GB2092293A

GB2092293A - A Solar Radiation Collector Having an Evacuated Interior

Info

Publication number: GB2092293A
Application number: GB8138254A
Authority: GB
Original assignee: Messerschmitt Bolkow Blohm AG
Current assignee: Airbus Defence and Space GmbH
Priority date: 1980-12-24
Filing date: 1981-12-18
Publication date: 1982-08-11
Also published as: DE3048951A1; GB2092293B; DE3048951C2

Abstract

The collector comprises a trough- like housing and a cover plate (2) which is pervious to radiation. Supporting elements (8, 19) are provided between the cover plate (2) and housing base (3). A radiation absorption system (not shown) is provided in the interior. The housing walls (1) consist, in cross-section, of two portions (4, 5) which are curved in opposite directions and connected by a flat portion (6) directed substantially perpendicular to the cover plate (2). The curved portions (5, 4) culminate respectively in the flat housing base (3) and in an edge lying parallel to cover plate 2. The housing walls (1) are made from elastic material, the supporting elements (8, 19) are mounted elastically and the housing walls (1) are supported from within on both sides of the curved portion (5) adjacent the housing base (3) by a load-bearing element (21). <IMAGE>

Description

SPECIFICATION A Radiation Collector Having an Evacuated Interior This invention relates to a radiation collector or having an evacuated interior which comprises a trough-like housing and a cover plate pervious to radiation, supporting elements which support the cover plate and which extend towards the housing base, as well as a radiation absorption system provided in the interior.

A radiation collector of this kind is already known from German Gebrauchsmuster No. 79 09 689. It comprises a housing, the walls of which are directed substantially perpendicular to the cover plate. The walls of the housing have an edge which is turned outwardly at a sharp angle to serve for application of the cover plate.

Vaulting is provided at the base of the housing and occupies aimost the entire collector surface.

The vaulting is arched or curved, in a transitional region between the base and the housing walls.

However, it remains unclear how, in the case of this known radiation collector, the housing walls are protected against the external pressure. If housing walls which are flat throughout almost the entire collector height are not of very great thickness, they require further reinforcement measures, for example complicated, expensive and relatively heavy flexural stiffenings.

Statements relative to the above are, however, not contained in German Gebrauchsmuster No.

79 09 689.

An object of the present invention is, therefore, to provide a radiation collector, of the kind mentioned at the beginning hereof, which has, with respect to the pressure difference occurring between the housing interior and the external atmosphere, the necessary stability. More particularly the aforesaid stability is to be achieved by an appropriate configuration of the housing walls. In this respect, attention is to be paid to production of the wall structure as simply and inexpensively as possible. Special stiffenings located adjacent the housing walls are to be avoided.

With this object in view the present invention provides a radiation collector of the aforementioned type characterised in that the housing walls are formed, in cross section, with two portions which curve in opposing directions, which are connected by a flat portion directed substantially perpendicular to the cover plate, which culminate at respective ends in the flat housing base and in an edge parallel to the cover plate and which are made from elastic material, the supporting elements are mounted elastically and the housing walls are supported from within on both sides of the curved portion adjacent the housing base.

Accordingiy, it is characteristic of the crosssectional shape of the housing walls that two portions are present which curve in opposite directions and are connected to one another by a flat portion, in which respect the flat portion is directed substantially perpendicular to the cover plate. The curved portion adjacent the cover plate ends in an edge parallel to said cover plate and the curved portion adjacent the housing base ends in the flat housing base. To stabilise this housing wall shape which is already designed in a special manner, provision is made for support of the housing walls from within on both sides of the curved portion adjacent the housing base. This is not provided in German Gebrauchsmuster No. 79 09 689.Furthermore support of the walls is not in the present invention accomplished by stiffenings which are connected securely to the housing walls. On the contrary, what is essential is that a defined place for the supporting measures is indicated in close coherence with the proposed housing wall shape. Finally, it is additionally required that the housing walls themselves are produced from elastic material and the supporting elements are mounted elastically.

Radiation collectors proposed by the invention are, with the correct material and dimensions, inherently stable, by virtue of the avoidance of complicated expensive wall stiffenings of slight weight and, moreover, easy to produce, especially in view of the possibility of producing the collector housing with the doubly-curved walls by the deep drawing process. Important dimensions or parameters of the housing walls are the radii of the two curved portions, the height of the flat portion, the wall thickness as well as the elastic properties of the wall material. By virtue of the oppositely extending curvatures, the radii of which will generally be of comparable order of magnitude, as well as the connecting flat portion, the housing walls, which are to be produced from elastic material, for example steel, have elastic spring properties.In other words, the housing walls are elastically compressible perpendicular to the cover plate in the direction of the flat housing wall portion. In this respect, the force occurring at the outer edge of the housing wall and counteracting the loading is, within a specific range, in proportion to the decrease in the overall height.

The supporting elements arranged between the housing base and the cover plate are mounted elastically. This elastic mounting permits, however, only a limited shortening of the overall height, since the supporting elements are of course present in order to maintain a specific spacing between the housing base and the cover plate. There then occurs, at the edge of the housing walls, a specific force which is dependent upon the dimensions thereof and which acts on the edge of the cover plate. The transmission of this force to the edge of the cover plate takes place for example where a sealing ring is disposed between the flat edge of the housing walls and the cover plate.The edge of the cover plate is thus exposed to two oppositely-directed forces or loadings, which act with respect to the surface of the cover plate as transverse forces and cause bending moments with respect to the points of support of the cover plate on the supporting elements.

It must be emphasised that the housing walls are also stabilised by supports provided on both sides of the curved portion adjacent the housing base. In this respect, it is essential that the bending moments which occur at the edge of these supports and which are caused by the external pressure on the housing walls do not exceed the critical, i.e. highest permissible, bending moment. For this, the wall thickness must indeed have a certain minimum value, which is, however, as a result of the overall wall structure, relatively low.It has been demonstrated that the critical bending moment occurring at the supported portion, as described, may be considerably reduced if the connecting flat portion does not, as in the case of the radiation collector of German Gebrauchsmuster No. 79 09 689, turn outwardiy at a sharp angle at its upper edge, but instead this sharp angle is replaced by a second, expediently dimensioned curved portion, the radius of curvature of which is of comparable order of magnitude to that of the first-mentioned curved portion adjacent the housing base. Appropriate wall parameters may be calculated with the aid of computing and statistical methods.

The housing base of the radiation collector of the present invention is, in contrast to that of the known radiation collector, flat. It is stressed substantially only in two dimensions. The curved portion adjacent the housing base behaves like a hollow quarter cylinder which is stressed by compression from the outside, in which respect the radius of curvature of this portion is limited by the pressure loadability of said portion. The height of the flat housing wall portion is determined substantially by the critical bending moment which is achieved more rapidly the more this flat portion is elongated at the expense of the second curved portion. The second curved portion, ending in the flat edge of the housing wall, behaves like a quarter cylinder which is acted upon by pressure from the inside. The pressure loading is transmitted as pull into the flat portion.

It proves to be advantageous to coordinate the dimensions and the elasticity of the housing walls in such a way that, upon loading of the cover plate by the external pressure, the bending moment acting in each case in the edge region of the cover plate with respect to the supporting elements situated nearest to the housing walls is to some extent as great as the bending moment acting in each case over the remaining supporting elements in the cover plate. This measure serves to distribute the loading as uniformly as possible over the cover plate and to prevent the occurrence of extremely large bending moments in the edge region of the cover plate.

Tubes, rods or bars, arranged substantially perpendicular to the cover plate may be used as the supporting elements. It is, however, also possible to use, for this purpose, supporting plates which are arranged substantially parallel to one another and perpendicular to the cover plate. In this respect it proves to be advantageous to select the width of the edge of the cover plate which protrudes beyond the ends of the supporting plates in the longitudinal direction thereof in such a way that to some extent equilibrium exists between the mutually opposing transverse forces which act on the edge of the cover plate and which occur on the one hand as a result of the external pressure bearing on the cover plate and on the other hand as a result of the elasticity of the housing walls.The transverse forces caused by the external pressure act in the edge region of the cover plate, insofar as the space situated thereunder is evacuated; they are relative to the supporting points corresponding to the ends of the supporting plates. The transverse force caused by the elasticity of the side walls acts, for example, by way of the sealing rings, on the edge region of the cover plate and is also relative to the said supporting points. In the event of equilibrium of these transverse forces, the loading of the plate regions situated between the said supporting points is as small as possible. The stipulation made earlier with respect to the bending moments applies to the longitudinal edges, facing the cover plate, of the two supporting plates situated furthest outwards adjacent the housing walls.

Advantageously, load-bearing elements which butt partially against the housing walls are used for supporting the housing walls on both sides of the curved portion adjacent the housing base.

These absorb the external pressure and transmit it into the inner supporting structure of the radiation collector, of which the supporting plates are an essential part. In particular it is proposed to design the load-bearing elements in such a way that they have, in cross-section, two limb portions which are orientated substantially at right angles to one another and which extend radially with respect to the housing wall curvature. Loadbearing elements of such a shape are particularly well suited to absorb the external pressure acting in the radial direction. Furthermore, provision is made for equipping the load-bearing elements with portions which extend parallel to the housing base and which are held fast against the housing base with the aid of the supporting elements. In order to accomplish this, base plates having profiles may, for example, be provided. On the one hand the profiles serve for holding the supporting elements and on the other hand they are pressed by said supporting elements against the housing base. The edges of these base plates may grip over the portions of the load-bearing elements which extend parallel to the housing base and thus restrain these in the desired position.

The invention will be described further, by way of example, with reference to the accompanying drawings in which: Fig. 1 is a partial cross-section through one embodiment of a radiation collector in accordance with the present invention which considered from above is substantially rectangular; Fig. 2 is a partial cross-section along the line Il-Il, of the radiation collector shown in Fig.,1; Fig. 3 is a partial cross-section through a second embodiment of a radiation collector of the invention; and Fig. 4 is a partial cross-section through a third embodiment of a radiation collector of the invention.

As shown in Fig. 1 a side wall 1, of a radiation collector in accordance with the invention has, in the centre, a flat portion 6, linking upwardly and downwardly respectively, two curved portions 4 and 5. These merge respectively into a flat upper edge 1 3 of the wall and a flat housing base 3. The flat edge 1 3 of the collector housing is bent up into a flange 17. A cover plate 2 lies on the edge 13, and inserted between the two is a sealing ring 7. The collector housing comprising the side walls 1 and the housing base 3 is made from steel plate and may be produced by the deep drawing process. The cover plate 2 consists of glass and the sealing ring 7 is made of silicon rubber.

Supporting plates, which each comprise two parts 8, 19, are arranged parallel one above the other between the cover plate 2 and the housing base 3. The upper part plates 8 consist of glass, the lower part plates 19 may, for example, be formed of flat steel. A profile plate 11, which has profiles bulged upwardly, for example in the shape of sine half-waves, rests on the housing base 3. These profiles are provided, with slots, located parallel to the plane of Fig. 1, into which the lower part plates 19 are inserted. A plurality of profiles are located adjacent one another across the width of the radiation collector. The two profiles situated in each case furthest outwards have additional recesses into which small guide plates 20 are inserted.These guide plates 20 serve to retain the upper part plates 8, which are superimposed onto the lower part plates 1 9 by way of an interposed strip 1 8 of elastic material. Mounted, for example bonded, onto the upper edges of the upper part plates 8 are similar strips 9 of elastic material, on which the cover plate 2 rests directly. The strips 1 8 and 9 of elastic material may, for example, be formed of silicon rubber. Supporting strips 12 which consist, for example, of sheet steel are inserted into the slots of the profiles. These supporting strips 12 are approximately the same width as the slots in the regions where they extend through the profile slots, but they are wider in the regions where they extend over the flat parts of the profile plate 11.

A load-bearing element 10 is provided in the region of the curved portion 5 of the housing wall 1 adjacent the flat housing base 3. The load bearing element 10 has two portions which are orientated perpendicular to one another, which extend radially with respect to the curvature and into which, at locations 14 and 22, pressure loads are introduced. Pressure loads are then introduced into the inner supporting structure of the radiation collector, particularly into the part plates 1 9 and 8 of the supporting plates. The load-bearing element 10 also has a portion which is parallel to the housing base 3 and which is held fast by the overlapping corners of the lower part plates 1 9 on the housing base 3.The load-bearing element 10 butts partially against the housing wall and is overlaid and held in place by severai supporting plates (perpendicular to the plane of Fig. 1).

Before the cover plate 2 is superimposed on the housing and before the radiation collector is evacuated, both the housing walls 1 and the strips 1 8 and 9 of elastic material are unloaded.

After the cover plate 2 is superimposed and during the evacuation, the overall structure is increasingly loaded. Upon reaching the final vacuum, the strips 18, 9 of elastic material are somewhat compressed, resulting in a reduced overall height of the collector. A result of this is that the doubly-arched housing 1 is also brought under pressure from above. In this way, an upwardly-directed reaction force arises which is transmitted by way of the sealing ring 7 to the edge 1 6 of the cover plate 2. Thus, transverse forces act on this edge from two mutually opposite directions. They act on the one hand from below in the region of the sealing ring and on the other hand from above between the sealing ring and the supporting point 1 5 afforded by the end of the upper part plate 8.The wall material and the dimensions of the housing wall 1, that is its thickness, radii of curvature of the two curved portions 4 and 5 as well as height of the flat portion 6, is so coordinated that the two transverse forces, defined above, are, with respect to the point 15, substantially in equilibrium. The result of this is that the cover plate is loaded as little as possible along t;ie lines connecting the points 1 5 of the supporting plates arranged one behind the other. Another important parameter in this respect is the position of the sealing ring 7.

Calculation of the housing wall composition and dimensions is effected with the aid of well known principles of materials science, for example the finite element calcuation. Of course, care must be taken that at the lines designated 14 and 22 the critical bending moment of the housing wall, beyond which the wall would tear, is not reached.

The further computation starts from this basic prerequisite.

The radiation absorption system arranged in the interior of the housing is not shown in the drawings. It may, for example, comrpise tubes which extend approximately at the height of the flat portion 6 of the housing wall in a plane, parallel to the cover plate, between the parallel to the supporting plates. The tubes may also extend around the ends of the supporting plates in the free space, approximately triangular in crosssection, which remains between the flat housing wall portion 6, the load-bearing element 10 and the upper part plate 8. The tubes may be connected in a good heat-conducting manner to radiation-absorbing plate bars which extend in approximately the same plane as the tubes themselves between the supporting plates. A heat-absorbing, gaseous or liquid medium flows through the tubes.

Fig. 2 shows a further partial cross-section along the line Il-Il in Fig. 1, in a plane perpendicular to the drawing plane of Fig. 1.

Support of the housing wall on both sides of the curved portion 5 adjacent the flat housing base 3 is effected in this case by means of appropriately shaped ends of the profiles of the profile plate 11 as well as load-bearing elements 21, which run along the housing wall perpendicular to the drawing plane of Fig. 2 and grip partially around the profiles. Load bearing for the absorption of the external pressure is thus effected in this case on the one hand by way of the load-bearing element 21 in the longitudinal direciton of the profiles and on the other hand by way of the part of the profile plate resting on the housing base 3 and the loadbearing element 21 in the transverse direction of the profiles.

In the evacuated state of the radiation collector, two different ending moments act on the edge 1 6 of the cover plate 2 with respect to the supporting line designated by 22. One result from the elastic housing wall 1 being under pressure and is transmitted by the sealing ring 7 to the edge 16 of the cover plate and the other results from the external pressure bearing on the cover plate 2 between the supporting line 22 and the sealing ring 7. These two bending moments are not required to cancel one another out.On the contrary, the bending moment caused by the external pressure is required to exceed the one caused by the wall elasticity by so much that the resultant bending moment acting on the supporting line 22 is substantially as high as the bending moment acting on the supporting line 23 or 24 associated with the supporting plate and situated further inwards, by virtue of the external pressure.

The desired result that the peak loads caused by the bending moments at the upper edges of the supporting plates are substantially the same over the entire cover plate is thus achieved.

Figs. 3 and 4 show, in a highly schematised manner, that other systems of supporting elements may also be used inside the radiation collector in accordance with the invention. Thus, in the case of the radiation collector of Fig. 3, the upper part plate of Fig. 1 is replaced by a differently-shaped upper part plate 26, which, compared with the first-mentioned part plate, has certain regions cut away so that integrated, tetragonal supporting bars arise. Discs 27 of elastic material, for example silicon rubber, are inserted between the cover plate 2 and the upper ends of the bars of the part plate 26 which support said cover plate 2.

In the exemplified embodiment shown in Fig. 4 the upper part plate is abolished. Its place is taken by supporting bars 25 which may, for example, be circular in cross-section and which are introduced into corresponding bores 29 of a supporting plate 28. The supporting bars 25, which may, in the same way as the upper part plate 26 of Fig. 3, consist of glass, are elastically mounted at their two ends with the aid of the discs 27 and 30 produced for example from silicon rubber. In the embodiment shown in Fig. 4, the same stipulation with respect to all four housing walls 1, regarding the resulting bending moments, as has already been made in connection with Fig. 2, applies. The place of the supporting line 23 of Fig. 2 is taken here by the supporting points of the cover plate 2 corresponding to the supporting bars 25. In the case of the radiation collector of Fig. 3 the stipulation mentioned above regarding the transverse forces applies at the depicted housing wall as well as at the opposing housing wall and, the stipulation regarding the resulting bending moments applies at the two other perpendicular housing walls.

Claims

1. A radiation collector having an evacuated interior which comprises a trough-like housing and a cover plate pervious to radiation, supporting elements which support the cover plate and which extend towards the housing base, as well as a radiation absorption system provided in the interior, characterised in that the housing walls are formed, in cross-section,with two portions which curve in opposing directions, which are connected by a flat portion directed substantially perpendicular to the cover plate, which culminate at respective ends in the flat housing base and in an edge parallel to the cover plate and which are made from elastic material, the supporting elements are mounted elastically and the housing walls are supported from within on both sides of the curved portion adjacent the housing base.

2. A radiation collector as claimed in claim 1, characterised in that the material and dimensions and thus the elasticity of the housing walls are so co-ordinated that, upon loading of the cover plate by external pressure, the bending moment acting in the edge region of the cover plate with respect to the supporting elements situated closest to the housing walls is substantially as great as the bending moment acting over the remaining supporting elements in the cover plate.

3. A radiation collector as claimed in claim 1 or 2, characterised in that the supporting elements comprise tubes or rods arranged substantially perpendicular to the cover plate.

4. A radiation collector as claimed in claim 1 or 2, characerised in that the supporting elements comprise supporting plates which are arranged substantially parallel to one another and perpendicular to the cover plate.

5. A radiation collector as claimed in claim 4, characterised in that the width of the edge of the cover plate protruding beyond the ends of the supporting plates in the longitudinal direction thereof is so selected that a substantial equilibrium exists between the mutually opposing transverse forces acting on the edge of the cover plate on the one hand as a result of the external pressure bearing on the cover plate and on the other hand as a result of the elasticity of the housing walls.

6. A radiation collector as claimed in any of claims 1 to 5, characterised in that load-bearing elements which butt partially against the housing walls on both sides of the curved portion adjacent the housing base are used for the support of the housing walls.

7. A radiation collector as claimed in claim 6, characterised in that the load-bearing elements have, in cross-section, two limb portions which are orientated substantially at right angles to one another and which extend radially with respect to the housing wall curvature.

8. A radiation collector as claimed in claim 7, characterised in that the load-bearing elements have portions which extend parallel to the housing base and which are retained with the aid of the supporting elements on the housing base.

9. A radiation collector having an evacuated interior substantially as hereinbefore described with reference to and as illustrated in Figs. 1 and 2 of the accompanying drawings.

1 0. A radiation collector as claimed in claim 9 but modified as hereinbefore described with reference to and as illustrated in either Fig. 3 or Fig. 4 of the accompanying drawings.