WO2022220735A1

WO2022220735A1 - A suspension device for a parabolic reflector solar device

Info

Publication number: WO2022220735A1
Application number: PCT/SE2022/050382
Authority: WO
Inventors: Christer PEKKALA; Benjamin AHLGREN; Jonatan Mossegård; Joakim BYSTRÖM
Original assignee: Absolicon Solar Collector Ab
Priority date: 2021-04-15
Filing date: 2022-04-19
Publication date: 2022-10-20
Also published as: EP4323702A1; SE2150468A1; SE544851C2

Abstract

A suspension device for keeping a receiver fluid tube (8) at a predetermined position in relation to a parabolic reflector (4), comprises a spoke (14) connected to said parabolic reflector (4) and to a bearing (16), said spoke (14) being adapted to keep said receiver fluid tube (8) at a predetermined distance from said parabolic reflector (4), said spoke (14) being5movably arranged in relation to said receiver fluid tube by means of said bearing (16), said receiver fluid tube (8) having an axis (A-A) in its elongation. In accordance with the invention, said bearing (16) comprises a substantially annular body (17), wherein said annular body (17) is adapted to slidingly receive a rod (36) parallel to the axis (A-A) of said receiver fluid tube (8), said rod being adapted to be connected to said receiver fluid tube (8).

Description

A SUSPENSION DEVICE FOR A PARABOLIC REFLECTOR SOLAR DEVICE

Technical field

The present invention relates to a suspension device for keeping a receiver fluid tube at a predetermined position in relation to a parabolic reflector, comprising a spoke connect ed to said parabolic reflector and to a bearing, said spoke being adapted to keep said receiv er fluid tube at a predetermined distance from said parabolic reflector, said spoke being movably arranged in relation to said receiver fluid tube by means of said bearing, said re ceiver fluid tube having an axis in its elongation.

It also relates to a solar collector comprising a receiver fluid tube, a parabolic reflec tor and such a suspension device.

Background

In modem society energy is consumed by people and industries, e.g. for producing various products, for transport and production of food. Energy could be produced in several forms and from different energy sources. For instance, electricity is often produced from hydroelectric power plants, combustion of coal, oil, or gas. Traditionally, heat has been pro duced from local combustion or district heating power plants.

With an increasing population and demands for services, energy consumption strong ly increases which significantly negatively affects our environment. Combustion produces large amount of carbon dioxide and other greenhouse gases. Hydroelectric power plants re quire large territories to be drowned, etc.

In order to reduce our footprint and negative impression on our environment, de mands have been raised for more clean and environmental friendly energy production. To day, renewable energy is produced from wind, sun, ocean waves, etc. The sun provides large amounts of energy to our planet in form of radiated sun beams. Solar radiation can be used by solar cells to generate electricity, e.g. in form of solar panels, or by solar collectors to generate thermal heat.

A concentrating solar collector uses mirrors, lenses, or combinations thereof, to focus the solar radiation in form of a point or a line. In trough-formed concentrating solar collec tors a reflector is formed as a curved elongated mirror, which reflects the solar radiation on a receiver arranged along a focus-line of the reflector. The receiver is commonly a black tube filled with a transport fluid, such as water, glycol, or oil. The tube is heated by the con centrated solar radiation and the heat is transferred to the transport fluid that is circulated in a system where the heated transport fluid could be used. The heated transport fluid may be used both as process heat in industrial processes as for district heating.

The term ’’PTC” (Parabolic Trough solar Collector) will be used in this disclosure to denote a concentrating solar collector with a trough-formed reflector arranged to concen trate solar light onto a fluid tube. Typically, PTCs will be pivoted to track the sun during the day and are controlled by a solar tracking arrangement.

A parabolic trough solar collector comprises an elongated reflector, which reflective surface in a cross-section describes a parabolic curve. The reflector focuses direct sunlight on a focus.

An example of such a suspension device and such a solar collector is disclosed in WO 2018/212705, disclosing a holder for securing a fluid tube to a parabolic trough reflec tor.

A tracking arrangement for parabolic trough solar collectors is known from WO2019/054912A1. The tracking arrangement of that document is adapted to pivot each of the parabolic trough solar collectors towards the traveling sun in order to focus the sun rays towards the receiver fluid tube. The document also discloses turning the trough upside down e.g. at night in order to reduce heat loss through radiation.

An evacuated glass tube encircling the receiver fluid tube in the elongation thereof between a pair of collars for reducing heat losses by convection from the receiver fluid tube is known from US 4 151 828. In order to maintain a hard vacuum, a tubular side arm of the glass tube is connected to a vacuum pump.

Summary

The object of the present invention is to reduce energy losses from the solar collec tor.

This object has been achieved by a suspension device as initially defined, and further comprising the features that said bearing comprises a substantially annular body, wherein said annular body is adapted to slidingly receive a rod parallel to the axis of said receiver fluid tube, said rod being adapted to be connected to said receiver fluid tube. Furthermore, the object has been solved by the solar collector as initially defined.

Hereby, axial expansion of the receiver fluid tube is allowed to be absorbed while re ducing energy losses by convection. Furthermore is achieved that the cover means remains fixed in relation to the receiver fluid tube, and that the spoke is rotatably movable in relation to the cover means.

Suitably, said annular body is provided with a groove or an opening parallel to said axis A- A, said groove or opening being adapted to receive said rod.

Hereby is achieved a sliding suspension of said rod.

Preferably, said suspension member comprises a pair of fastening members connect ed to said rod on either sides of the bearing, said fastening members being adapted to be connected to said receiver fluid tube.

Hereby is achieved an interconnection of the rod and the receiver fluid tube in such a way that the rod is allowed to move along the axis A- A together with the receiver fluid tube. Suitably, said annular body is provided with a radially inner surface adapted to slidingly bear against said receiver fluid tube. Hereby the bearing is allowed to move about the cir cumference of as well as longitudinally along the receiver fluid tube.

Preferably, said annular body comprises at least one radially inwards directed protru sion, said protrusion being provided with said radially inner surface.

Alternatively, said annular body comprises at least two radially inwards directed pro trusions, each protrusion being circumferentially and/or axially separated from one another, said protrusions being provided with said radially inner surface.

Alternatively, or in addition, said bearing is provided with at least one radially out wards directed protrusion, said protrusion having a radially outer surface adapted to bear against a bearing lining or a bearing housing.

Alternatively, or in addition, said radially outwards directed protrusion is provided with at least one axially directed surface, adapted to receive an axial end surface of a cover member.

Hereby is achieved a reduced contact area, and in turn a reduced energy loss from the fluid tube by conduction.

Suitably, said spoke is provided with first and second annular clutch members, said bearing lining or said bearing housing being provided with an annular, peripheral groove adapted to receive said first and second annular clutch members. Hereby is achieved a rotatable connection of the parabolic reflector and the receiver fluid tube.

Preferably, said radially outward directed protrusion is provided with an axially di rected projection, adapted to receive circumferentially opposite edges of a slit of a cover member.

Hereby is achieved reduced energy loss due to convection.

Suitably, said annular body is divided into a pair of semi-annular bearing parts. Hereby, the annular body is allowed to be connected to the receiver fluid tube in an efficient manner.

Preferably, the annular body comprises a low friction, heat insulating material.

More particularly, the annular body comprises a polymer material, such as poly- aryletherketone (PAEK). Alternatively, or in addition, the annular body comprises a ceramic material.

Hereby, is achieved reduced energy loss due to conduction.

Brief description of drawings

The solution will now be described in more detail by means of exemplifying embod iments and with reference to the accompanying drawings, in which:

Figure 1A is a perspective schematic view of a solar collector including a receiver fluid tube, a reflector, a suspension means and a cover means connected to the receiver fluid tube;

Figure IB is a cross-section along lines IB-IB in Fig. 1A;

Figure 2A illustrates schematically an alternative suspension means and cover means;

Figure 2B is a partial side view of the cover means and suspension means shown in Fig. 2A;

Figure 3A is a cross-section of the cover means and suspension means along line IIIA - IIIA in Figure 2B;

Figure 3B is a cross-section of the cover means and suspension means according to an alter native embodiment;

Figure 3C is a cross-section of the cover means and suspension means according to yet an other alternative embodiment;

Figure 3D is a cross-section of the cover means according to yet another alternative embod iment; Figure 4 A is a perspective view of a portion of a further embodiment of the cover means and suspension means including a bearing;

Figure 4B is an exploded view of the cover means and the suspension means shown in Fig 4 A, and bearing parts;

Figure 4C is a cross-section of the cover means and suspension means of Fig 4A along a vertical plane through the axis A-A;

Figure 4D is an exploded view of an alternative cover means, and suspension means, and bearing parts;

Figures 5A - 5B illustrate the upper bearing part in different perspective views;

Figures 5C - 5D illustrate the lower bearing part in different perspective views;

Figure 5E illustrates an alternative embodiment of the bearing shown in Figs 5A - 5D; Figure 6A illustrates a single part bearing;

Figure 6B illustrates a bearing divided in a vertical plane; and

Figure 7 is a cross-section of an alternative cover means and suspension means.

Detailed description

Heat could be lost by three mechanisms: radiation, conduction, and convection. Ra diation could effectively be prevented by arranging so called selective surfaces, and conduc tion could be prevented by arranging appropriate insulations. Convection on the other hand arises when air flows close hot components and ventilates heat away. For open solar collec tors, natural convection from the wind is difficult to prevent. However, in covered or closed solar collector, even if such natural convection does not arise, internal air swirls arise and pass the receiver fluid tube. The solution that will be disclosed below, will prevent such in ternal convection by blocking internal air swirls inside the solar collectors.

By arranging cover means that blocks internal convection in the solar collectors, the efficiency of the solar collector is improved. This improved efficiency could be used e.g. for raising the temperature of the fluid in the receiver fluid tube, or increasing the amount of fluid that is transported in the receiver fluid tube. In experiments, the temperature has could be raised from 160 to 200 °C with the same amount of fluid transported in the receiver fluid tube. Figs. 1A and IB show a solar collector 2 comprising an elongated parabolic reflector 4, i.e. a PTC, provided with gables 6a, 6b at each end. The parabolic reflector 4 and the ga bles 6a, 6b are together rotatably arranged about a static receiver fluid tube 8 and a cover means 10 by means of a suspension means 9. The cover means 10 comprises first and sec ond cover members 12a, 12b non-rotatably attached to the static receiver fluid tube 8.

The parabolic reflector 4 is covered with a coated glass pane 11, for reducing ther mal losses by convection from the solar collector. Of course, the coated glass pane 11 may also protect the reflector 4 and the receiver fluid tube 8 from environmental effects that could decrease performance, e.g, rain, snow, sandstorms, dust, etc.

The first and second cover members 12a, 12b are arranged coaxially with the receiv er fluid tube 8 along axis A-A. The first and second cover members 12a, 12b are provided with an opening 7 in the form of an elongated slit 13 substantially below a horisontal plane through said axis A-A.

According to the embodiment of Figs. 1A-1B, the suspension means 9 comprises three spokes 14a, 14b, 14c arranged between the parabolic reflector 4 and the receiver fluid tube 8 by means of first, second and third bearings 16a, 16b, 16c, slidingly arranged on said receiver fluid tube 8. As shown in the lower enlargement of Fig. 1A, the bearings 16a, 16b, 16c preferably comprise an annular bearing body 17 including pair of semi-annular bearing parts 18a, 18b of a sliding bearing peripherally encompassed by a bearing lining 20 inside peripheral bearing housing 22. The bearing housing 22 and the bearing lining 20 may be substituted by a combined bearing housing provided with an inner surface acting as bearing lining. The radially inner surface 23 of the bearing parts slidingly bear against the exterior surface of the receiver fluid tube 8.

In case the receiver fluid tube is detachable from the parabolic reflector 4, said annu lar body 17 may instead comprise a singular annular bearing part.

In this exemplifying embodiment the parabolic reflector 4 is rotatably arranged to pivot about the receiver fluid tube 8, by a mechanism in form of a drum (not referred to) surrounding the receiver fluid tube 8 and a wire encircling the drum. By implementing such a tracking mechanism, the parabolic reflector 4 may follow the travelling sun and direct its aperture towards the solar radiation. It is hereby possible to keep focus of the sun rays to wards the receiver fluid tube 8 during day time hours. Furthermore, by selecting the dimen sions of the wire and drum, heat loss by radiation may be reduced by turning the parabolic trough substantially upside-down during night hours. It is to be noted that the tracking mechanism may be alternatively implemented within the inventive concept, e.g. by means of a cogwheel encircling the receiver fluid tube 8 and a toothed rack by which the cogwheel is rotated.

It is contemplated that the bearings 16a, 16b, 16c do not only perform a rotatable movement, due to the above described pivotal moment of the reflector, but also an axial movement along axis A- A, due to the longitudinal expansion and contraction of the receiver fluid tube 8, because of the varying heat of the focussed sun rays.

The first cover member 12a is rigidly attached to the receiver fluid tube 8. For this purpose, as shown in the upper enlargement of Fig. 1A, said suspension means 9 comprises a suspension member 30 including a clamp 32 and a partly annular (i.e. provided with an opening 7) heat insulating ring 34, of only little axial extension at each end of the first cover member 12a. More particularly, the first cover member 12a is attached to the receiver fluid tube 8 between, however not connected to, the bearings 16a and 16b. The cover member 12b is attached to the receiver fluid tube 8 in a corresponding manner between the bearings 16b and 16c. For facilitating understanding the Fig 1A, the cover members 12a, 12b have been shown as being separated a distance from the bearings. However, in order to reduce heat losses by convection, it is to be understood that the cover members 12a, 12b are to be arranged as close as possible to the bearings 16a, 16b, 16c.

Fig. 2 A and 2B show another embodiment of the solar collector 2. As already men tioned above in connection with the first embodiment, the first cover member 12a is ar ranged between but not connected to the first and second bearings 16a, 16b and is fixed to the receiver fluid tube 8 by a suspension means 9 in the form of a suspension member 30.

As mentioned in connection with the first embodiment, the cover means 10 is provided with an opening 7 having the shape of an elongated slit 13. The broken line D (Fig 2B) indicates the imaginary perimeter of the cover member 12a.

Also in this embodiment, the suspension member 30 keeps the first cover member 12a in a coaxial inter-relationship with said receiver fluid tube 8. The suspension member 30 of a heat insulating material, comprises a clamp 32 connected the exterior of the cover member 12a and to a rod 36 extending in both directions from said clamp 32 along said axis A-A to fastening means 37, such as clamping rings 38a, 38b, securing the cover means 10 coaxially with the receiver fluid tube 8. It is contemplated that in case the material of the rod 36 is chosen such that it has substantially the same expansion coefficient as the receiver fluid tube 8, the rod 36 will ex pand correspondingly to the expansion and contraction of the receiver fluid tube 8 due to the heat of the sun rays, and thus, the cover member 12a will remain substantially static in rela tion to the receiver fluid tube 8.

The cover member 12b is suspended on the receiver fluid tube 8 in a corresponding manner.

Fig 3A is a side view in cross-section along line IIIA-IIIA in Fig. 2B. The cover member 12a is substantially circular, but edges 40a, 40b define them between said open slit 13. The slit 13 is broad enough to allow introduction radially through the slit 13 of the re ceiver fluid tube 8 and the clamping ring 38a preferably also said clamping ring 38b of the suspension member 30. As already mentioned above, the receiver fluid tube 8 and the cover member 12a are arranged coaxially with axis A-A.

As shown in Fig. 3B, the slit 13 of the cover means 10 may instead be narrow, i.e. to a few degrees of a circle and thus open. In case the cover member is made of a rigid materi al, this of course requires lengthwise sliding attachment of the cover member 12a onto the clamping ring 38a (and clamping ring 38b) of the suspension member 30.

Fig. 3C shows yet another embodiment, according to which the cross-section of the cover means 10 is substantially a half circle between edges 40a, 40b, i.e. the slit 13 being substantially 180° of a circle.

In Figs. 3A - 3C, the cross-section of the cover member 12a has been shown as being substantially circular. It should however be noted that it may instead be substantially polyg onal, such as triangular, square, pentagonal etc., and including a slit below the horizontal plane through axis A-A of the receiver fluid tube.

Common for the embodiments of Figs. 3 A - 3C is that the slit is arranged substantial ly below a horizontal plane through axis A-A. By the cover means 10 shown in figs. 3A - 3C, heat losses by convection are reduced to a surprisingly large extent, despite the fact that the cover means is neither evacuated, nor closed, but is instead provided with a slit 13.

However, the inventive concept is not limited to arrange the opening of the cover member as an elongated slit along the entire length of the cover member as described above.

In an alternative exemplifying embodiment, instead a plurality of shorter slits are provided in the cover members such that the rods and clamping rings above are enabled to move in the slits to compensate for expansion of the receiver fluid tube, i.e. typically lengthwise expansion.

In Fig 3D, an alternative design of a cover means 10 is shown. Here, a cover member 12a has a U-shaped form and is configured to be arranged such that the U is turned upside- down. The cover member 12a is still arranged co-axially about the receiver fluid tube 8 and its axis A-A. The slit 13 between the edges 40a, 40b is an opening between parallel legs of the cover member 12a. With this design the gravity will prevent that the cover means 12a rotates with the reflector, i.e. the cover means 12a will be kept non-rotatably arranged in relation to the receiver fluid tube 8 by its mass. The cover member 12a may be provided by appropriate weights at its ends 40a, 40b to further ensure that its centre of gravity is located below the axis A-A.

By this disclosed design the suspension member 30 illustrated in Fig 4A designed with fewer parts. For instance, the clamping rings 38a, 38b, and the rod 36 could be omitted and the bearing parts 18b could be designed without the groove 44.

In yet another alternative embodiment, no slits are provided in the cover members, but their ends are open.

As it surprisingly has shown that a proper reduction of convection could be achieved also without evacuating the cover member, the cover member could be either provided with a slit along the cover members full length, partial slits by the receiver holders, or openings at its ends. By eliminating the need for vacuumizing the cover member, a plurality of ad vantages may be achieved, such as: a cheaper manufacturing and installation process; a less sensitive arrangement as no risk for leakage arise; receiver fluid tubes and cover members could be manufactured and installed separately; etc.

Figs. 4A - 4C show an alternative embodiment of a cover means 10, according to which the suspension means 9 integrally comprises the spoke 14.

The clamping rings 38a, 38b of the suspension member 30 are connected to the re ceiver fluid tube 8 indicated with broken lines in Fig. 4A. As described above, the clamping rings 38a, 38b are inter-connected by the rod 36, extending parallel to axis A-A.

The bearing 16 comprises an annular bearing body 17, including two semi-annular upper and lower parts 18a, 18b. By upper part is meant substantially above a horizontal plane through the axis A-A. Likewise, by lower part is meant substantially below a horizon tal plane through said axis A-A. The lower part 18b comprises a groove 44, adapted to re- ceive rod 36 of the suspension member 30. The groove 44 is arranged parallel to the axis A- A.

As shown in Figs. 4A and 4B, the exterior of the bearing 16 is provided with a plu rality of radially directed protrusions 46, having a peripheral radially outwardly directed contact surface 48 intended to contact a radial inner surface 52 of a bearing lining 20. The exterior of the bearing 16 is furthermore provided with a pair of annular grooves 62 (see also Figs 5A - 5D), each groove 62 being adapted to receive an O-ring 50, 51, respectively, in turn adapted to bear against the inner surface of cover members 12a, 12b, respectively.

The protrusions 46 are on each side provided with an axially directed surface 54a, 54b adapted to abut the axial end surface 56 of cover members 12a and 12b, respectively.

The bearing lining 20 is provided about its circumference with an annular peripheral groove 58, adapted to receive annular clutch members 60a, 60b. The clutch members 60a, 60b (see Fig. 4B) are adapted to maintain the two semi-annular upper and lower parts 18a, 18b inside said bearing lining 20, and to maintain the semi-annular bearing parts 18a, 18b on the receiver fluid tube 8, and furthermore to keep the axial end surfaces 56 of the cover members 12a and 12b in abutting relationship with the axially directed surface 54a, 54b of the protrusions 46.

Correspondingly as illustrated in Fig 2B, the imaginary perimeter D of the cover means 12a, 12b is illustrated by a dash-dotted line in Fig 4C.

Fig 4D illustrates an alternative embodiment to the one shown in Fig 4B, and the same reference numbers will be applied when appropriate. Fig 4D illustrates the implemen tation of the U-formed cover members 12a, 12b of the alternative embodiment shown in Fig 3D. In order to facilitate the understanding, we here focus on describing and emphasising the differences between these embodiments.

To enable the U-formed cover members 12a, 12b to be used, the bearing lining 20 is equipped with recesses 58’ configured to enable the ends of the cover members 12a, 12b to extend through the bearing lining 20. The peripheral grooves 58’ are located such that the cover members’ 12a, 12b ends may be arranged in the recesses 58’ without touching the clutch members 60a, 60b of the spoke 9.

As described above in another embodiment, the gravity and the mass of the cover members 12a, 12b, ensure that the cover members 12a, 12b, are prevented from rotating with the reflector (not shown), i.e. the cover members 12a, 12b are non-rotatably arranged with respect to the receiver fluid tube 8. Thereby, in this embodiment the suspension mem ber 30 may be designed with fewer parts as described with reference to Fig 3D. The second functionality of the suspension member, i.e. to keep the cover members 12a, 12b at a dis tance from the receiver fluid tube 8, is facilitated by the recesses 58’ of the bearing lining 20.

Regarding the embodiments illustrated by the Figs 4A-4D, they are configured to keep the cover members (12a, 12b) non-rotatably arranged in relation to the receiver fluid tube 8. Either by the suspension member 30 with clamping rings 38a, 38b, and the rod 36 (as shown in Fig 4B), or by the bearing 16 with its bearing lining 20 with recesses 58’ (as shown in Fig 4D).

Figs 5 A - 5D show the semi-annular bearing parts 18a, 18b in more detail. Both parts 18a, 18b are provided with the above mentioned radial protrusions 46 having axial abutment surfaces 54a, 54b, serving as axial end surface 56 for the cover members 12a and 12b (see Figs 4B - 4C).

The lowermost protrusion 46 of the lower bearing part 18b (see Fig 5C) is provided in opposite directions with an axially directed protrusion 61, provided with circumferential ly directed abutment surfaces 63 a, 63b adapted to abut the edges 40a, 40b of the cover members 12a, 12b (see Figs. 3A - 3C).

The above mentioned groove 44 is provided axially in the lower bearing part 18b, i.e. below a horizontal plane through the axis A- A and is adapted to receive the rod 36 (see Fig. 4B).

Each of the semi-annular bearing parts 18a, 18b is provided with a pair of annular grooves 62 for receiving an O-ring (see fig. 4B), respectively. The provision of an O-ring in the annular grooves 62, i.e. between the bearing 16 and the cover member 12a, 12b adds to reduced energy loss by convection.

Each of the semi-annular bearing parts 18a, 18b is also provided with radially, in wardly directed protrusions 64. The inwardly directed protrusions 64 are each provided with a sliding surface 66, intended to bear against the exterior surface of the receiver fluid tube 8. The provision of sliding surfaces 66 on protrusions 64, rather than a single inwardly di rected sliding surface of the bearing 16, adds to reduced energy loss by conduction.

Of course, the bearing lining 20 may be substituted by a bearing housing. On the oth er hand, depending on the size of the bearing lining 20, a bearing housing may be added between the clutch members and the bearing lining 20. It is contemplated that in case long cover members are provided, a muff may be added on each side of the bearing lining 20 or bearing housing.

When heated by the sun rays, the receiver fluid tube 8 will expand, in particular in its longitudinal direction. By allowing the rod 36 to slide in the groove 44, the expansion due to the heat of focussed solar radiation onto the receiver fluid tube 8 will be absorbed, and will thus not affect the durability of the cover members 12a, 12b, having a much lower coef ficient of expansion than that of the receiver fluid tube 8. By means of the rod 36, slidable in the groove 44, the position of the cover members 12a, 12b will remain substantially static in relation to the receiver fluid tube 8.

The material of the receiver fluid tube 8 is metal and preferably steel, stainless steel, copper or aluminium.

The material of the bearings 16, 16a, 16b, 16c is chosen in all of the above described embodiments such that it has a low friction in relation to the receiver fluid tube 8 and with stands high temperatures, such a ceramic material or a high temperature polymeric material, such as a polyaryletherketone (PAEK) material, e.g. polyether ether ketone (PEEK). Such materials also reduce thermal losses of the solar collector due to conduction.

Of course, the semi-annular bearing 18a, 18b may comprise a radial inner surface as described in connection with Figs 1A above. On the other hand, the bearings described in connection with Figs. 1A - IB and Figs 2A - 2B, respectively, may comprise radially di rected protrusions provided with an inner, radially directed surface intended to bear against the receiver fluid tube 8.

Fig. 5E shows ab alternative embodiment of the bearing 16, comprising a pair of semi-annular bearing parts 18a, 18b divided in a horizontal plane through the axis A- A, in a manner corresponding to that of Figs 5A - 5D, however provided with a pair of axially ex tending grooves 44a, 44b underneath said horizontal plane. The pair of grooves 44a, 44b are adapted to receive a pair of rods 36 to be connected to the clamping rings 38a, 38b.

Fig 6 A shows an alternative embodiment of the bearing 16, comprising a single an nular body. A trough-hole 68 is provided in a lowermost portion of the annular body rela tive to a horizontal plane through the axis A-A. The through-hole 68 is adapted to receive the rod 36. Of course, in case the suspension means 9 comprises a pair of rods 36 to be con- nected to the clamping rings 38a, 38b. In such a case, the annular body is provided with two through-holes 68, one for each rod 36.

Fig 6B shows yet another alternative embodiment of the bearing 16, comprising a pair of semi-annular bearing parts 18a, 18b divided in a vertical plane through the axis A-A. Each semi-annular bearing part 18a, 18b is provided with an axially extending groove 69a, 69b of semi-circular cross-section in the lowermost portion of the annular body relative to a horizontal plane through the axis A-A. The grooves 69a, 69b are facing one another, togeth er forming a circular through-hole adapted to receive the rod 36.

Of course, the semi-annular bearing parts 18a, 18b shown in Fig 6B may be provided with one or two grooves 44 of the kind shown in Figs 5A-5E or with one or two axially ex tending through holes 68, as described in connection with Fig. 6A.

It is to be understood that in the embodiment shown in Figs 5A - 5E, the semi- annular bearing parts 18a, 18b may instead be divided vertically or at any angle.

It is to be understood that the cross-section of the rod 36 may have any shape, such as circular or pentagonal. It is also to be understood that the groove 44, the through hole 68 and the semi-circular grooves 69a, 69b may have any cross-section, respectively that is suit able for receiving said rod 36.

It is contemplated that the bearing may comprise ball bearings or roller bearings.

The material of the cover members 12a, 12b is preferably transparent and may com prise glass, or a polymer, such as plexiglass. The cover member 12 may instead comprise a thin film of a polymer, such as a PEAK, e.g. PEEK.

As shown in Fig 7, the cover means 10 may comprise a thiu polymer film 70 to be suspended on a suspension means 9 comprising radially directed suspension members 72 attached to the receiver fluid tube 8 by means of a fastening means 74, such as spring clamps, the suspension members 72 extending radially away from the receiver fluid tube 8. The suspension means 9 suspends the film 70 in such a way to provide an elongated open ing 7 underneath a horizontal plane through the axis A-A of the receiver fluid tube 8.

It is contemplated that the cover member 12, 12a, 12b of the kind shown in Figs. 3A - 3C may be suspended on suspension means of the kind shown in Fig. 7.

It is noted that in all of the above described embodiments, the elongated opening 7 may instead of a slit 13 be made as a plurality of discreet openings, such as circular, oval or elongated holes. The openings need not be arranged in a line, but may be spread randomly over the lower region of the cover member, i.e. underneath a horizontal plane through the axis A-A.

In the embodiments above, it has been described that the cover means 10 comprises two or three cover members 12a, 12b. It should however be understood that the number of cover members may be a single one or more than two, such as three, four etc. Consequently, also the number of spokes 14 may vary depending on the number of cover members and/or the length of each cover members 12.

Reference signs used

2 solar collector

4 parabolic reflector

6a, 6b gables

7 opening

8 receiver fluid tube

9 suspension means

10 cover means 11 glass pane

12, 12a, 12b cover member 13 slit

14, 14a, 14b, 14c spoke 16, 16a, 16b, 16c bearing 17 annular bearing body

18a, 18b semi-annular bearing parts 20 bearing lining 22 bearing housing 23 radial inner surface 26 toothed rack 28 cogwheel 30 suspension member 32 clamp 34 heat insulating ring 36 rod 37 fastening means

38a, 38b clamping ring 40a, 40b edges 44 groove 46 radially directed protrusion

48 radially directed contact surface

50, 51 O-ring 52 radial inner surface

54a, 54b axially directed surface 56 axial end surface

58 annular peripheral groove 58’ cover recesses

60a, 60b annular clutch members 61 axially directed protrusion 62 annular groove

64 inwardly directed protrusion 66 sliding surface 70 film 72 radially directed suspension members

A-A axis

D imaginary diameter

Numbered embodiments, NEE

NEE l.A suspension device for keeping a receiver fluid tube (8) at a predetermined position in relation to a parabolic reflector (4), comprising a spoke (14) connected to said par abolic reflector (4) and to a bearing (16), said spoke (14) being adapted to keep said receiver fluid tube (8) at a predetermined distance from said parabolic reflector (4), said spoke (14) being movably arranged in relation to said receiver fluid tube by means of said bearing (16), said receiver fluid tube (8) having an axis (A- A) in its elongation, characterized in that said bearing (16) comprises a substantially annular body (17), wherein said annular body (17) is adapted to slidingly receive a rod (36) parallel to the axis (A- A) of said receiver fluid tube (8), said rod being adapted to be connected to said receiver fluid tube (8).

NEE2.A suspension device according to NEE 1, wherein said annular body (17) is provided with a groove (44) or an opening parallel to said axis A- A, said groove (44) or open ing being adapted to receive said rod (36).

NEE3.A suspension device according to NEE 1 or 2, wherein said suspension member (30) comprises a pair of fastening members (38a, 38b) connected to said rod (30) on either sides of the bearing (16), said fastening members (38a, 38b) being adapted to be con nected to said receiver fluid tube (8).

NEE4.A suspension device according to any one of NEEs 1 to 3, wherein said annular body (17) is provided with a radially inner surface (23) adapted to slidingly bear against said receiver fluid tube (8).

NEE5.A suspension device according to NEE 4, wherein said annular body (17) comprises at least one radially inwards directed protrusion (47), said protrusion (47) being pro vided with said radially inner surface (23).

NEE6.A suspension device according to NEE 3 or 4, wherein said annular body (17) com prises at least two radially inwards directed protrusions (47), each protrusion (47) be- ing circumferentially and/or axially separated from one another, said protrusions (47) being provided with said radially inner surface (23).

NEE7. A suspension device according to any one of the preceding NEEs, wherein said bear ing (16) is provided with at least one radially outwards directed protrusion (46), said protrusion (46) having a radially outer surface (48) adapted to bear against a bearing lining (20) or a bearing housing (22).

NEE8. A suspension device according to NEE 7, wherein said radially outwards directed protrusion (46) is provided with at least one axially directed surface (54a, 54b), adapted to receive an axial end surface (56) of a cover member (12).

NEE9.A suspension device according to NEE 7 or 8, wherein said spoke (14; 14a, 14b, 14c) is provided with first and second annular clutch members (60a, 60b), said bearing lin ing (20) or said bearing housing (22) being provided with an annular, peripheral groove (58) adapted to receive said first and second annular clutch members (60a, 60b).

NEE 10. A suspension device according to any one of NEEs 7 to 9, wherein said radial ly outward directed protrusion (46) is provided with an axially directed projection (61), adapted to receive circumferentially opposite edges (40a, 40b) of a slit (13) of a cover member (12).

NEE1 1. A suspension device according to any one of the preceding claims, wherein said annular body (17) is divided into a pair of semi-annular bearing parts (18a, 18b).

NEE 12. A suspension device according to any one of the preceding NEEs, wherein the annular body (17) comprises a low friction, heat insulating material.

NEE 13. A suspension device according to claim 12, wherein the annular body (17) comprises a polymer material, such as polyaryl etherketone (PAEK).

NEE 14. A suspension device according to NEE 12, wherein the annular body (17) comprises a ceramic material. NEE 15. A solar collector comprising a receiver fluid tube (8), a parabolic reflector (4) and a suspension device according to any one of the preceding claims, wherein the coefficient of expansion of the material of said rod (36) is substantially the same as that of the receiver fluid tube (8).

Claims

1. A suspension device for keeping a receiver fluid tube (8) at a predetermined posi tion in relation to a parabolic reflector (4), comprising a spoke (14) connected to said parabolic reflector (4) and to a bearing (16), said spoke (14) being adapted to keep said receiver fluid tube (8) at a predetermined distance from said parabolic reflector (4), said spoke (14) being movably arranged in relation to said receiver fluid tube by means of said bearing (16), said receiver fluid tube (8) having an axis (A- A) in its elongation, characterized in that said bearing (16) is further configured to keep a cover member (12a, 12b) non-rotatably arranged in relation to the receiver fluid tube 8.

2. A suspension device according to claim 1, wherein said bearing (16) is provided with at least one radially outwards directed protrusion (46), said protrusion (46) hav ing a radially outer surface (48) adapted to bear against a bearing lining (20) or a bearing housing (22), the bearing lining (20) comprising recesses (58’) configured to enable ends of the cover member (12a, 12b) to extend through.

3. A suspension device according to claim 1, wherein said bearing (16) comprises a substantially annular body (17), wherein said annular body (17) is adapted to sliding - ly receive a rod (36) parallel to the axis (A- A) of said receiver fluid tube (8), said rod being adapted to be connected to said receiver fluid tube (8).

4. A suspension device according to claim 2, wherein said annular body (17) is pro vided with a groove (44) or an opening parallel to said axis A- A, said groove (44) or opening being adapted to receive said rod (36).

5. A suspension device according to claim 3 or 4, wherein said suspension member (30) comprises a pair of fastening members (38a, 38b) connected to said rod (30) on either sides of the bearing (16), said fastening members (38a, 38b) being adapted to be connected to said receiver fluid tube (8).

6. A suspension device according to any one of claims 3 to 5, wherein said annular body (17) is provided with a radially inner surface (23) adapted to slidingly bear against said receiver fluid tube (8).

7. A suspension device according to claim 6, wherein said annular body (17) compris es at least one radially inwards directed protrusion (47), said protrusion (47) being provided with said radially inner surface (23).

8. A suspension device according to claim 5 or 6, wherein said annular body (17) comprises at least two radially inwards directed protrusions (47), each protrusion (47) being circumferentially and/or axially separated from one another, said protru sions (47) being provided with said radially inner surface (23).

9. A suspension device according to any one of the claims 3 to 8, wherein said bearing (16) is provided with at least one radially outwards directed protrusion (46), said pro trusion (46) having a radially outer surface (48) adapted to bear against a bearing lin ing (20) or a bearing housing (22).

10. A suspension device according to claim 9, wherein said radially outwards directed protrusion (46) is provided with at least one axially directed surface (54a, 54b), adapted to receive an axial end surface (56) of a cover member (12).

11. A suspension device according to claim 9 or 10, wherein said spoke (14; 14a, 14b, 14c) is provided with first and second annular clutch members (60a, 60b), said bear ing lining (20) or said bearing housing (22) being provided with an annular, periph eral groove (58) adapted to receive said first and second annular clutch members (60a, 60b).

12. A suspension device according to any one of claims claim 9 to 11, wherein said ra dially outward directed protrusion (46) is provided with an axially directed projection (61), adapted to receive circumferentially opposite edges (40a, 40b) of a slit (13) of a cover member (12).

13. A suspension device according to any one of the preceding claims, wherein said an nular body (17) is divided into a pair of semi-annular bearing parts (18a, 18b).

14. A suspension device according to any one of the preceding claims, wherein the an nular body (17) comprises a low friction, heat insulating material.

15. A suspension device according to claim 14, wherein the annular body (17) com- prises a polymer material, such as polyaryletherketone (PAEK).

16. A suspension device according to claim 14, wherein the annular body (17) com prises a ceramic material.

17. A solar collector comprising a receiver fluid tube (8), a parabolic reflector (4) and a suspension device according to any one of the preceding claims, wherein the coeffi cient of expansion of the material of said rod (36) is substantially the same as that of the receiver fluid tube (8).