower 10c at the right end 10a d the unit.The brine evacuation tube 56 is connected to connector 66, mounted at the right end of the line joining one to the two planes 16a, 16b of the common dividing wall 16. L removal of fresh water and brine will be achieved by siphon or pumps that are not shown.The tube 58 terminates in a conduct 70, which has a permeable wall, installed above the second condensing chamber 30, to moisten the outer covers 38c, 38d of the condensation chambers Figure 2 is a cross-section of a solar windlass 10 installed in a cradle 72, adapted to ensure the base of the condensation chamber 14 is kept clear, and to keep it exposed to the open air. , the cun 72 is mounted on feet 74 fixed to the floor (or to the bottom of a stretch of surface water). The cradle 72 has rigid longitudinal members 76, 78 of the circular transverse cut connected together by transverse pieces 80 by cloth strips 82 attached to the longitudinal members 76 and 78 by any convenient means. These strips 8 can be accommodated to carry, if appropriate, the conduits 84a, 84b, identical to the conduits 40 and 70, fed with seawater by the tube 58 or with brine by the tube 56, and intended to moisten the permanently the hydrophilic cover 38c of the outer base of the two tubes 14a, 14b of the first condensation chamber 14. Together with the upper portion of the evaporation chamber 12, the edges, conveniently put together in a U-shape (see the enlarged view 2a), of a relatively wide pull having two layers 36e and 38e, identical to those 36a and 38a of the wall of the chamber 12, are sewn. The hydrophilic layer 38e is inside and in contact with the hydrophilic nap 38a of the evaporation chamber 12, leaving the impermeable layer 36e outside. In this way, conduit 40, adapted to feed the evaporation chamber 12, was constituted with seawater to moisten, through capillary action and gravity, the two hydrophilic layers 38a, 38b that line the inside of this chamber 12. With In order to ensure that the membrane 36a remains impermeable, strips of the same material 36f, 36g are stuck to it, on each of the seams thus formed. According to FIG. 1, an elongated opening 10O is provided in the wall of the right end 10a of the still 10. This opening allows it to be fixed or electric blower 28, and the initial inflation of the apparatus is then sealed in an airtight manner. air through convenient means. Additionally, an electrical casing, not shown, is provided to power the blower 28. Along with the two longitudinal bond lines d the walls of the chambers 12 and 14, of the common divider wall 16 and the cover 46, two ropes 86a, 86b are mounted on which the fasteners 88a, 88b are hooked allowing the still 10 to be secured on the longitudinal members 76, 78 of the cradle 72. When the unit 10 is installed on the ground, a channel 90 to recover the brine. Figure 3 is a cross-sectional view of a solar still 10 ', installed in a stretch of water. This still 10 'differs mainly from the alembic 10 in the stabilization means which are constituted by the water-filled ballasting elements 92a, 92b symmetrically welded along the cylindrical housing generation lines. The left portion of the base common to the main bases 14a, 14b of the first condensation chamber 14 carries a thermally insulating cover 46 while, on the right portion of this base, the hydrophilic cover 38c will be unnecessary. The outer walls of the evaporation chamber 12 and the first condensation chamber are provided from marine-type materials, similar to that used for inflatable boats. Fastening rings (not shown) are attached to these ballasting elements. The tube 56 for evacuating the brine will be submerged and accommodated vertically. Its length will allow the excess internal pressure of the 10"still to be limited to a given arbitrary value (5 centimeters for 50 hPa, for example), according to Figure 4, and in correspondence with the reference numerals of Figure 1, there is shown a diagrammatic perspective view of the solar still 110 for producing fresh water The still 110 has the shape of a large pneumatic mattress having a plurality (limited 5 in the drawing) of distillation cells mounted in series Each of these distillation cells will comprise an evaporation chamber 12-1 ... 12 -5, a first condensation chamber 14-1 ... 14-5 and a second condensation chamber 30 -1 ... 30-5 These three types of chamber have double walls (impermeable black membrane and hydrophilic nappa) respectively arranged as those of chambers 12, 14 and 30 of Figure 1. Internal hydrophilic layers 38a, 38b of the evaporation chambers 12-1 ... 12-5 are fed with the water to be distilled through ducts 40-1 ... 40-5 -JR. the outer hydrophilic webs 38c, 38d of the two types of condensation chamber 14-1 ... 14-5 and 30-1 ... 30-5, are fed through tubes and conduits, not shown, similar to the 58, 70, 84 e Figures 1 and 2. At the edge of the mattress formed by the still 11 shown in Figure 5, the sleeves 24-2 ... 24-5 equivalent to the intermediate part 24 of Figure 1 can be seen , pair the adjacent ends of the pairs of cameras 12 2 / 14-2 ... 12-5 / 14-5. The sleeving of the pair of 12 1 / 14-1 chambers has not been shown in order to provide visibility of the openings formed in the walls of the adjacent ends of these chambers. Two protection chambers 112a and 112b are respectively associated with the first evaporation chamber 12-1 and the last condensation chamber 14-5 of the apparatus. These chamber 112a, 112b are semicircular cross section. The common divider 16c of the chambers 12-1 and 112a and the, 16d, of the chamber 14-5 and 112b include some perforations through which the chambers 112a, 112b are filled with non-renewed humid air. A single inflatable transparent cover 114 covers the walls exposed to the sun of the five evaporation chambers 12-1 ... 12 -5. The outer walls of the evaporation chamber and the first still condensing chambers 110 have a bulky shape, their common dividing walls being flat. The cross-sectional shape of these chambers is that of a circular sector, with an apex angle of approximately 40 °, with the vertex downwards in the case of the evaporation chambers and upwards for the first condensation chambers. Under these conditions, the total length of the two radii in this sector is approximately three times larger than the circular line. The edges of the common dividing walls 16-1 ... 16-9 of the still 110 are fixed to the outer walls of the corresponding chambers in two different ways. The fastenings will consist of seams in the cases of the vertices of the first condensation chambers, since the internal hydrophilic covers 38a of the adjacent hot zones of two successive evaporation chambers such as 12-1 and 12-2 are in contact with the external hydrophilic cover 38b of the first condensation chamber such as 14-1. These seams will become environmentally sealed, by any convenient element, with respect to the dry air layer trapped under the transparent cover 114. The other type of fastener will be a weld between the vertices of the outer membrane 36b of the evaporation chambers and two. inner membranes 36c of two first condensing chambers attached. The tubes (not shown) for the evacuation of distilled water and brine produced by each distillation cell are connected to the collection duct elements, linked to two tubes at 54 and 56 as in Figure 1. Accordingly, with the Figure 4, the second condensation chamber 30-5 includes an outlet opening (not visible) on which the inlet hose 116 of the blowout 128 is connected. Similarly, the common dividing wall of the right extremity of the evaporation chamber 12-1 has an inlet opening in which the outlet hose 118 of the blower 128 is connected. The output of a turbine 120 is connected to this hose 118, the turbine inlet is in communication with the external part. The function of this turbine 120 is to maintain a constant pressure difference (1 to 2 hPa) inside the distillation cells with respect to the outside regardless of the temperature and pressure conditions. The first condensing chambers 14-1 ... 14-discharge into the second condensation chambers 30-1 ... 30-and the last one constitutes the preliminary chambers for the evaporation chambers 12-1 ... 12 -2. With respect to the evaporation chamber and the first condensation chamber of a given distillation cell, these are mutually communicated either indirectly via sleeves or directly via an aperture formed in their common dividing wall. By way of example, a still 110 can comprise ten distillation cells each 40 centimeters wide, 60 meters long and 60 centimeters high. The still 110 is adapted to be installed at ground level, in a stretch of water or in a mattress. As it is installed at ground level, the common external base of the first condensing chambers does not lead to the insulating stream 42 nor a moist hydrophilic cover 38c, but the moist hydrophilic covers 38d of the second condensation chambers will be on their side completely clear of the earth, achieved by any convenient means, f Additionally will include clamping rings, fixed to the external chambers 112a, 112b. Thanks to these measures, the solar stills provide 10-10 raw and 110 qu are easy to manufacture and relatively cheap (similar to the cost of inflatable boats), having a high performance, which are easy to implement and maintain , and are able to withstand strong winds. Indeed, with reference to Figure 1 (for this arguments would also be substantially identical co with respect to Figure 4), thanks to the sec air layer trapped under the sealed transparent cover 46b, protecting the hot zone of the evaporation chamber 12. , the heat absorbed from these zones is noticeably greater than that absorbed by the hot zones of the conventional type solar stills. This is because a problem has been eliminated, that of the reduced heat rise as a result of the shadow produced by condensed water droplets which was relatively significant in the case of the condensation surface constituted by the internal surface of the space described in FIG. the patent cited in the introduction. When it reaches the first condensation chamber 14, the water vapor carried along with the hot air leaving the evaporation chamber 12 immediately condenses to diffusion and, recycling the latent heat, onto the waterproof walls 36c, at a lower temperature, of the common dividing walls 16a, 16b, of the first condensation chamber 14. The presence of a relatively long thermally insulating cover 46a that begins at the entrance to the first condensation chamber prevents deviation towards a area that is cooled from the outside, from the hot air - which has a high content of water vapor, dragging the partial condensation of this steam without recycling the latent heat. As mentioned above, this phenomenon of condensation with significant recycling of heat latent continues throughout the passage through this first condensation chamber 14, with air that is becoming less and less hot and humid, until the end cooling of this air , carried out in the second condensation chamber / before returning to the evaporation chamber. As the air progresses progressively towards the first condensation chamber 14, it becomes drier and cooler which means that the recovery of the latent heat of the condensation becomes less effective. To compensate for this decrease, a first and second additional condensation, but without recycling the latent heat, is performed on the inner wall of the right portion of the outer bas of the condensing chamber 14 and that of the second condensation chamber 30. In both cases, the external walls mentioned have hydrophilic covers 38c, 38 exposed to the outside air and kept constantly moistened, which causes them to adopt a dewpoint temperature of this air, which is particularly low in the dry regions. It will be noted that these external hydrophilic covers 38c, 38d are exposed to unavoidable wear and thus will be made of a suitable material, for example a good cotton cloth. From the above, it turns out that with a significantly greater amount of heat absorbed, the multiple condensation zones have good recovery of latent heat for the first of these zones and a temperature that is particularly low for the latter, and the solar stills for producing fresh water. according to the optimum embodiments of the present invention, they have a performance which, a priori, is greater than two and, in any case, notably greater than all the conventional apparatuses described up to now. To this technical advantage, economic conditions of construction, operation and maintenance are added which are also particularly valuable. The dimensions and shape (cylinders or mattresses) of the solar stills to produce fresh water according to the invention will be adapted to the respective market. The industrial facilities for producing fresh water will include a plurality of units each having a relatively large absorbent surface. In such a facility, every hectare occupied on the land will produce, per day, a total volume of fresh water of the order of 200 cubic meters. For the domestic market, a mattress (or a set of cylinders) with an absorbent surface of around 1 square meter will be proposed, for installation on the ground or on a terrace. This will allow a family to have 200 liters of fresh water per day. For victims of marine accidents, a mattress (or cylinders) fitted with ballasting elements will be proposed, to be filled with water, having an absorbent surface area of one to two square meters. For boating, this will be a floating device that has an absorbent surface area of 10 to 20 square meters. Figure 5 is a cross-sectional view of a non-optimal modality that nevertheless is of interest, of a solar still to produce fresh water according to the invention. This still 150 comprises a closed space 15 having a transparent wall 154 which is relatively well sealed. For example, it will be of the agricultural greenhouse type with a transparent polyethylene wall, with the archways 156 installed on the ground at regular intervals. The closed space 152 will for example have several tens of meters in length several meters in height and width. A rigid gutter 15 for the, seawater supply is suspended mediant hangers 160 of the arches 156. The enclosed space 15 will house an evaporation chamber 162 whose longitudinal wall is formed by an outer black polyethylene impermeable membrane 164, provided with an internal cover formed by a nappa hydrophilic 166. The edges of this membrane and this layer are fixed by fasteners (not shown) on the edges of the gutter 158, so that the membrane 164 and the lap 166 are immersed in the seawater provided by the gutter 158. A blower electric 168, mounted on a frame suspended from a closed space arch 156, is installed on the end wall upstream of the evaporation chamber 162. In operation, the blower 168 inflates this chamber 162 causing this wall to take the form of a large circular cross-section cylinder. When the blower 168 stops, the chamber 162 deflates and its base rests * on the ground. The end wall downstream of the evaporation chamber 162 includes a wide opening in its upper portion. A brine evacuation tube 172 is connected to a low point of the baseline of this evaporation chamber. The base of the closed space 152 includes a waterproof cover 153. Additionally, this base 153 has a slight longitudinal inclination as well as two symmetrical side slopes. ending in the gutters d collection of fresh water 176-178, accommodated in the lower part of the vertical walls of the closed space 152 The gutters are connected to elements of external conduits to evacuate fresh water, not shown. The operation of the solar still 150 is similar to that of the apparatus shown in Figure 1. It differs from it however because the condensing surface is constituted by the internal face of the transparent wall of closed space 152 and not by the wall of a condensing chamber assigned only for this function. Under these conditions, the condensation deposited on the inner side of the enclosed space decreases somewhat the solar radiation absorbed by the black wall of the evaporation chamber 162. Co with respect to the drops of condensed water which, under its own weight, fall on the waterproof membrane 164, they finally reach the freshwater collection gutter element 176 178. One of the disadvantages of conventional solder stills, described in the patent cited in the introduction, is thus eliminated. It will be noted that a certain amount of recovery of latent heat from the vapor condensation may probably occur on the wall in the shadow of the "evaporation chamber 162. The still performance is better than that of the conventional apparatus per clearly notably less than that of the apparatus according to Figures 1 and 4. The invention is not limited to the modalities described above In fact, in a solar still, to produce fresh water according to figures 5, the blower can be eliminated, and the chamber Cylindrical evaporation can be replaced by a flat surface stretched on a frame, conveniently oriented so that faces the sun, which takes the form of a black waterproof membrane provist with a hydrophilic coating.Similarly, in a solar still smaller dimensions According to Figure 1, the blower can be removed together with the first condensation chamber, and the evaporation chamber can be removed. blar in a U-shape, the rest of the condensation chamber fits between two ends of the latter. In both cases, the natural diffusion of the vapor is produced from the hot, humid hydrophilic nap towards a condensation surface which is relatively cold. In the second case, it can, with reduced means and low yield, produce the daily freshwater requirements of a victim of an air accident or a camper. If we now turn to the question of the economy of the construction and operation of solar stills to produce fresh water according to the invention, described above, it will be seen that its main component is a novel material consisting of a black polyethylene membrane glued to a hydrophilic nonwoven cellulose web. The cost of this material is less than one French franc per square meter. Taking into account, first, the low costs of operation and maintenance of the industrial solar plant to produce fresh water that incorporates a large number of solar stills according to the invention and, in second place, the low cost of renewing components (life The usefulness of the membrane is estimated to be about two years. The cost of a cubic meter of fresh water, produced by an unit, should, in dry regions near the coast, be, to the maximum, of the same order of magnitude as the of water to drink, supplied in temperate regions of the globe from the river and the friar mantle. In the case of large industrial solar installations that produce thousands of cubic meters of fresh water per day, it will be the recovery of the brine and its collection in a marsh. The income from selling the salt thus obtained will make it possible to divide the investment between the two products and in this way greatly reduce the cost • price per cubic meter of the fresh water produced. The possible uses of distilled water thus produced will, possibly after convenient treatment, be identical to those of fresh water available in temperate regions (domestic, industrial and agricultural). The implementation of the invention resides in the availability of a novel industrial product, designed to be used to form the external wall of the evaporation chamber of a solar cell to produce fresh water. This novel industrial product comprises two components. One of them is a flexible membrane, which is waterproof and of dark colo which has a good mechanical resistance, a good capacity to withstand ultraviolet radiation and water salad (film, black polyethylene, for example). The other component is a hydrophilic layer that has a good ability to withstand salt water (preferably non-woven cellulose material). The two components are joined together by adhesive elements that respect the specific characteristics of each one of them. Regarding the common dividing walls described, it will be noted that the colo of the membrane is of no importance and, under these conditions, impermeable white membranes may be employed.

'Cellulose coating as commonly used in hospitals to protect bed mattresses, always provided that these membranes hold salt water and are approved for contact with food.

Claims (14)

1. A solar still for producing fresh water which comprises: an evaporation chamber (12-162), having a flexible slightly stretched wall, constituted by a dark waterproof membrane (36a, 164), exposed to sunlight, provided with a cover hydrophilic (38a, 166) accommodated in the shade; a condensation chamber (14, 30, 152) having an impermeable wall (36c, 154), in contact with the external means adapted to dissipate, in this medium, the latent heat of condensation of the steam produced; characterized in that: the evaporation chamber (12-162) has an elongated shape, and, by its ends (22, 26), communicated with the condensation chamber (14, 30, 152), - a blower (28) is installed in the apparatus, to cause a closed cycle circulation of air flow between the two chambers (12-14 / 30 or 162-152); a conduit (40, 158), fed with water to be distilled, adapts to distribute this water, mediated capillarity and gravity, on the hydrophilic cover (38a, 166); a conduit (54, 176), adapted to evacuate the produced fresh water, is installed at a low point (64) of the condensation chamber (14/30, 152); a conduit (56, 172) adapted to evacuate the produced brine, is installed at a low point (56) of the evaporation chamber (12, 162).

2. The solar still for producing fresh water according to claim 1, characterized in that: the evaporation chamber (162) is installed under a closed transparent space (152) and inflated by the action of the blower (28), - the The condensation chamber is constituted by the volume of the closed space (152) external to the evaporation chamber (162), the vapor condensing on the internal face of the closed space.

3. The solar still for producing fresh water according to claim 1, comprising an evaporation chamber (12) provided with a transparent thermally insulating cover (46b), - characterized in that: the evaporation chamber (12) and the chamber d) condensation (30) - both have flexible impermeable walls and communicate with each other through the openings (22, 26) formed in the upper portions of the extreme dividing walls (18, 20) of the evaporation chamber (12); ~ the condensation chamber (30) is in shadow, and its wall in contact with the external medium is provided with an external hydrophilic cover (38d), kept moist by any convenient element, at least the part exposed to the air of the medium external; suitable elements for (10e-54, 120) s associated with the blower (28,) to allow the two chamber (12, 30) to inflate and maintain a slight excessive pressure.

4. The solar still to produce fresh water according to claim 1, includes an evaporation chamber (12) provided with a transparent thermally insulating cover (46b), - characterized in that: the evaporation chamber (12) and the chamber d condensation (14) both have flexible impermeable walls and communicate with each other through the openings (22, 26), formed in the upper portions of the extreme partition walls (18, 20) of the evaporation chamber (12); the condensation chamber (14) is in the shade and its wall (36c), in contact with the external medium, is provided with an external hydrophilic cover (38c), which is kept moist by means of suitable elements, at least in the exposed part to the air of the external medium, - the condensation chamber (14) is additionally separated from the evaporation chamber (12) by a longitudinal common dividing wall (16) adapted for recycling, in the evaporation chamber (12) a part of the heat latent d condensation of the steam, - convenient elements (lOd, 54, 120) is associated with the blower (28) to allow the two chambers (12, 14) inflate and maintain in them a slight excessive pressure.

5. The solar still for producing fresh water according to claim 1, includes an evaporation chamber (12) provided with a transparent thermally insulating cover (46b), - characterized in that: a first condensation chamber (14) separates from the evaporation chamber (12) by means of a longitudinal common dividing wall (16), adapted to ensure and recycle the latent heat of condensation in the evaporation chamber (12); a second condensation chamber (30), accommodated in the shadow that follows the first condensation chamber (14), which forms a preliminary chamber for the evaporation chamber (12), is provided with an external hydrophilic cover (38d) that it is kept moist by any convenient element and, at least for the most part, it is exposed to the air from the external environment; the evaporation chamber (12) as well as the first condensation chamber (14) and the second condensation chamber (30) all have flexible impermeable walls the openings (22, 26), formed in the upper portions of the extreme partition walls of The evaporation chamber (12) provides communication between the end downstream of the evaporation chamber (12) and end upstream of the first condensation chamber (14) and the upstream end of this chamber (12) with the current end down the second condensation chamber (30), - the blower (28) establishes a closed cycle d air circulation in the three chambers (12, 14, 30) suitable elements (10, 54, 120) are associated with the same to allow inflation of the three chambers (12, 14, 30) to maintain a slightly excessive pressure therein.

6. The solar still according to claim 5, characterized in that the first condensation chamber (14) is thermally well insulated (46a) from external medium.

7. The solar still according to claim 5, characterized in that the first condensation chamber (14) has a wall (36c) in contact with the external medium, this wall (36c) is provided with an insulating cover (46a) and / or a hydrophilic cover (38c), which is kept moist by any convenient means.

8. The solar still according to one of claims 3, 4, 5, characterized in that the element for establishing the excessive pressure preferably comprises a small turbine (120) that pulls the outside air. The solar still according to one of claims 4 and 5, characterized in that the longitudinal common dividing wall (16), which separates the evaporation chamber (12) and the condensation chambers (14), has an impermeable membrane ( 36b) on the side of the condensing chamber (14) and a hydrophilic cover (38b) next to the evaporation chamber (12), this cover (38b) is supplied with the water to be distilled at any time. convenient element. 10. The solar still according to claim 9, characterized in that the geometric cross-sectional shape of the common divider wall (16) is adapted to maximize the heat exchange between the condensation chamber (14) and the evaporation chamber. (12) 11. The solar still according to claim 5, characterized in that the flexible conduit (14c, d), installed between the downstream end of the first condensation chamber (14) and the upstream end of the second condensation chamber ( 30), is adapted to maximize heat exchange between the flow of the hot moist air exiting the conduit (14c, d) and the inner surface of the external wall of the second condensation chamber (30). The solar still according to one of claims 3, 4, 5, characterized in that it has the shape of an elongated cylinder having a circular transverse cut, inflated with air under slight excessive pressure, which surrounds the different chambers (12, 14, 30) of the apparatus (10). 13. The solar still for producing fresh water according to claim 4, characterized in that: the apparatus constitutes a type of large pneumatic tire (110), formed by a plurality of distillation cells; each distillation cell comprises, arranged in series, an evaporation chamber (12-1 ... 12-5) and a condensation chamber (14-1 ... 14-5); a single blower (128), installed externally of the mattress (110) is linked to the distillation cells d so that it establishes a closed cycle of air circulation and is successively in the different cells or separately within each of the cells, - a turbine (120) that pulls the air from outside, adapts to maintain a slightly excessive pressure inside of several chambers of the apparatus; symmetric oblique common dividing walls (16-1 ... 16-9) fixed to two surfaces of the appliance, - • separating the evaporation chambers (12-1 ... 12-5) from the condensation chambers (14-1 ... 14 -5) and which provide these two types of chamber with a cross section having the shape of a narrow elongated circular sector, - a single thermally insulating transparent cover (114) covering the portion of the apparatus surface (110) exposed to the sun, formed by the adjoining hot zones of the evaporation chambers (12-1 ... 12-5). 14. The solar still for producing fresh water according to any of claims 5, 6 or 7, characterized in that: the apparatus constitutes a type of large pneumatic tire (110), formed by a plurality of distillation cells; each distillation cell comprises, as a series, an evaporation chamber (12-1 ... 12-5) and a condensation chamber (14-1 ...- 14-5); a single blower (128), installed externally of the mattress (110), is linked to the distillation cell d so that it establishes a closed cycle of air circulation and is successively in the different cells or separately within each of the cells, - a turbine (120) pulling the air from the outside, it adapts to maintain a slightly excessive pressure inside of several chambers of the apparatus, - symmetrical oblique common dividing walls (16-1 ... 16-9) fixed to two surfaces of the apparatus , which separates the evaporation chambers (12-1 ... 12-5) from the condensation chambers (14-1 ... 14-5) and which provide these two types of chamber with a cross section that has the shape of a narrow elongated circular sector; a single, thermally insulating transparent cover (114) covering the portion of the apparatus surface (110) exposed to the sun, formed by the adjoining hot zones of the evaporation chambers (12-1 ... 12-5).