US20170067666A1

US20170067666A1 - Open-flow solar collector

Info

Publication number: US20170067666A1
Application number: US14/847,009
Authority: US
Inventors: Alexander Levin
Original assignee: Individual
Current assignee: Individual
Priority date: 2015-09-08
Filing date: 2015-09-08
Publication date: 2017-03-09

Abstract

The invention relates to a field of open-flow solar collectors, and specifically to flat solar collectors with wetting the underneath sides of their solar radiation absorbing plates with liquid heat transfer medium. More specifically, the invention proposes the flat solar collector, which operates with relatively low flow rate of the heat transfer medium on the backside of the solar radiation absorbing plate, with flow in the form of some rivulets. The invention discloses some technical solutions, which restrict meandering rivulets' flow.

These technical solutions are based on application of longitudinal strips attached by permanent magnets to the backside of the solar radiation absorbing plate fabricated from ferromagnetic metal.

Description

This application is a divisional of Ser. No. 13/714,697 filed Dec. 14, 2012, which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The invention relates to the field of flat-plate solar collectors and, particularly, to open-flow flat-plate solar collectors.

BACKGROUND OF THE INVENTION

The invention relates to a field of open-flow flat-plate solar collectors, and, specifically, to flat-plate solar collectors with wetting the underneath sides of their solar radiation absorbing plates by liquid heat transfer medium.
Such solar flat-plate collectors and heat transferring units are disclosed in some US patents.
U.S. Pat. No. 4,003,365 discloses a structure for collecting solar energy and storing the same as heat in a body of water. An inclined southerly wall is provided with a solar absorption surface protected from convection losses by a transparent membrane overlaying the absorption surface. The absorption surface is also formed as a membrane which is wetted at its underside within the structure by water spray and as solar radiation is absorbed and converted to heat at the membrane, the water at the underside of the membrane is heated. This heated water drops from the membrane and flows to a reservoir.
U.S. Pat. No. 4,085,732 describes a method and apparatus for heating a liquid using solar energy. Through the use of an absorber plate made of a sheet of copper or any other similar conductive metal, the heat from the sun is captured. The front surface of the plate is covered with a dark absorbent coating. The heat absorbed by the copper sheet is conducted to a thin film of liquid such as water which is fed by gravity down the backside of the plate from a supply line disposed adjacent to the top of the backside of the plate. The liquid absorbs the heat from the plate as it flows downward covering the backside of the plate and is discharged at the bottom of the plate into a drain line. The drain line removes the heated liquid from the apparatus.
U.S. Pat. No. 5,460,164 discloses a solar heat collector roof comprises an absorber plate (1) for incident radiation energy and a heat exchange plate placed directly thereunder. The heat exchange plate is corrugated in such a manner that it comprises channels extending down along the roof. The heat exchange plate is moreover in direct contact with the absorber plate thereabove. A heat carrying or heat removing liquid medium, e.g. water, flows in the channels. The liquid medium, which removes heat from the heat exchange plate, is supplied at such a rate that the flow rate down along the roof in the channels lies below the rate at which the surface tension of the heat carrying medium is broken, so that a winding (meandering) and travelling flow pattern is imparted thereby to the liquid medium, and up along the channel walls.
U.S. Pat. No. 4,261,337 describes a solar heat collector includes an enclosure having a solar energy transmitting cover member and a solar energy absorbing base member. Within the enclosure, structure is provided, connected to a fluid inlet, for causing a stream or film of fluid to flow along the interior surface of the cover member. The same structure may be used to impart a separate flow of fluid along the energy absorbing base member. The cover member is oriented to prevent the gravitational forces on the fluid stream, flowing along the interior surface of the cover member, from overcoming the adhesion forces between the stream and the interior surface of the cover member. This stream removes condensation from the cover member as it captures heat therefrom. The stream may be created by spraying fluid on the interior surface of the cover member or by a fluid dispensing member having a fluid outlet adjacent the interior surface of the cover. Means for distributing the fluid across the interior surface as same flows therealong may also be provided.
U.S. Pat. No. 4,121,568 teaches a system for collecting heat energy from solar radiation to heat a liquid medium. The system includes a solar radiation collector plate which has its rear face adapted to cause a liquid medium to be in direct thermal contact with the rear face of the plate while flowing over and covering essentially all of the rear face. According to one important aspect of the invention, the rear face is provided with a material having capillary attraction properties to spread a liquid medium across essentially all of the rear face of the plate so that the liquid medium absorbs large amounts of heat energy from the collector plate.
U.S. Pat. No. 4,108,057 teaches a solar water heater is positioned in an inclined manner with an inlet at the upper portion and an outlet at the lower portion so that the water flows downwardly over a series of corrugations extending transversely to the direction of flow of water, the water spilling over each corrugation in turn.
U.S. Pat. No. 4,124,020 describes a solar energy collector has a corrugated, inclined plate exposed to solar rays on a blackened front or top side thereof. A heat-absorbing liquid carrier adheres to an opposite rear or undersurface of the plate in the form of a thin sheet by surface tension, and is directed gravitationally to a collection trough at the bottom edge of the plate.
U.S. Pat. No. 3,995,804 discloses an inclined heat absorptive and conductive panel including downwardly opening inverted V-shaped grooves formed therein extending downwardly from the upper end portion of the panel toward the lower end portion of the panel is provided. In addition, structure is provided for introducing a heat absorptive liquid into the upper end portions of the grooves and second structure is provided for receiving and collecting liquid from the lower ends of the grooves. The cross sectional shape and size of the grooves is such to allow at least substantially all of the liquid introduced into the upper ends thereof to be retained therein by the cohesive and surface tension properties of the liquid during its movement downwardly through the grooves by gravity toward the lower end of the panel. The panel comprises an inclined partition secured across the interior of an upwardly opening housing and a substantially fluid tight cover is secured across the top of the housing above the panel. Further, the structure by which liquid flowing downwardly to the lower end of the panel is collected includes additional structure whereby a partial vacuum is maintained within the housing between the transparent cover and the heat absorptive panel.
U.S. Pat. No. 3,943,911 discloses a solar heat exchanger, which comprises: A. a base and an extended surface thereon for facing frontwardly toward the sun, B. means communicating with said surface to conduct liquid to flow in dispersed condition adjacent said surface, and C. a sheet overlying said surface and spaced therefrom sufficiently closely to cooperate therewith for filming the flowing liquid, said sheet adapted to receive solar radiation for promoting heat transfer to the filmed and flowing liquid
U.S. Pat. No. 3,146,774 describes a solar collector, which is constructed similarly to the solar collector of U.S. Pat. No. 3,943,911.
These patents have a common drawback: in order to ensure complete wetting of the backside of the absorbing plate they would be forced to apply relatively high flow rates (200 kg/mh or more) of water or aqueous solution supplied into their distributing pipes. This value of the required flow rate is presented, for example, in the book: S. S. Kutateladze HANDBOOK OF HYDRODYNAMIC PRESSURE DROPS AND HEAT TRANSFER, Energoatomizdat, Moscow 1990, p. 178 (in Russian).
On the other hand, flow rate of 40 kg/mh or less is sufficient for a common 1.8-square-meter flat plate solar collector. For the flat plate solar collectors, which are intended to concentrate a diluted solution of liquid desiccant (as, for example, aqueous solutions of LiCl or CaCl.sub.2) this flow rate can be estimated as 10-15 l/hm.
In such a way, the aforementioned common solar collectors require usage of pumps with relatively high power; it leads to additional expenses for equipment and electric energy.
Only U.S. Pat. No. 3,995,804 has not this drawback and can operate with low flow rates. However, this patent does not give solution of anticorrosive polymer coating of the backside of the solar radiation absorbing plate (such polymer coating can fulfill the inverted V-shaped grooves described in this patent). In addition, U.S. Pat. No. 3,995,804 does not solve a problem of a relatively small general surface of rivulets flowing on the backside of the solar radiation absorbing panel.
Secondly, it is known that oxygen entering into an open loop hydraulic solar system will cause rust in any iron or steel component. Such systems should have copper, bronze, brass, stainless steel, plastic, rubber components in the plumbing loop.
Therefore, if the solar radiation absorbing plate is fabricated from a common carbon steel sheet, its backside to be coated with a layer of thermo-stable polymer anticorrosive material.

BRIEF SUMMARY OF THE INVENTION

This invention proposes a design of a flat-plate solar collector, which is characterized by rivulets' flow on the backside of its solar radiation absorbing plate; i.e. flow rate of water, antifreeze liquid medium or aqueous solution supplied on the upper section of the backside of the solar radiation absorbing plate is significantly lower than the minimum flow rate, which ensures formation of an entire liquid film flowing on the backside of this solar radiation absorbing plate.
It is known that for low magnitudes of liquid flow rate on an inclined or vertical plate the liquid flow pattern is characterized by a system of narrow rivulets with relatively small width (for water and aqueous solutions in the order of 1-8 millimeters).
Detailed theoretic analysis of rivulets' flow and their stability is presented in the article: E. S. Benilov, “On the stability of shallow rivulets”, J. Fluid Mech. (2009), vol. 636, pp. 455÷474. Pp. 461÷462 of this article gives demonstration of stability of a rivulet flowing on the underside (backside) of an inclined plate.
The article: A. Daerr et al. “General Mechanism for the Meandering Instability of Rivulets of Newtonian Fluids”, PHYSICAL REVIEW LETTER, SPRL 106, 184501 (2011) demonstrates that a rivulet flowing down an inclined plane often does not follow a straight path, but starts to meander spontaneously. This instability is the result of two key ingredients: fluid inertia and anisotropy of the friction between the rivulet and a substrate. Meandering only occurs if the motion normal to the instantaneous flow direction is more difficult than parallel to it. Above the threshold, the rivulet follows an irregular pattern with a typical wavelength of a few cm.
The article: Nolwenn L E GRAND-PITEIRA et al. “What governs rivulet meanders on an inclined plane?”, Oct. 11, 2005, CCSD—00011140, Internet, shows that a rivulet flow is highly hysteretic: the shape of the meanders varies with flow rate only for increasing flow rates, and the straight rivulet regime does not appear for decreasing flow rate.
Also, a main object of this invention is to provide simple means limiting the meandering phenomena of rivulets flowing on the backside of a solar radiation absorbing plate.
A flat-plate solar collector, which is proposed in this invention, is designed from following main units:
a housing with an internal thermal insulation of its bottom and side walls; the internal surfaces of the layers of the thermal insulation are covered with impervious layers;
a glazing of the upper aperture of the housing (in some designs of the solar collector the glazing may be omitted);
a solar radiation absorbing plate, which is fastened underneath the glazing in the housing and sealed with this housing or with the impervious side walls' layers of the thermal insulation;
a distributing pipe; the proximal section of this distributing pipe is placed outside the housing, and its middle and distal sections are installed on the backside of the solar radiation absorbing plate; the middle and distal sections of this distributing pipe are provided with openings (or nozzles), which supply evenly water or aqueous solution on the upper section of the backside of the solar radiation absorbing plate; the upper section of the absorbing plate backside is provided with some pipe clips serving for fastening the distributing pipe;
rivulets' flow restricting longitudinal means, which divide the backside of the solar radiation absorbing plate into a set of parallel zones; these rivulets' flow restricting longitudinal means entrap the rivulets when they meet the rivulets' flow restricting longitudinal means with following transformation of the shapes of these rivulets and flowing the rivulets in their transformed shapes along the rivulets' flow restricting longitudinal means;
an outlet connection, which is situated in lower section of the housing of the solar collector and serves for withdrawing the water, aqueous solutions or another liquid medium from the internal space of the flat solar collector (the space between the solar radiation absorbing plate and the impervious layer of the thermal insulation);
a venting opening, which provides fluid communication of the internal space of the flat solar collector with the surrounding atmosphere.
The flat solar collector, which is intended for evaporation and concentration of aqueous solutions, should be provided with an inlet connection and an outlet connection for supplying and removal of the air. In this case the venting opening may be lacking.
The rivulets' flow restricting longitudinal means can be designed on the base of several physical principles.
These restricting means may operate on the base of capillary forces, gravitational force or by application of body force tangent to the substrate surface in opposite direction as a driving shear surface (see, for example, S Marshall and S. Wang CONTACT LINE FINGERING AND RIVULET FORMATION IN THE PRESENCE OF SURFACE CONTAMINATION, Computers & Fluids, V. 34, Issue 6 Jul. 2006, pp. 664-683).
It should be noted, that for very low values of flow rate a drop-wise flow can precede formation of rivulets' flow. The invention proposes in this case the same flow restricting longitudinal means as for rivulets' flow.
In the first version of this invention there are a bank of strips which may be fabricated from any corrosion-resisting material (steel with anticorrosive coating, copper, thermo-stable polymer etc.).
Each strip in this version is provided with one or two longitudinal beads and some openings with vertical flanging; an O-ring (or a back-up ring) is inserted into each opening; a tapered conical permanent magnet keeps close this O-ring (or back-up ring) against the opening flanging; the tapered conical permanent magnet is inserted into the opening until its immediate contact with the backside of the solar radiation absorbing plate with attendant deformation of the O-ring (or the back-up ring).
In a simpler version of this technical solution, the strips are provided with some openings and O-rings (or back-up rings), which are placed concentrically with these openings; the diameter of each opening lies in the interval between the inner diameter of the O-ring and its outer diameter.
A tapered conical permanent magnet, which has its top diameter somewhat smaller that the inner diameter of the O-ring and its base diameter somewhat larger that the inner diameter of the O-ring, is inserted with its tapered section into the opening until its immediate contact with the backside of the solar radiation absorbing plate. The top and base diameters of the O-ring are chosen in such a way, that this insertion causes radial extension of the O-ring, and friction forces between the tapered conical permanent magnet and this O-ring held in place the strip in contact with the backside of the solar radiation absorbing plate.
In the next version of the invention the longitudinal strips, which are provided with two longitudinal beads (two lateral strips are provided with one bead each one), are designed as a grate with a frame comprising two lateral strips with one bead each one and upper and lower webs joining the beads of the neighboring longitudinal strips.
The gap between the webs and the backside of the solar radiation absorbing plate is chosen in such a way, that it allows free entrance of the rivulets flowing on the backside of the solar radiation absorbing plate to the areas between the neighboring longitudinal strips. The grate may be fastened on the backside of the solar radiation absorbing plate by the same means as in the case of the longitudinal strips.
The proposed solar collector should be installed with a certain angle of inclination to the horizontal plane.
In addition, the upper and lower edges of the solar radiation absorbing plate of the installed solar collector may have a distinct angle of inclination with respect to the horizontal plane, this provides possibility that most of rivulets will contact with the rivulets' flow restricting longitudinal means from a same side.
The distributing pipe may be designed in such a manner, which ensures immediate contact of a supplied liquid medium (water, aqueous solution or thermo-stable organic liquid) with the upper section of the backside of the solar radiation absorbing plate.
For example, the distributing pipe may be designed in a following form: the distal end of the distributing pipe is sealed and there is a set of openings in the wall of this distributing pipe, which are arranged in line. The wall openings are provided with outlet connections and the distal ends of the outlet connections are terminated with flexible sleeves; also, it allows installation of the distributing pipe on the backside of the absorbing plate in such a manner that the distal ends of the flexible sleeves will be in immediate contact with the backside of the solar radiation absorbing plate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 demonstrates a vertical cross-section of a flat solar open-flow collector.

FIG. 2a , FIG. 2b and FIG. 2c are a top view and transverse cross-sections A-A and B-B of a grate-wise bank of strips with beads, wherein these strips are provided with openings.

FIG. 3a and FIG. 3b are cutaway transverse views of the solar radiation absorbing plate with fastening a strip (FIG. 3a ) or a grate-wise bank of strips (FIG. 3b ) by permanent magnets, wherein the strip or of the grate-wise bank of strips are provided with openings.

FIG. 4a and FIG. 4b are cutaway transverse views of the solar radiation absorbing plate with fastening a strip (FIG. 4a ) or a grate-wise bank of strips (FIG. 4b ) by permanent magnets, wherein the strip (or the grate-wise bank of strips) is provided with flanged openings.

FIG. 5a and FIG. 5b are cutaway transverse views of the solar radiation absorbing plate with fastening a strip with one bead (FIG. 5a ) or a strip with two beads (FIG. 5b ) by external permanent magnets.

FIG. bis a cutaway transverse view of the upper section of the solar radiation absorbing plate with the installed distributing pipe.

DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 demonstrates a vertical cross-section of a flat solar open-flow collector 100.
It comprises:
housing 101;
thermal insulation layers 102; the internal surfaces of the layers of the thermal insulation 102 are covered with impervious layers;
glazing 103 of the aperture of housing 101;
a solar radiation absorbing plate 104 which is installed underneath glazing 103 and sealed with housing 101; the front side of the solar radiation absorbing plate 104 is provided with a solar radiation absorbing coating 105 and its backside—with a corrosion resisting coating 106; this solar radiation absorbing plate 104 is fabricated from ferromagnetic metal;
a distributing pipe 108; the proximal section of this distributing pipe 108 is placed outside housing 101 and its middle and distal sections are situated underneath of the backside of the solar radiation absorbing plate 104; the distributing pipe 108 is installed on the backside by pipe clips 112;
longitudinal strips 107 with beads 113, openings 114 dividing the backside of the solar radiation absorbing plate 104 into a set of parallel zones; these longitudinal strips 107 with the beads 113 entrap the rivulets when they meet the longitudinal strips 107 with following flow of the rivulets along these longitudinal strips 107; permanent magnets 115 serves for fastening the longitudinal strips 107 on solar radiation absorbing plate 104;
an outlet connection 110 which is situated at the bottom section of the internal space 111 of the solar collector 100 and serves for withdrawing the water or aqueous solutions;
a venting opening 109 which provides fluid communication of the internal space 111 of the solar collector 100 with the surrounding atmosphere.
FIG. 2a , FIG. 2b and FIG. 2c are a top view and transverse cross-sections A-A and B-B of a grate-wise bank 200 of strips with beads, wherein these strips are provided with openings.
It comprises: terminal strips 201 with beads 202; intervening strips 203 with their beads 204; webs 205; openings 206, which are formed in terminal strips 201 and intervening strips 203.
FIG. 3a and FIG. 3b are cutaway transverse views of the solar radiation absorbing plate with fastening a strip (FIG. 3a ) or a grate-wise bank of strips (FIG. 3b ) by permanent magnets, wherein the strip or of the grate-wise bank of strips are provided with openings.
FIG. 3a comprises: a solar radiation absorbing plate 301 fabricated from ferromagnetic metal; the front side of this solar radiation absorbing plate 301 is provided with a solar radiation absorbing coating 302; the backside of the solar radiation absorbing plate 301 is provided with a corrosion resisting coating 303. Strip 304, which is fabricated corrosion resisting material, is installed on the backside of the solar radiation absorbing plate 301; this strip 304 is provided with two beads 305.
Strip 304 is provided with some openings 306, which serve for installation of O-rings 307 and truncated conical permanent magnets 308.
FIG. 3b comprises: the solar radiation absorbing plate 301 fabricated from ferromagnetic metal; the front side of this solar radiation absorbing plate 301 is provided with the solar radiation absorbing coating 302; the backside of the solar radiation absorbing plate 301 is provided with the corrosion resisting coating 303. Strip 310, which is fabricated from corrosion resisting material and presents a section of a grate-wise bank of the strips, is installed on the backside of the solar radiation absorbing plate 301; this strip is provided with two beads 313. Webs 311 serve for joining beads 313 of the aforementioned bank of strips 310.
Strip 310 is provided with some openings 312, which serve for installation of O-rings 314 and truncated conical permanent magnets 315.
FIG. 4a and FIG. 4b are cutaway transverse views of a solar radiation absorbing plate with fastening a strip (FIG. 4a ) or a grate-wise bank of strips (FIG. 4b ) by permanent magnets, wherein the strip or the grate-wise bank of the strips are provided with flanged openings.
FIG. 4a comprises: the solar radiation absorbing plate 401 fabricated from ferromagnetic metal; the front side of this solar radiation absorbing plate 401 is provided with a radiation absorbing coating 402; the backside of the solar radiation absorbing plate 401 is provided with a corrosion resisting coating 403. Strip 404, which is fabricated from corrosion resisting material, is installed on the backside of the absorbing plate 401; this strip is provided with two beads 405. Strip 404 is provided with some openings with outward flanges 406, which serve for installation of O-rings 408 and truncated conical permanent magnets 409.
FIG. 4b comprises: the solar radiation absorbing plate 401 fabricated from ferromagnetic metal; the front side of this solar radiation absorbing plate 401 is provided with the radiation absorbing coating 402; the backside of the solar radiation absorbing plate 401 is provided with the corrosion resisting coating 403. Strip 410, which is fabricated from corrosion resisting material and presents a section of a grate-wise bank of such strips, is installed on the backside of the absorbing plate 401; this strip is provided with two beads 411. Webs 412 serve for joining beads 411 of the aforementioned bank of strips 410.
Strip 410 is provided with some openings with outward flanges 413, which serve for installation of O-rings 415 and truncated conical permanent magnet 416.
FIG. 5a and FIG. 5b are cutaway transverse views of a solar radiation absorbing plate 501 with fastening a strip with one bead (FIG. 5a ) or a strip with two beads (FIG. 5b ) by external permanent magnets.
FIG. 5a comprises: the solar radiation absorbing plate 501 fabricated from ferromagnetic metal; the front side of this solar radiation absorbing plate 501 is provided with a solar radiation absorbing coating 502; the backside of the solar radiation absorbing plate 501 is provided with a corrosion resisting coating 503. Strip 504, which is fabricated from ferromagnetic steel, is installed on the backside of the solar radiation absorbing plate 501; this strip is provided with one bead 505 and covered (including bead 505) with a corrosion resisting coating 506. Strip 504 is secured on the solar radiation absorbing plate 501 by a permanent magnet 507.
FIG. 5b comprises: the solar radiation absorbing plate 501 fabricated from ferromagnetic metal; the front side of this solar radiation absorbing plate 501 is provided with the radiation absorbing coating 502; the backside of the solar radiation absorbing plate 501 is provided with the corrosion resisting coating 503. Strip 508, which is fabricated from ferromagnetic metal, is installed on the backside of the solar radiation absorbing plate 501; this strip is provided with two beads 509 and covered (including beads 509) with a corrosion resisting coating 510. Strip 508 is secured on the solar radiation absorbing plate 501 by a permanent magnet 511.
FIG. bis a cutaway transverse view of the upper section of a solar radiation absorbing plate 601 with a distributing pipe 604, which is installed on the upper section of the backside of the solar radiation absorbing plate 601.
The drawing depicts: the solar radiation absorbing plate 601; the front side of this absorbing plate 601 is provided with a radiation absorbing coating 602; the backside of the solar radiation absorbing plate 601 is provided with a corrosion resisting coating 603; the distributing pipe 604 is provided with nozzles 605, which are terminated with flexible sleeves 606; pipe clips 607 are installed on the backside of the absorbing plate and serve for securing the distributing pipe 604.

Claims

1. A flat open-flow solar collector consisting of following main units:

a housing with an internal thermal insulation of its bottom and side walls; the internal surfaces of the layers of said internal thermal insulation are covered with impervious layers;

a solar radiation absorbing plate, which is fastened in said housing and joined with said housing; said solar radiation absorbing plate is fabricated from ferromagnetic metal; the upper side of said solar radiation absorbing plate is covered with solar radiation absorbing paint at least in visible range of electromagnetic radiation and the backside of said solar radiation absorbing plate is covered with corrosion resistive coating;

a distributing pipe; the proximal section of said distributing pipe is placed outside said housing, and its middle and distal sections are installed on the backside of said solar radiation absorbing plate; said distributing pipe is provided with openings, which supply evenly water or other liquid mediums on the upper section of said backside of said solar radiation absorbing plate; the upper section of said backside of said solar radiation absorbing plate is provided with some pipe clips serving for fastening said distributing pipe;

rivulets' flow restricting longitudinal means, which divide the backside of said solar radiation absorbing plate into a set of longitudinal parallel zones; said rivulets' flow restricting longitudinal means entrap the rivulets when they meet said rivulets' flow restricting longitudinal means with transforming the shapes of transverse cross-sections of said rivulets and following flow of said transformed-shape rivulets along said rivulets' flow restricting longitudinal means; said rivulets' flow restricting longitudinal means are designed as parallel metal strips with ferromagnetic properties like said ferromagnetic metal of the solar radiation absorbing plate; said metal strips are covered on their both sides and their edges with a corrosive resisting paint and they are placed apart longitudinally with a certain mutual interval on the backside of said solar radiation absorbing plate; each said metal strip is fastened on the backside of said solar radiation absorbing plate by some permanent magnets;

an outlet connection, which is situated in lower section of said housing of said open-flow solar collector and serves for withdrawing the water or other liquid mediums from the internal space between said solar radiation absorbing plate and said impervious layers of said internal thermal insulation;

a venting opening, which provides fluid communication of said space between said solar radiation absorbing plate and said impervious layers with the surrounding atmosphere.

2. A flat open-flow solar collector as claimed in claim 1, wherein said flat open-flow solar collector serves for evaporation and concentration of aqueous solutions; said flat open-flow solar collector is provided with inlet and outlet connections for supply of the air into the space between the solar radiation absorbing plate and the impervious layers of the thermal insulation and removal of the air from said space.

3. A flat open-flow solar collector as claimed in claim 1, wherein the housing is provided with glazing covering the aperture of said housing.

4. A flat open-flow solar collector as claimed in claim 1, wherein each metal strip is provided with at least one longitudinal bead with forming a wedge-wise gap between said bead and the adjacent surface of the backside of the solar radiation absorbing plate.

5. A flat open-flow solar collector as claimed in claim 4, wherein the strips are fabricated from anticorrosive material and provided with some openings; there are O-rings, which are placed concentrically with said openings; the diameter of each said opening lies in the interval between the inner diameter of said O-rings and their outer diameter; tapered conical permanent magnets, which have their top diameter somewhat smaller that the inner diameter of said O-rings and the base diameter of said tapered conical permanent magnets is somewhat larger than the inner diameter of said O-rings, are inserted with their tapered sections into said openings and said O-rings until their immediate contact with the backside of the solar radiation absorbing plate; said top and base diameters of said O-rings are chosen in such a way, that insertion of said tapered conical permanent magnets causes radial extending of said O-rings and friction forces between said tapered conical permanent magnets and said O-rings held in place said strips in contact with the backside of the solar radiation absorbing plate.

6. A flat open-flow solar collector as claimed in claim 4, wherein the strips are fabricated from anticorrosive material and provided with some openings; each said opening is provided with a vertical flanging, and there is the O-ring, which is inserted into said opening; the tapered conical permanent magnet keeps close said O-ring against said opening flanging; said tapered conical permanent magnet is inserted into said opening flanging until its immediate contact with the backside of the absorbing plate with attendant deformation of said O-ring.

7. A flat open-flow solar collector as claimed in claim 4, wherein the longitudinal strips provided with two longitudinal beads each one and two lateral strips provided with one longitudinal bead each one are joined with forming a grate with a frame comprising said two lateral strips; the upper and lower sections of said longitudinal strips' beads and said beads of said lateral strips are joined together by upper and lower webs.

8. A flat open-flow solar collector as claimed in claim 7, wherein the longitudinal strips and the lateral longitudinal strips of the grate are provided with openings.

9. A flat open-flow solar collector as claimed in claim 7, wherein the longitudinal strips and the lateral longitudinal strips of the grate are provided with flanged openings.

10. A flat open-flow solar collector as claimed in claim 1, wherein the distributing pipe is provided with nozzles, which are terminated with flexible sleeves; pipe clips are installed on the backside of the solar radiation absorbing plate and serve for securing said distributing pipe.

11. A flat open-flow solar collector as claimed in claim 10, wherein the distal ends of the flexible sleeves are sealed and the longitudinal sections of their walls facing to the backside of the solar radiation absorbing plate are provided with some openings.