GB2095393A

GB2095393A - Thermal coupling for solar collector

Info

Publication number: GB2095393A
Application number: GB8208303A
Authority: GB
Original assignee: DENCO AIR Ltd; General Electric Co PLC
Current assignee: DENCO AIR Ltd; General Electric Co PLC
Priority date: 1981-03-23
Filing date: 1982-03-22
Publication date: 1982-09-29
Also published as: GB2095393B

Abstract

An arrangement for thermally coupling a solar energy collector (12), including a heat pipe (5), to a part of a heat-extraction system (3, 4) consists of a first metal bearing member (6) provided with a male bearing surface and a second metal bearing member (2) provided with a corresponding female bearing surface adapted to receive the first member to form a rotatable coupling having at least one degree of freedom. The bearing surfaces may be spherical or part spherical, cylindrical or part cylindrical, or frusto-conical or part frusto-conical, and may be urged against each other by spring means (10). <IMAGE>

Description

SPECIFICATION Flexible solar collector coupling This invention relates to solar heating systems comprisng one or more solar energy collectors and a heat-extraction system, such as a pipe or other vessel containing fluid, which is heated by thermal energy derived from the collectors, wherein the collector or collectors is or are of the vacuumjacketed heat-collecting tube type, that is to say the type consisting essentially of a sealed metal tube containing a fluid heat carrier medium and mainly surrounded by an evacuated jacket at least part of which is transparent to solar radiation, the tube being sealed through one end of the jacket and, in use of the collector, the end of the metal tube external to the jacket being connected to a heatextraction system for the transmission of heat thereto.

The heat-extraction system may comprise, for example, a fluid-containing pipe, and usually a large number of said solar energy collectors will be coupled to such a pipe, arranged on either side of the pipe along its length, suitably in herring-bone fashion.

The invention is more particularly concerned with means for coupling the heat-collecting metal tube of such a solar energy coilector to a part of a heatextraction system, an object of the invention being the provision of a detachable thermal coupling arrangement which is sufficiently flexibie to alleviate thermal strains caused by uneven heating of the collector jacket and by the differing thermal expansivities of the jacket and the heat-collecting tube.

According to the invention, an arrangement for thermally coupling a solar energy collector of the vacuum-jacketed heat-cilecting tube type to a part of a heat-extraction system comprises a first metal bearing member provided with a male bearing member provided with a male bearing surface and a second metal bearing member provided with a corresponding female bearing surface adapted to receive the first member to form a rotatable coupling having at least one degree of freedom, one of said members being attached to the end of the heatcollecting tube external to the collector jacket, and the other of said members being adapted to be attached to a part of the heat-extraction system, and means being provided for urging the two said bearing surfaces against each other.The said bearing surfaces may be cylindrical or part cylindrical, frusto-conical or part frusto-conical, or spherical or part spherical. These types of coupling will subsequently be referred to as "cylindrical", "frustoconical" and "spherical" couplings respectively.

The bearing surfaces are preferably urged against each other by spring means.

In the case where the join is cylindrical, the said first and second bearing members (hereinafter referred to as the "male" and "female" members respectively) are preferably urged against each other by spring means acting radially with respect to the coupling, which conveniently acts on the vacuum jacket of the solar collector. The ball and socket members of a spherical coupling may of course also be urged against one another by spring means acting in a similar manner. In the case where the coupling is frusto-conical, the male and female members are preferably held together by axial spring means associated with the coupling.

The part of the solar energy collector remote from the coupling is peferably freely supported, so as to permit movement of the collector in response to rotation of the male member in the female member.

Preferably the female member is thermally connected to the pipe or other part of the heat-extraction system, and the male member is thermally connected to the heat-collecting tube of the solar energy collector.

In the case where the coupling is cylindrical or frusto-conical the axis of rotation of the coupling is preferably perpendicular to the axis of the said fluid containing heat extraction pipe, which in use, is preferably mounted horizontally.

The coupling arrangement of the invention has a number of advantages over rigid couplings. In particular a solar heating system incorporating an array of solar energy collectors coupled to a heatextraction system in the manner described above may be easily disassembled and reassembled, thus considerably simplifying transport of the system.

Furthermore, broken solar collectors may be easily replaced. Both these advantages are especially important when such systems are used in remote areas. The freedom of movement of the collectors also minimises sudden strains caused by gusts of wind acting on the collectors, as well as strains caused by differential heating and expansion of the parts of the collectors. This is advantageous in view of the relatively fragile nature of the seals between the vacuum jackets (which are usually of glass) and the heat-collecting tubes of the solar collectors.

In the case where the coupling is of the spherical type freedom of orientation of the coupling in the vertical plane is preferably limited by two or more guides extending from the socket member, which member suitably consists of a tubular casting.

Alternatively the socket member may be adapted to be connected to the exterior of part of a heatextraction system; for example to the outside of a heat-extraction pipe. The ball and socket members are both preferably made of copper or brass, and the thermal contact between them may be improved by smearing the joint surfaces with a thermally conducting grease. The ball member may be attached to the heat-collecting tube via a closely fitting tube which surrounds the tip of the heat-collecting tube and is integral with the male member.

In the case where the coupling is of the cylindrical type, a stop means is preferably provided for limiting relative axial movement of the coupled members.

For example the male member may incorporate a dumb-bell shaped portion, of which the central cylindrical surface engages the female cylindrical surface and the end cheeks straddle the female bearing member and thereby limit the relative axial movement of the two members, although some degree of axial movement may be permitted. Preferably the freedom of orientation of the joint is limited by two or more guides surrounding and extending from the female member. The male and female members are both preferably made of copper or brass, and the thermal contact between them may be improved by smearing the bearing surfaces with thermally conducting grease. One of the membes may be attached to the heat-collecting tube via a closely fitting tube which surrounds the tip of the heat-collecting tube and is integral with the bearing.

The other member is preferably adapted to be partially inserted into, and sealed to, a heatextraction pipe which forms part of the heatextraction system and is connected to a plurality of solar energy collectors by similar rotatable joints.

Heat is transferred from the said other member by fluid flowing through the heat-extraction pipe. Pre ferably the part of the member which is adapted to be inserted into the heat-extraction pipe carries one or more fins which make contact with the flowing fluid and thereby improve the rate of heat transfer from the solar energy collector. Preferably the fins are integral with the said member and are adapted to lie parallel to the flow of fluid in order to reduce turbulence.

Alternatively a section of the tube may be formed integrally with one of the bearing members and may incroporate heat-transfer fins on its inner surface adjacent to the said bearing member.

Specific embodiments of the invention will now be described by way of example with reference to Figures 1,2 and 3 of the accompanying drawings, of which: Figure 1 is a schematic part-sectional view of one coupled solar collection assembly of a solar energy collector and part of a heat-extraction system; Figure 2 is a section taken on line A-A of Figure 1; and Figure 3 is a schematic part-sectional view of another coupled solar collection assembly of a solar energy collector and part of a heat-extraction system.

Figure 1 shows a first cylindrical bearing member 1 coupled to a second bearing member 2, which is integral with a tubular section 3. The tubular section 3 is connected to a heat-extraction pipe 4, through which a heat extraction fluid flows. The bearing member 1 is connected by a heat pipe 5 to a vacuum jacketed solar energy collector (not shown) of the type described in or co-pending patent application No. 8108974, for example. The bearing member 2 is held against the bearing member 1 by a spring (not shown) acting on the solar energy collector and axially iocated by means of end-cheeks 6, as best seen in Figure 2. In use, heat conducted from the heat pipe 5 to the bearing member 2 is transferred to the heat extraction fluid through fins 7 (Figure 2).

In a modification of the coupling described the first bearing member 1, instead of being cylindrical may taper towards its ends, the inner surface of the second bearing member 2 being of a complementary shape. In a further modification the first bearing member 1 may be of frusto-conical shape urged axially into a complementary frusto-conical female surface of the second bearing member. Other shapes of bearing members allowing one or more degrees of freedom may alternatively be employed.

Referring to Figure 3, a solar energy collector 12, of the vacuum-jacketed heat-collecting tube type, is coupled to a heat-pipe 5 partially filled with heatextracting fluid (not shown). A socket member 2 which contains a hemispherical recess 13 is welded to the heat-extraction pipe 4, and a ball member 6 is seated in the recess 13: a small gap is shown for clarity, but in practice the ball is wholly in contact with the recess wall. The socket member 2 is provided with fins 7 which in use, transfer heat to a heat extraction fluid (not shown) flowing through the pipe 4. The ball 6 carries a tubular extension 8 which is welded to the heat-pipe 5 of the collector. An evacuated glass jacket 13 is sealed at its neck to the heat-collecting tube. The solar collector and its associated ball member are supported by a stirrup 9 surrounding the jacket so that the latter has considerable freedom of movement, and the ball member is urged into close thermal contact with the socket member by a spring 10 acting on the free end of the jacket; angular movement of the collector is limited by guides 1 incorporated in the socket member 2. As mentioned above, the ball and socket joint may be smeared with thermally conducting grease (not shown) to enchance the thermal contact. The pipe 5, the socket member 2, and the protruding end of the tube 8 are preferably covered by thermal insulation (not shown).

Typically, the solar energy collector would be about 1.8 metres long and 65 mm in diameter, and would give a thermal power output of about 50 watts.

Claims

1. An arrangement for thermally coupling a solar energy collector of the vacuum-jacketed heatcollecting tube type to a part of a heat-extraction system, comprising a first metal bearing member provided with a male bearing surface and a second metal bearing member provided with a corresponding female bearing surface adapted to receive the first member to form a rotatable coupling having at least one degree of freedom, one of said members being attached to the end of the heat-collecting tube external to the collector jacket, and the other of said members being adapted to be attached to a part of the heat extraction system, and means being provided for urging the two said bearing surfaces against each other.

2. An arrangement according to Claim 1 in which the said bearing surfaces are cylindrical or partcylindrical.

3. An arrangement according to Claim 1 in which the said bearing surfaces are frusto-conical or part frusto-conical.

4. An arrangement according to Claim 1 in which the said bearing surfaces are spherical or part spherical.

5. An arrangement according to any of Claims 2, 3 or 4 in which the said bearing surfaces are urged against each other by spring means.

6. An arrangement according to Claim 2 or Claim 3 in which the axis of rotation of the coupling is perpendicular to the axis of the fluid-containing heat extraction pipe.

7. An arrangement according to any preceding Claim in which the part of the solar energy collector remote from the coupling is freely supported.

8. An arrangement according to any preceding Claim in which the female member is thermally connected to the pipe or other part of the heatextraction system and the male member is thermally connected to the heat-collecting tube of the solar energy collector.

9. An arrangement according to any preceding Claim in which the freedom or orientation of the coupling is limited by two or more guide portions extending from the socket member.

10. An arrangement according to any preceding Claim in which heat is transferred from the coupling to fluid flowing through the heat-extraction system via one or more fins.

11. An arrangement according to Claim 12 in which one or more of the said fins is oriented substantially parallel to the direction of fluid flow.

12. A couple solar collection assembly substantially as described hereinabove with reference to Figures 1 and 2 of the accompanying drawings.

13. A coupled solar collection assembly substantially as described hereinabove with reference to Figure 3 of the accompanying drawings.