WO2008090461A2

WO2008090461A2 - Solar collector for heating a thermovector fluid

Info

Publication number: WO2008090461A2
Application number: PCT/IB2008/000176
Authority: WO
Inventors: Alessancro Bozzoli; Guido Cicolini; Giordano Contin; Francesco Fontana; Luca Pomari
Original assignee: Kloben S.A.S. Di Turco Adelino E C.
Priority date: 2007-01-25
Filing date: 2008-01-25
Publication date: 2008-07-31
Also published as: ITMO20070022A1; WO2008090461A3

Abstract

Solar collector for heating a thermovector fluid comprising a plurality of tubular elements (2) arranged substantially side by side and having at least one duct (4) through which can flow a thermovector fluid and heat exchange means (5) between at least one irradiation source and the duct (4). The heat exchange means (5) comprises a first tubular section (7) that is suitable for being irradiated by the irradiation source and inside which a second tubular section (8) is fitted longitudinally, the duct comprising an inter-space (23) defined between the first and the second (8) section.

Description

SOLAR COLLECTOR FOR HEATING A THERMOVECTOR FLUID

Technical Field

The present invention relates to a solar collector for heating a thermovector fluid. Background Ail

It is known how the need is particularly felt to design devices that use renewable energy resources in an increasingly more efficient and cost-effective way that makes convenient their exploitation. With reference to the solar collector sector, the need is especially felt to upgrade the efficiency of the current devices to reduce or eliminate the need to support the solar collectors with an electric or fuel heating system. Traditional solar collectors mainly perform a function of heating water or other fluids for domestic or industrial purpose, and for every other sector where the need exists to use water or hot air, with the praiseworthy advantage of obtaining heat in an environment-friendly way.

Known heat solar collectors are split into two categories: flat solar collectors and pipe collectors.

Pipe collectors, to which reference is made, comprise a plurality of round- shaped tubular elements, hydraulically connected in parallel and parallel with each other, which are exposed to sunlight.

The outer surface of these tubular elements is composed of a first transparent borosilicate glass pipe; this pipe is closed at one end, while the other end is associated integral with a second pipe. This second pipe is fitted longitudinally inside the first pipe, is closed at the corresponding closed end of the first pipe, and is made of glass.

Between the first and the second pipe, a vacuum is created to restrict or cancel heat loss by convection and conduction.

On the outer surface of the second pipe, a layer of selective material can be applied, studied to maximise the absorption of solar energy and minimise the re- emission of this energy in the form of infra-red rays.

Inside the second pipe is located the heat transfer unit, composed of a heat absorbing element, usually a sheet of conducting material, and of a heat absorbing and transfer circuit, a pipe generally made of copper that extends along the entire length of the tubular element and is folded on itself, so as to have the entry and exit ends on the same side in which the first pipe and the second pipe are integrally associated. The heat transfer circuit can be made in numerous different ways, such as, e.g. two concentric pipes, the outer one closed at one end and the inner one open, or a single pipe along which, longitudinally, a separator element runs. Inside the heat transfer circuit circulates a thermovector fluid, such as, e.g., water, liquid or gaseous mixes, which collects heat from the absorber element; the absorber element must therefore have a large exposure surface to intercept as much solar radiation as possible, and at the same time, have a large contact surface with the heat transfer circuit to upgrade heat exchange. For this purpose, sheets are used, e.g., made of copper or aluminium, that follow the circular shape of the inner glass pipe and also envelop the heat transfer circuit in which the thermovector fluid circulates.

Once heated, the thermovector fluid exchanges the heat just acquired with the water contained in a tank with heat accumulator functions. The accumulated heat is then used for domestic purposes (heating, domestic hot water, etc.), while the thermovector fluid starts another cycle inside the solar collector circuit.

These vacuum solar collectors do however have a number of drawbacks. In particular, a thermal gradient is formed that blocks the perfect conduction of the thermal energy, between the innermost area of the heat transfer circuit, where the fluid flows at a relatively low temperature, and an outermost area, where the thermovector fluid flows at a higher temperature being nearer to the absorber element.

Another drawback is represented by the fact that a thermal gradient is also created, and therefore a drop in efficiency, on the absorber element, and more specifically at the part in contact with the heat transfer circuit which will be considerably cooler than the remaining surface exposed to direct solar radiation. Another drawback stems from the fact that the contact between thermovector fluid and heated surfaces is limited to the linear flow of the fluid inside the circuit.

Object of the Invention

The main aim of this invention is to provide a solar collector for heating a thermovector fluid that permits exploiting the thermal energy produced by solar radiation in a more efficient way, making it possible to amortise the cost of the plant and its installation more quickly than is required for a traditional plant. Another object of the present invention is that of making more efficient heat exchange and, therefore, the transfer of the thermovector fluid energy inside the solar collector. A further object of the present invention is to develop a technical solution that permits increasing heat absorption and upgrades the heat exchange between the thermovector fluid and the hot irradiated surfaces_., by means of an increase in the contact surface. Another object of the present invention is to provide a solar collector for heating a thermovector fluid that allows to overcome the mentioned drawbacks of the known technique within the ambit of a simple and rational solution, which is easy and effective to use, as well as having a fairly low cost. The above objects are all achieved by the present solar collector for heating a thermovector fluid that comprises a plurality of tubular elements arranged substantially side by side and having at least one duct through which can flow a thermovector fluid and heat exchange means between at least one irradiation source and said duct, characterized in that said heat exchange means comprise a first tubular section that is suitable for being irradiated by said irradiation source and inside which a second tubular section is fitted longitudinally, said duct comprising an inter-space defined between said first and said second section. Brief Description of the Drawings

Further characteristics and advantages of the present invention will appear more evident from the description of a preferred, but not exclusive, embodiment of a solar collector for heating a theπnovector fluid, illustrated indicatively by way of non limiting example in the accompanying drawings, wherein: figure 1 is a view of a solar collector according to the invention; figure 2 is a section view of a tubular element of a solar collector in a possible embodiment according to the invention; figure 3 is a view of a detail of a tubular element of a solar collector in a possibile embodiment; figure 4 is a view of a detail of a tubular element of a solar collector in a further embodiment.

Embodiments of the Invention

With particular reference to such figures, a solar collector for heating a thermovector fluid, has been globally indicated by 1.

The solar collector 1 comprises a plurality of tubular elements 2, arranged parallel and side by side to which are associated means of concentrating the solar rays, of the type of substantially curved reflecting elements 3 (CPC -

Compound Parabolic Concentrator).

The tubular elements 2 each comprise at least one duct 4, heat exchange means

5 and turbulence generation means 6. Along the duct 4 a thermovector fluid can flow for the purpose of taking the heat absorbed by the heat exchange means 5 and then yielding this to the water or to the air going to the various units.

The heat exchange means 5 comprise a first tubular section 7 and a second tubular section 8 for each of the tubular elements 2. The first tubular section 7 extends in the direction of the length of the tubular elements 2 and is suitable for being irradiated by the irradiation source, usually the sun.

In actual fact, the first tubular section 7 allows converting into thermal energy the energy received in the form of electromagnetic irradiation and is covered on the outside with a special spectrally selective covering 9 which increases the absorption of the solar radiation and restricts the dispersion of heat by re- irradiation.

Inside the first tubular section 7, the second tubular section 8 is fitted longitudinally, in particular fitted parallel and coaxial. Between the first tubular section 7 and the second tubular section 8 an inter-space 10 is defined.

The first tubular section 7 can essentially be made of glass or metal, but the application of composite materials such as plastic or ceramics cannot be ruled out.

The second tubular section 8 has an inlet end 11 of the thermovector fluid and an open end 12 opposite to the inlet end 11. The first tubular section 7 has a closed end 13 arranged close to the open end 12 of the second tubular section 8, and an outlet end 14 that communicates with a beak 15 suitable for the outflow of the thermovector fluid which has already circulated inside the duct 4.

Advantageously, the outer surface 16 of the second tubular section 8 is arranged close to the inner surface 17 of the first tubular section 7; this feature allows obtaining a pellicular flow of the thermovector fluid, minimising the thermal gradient between the different surfaces and increasing the thermal efficiency of the system.

In particular, the distance between the inner surface 17 and the outer surface 16 is included within a range of values between 0.5 mm and 5 mm; this distance therefore defines the thickness of the inter- space 10.

The duct 4 extends along the space defined inside the second tubular section 8 and along the inter-space 10.

The surfaces that delimit the duct 4, therefore, consist in the inner surface 18 of the second tubular section 8, in the outer surface 16 of the second tubular section 8 and in the inner surface 17 of the first tubular section 7.

The turbulence generation means 6 comprise a series of elements or devices suitable for breaking the laminar flow of the thermovector fluid inside the duct 4 and, in particular, are arranged inside the inter-space 10; in the particular embodiment of the invention shown in the illustrations, the turbulence generation means consist of turbulators 19 and protuberances 20 obtained on the outer surface 16 of the second tubular section 8 and, in addition or alternatively, on the inner surface 17 of the first tubular section 7.

The turbulators 19 are suitable for creating a substantially helical movement inside the duct 4 that allows extending the average course of the thermovector fluid in contact with the hot surface of the first tubular section 7.

The protuberances 20 generate a swirling movement that keeps the thermovector fluid longer inside the duct 4, with consequent greater accumulation of thermal energy.

Embodiments of the invention cannot however be ruled out in which the turbulence generation means 6 are composed, e.g., of guides suitable for channelling the fluid, seals, grooves, fins or connection bodies for connecting the duct delimitation surfaces 4.

Advantageously, to favour the thermal deformation of the duct 4 caused by the high temperatures reached during exposure to the sun, the turbulence generation means 6 are deformable in an elastic way. The thermovector fluid used inside the duct 4 is usually liquid or gaseous; in the case of its being liquid, the use must be entailed of a fluid with a viscosity that is not too high and which does not switch to solid state when the temperatures drop.

The solar collector to which the invention refers also comprises thermal insulation means 21 of the heat exchange means 5.

The thermal insulation means 21 comprise a first pipe 22, substantially transparent, which is arranged covering the heat exchange means 5 and which has a closed end and an opposite end 22a.

The first pipe 22 is made of borosilicate glass, this being a material that does not stop electromagnetic radiation and is strong enough to remain exposed in the open.

In the embodiment of the invention shown in the figures 2 and 3, between the first pipe 22 and the first tubular section 7 a separation interstice 23 is defined in which vacuum has to be created in the most accurate way possible, meaning that inside this there is a residual presence of extremely rarefied gas.

In this embodiment, the first tubular section 7 is advantageously associated irremovable with the first pipe 22 with an S welding of the glass-metal type, meaning a welding between a first glass component (the pipe 22) and a second metal component (the first tubular section 7). Usefully, the welding S is applied at the exit end 14 of the first tubular section 7 and of the opposite end 22a of the first pipe 22, arranged substantially mated the one with the other. In the embodiment of the invention shown in figure 4, on the other hand, besides the first pipe 22, the thermal insulation means 21 further comprise a second covering pipe 24.

The second pipe 24 is made of glass, is closed at one end, is longitudinally and coaxially fitted inside the first pipe 22 and is arranged around the first tubular section 7, to which it is associated irremovably by means of a glass-metal welding, not shown in the illustrations.

Unlike the previous embodiment, in the figure 4 the separation interstice 23 is defined between the first pipe 22 and the second pipe 24. Furthermore, the covering 9 is applied on the surface of the second pipe 24 facing the separation interstice 23.

It has in point of fact being ascertained how the described invention achieves the proposed objects and, in particular, the fact is underlined that the solar collector according to the invention peπnits achieving an energy efficiency not obtainable with traditional solar collectors.

Furthermore, it is pointed out that a more efficient solar collector makes advantageous, through a quicker amortisation of installation costs, the use of a device that exploits clean energy, to the benefit of the user and of the natural environment. The invention thus conceived is susceptible to numerous modifications and variations, all of which falling within the scope of the inventive concept.

Furthermore all the details can be replaced with others that are technically equivalent.

In practice, the materials used, as well as the contingent shapes and dimensions, may be any according to requirements without because of this moving outside the protection scope of the following claims.

Claims

1) Solar collector for heating a thermovector fluid that comprises a plurality of tubular elements arranged substantially side by side and having at least one duct through which can flow a thermovector fluid and heat exchange means between at least one irradiation source and said duct, characterized in that said heat exchange means comprise a first tubular section that is suitable for being irradiated by said irradiation source and inside which a second tubular section is fitted longitudinally, said duct comprising an inter-space defined between said first and said second section. 2) Solar collector according to claim I₅ characterized in that said second tubular section has an inlet end of said thermovector fluid and an open end opposite to the inlet end, and said first tubular section has a closed end arranged close to said open end and an outlet end opposite said closed end.

3) Solar collector according to one or more of the preceding claims, characterized in that said first tubular section and said second tubular section are parallel.

4) Solar collector according to one or more of the preceding claims, characterized in that said first tubular section and said second tubular section are coaxial. 5) Solar collector according to one or more of the preceding claims, characterized in that the outer surface of said second tubular section is arranged close to the inner surface of said first tubular section.

6) Solar collector according to one or more of the preceding claims, characterized in that the distance between said inner surface of said first tubular section and said outer surface of said second tubular section is included within a range of values between 0.5 mm and 10 mm.

7) Solar collector according to one or more of the preceding claims, characterized in that at least one of said tubular means comprises thermal insulation means of said heat exchange means. 8) Solar collector according to one or more of the preceding claims, characterized in that said thermal insulation means comprise at least one first pipe, substantially transparent, covering said heat exchange means. 9) Solar collector according to one or more of the preceding claims, characterized in that said first pipe is closed at one end.

10) Solar collector according to one or more of the preceding claims, characterized in that said first pipe is in borosilicate glass. 11) Solar collector according to one or more of the preceding claims, characterized in that said thermal insulation means comprise at least one second pipe covering said heat exchange means and which can be fitted longitudinally inside said first pipe.

12) Solar collector according to one or more of the preceding claims, characterized in that said second pipe is coaxial to said first pipe.

13) Solar collector according to one or more of the preceding claims, characterized in that said second pipe is closed at one end.

14) Solar collector according to one or more of the preceding claims, characterized in that said thermal insulation means comprise a separation interstice defined between said first pipe and at least one between said second pipe and said heat exchange means.

15) Solar collector according to one or more of the preceding claims, characterized in that said interstice is substantially empty.

16) Solar collector according to one or more of the preceding claims, characterized in that at least one between said first tubular section and said second tubular section is substantially made of metal.

17) Solar collector according to one or more of the preceding claims, characterized in that at least one among said first tubular section, said first pipe and said second pipe is substantially made of glass. 18) Solar collector according to one or more of the preceding claims, characterized in that said first tubular section is associated irremovable with at least one between said first pipe and said second pipe.

19) Solar collector according to one or more of the preceding claims, characterized in that said first tubular section is associated irremovable with at least one between said first pipe and said second pipe with a welding of the glass-metal type.

20) Solar collector according to one or more of the preceding claims, characterized in that at least one of said tubular elements comprises turbulence generation means for generating turbulence in said thermovector fluid inside said duct.

21) Solar collector according to one or more of the preceding claims, characterized in that said generation means comprise connection bodies for connecting the delimitation surfaces of said duct.

22) Solar collector according to one or more of the preceding claims, characterized in that said generation means comprise at least one turbolator.

23) Solar collector according to one or more of the preceding claims, characterized in that said generation means comprise at least one protuberance obtained on the delimitation surfaces of said duct.

24) Solar collector according to one or more of the preceding claims, characterized in that said generation means comprise at least one fin obtained on the delimitation surfaces of said duct. 25) Solar collector according to one or more of the preceding claims, characterized in that said generation means comprise at least one groove obtained on at least one of the delimitation surfaces of said duct.

26) Solar collector according to one or more of the preceding claims, characterized in that said generation means are deformable in a substantially elastic way.

27) Solar collector according to one or more of the preceding claims, characterized in that at least one between said first tubular section and said second pipe comprises a spectrally selective covering.

28) Solar collector according to one or more of the preceding claims, characterized in that at least one of said tubular elements is associated to concentration means for concentrating the solar rays.

29) Solar collector according to one or more of the preceding claims, characterized in that said concentration means are substantially curved reflecting elements. 30) Solar collector according to one or more of the preceding claims, characterized in that said turbulence comprises a substantially helical movement of at least one part of said thermovector fluid. 31) Solar collector according to one or more of the preceding claims, characterized in that said thermovector fluid is substantially gaseous.

32) Solar collector according to one or more of the preceding claims, characterized in that said thermovector fluid is substantially liquid. 33) Tubular element associable to a solar collector for heating a thermovector fluid that comprises at least one duct through which can flow a thermovector fluid and heat exchange means between at least one irradiation source and said duct, characterized in that said heat exchange means comprise a first tubular section that is suitable for being irradiated by said irradiation source and inside which a second tubular section is fitted longitudinally, said duct comprising an inter-space defined between said first and said second section.