WO2011042657A2

WO2011042657A2 - Solar collector and system for producing hot water comprising such solar collectors

Info

Publication number: WO2011042657A2
Application number: PCT/FR2010/052100
Authority: WO
Inventors: Michel Louis Wohrer; Christian LENÔTRE
Original assignee: Sophia Antipolis Energie Developpement
Priority date: 2009-10-09
Filing date: 2010-10-06
Publication date: 2011-04-14
Also published as: FR2951253A1; WO2011042657A3; CN102844627A; EP2486340A2; FR2951253B1

Abstract

The invention relates to a solar collector (26) including: a confined space (52) defined by an outer tube (54) and an inner tube (56) arranged inside the outer tube (54), the confined space (52) comprising a thermal insulation means suitable for reducing thermal convection and thermal conduction; a layer (58) for absorbing solar radiation (R_s) placed against the inner tube (56); and a thermal conduction means (60) suitable for transferring the heat energy received from the solar radiation (R_s) via the absorption layer (58) to a heat-transport fluid (10). The absorption layer (58) extends over only one portion of the circumference of the inner tube (56).

Description

Solar collector, and hot water production system comprising such solar collectors

The present invention relates to a solar collector of the type comprising:

an enclosed space delimited by an outer tube and an inner tube disposed inside the outer tube, the enclosed space comprising thermal insulation means capable of reducing thermal convection and thermal conduction,

an absorption layer of the solar radiation disposed against the inner tube, and

- Thermal conduction means adapted to transfer the heat energy received from the solar radiation via the absorption layer to a heat transfer fluid.

The invention also relates to a system for producing hot water from solar energy comprising:

a plurality of such solar collectors capable of heating a heat transfer fluid from solar energy, and

a heat transfer fluid transport circuit between the solar collectors and a user of hot water.

There is known a vacuum tube solar collector comprising an outer tube and an inner tube, the tubes being concentric and substantially cylindrical. Each tube is closed at one of its ends, and the tubes are sealed to each other, at the other of their ends. The solar collector comprises a solar radiation absorption layer disposed over the entire periphery of an outer surface of the inner tube, facing the outer tube. The solar collector also comprises means for transferring the heat energy from the solar radiation to a heat transfer fluid. The heat transfer fluid circulates in a transport circuit connecting a field of solar collectors to a user of hot water.

The thermal efficiency up to the heat transfer fluid is not optimal, because of the significant heat losses by blackbody radiation of the tubes.

An object of the invention is therefore to improve the thermal efficiency up to the coolant, by reducing radiation heat losses.

To this end, the invention relates to a solar collector of the aforementioned type, characterized in that the absorption layer extends over only a portion of the circumference of the inner tube.

According to other embodiments, the solar collector comprises one or more of the following characteristics, taken separately or in any technically possible combination: a transverse section of the absorption layer extends angularly over an angular value of between 140 ° and 220 °, preferably between 160 ° and 200 °, more preferably substantially equal to 180 °;

the inner tube has an outer surface facing the outer tube, and an inner surface, and the absorption layer is disposed against said outer surface;

- A cross section of the outer tube and / or the inner tube is circular in shape;

the thermal conduction means comprise a heat pipe comprising a hot part arranged inside the outer tube, a cold part disposed outside the outer tube, and a reservoir containing a two-phase heat-pipe fluid and extending over the hot part. and the cold part;

the reservoir is applied at least locally against an inner surface of the inner tube;

the thermal conduction means comprise a thermally conductive interface, arranged between the absorption layer and the hot part of the heat pipe;

the hot part of the heat pipe is in the form of a half-cylinder;

a cross section of the hot part is substantially opposite the cross section of the absorption layer;

- A cross section of the hot part extends angularly over an angular value between 180 ° and 220 °, preferably substantially equal to 200 °.

The invention also relates to a hot water production system of the aforementioned type, characterized in that the solar collectors are as defined above.

The invention and its advantages will appear more clearly on reading the description which follows, given solely by way of example and with reference to the appended drawings, in which:

FIG. 1 is a schematic representation of a hot water production system according to the invention,

FIG. 2 is a schematic side view of a solar collector connected to a heat transfer fluid transport circuit of the hot water production system of FIG. 1, and

- Figure 3 is a sectional view along the plane III of Figure 2.

In FIG. 1, the hot water production system 2 comprises means 8 for heating by solar energy a heat transfer fluid 10, means 12 for storing the thermal energy and a closed circuit 14 for transporting the coolant 10 to a user of hot water. The circuit 14 connects the heating means 8, the storage means 12 and the hot water user 15.

The hot water production system 2 comprises a storage tank 16 for unloading the heat transport fluid transport circuit 14.

The hot water production system 2 comprises a control loop 18 comprising a mixer 20 and a first pump 22. The installation comprises means 24 for remote control of the loop 18.

The heating means 8 comprise a plurality of solar collectors 26 described in more detail below with reference to FIGS. 2 and 3.

The coolant 10 is, for example, water used at a maximum temperature of 150 ° C and a maximum pressure of 6 bar.

The circuit 14 comprises a plurality of valves 28, the mixer 20, the first pump 22 and a second pump 30. The circulation of the fluid 10 in the circuit 14 is provided by the two pumps 22, 30.

The storage means 12 and the circuit 14 are insulated by an insulator, not shown.

The user of hot water 15 comprises a heat exchanger 40, in the form of a coil, intended to exploit the heat transported by the coolant 10.

In FIG. 2, the circuit 14 comprises a conduit 48 for transporting the coolant 10, and a thermally insulating sheath 50 disposed on the periphery of the pipe 48. The pipe 48 is in the form of a cylinder with an axis oriented according to a substantially horizontal plane H.

The solar collector 26 comprises an enclosed space 52 bounded by an outer tube 54 and an inner tube 56 disposed within the outer tube 54, and a layer 58 of absorption of solar radiation R _s disposed against the inner tube 56. The solar collector 26 also comprises thermal conduction means 60 capable of transferring the heat energy received from the solar radiation R _s by the absorption layer 58 to the coolant 10.

The enclosed space 52 comprises thermal insulation means capable of reducing thermal convection and thermal conduction. Most of the losses then remain due to thermal radiation. The confined space 52 is, for example, under vacuum.

In the embodiment of Figures 2 and 3, the tubes 54, 56, substantially cylindrical, have a circular section and are concentric with axis I. Each tube 54, 56 is closed, in the form of a half-sphere in one of its ends, and the tubes 54, 56 are sealed to each other, at the other of their ends. The inner tube 56 comprises an outer surface 62A facing the outer tube 54, and an inner surface 62B.

The solar collector 26 also has an isolation plug 63 inserted into the open end of the inner tube 56.

The absorption layer 58 extends over only a portion of the circumference of the inner tube 56, as shown in FIG. 3. A cross section of the absorption layer 58 extends angularly over an angular value A of between 140. ° and 220 °, preferably between 160 ° and 200 °, more preferably substantially equal to 180 °. The solar collector 26 then comprises a portion of the circumference of the inner tube 56 on which the absorption layer 58 does not extend. This portion of the circumference of the inner tube 56 extends angularly over an angular value equal to (360 ° -A). In other words, the solar collector 26 comprises, for example, a complementary angular portion consisting solely of the inner tube 56 and the outer tube 54 separated by the vacuum contained in the space 52. This complementary angular portion extends angularly over an angular value equal to (360 ° - A). In the complementary angular portion, the tubes 54, 56 are substantially transparent and able to pass visible light.

The absorption layer 58 is, for example, capable of being oriented towards the sky in the direction of the solar radiation R _s , the portion of the circumference of the inner tube 56 on which the absorption layer 58 does not extend being then oriented towards the ground.

The absorption layer 58 is, for example, substantially in the form of a half-cylinder and disposed against the outer surface 62A of the inner tube. A cross section of the absorption layer 58 is then shaped as a circular arc of angle A.

The absorption layer 58 comprises a selective material absorbing solar radiation, that is to say the band of the electromagnetic spectrum of wavelength substantially between 0.25 μηη and 2.5 μηη. The selective absorption layer 58 is, for example, made in a composite manner with a plurality of aluminum nitrite layers disposed on an aluminum metal substrate, or on a stainless steel substrate, or on a copper substrate . Alternatively, the absorption layer 58 is made in a composite manner with a plurality of copper nitride, iron nitride or chromium nitride layers disposed on a metal substrate.

The absorption layer 58 is made for example by cathodic sputtering of the materials of the selective layers against the inner tube 56, masking or omitting the portion of the circumference of the inner tube 56 on which the absorption layer 58 is not intended to expand. The thermal conduction means 60 comprise, for example, a heat pipe 64 formed of a sheet having a left surface conforming to the shape of the inner tube 56 on the one hand, and the transport conduit 48 on the other hand, as shown in FIG. Figure 2. The heat pipe 64 has a hot portion 66 arranged inside the inner tube 56 and a cold part 68 disposed outside the tubes 54, 56. The heat pipe 64 also comprises a tank 70 formed of a set of channels 71 connected to each other by a web conferring the heat pipe sheet structure. The reservoir 70 contains a biphasic fluid heat pipe 72, and extends over the hot portion 66 and the cold portion 68. For the hot portion 66 of the heat pipe, the reservoir 70 is applied, at least locally, against the inner surface 62B of the pipe inside.

The thermal conduction means 60 also comprise a thermally conductive interface 74, visible in FIG. 3, arranged between the hot part 66 of the heat pipe and the tubes 54, 56. More specifically, the conductive interface 74 is disposed between the inner surface 62B. of the inner tube and the hot part 66 of the heat pipe.

The heat pipe 64 comprises a narrowing, not shown, of its circumferential extent between the hot part 66 and the cold part 68, with respect to its extent in the running part of the hot and cold parts 66. The shrinkage forms a connecting hinge between the hot part 66 and the cold part 68.

The heat pipe 64 is formed of two sheets 76A, 76B visible in Figure 3 and fixed together. The sheets 76A, 76B of the heat pipe are, for example, metal sheets fused together outside the zones defining the channels 71. The metal sheets 76A, 76B are, for example, made of aluminum.

The hot part 66 of the heat pipe is in the form of a half-cylinder of axis I, as shown in FIG. 3. The cross section of the hot part 66 is in the form of a circular arc of angle B between 180 ° and 220 °, preferably substantially equal to 200 °. The cross section of the hot portion 66 is substantially opposite the cross section of the absorption layer 58.

In the embodiment of Figure 3, the cross section of the absorption layer 58 is disposed against the inner tube 56 only facing the cross section of the hot portion 66. The cross section of the absorption layer 58 and the cross section of the hot portion 66 are adapted to be oriented towards the sky in the direction of the solar radiation R _s , the complementary angular portion of the solar collector consisting solely of the inner tube 56 and the outer tube 54 separated by the vacuum contained in the space 52 then being oriented towards the ground.

The hot part 66 of the heat pipe and in particular the part of the tank 70 contained in this hot part is applied against the inner surface 62B of the inner tube. The cold part 68 of the heat pipe is in the form of an X-axis half-cylinder arranged between the pipe 48 and the insulating sheath 50 being wound around the pipe 48, as represented in FIG. 2.

The axis I is inclined relative to the horizontal plane H and forms with the horizontal plane H an inclination angle C. The value of the inclination angle C is greater than 5 °, preferably greater than 30 °.

The tank 70 comprises, for example, three channels 71 for circulating the heat pipe fluid 72. The three circulation channels 71 are connected and form, with their extension in the cold part 68, a closed circuit for the heat pipe fluid 72.

Each channel 71 of the tank is formed by a gap between the two sheets

76A, 76B.

The biphasic fluid heat pipe 72 is, for example, water, methanol, ethanol, heptane, a refrigerant HFC, or a refrigerant HCFC.

Each solar collector 26 is fixed to the duct 48 by means of a fastener 76, as shown in FIG. 2. The fastener 76 comprises a first portion 76A of cylindrical shape and a second portion 76B of flat shape, the first and second portions 76A, 76B being connected by a bend 76C. The fastener 76 is thermally conductive, and is, for example, made of aluminum. The first portion 76A is arranged in contact with the duct 48, between the duct 48 and the thermally insulating sheath 50, diametrically opposite the hot portion 68 of the heat pipe with respect to the duct 48. The second portion 76B is arranged in contact with the heat pipe. 64. The fastener 76 is attached to the heat pipe 64 via first fastening means 76D and second fastening means 76E extending through respective orifices of the fastener 76 and the heat pipe 64.

The operating temperature of the vacuum tube solar collectors 26 is between 80 ° C and 150 ° C.

The operation of the hot water production system, and in particular the solar collectors, will now be described.

The solar collectors 26 of the heating means 6 capture, during the day, the solar radiation R _s , then transmit to the coolant 10 the thermal energy associated with solar radiation R _s .

More specifically, the solar radiation R _s is absorbed by the selective material of the absorption layer 58 of each sensor, the outer tube 54 allowing the passage of solar radiation R _s . The heat energy associated with the absorption of the solar radiation R _s is then transmitted to the heat pipe 64 via the inner tube 56 and the thermally conductive interface 74. The vacuum in the enclosed space 52 ensures insulation with respect to thermal convection and thermal conduction, the outer tube ensuring a greenhouse effect.

The thermal energy transmitted to the hot part 66 of the heat pipe gradually causes a phase change of the heat pipe fluid 72, from its being liquid to its gaseous state. The biphasic fluid heat pipe in the gaseous state then rises in the direction of the cold part 68 of the heat pipe, through the various channels 71 of the tank. Since the reservoir 70 is applied at least locally against the absorption layer 58 in the hot part 66 of the heat pipe, the thermal conduction is improved between the absorption layer 58 and the heat sink fluid 72, so that the losses of radiation heat is further reduced.

The heat transported by the heat pipe fluid 72 from the hot part 66 to the cold part 68 is then transmitted to the heat transfer fluid 10 by thermal conduction between the channels 71 arranged in the cold part 68 and the conduit 48 of the circuit. This thermal conduction then causes an increase in the temperature of the coolant 10 and a lowering of the temperature of the heat pipe fluid 72.

Following the lowering of the temperature of the heat pipe fluid 72, the heat pipe fluid 72 again changes phase progressively, from its gaseous state to its liquid state. The heat pipe fluid in the liquid state then descends by gravitation from the cold part 68 to the hot part 66, by the angle of inclination C, in order to transport again heat energy from the solar radiation.

The storage means 12 then serve as buffers between the thermal energy produced by the solar collectors 26 of the heating means and that consumed by the user of hot water 15. The heating means 12 thus make it possible to decouple the production of heat of solar availability.

Several operating modes can be envisaged at the level of the hot water production system 2, using the valves 28, the mixer 20 and the pumps 22, 30: the storage of heat energy alone, the direct production of energy thermal, storage and production of thermal energy, the destocking of thermal energy and the direct production of thermal energy, and the destocking of thermal energy alone.

The regulation loop 18 makes it possible to adapt the quantity of heat energy supplied by the hot water production system 2.

The absorption layer 58 extending, according to the invention, on only a portion of the circumference of the inner tube 56, reduces the heat loss. Indeed, the absorption layer 58 is comparable to a black body and radiates when the solar collector 26 receives the solar radiation R _s . This black body radiation causes an emission of infrared waves bouncing in the enclosed space 52 between tubes 54, 56, and partially escaping the greenhouse effect. The portion of the circumference of the inner tube 56 which does not have an absorption layer on contact with it then generates a lower blackbody radiation. The solar collector 26 according to the invention therefore makes it possible to reduce the blackbody radiation and the associated heat losses compared with a conventional tube solar collector.

In addition, the absorption layer 58 extending over only a portion of the circumference of the inner tube 56, the solar collector 26 according to the invention also reduces costs.

It is thus conceivable that the solar collector according to the invention makes it possible to ensure a better thermal efficiency from the outer tube to the coolant, by limiting the heat losses by radiation.

Claims

1. Solar collector (26) of the type comprising:

- an enclosed space (52) delimited by an outer tube (54) and an inner tube (56) disposed inside the outer tube (54), the enclosed space (52) comprising thermal insulation means adapted to reduce thermal convection and thermal conduction,

a layer (58) for absorbing solar radiation (R _s ) disposed against the inner tube (56), and

thermal conduction means (60) capable of transferring the heat energy received from the solar radiation (R _s ) via the absorption layer (58) to a heat transfer fluid (10),

characterized in that the absorption layer (58) extends over only a portion of the circumference of the inner tube (56), and in that the thermal conduction means (60) comprises a heat pipe (64) having a hot portion (66) arranged inside the outer tube (54), a cold portion (68) disposed outside the outer tube (54), and a reservoir (70) containing a biphasic fluid heat pipe (72) and extending over the hot portion (66) and the cold portion (68).

2. - solar collector (26) according to claim 1, wherein a cross section of the absorption layer (58) extends angularly over an angular value (A) between 140 ° and 220 °, preferably between 160 ° and 200 °, more preferably substantially equal to 180 °.

The solar collector (26) of claim 1 or 2, wherein the inner tube (56) has an outer surface (62A) facing the outer tube (54), and an inner surface (62B), and wherein the absorption layer (58) is disposed against said outer surface (62A).

4. - solar collector (26) according to any one of the preceding claims, wherein a cross section of the outer tube (54) and / or the inner tube (56) is circular in shape.

5. - solar collector (26) according to any one of the preceding claims, wherein the reservoir (70) is applied at least locally against an inner surface (62B) of the inner tube (56).

6. - solar collector (26) according to any one of the preceding claims, wherein the thermal conduction means (60) comprise a thermally conductive interface (74), arranged between the absorption layer (58) and the hot part (66) of the heat pipe.

7. - solar collector (26) according to any one of the preceding claims, wherein the hot part (66) of the heat pipe is in the form of a half-cylinder.

8. - solar collector (26) according to any one of the preceding claims, wherein a cross section of the hot part (66) is substantially opposite the cross section of the absorption layer (58).

9. - solar collector (26) according to any one of the preceding claims, wherein a cross section of the hot portion (66) extends angularly to an angular value (B) of between 180 ° and 220 °, preferably substantially equal to 200 °.

10. - System (2) for producing hot water from solar energy comprising:

a plurality of solar collectors adapted to heat a heat transfer fluid (10) from solar energy, and

a circuit (14) for transporting the coolant (10) between the solar collectors (26) and a user (80) of hot water,

characterized in that the solar collectors (26) are in accordance with any one of the preceding claims.