FR2460454A1 - Tubular solar radiation collector wrapped in heat-conductive film - is made of silicone rubber or polyethylene, PVC nylon, polyester or polyurethane (BE 04.02.80) - Google Patents

Abstract

Solar collector comprises a tube with >=1 straight section serving to allow a heat-carrying fluid to flow through it. It is made of organosilicone rubber or an organic thermoplastics, and has >=2 flexible heat-conductive foils of coherent or non-coherent structure which are fastened to one another and envelope the tube from both sides. Ratio of width of the foils along the straight section of the tube; outer dia. of the tube = 2.5-10. Tube may be made of low pressure polyethylene, PVC, a polyamide, polyester, butyl rubber, EPR rubber or a polyurethane. When made of a silicone rubber, it is mfd. from cured diorganosiloxane rubber contg. mineral filler and a peroxide.

Description

The present invention in which Messieurs Jean participated
Louis MARCHAND-and Daniel SEMANAZ, relates to an element absorbing solar radiations intended to equip solar energy collectors.

 There are many embodiments of solar energy sensors based on the greenhouse effect, associated with the black body effect. These collectors generally include hollow plates or tubes absorbing solar radiation placed inside transparent enclosures ensuring the greenhouse effect. Inside the plates or tubes circulate heat transfer fluids intended to transport the heat due to solar radiations towards colder zones.

 Such solar energy collectors are described for example in the French patent application published under the number 2 298 066.

The sensor described in this application comprises, inside an enclosure, an absorbing element consisting of a metal plate with a rough surface or painted black, on the side not exposed to the sun is fixed a tubular metal coil. Although such an absorbent element is generally suitable, it has drawbacks.

Indeed it is heavy and rigid and therefore bulky, which makes it difficult to install and transport.

 It was then envisaged to produce absorbent elements which are not rigid and which can be rolled up in order to facilitate transport. Such absorbing elements are described in the French patent application published under the number 2,307,233. The absorbing element described in this patent application consists of a flexible material shaped so as to constitute a circuit of channels for the circulation of the heat-transfer fluid. . Such an absorbent element is easily transportable since it can be rolled up, but it has the disadvantage of poorly withstanding the frost or a pressure of the heat transfer fluid greater than atmospheric pressure, moreover the circulation of the heat transfer fluid undergoes changes of direction of 180 which create significant pressure losses.

 An object of the invention is a solar radiation absorbing element which is easily transportable while ensuring good absorption of solar radiation.

 Another object of the invention is an absorbing element of low cost price and easy installation.

A solar radiation absorbing element has now been found, characterized in that it comprises
- at least one tube having at least one rectilinear zone, said tube serving for the circulation of the heat-transfer fluid and being shredded in a material chosen from organic or organosilicon rubbers or organic thermoplastic products,
- At least two flexible thermally conductive sheets of continuous or discontinuous structure fixed in pairs, face to face, enclosing between them at least two rectilinear zones of tube.

 The tube used for the circulation of the heat transfer fluid must be made of a material having good resistance to thermal aging and to corrosion while having sufficient thermal conductivity. In addition, if the tube is used to convey sanitary water, the material must be of food quality and resistant to scaling.

The tube can, for example, be made of a material chosen from
- organic thermoplastic materials such as low density polyethylene, polyvinyl chloride, polyamides, polyesters,
- elastomer materials such as natural or synthetic organic rubbers, organosilicon rubbers.

 The organic rubbers are preferably chosen from the group of heat resistant ones such as: butyl rubbers, ethylene-propylene, polyurethanes.

 Organosilicon rubbers all have good heat resistance; they can therefore be chosen from the group of easily extrudable and hardenable ones. Preferably, the elastomers obtained by hot curing, above 100 OC, of compositions - mainly containing diorganopolysiloxane gums, mineral fillers and organic peroxides, are used.

 Such compositions are described in French patents published under the numbers 1 142 443, 1 382 285, 1 486 530, 2 017 663.

 It is also possible to use the elastomers obtained by hot curing, above 60 ° C., of compositions mainly containing diorganopolysiloxane polymers carrying a small amount of vinyl or allyl radicals (approximately 0.1 to 1%) relative to the whole. radicals linked to silicon atoms), possibly mineral charges, hydrogenoorganopolysiloxanes and a platinum catalyst.

 Such compositions are described in French patents published under the numbers 1 314 679, 1 360 908, 1 511 598, 2 016 914, 2 202 915.

 The section of the tube can be of simple geometric shape, for example oval, elliptical, square, preferably the section of the tube is circular.

 The diameter of the tubes (the term "dianeter" used here applies to the external diameter) can vary within a wide range of values. If, however, it is desired to manufacture absorbers which are easy to handle and easy to install, it is advantageous to choose tubes whose diameter is between 5 and 50 mm, preferably between 7 and 40 mm; the thickness of the wall of the tubes, linked to this diameter, is usually between 0.2 and 4 mm, and preferably between 0.3 and 3 mm.

 If the heat transfer fluid, which can be a gas, for example air, or a liquid, for example water, circulates in the tube at a pressure higher than atmospheric pressure, or if the liquid can freeze, the tube will preferably be reinforced by an external sheathing consisting of a network of wires or fibers. This network can consist of synthetic yarns or fibers, for example made of polyamide, polyester, polyamide imide, or glass fibers or metallic yarns. it can be made from single threads such as horsehair or threads or fibers previously formed into strands. In order to constitute the external network, the wires or fibers can be wound in a helix outside the tube, by reference they will be braided, knitted or woven.

 An outer sheath formed by a network of metallic wires advantageously covers, using its wires, from 25 to 85% of the surface of the tube, and preferably from 30 to 75%. The metal wires can be made of copper, aluminum or steel and their diameter can be between 0.05 and 0.4 mm, and preferably between 0.08 and 0.35 mm.

 The outer sheathing can be simultaneously manufactured and deposited, on the external surface of the tube directly at the outlet of the extruders used to manufacture the tubes. it provides the tubes with resistance to fluid circulation pressures greater than 10 bars.

 In the present description, reference will be made, for convenience, only to the "tube". it is understood that said tube can be sheathed or not and is intended to convey the heat transfer fluid.

 The thermally conductive sheets are made of a material which is a good conductor of heat. They can be made of plastic loaded, for example, with carbon black or metallic particles. Preferably they are made of metal, metals such as copper, steel, aluminum are very suitable.

 Aluminum is preferably used.

 By "continuous structure" of the thermally conductive sheets is meant that the structure of the sheets has no holes, thus sheets of continuous structure are similar to thick films or thin sheets.

 The thickness of the thermally conductive sheets of continuous structure must be sufficient to absorb and transmit significant flows of heat as well as to resist the stresses exerted on the absorbent elements during their manufacture and during their conditioning and installation. Thicknesses between 0.02 and 0.3 mm are generally suitable.

 By "discontinuous structure" of the thermally conductive sheets is meant that the structure of the sheets has holes, thus sheets of discontinuous structure can be made for example of fabrics obtained by weaving, knitting, braiding or twisting.

 The fabric can be produced with metallic wires, for example copper, steel, aluminum, the diameter of which is between 0.1 and 0.4 mm, preferably between 0.15 and 0.35 mm. Advantageously, the fabric has a tight texture so that the surface of the holes represents at most 60% of the total surface of the sheet.

 The thickness of the thermally conductive sheets of discontinuous structure is greater than that of the thermally conductive sheets of continuous structure, it can reach in the areas where the wires cross from 0.2 to 0.8 mm.

 The thermally conductive sheets are fixed in pairs, face to face, enclosing the rectilinear regions of the tube in such a way that, in a substantially diametral plane of the tube, they protrude on either side of the latter.

 By “width of thermally conductive sheet associated with the tube”, is meant the width or the portion of width of the thermally conductive sheet counted perpendicular to the axis of the tube and which participates in the heat exchanges with the rectilinear zone of said tube on the part and other of which it is situated. Below, when describing the various embodiments of the absorbing element, this concept will be clarified.

 Those skilled in the art will be able to determine, as a function of the thickness of the thermally conductive sheets, of the diameter of the tube, of the quantities of heat to be conveyed, the ratio of the width of the thermally conductive sheet associated with the tube, to the outside diameter of the tube. Generally, the ratio of the width of the thermally conductive sheet associated with the tubes to the diameter of the tube is between 2.5 and 10. and preferably between 3.5 and 8.

 The face-to-face fixing of the thermally conductive sheets of continuous structure can, for example be carried out by hot gluing.

This technique involves the use of sheets previously coated, on one side, with a fusible varnish based on usual organic compounds such as polyethylene, epoxy or acrylic resins or polyimides, or polyamide imides, or else silicone.

 The coated faces of the sheets are placed one against the other and bonding takes place by application, on either side of the zones where the tube is housed, for example a roller brought to the heat-bonding temperature of the varnish. Generally this temperature is in the range 100 - 220 OC.

 The fixing of the two sheets can be ensured by other methods of the same efficiency as the fusing.

 One can, for example fix the sheets by riveting or even by welding.

 The face to face fixing of the thermally conductive sheets of discontinuous structure is preferably carried out by welding.

 Thus by using thermally conductive sheets formed from copper, aluminum or tin-plated steel wires, it is easy, by passing the tube-sheet assembly between two heated rollers, around 200 - 400 OC, with circular grooves, effectively fix the two sheets by welding on either side of the tube, the latter being, with the sheet part which surrounds it, in the circular grooves of the rollers. If the copper, aluminum or steel wires are not tinned, the sheets can be spot welded using an electric welding machine.

 Preferably the outer face of the thermally conductive sheet exposed to the sun's rays is dark in color and mat in appearance. For this it can be coated with a paint, for example black, gray, green, red, blue, intended to absorb the sun's rays.

 The face of the absorbent element not exposed to the sun can be covered with a layer of cellular material. The role of this layer is to ensure good thermal insulation with respect to the surface on which this face will be in contact after the installation of the absorbing element.

 The thickness of the cellular material is not critical; it is however judicious, to avoid appreciably increasing the cost of the absorbent element, to use a thickness of between 0.3 mm and 40 mm.

 As an indication, the cellular material can be chosen from phenolic foams, polyvinyl chloride foams or polyurethane foams or even be made of glass or rock wool.

 Reference has been made above to two thermally conductive sheets for convenience, but it is understood that absorbing elements comprising a thermally conductive sheet exposed to the sun and a thermally conductive sheet not exposed to the sun obtained for example by folding a single thermally conductive sheet of surface equal to the sum of the surfaces of the two thermally conductive sheets are part of the invention and that even in this case, reference will be made to two thermally conductive sheets.

 The geometrical shape of the thermally conductive sheets is not critical, preferably one chooses thermally conductive sheets of simple geometric shape, not for example square or rectangular.

 The understanding of the invention will be facilitated by the attached figures which illustrate by way of examples, schematically and without a determined scale, various embodiments of absorber elements according to the present invention.

 Figure 1 is a top view of a first embodiment of an absorbent element according to the present invention.

 Figure 2 is a top view of a second embodiment of an absorbent element according to the invention.

 Figure 3 is a sectional view through a plane III-III perpendicular to the thermally conductive sheets and to the axes of the rectilinear zones of the tube of an absorbent element according to the first or second embodiments and comprising a layer of cellular material on the: faee of the absorber element not exposed to the sun.

 Figures 4, 5 and 6 are top views of a third, fourth and fifth embodiments of the absorber element according to the invention.

 The absorbing element according to the invention, a first embodiment of which is shown in FIG. 1, consists of a tube (1) comprising several rectilinear zones sandwiched between two thermally conductive sheets (2, 3). The straight areas of the tube (I) are connected in series and in a zig-zag by elbows (6). The elbows (6) can be formed by bending the tube (1).

 The inlet and outlet pipes (4) and (5) of the heat transfer fluid may be pieces of tubes added for example by welding or gluing to the tube (1), preferably they are parts of the tube (1).

 The thermally conductive sheets (2, 3) are fixed face to face by enclosing the tube in such a way that preferably the part of thermally conductive sheet situated between two rectilinear zones is in a substantially diametral plane of the tube and that they protrude on either side. other of the extreme rectilinear zones of the tube.

 The width of the thermally conductive sheets associated with the tube is not arbitrary, it is chosen so that the ratio of the width of the thermally conductive sheet associated with the tube to the outside diameter of the tube is between 2.5 and 10 and preferably between 3.5 and 8.

Thus, a tube with an outside diameter of 20 mm is associated with a width of thermally conductive sheets of between 50 and 200 mm.

 The thermally conductive sheets of the absorbent element are generally spread out flat on the floor of the transparent enclosures ensuring the greenhouse effect. They can however easily be corrugated appropriately in order to ensure a better concentration of the heat flow in the direction of the heat transfer tube.

 The thermally conductive sheets can also be kept inclined with respect to the floor of the enclosure by any suitable means if the floor of the enclosure is horizontal. This arrangement promotes the absorption of solar radiation.

 The absorbent element according to the second embodiment shown in Figure 2, is similar to the absorbent element shown in Figure 1 but the elbows (6) are covered by the thermally conductive sheet (2) exposed to the sun and not covered by the thermally conductive sheet (3) not exposed to the sun. The connection tubes can be formed by stripping the tube (1) by cutting into (7) and (8) the heat-conducting sheets.

 Figure 3 is a sectional view through a plane III-III perpendicular to the thermally conductive sheets of an absorbent element according to the first or second embodiments provided on the side not exposed to the sun with a layer of cellular material (9).

 In the first and second embodiments of the absorber element according to the invention, preferably the rectilinear regions of the tube are parallel to each other and regularly distributed between the thermally conductive sheets.

 The zone of thermally conductive sheet delimited by two contiguous rectilinear zones of tube is associated by half, with the two rectilinear zones of tube which delimit it.

 The distance between two contiguous rectilinear zones of the tube is chosen such that the ratio of the width share of the thermally conductive sheet which participates in heat exchanges with a rectilinear zone of the tube to the outside diameter of the said tube is between 2.5 and 10 and preferably between 3.5 and 8.

 Although in the above description reference has been made to the "straight areas" of tubes, this does not exclude the production of absorbing elements using tubes comprising, for example, transverse corrugations. An absorbing element according to the invention comprising such a tube is shown in FIG. 4. Thus the term "rectilinear zone" will denote both portions of effectively rectilinear tube and zones of generally rectilinear tube.

 Of course, two adjacent rectilinear zones can belong to a mime tube (FIG. 7) or to two different tubes (FIG. 5).

 The absorbent elements according to the invention may also comprise several tubes sandwiched between the thermally conductive sheets.

Two embodiments of such absorber elements are shown in FIGS. 5 and 6.

 The absorbing element according to the invention, a fourth embodiment of which is shown in FIG. 5, comprises a plurality of substantially parallel tubes (1), sandwiched between two thermally conductive sheets, each tube comprises connection pipes (4, 5).

Advantageously, such absorbing elements are connected in series, the homologous tubes of two adjacent absorbing elements being themselves connected in series.

 The absorber element according to the invention, a fifth embodiment of which is shown in FIG. 6, comprises two tubes (1) sandwiched between two thermally conductive sheets, the two tubes are arranged between the thermally conductive sheets in a manner similar to that of the tube of The absorbing element according to the first embodiment.

 Of course the various embodiments of the absorber element according to the invention described above are in no way limiting and other embodiments within the reach of ordinary skill in the art are part of the present invention.

 For example, the rectilinear zones of tube can be sandwiched between two thermally conductive sheets such that the thermally conductive sheet not exposed to the sun is in the form of a plurality of segments of tape, the rectilinear zones of tube being sandwiched substantially along the median axis. said ribbon. The width of the thermally conductive sheet associated with the tube will in this case be the width of the thermally conductive sheet exposed to the sun associated with the tube.

 The absorbers according to the present invention described above are mainly used as solar radiation absorbers. However, they can also be used as a heat exchanger. For this, it suffices to send a fluid brought into the tube brought to a temperature at least 20 ° C. higher than that of the atmosphere which it is desired to heat. The calorific power supplied by these exchangers is of the order of that of the usual cast iron or sheet steel radiators. In the case of this use of the absorbing elements, it is not essential, for their correct operation, to paint a matt and dark color on the surface of the thermally conductive sheets.

 The solar radiation absorbing elements according to the invention have many advantages.

 Indeed, as they are not rigid, it is easy to transport them to the places of implementation in the form of rolls, to unwind them and to cut them to the desired length. Connecting the tube of the absorber element to the heat transfer fluid circuit is easy to do since it suffices to strip the ends of the tube and provide them with suitable fittings.

 Due to the choice of materials used for their construction, the absorbent elements according to the invention are not subjected to low thermal stresses and they resist frost and corrosion well.

The choice of materials used for the tube also gives it good resistance to scaling and "food quality".

 The absorber elements according to the invention can thus be easily arranged in transparent enclosures ensuring the greenhouse effect.

 In addition, such absorbing elements are easy to manufacture and possibly to assemble, and the low price of the raw materials used in their manufacture, as well as their ease of installation, provide great advantages to users.

Claims (17)

 1 - solar radiation absorbing element, characterized in that it comprises  - at least one tube having at least one rectilinear zone, said tube serving for the circulation of the heat-transfer fluid and being made of a material chosen from organic or organosilicon rubbers or organic thermoplastic products,  - At least two flexible thermally conductive sheets of continuous or discontinuous structure fixed two-by-two face to face, enclosing between them at least two rectilinear zones of tube.  2 - absorber element according to claim 1, characterized in that the ratio of the width or the portion of width of thermally conductive sheet associated with a rectilinear region of the tube to the outside diameter of said tBbe is between 2.5 and 10.  3 - absorber element according to any one of claims 1 or 2, characterized in that, between two thermally conductive sheets are enclosed at least two rectilinear zones of the tube, said rectilinear zones being interconnected by an elbow.  4 - absorber element according to any one of claims 1 to 3, characterized in that the tube has a diameter between 5 and 50 mm, preferably between 7 and 40 mm.  5 - absorber element according to any one of claims 1 to 4, characterized in that the tube is formed of an organic thermoplastic material chosen from low density polyethylene, polyvinyl chloride, polaymides, polyesters.  6 - absorber element according to any one of claims 1 to 4, caractSrisé in that the tube is formed of an organic rubber chosen from butyl, ethylene-propylene, polyurethane rubbers.  7 - absorber element according to any one of claims 1 to 4, characterized in that the tube is formed of an organosilicon rubber obtained by hot curing of compositions mainly comprising diorganopolysiloxane gums, mineral fillers, organic peroxides.  8 - Elfnent absorber according to any one of claims 1 to 7, characterized in that the thermally conductive sheets are fixed two to two face against face by heat sealing, welding or riveting.  9 - absorber element according to any one of claims 1 to 8, characterized in that the thermally conductive sheets are metallic sheets.  10 - absorber element according to any one of claims 1 to 9, characterized in that the metal sheets of continuous structure are sheets of thickness between 0.02 and 0.3 mm.  il - absorber element according to any one of claims 1 to 9, characterized in that the metal sheets of discontinuous structure are a fabric of metal wires with a diameter between 0.1 and 0.4 mm.  12 - absorber element according to any one of claims a to 11, characterized in that the metal sheets are made of aluminum.  13 - absorber element according to any one of claims 1 to 12, characterized in that the outer face of the thermally conductive sheet exposed to the sun is dark in color and matt in appearance.  14 - absorber element according to any one of claims 1 to 13, characterized in that the thermally conductive sheet not exposed to the sun is in the form of a plurality of ribbon segments.  15 - absorber element according to any one of claims 1 to 14, characterized in that the face of the absorbent element not exposed to the sun is covered with a layer of cellular material.  16 - absorber element according to any one of claims 1 to 15, characterized in that the tube is reinforced by an outer sheath consisting of a network of synthetic fibers or glass fibers.  17 - absorber element according to any one of claims i to 16, characterized in that the tube is reinforced by an external sheathing consisting of a network of metal wires of average diameter between 0.05 and 0.4 mm.  18 - Use of an absorbent element according to any one of claims 1 to 12, 14 to 17 as a heat exchanger.