WO1994010513A1

WO1994010513A1 - Apparatus for receiving sun radiation and method for preparing such an apparatus

Info

Publication number: WO1994010513A1
Application number: PCT/NL1993/000218
Authority: WO
Inventors: Antonius Bernardus Schaap
Original assignee: Level Energietechniek B.V.
Priority date: 1992-10-27
Filing date: 1993-10-27
Publication date: 1994-05-11
Also published as: NL9201863A

Abstract

The invention relates to an apparatus for collecting and converting light into thermal energy, comprising: a collecting and converting member (3), a gas-tight envelope for the collecting and converting member which comprises two dish-like bodies (1, 2), at least one of which is at least partially transparent, and a tension ring (6) encircling both dish-like bodies (1, 2) on their periphery which exerts an inward directed force on the rim of the dish-like bodies (1, 2); and means (4) for carrying the thermal energy out of the envelope, wherein the tension ring (6) is adapted for distributing the force exerted on the rim of the dish-like bodies (1, 2) uniformly along the periphery. As a result of these steps a compensation of forces occurs along the rim such that a robust entity results which can be used in numerous situations.

Description

APPARATUS FOR RECEIVING SUN RADIATION AND METHOD FOR PREPARING SUCH AN APPARATUS

The invention relates to an apparatus for collecting and converting light into thermal energy, comprising: a collecting and converting member; an envelope for the collecting and converting member which comprises two dish-like bodies, at least one of which is at least partially transparent, and a tension ring encircling both dish-like bodies on their periphery which, when the pressure inside the envelope is decreased, exerts an inward directed force on the rim of the dish-like bodies; and means for carrying the thermal energy out of the envelope.

Such an apparatus is known from GB-A-2005402 and from US-A-4185616.

Such an apparatus has advantages compared to other already existing apparatus for utilizing solar energy in the form of light. Such known apparatus comprise an envelope of a glass tube for the light-absorbing member and generally have a much smaller absorbent surface, whereby the power is much smaller. The apparatus known from the cited literature refer¬ ence has a much greater power.

The dishes known from the said literature reference are however almost impossible to realize in practice; it is not possible to manufacture such dishes outside a laboratory situation. The forces exerted on the glass by the air pressure on the outside as a result of the vacuum are in any case so great that they will break very quick¬ ly.

The object of the present invention is to provide such an apparatus which can also be applied outside the laboratory situation and which is suitable for use in the building industry.

This object is achieved in that the tension ring is adapted for distributing the force exerted on the rim of the dish-like bodies uniformly along the periphery.

As a result of these steps a compensation of forces occurs along the rim such that a robust entity is created which can be used in numerous situations. The invention will be further elucidated hereinbelow with reference to a number of embodiments as shown in the annexed drawings.

Figure 1 shows in section a prior art vacuum enve¬ lope for a light-absorbing body by dish-like bodies connected on the rim by a tension ring;

Figure 2 shows a top view of the apparatus depicted in figure 1;

Figure 3 shows a detail view of the passage of a conduit through one of the dish-like bodies and the arranging of the tension ring round the rim of the dish¬ es;

Figure 4 shows an alternative construction for effecting arrangement of the tension ring round the rim of the dishes; Figure 5 shows a known tensioning device for tight¬ ening a tension ring using a tensioning bolt;

Figure 6 shows a section along the line VI-VI in figure 5;

Figure 7 shows a tensioning device with two tension- ing bolts wherein no deviation in the inward directed force is generated by the tensioning device;

Figure 8 is a view of the tensioning device along the line VIII-VIII in figure 7;

Figure 9 shows a variant of the known tensioning device according to figures 5 and 6, wherein due to a slide path the inward directed force is distributed more uniformly over the rim of the dishes;

Figure 10 shows a section of the mechanism in figure 9 along the line X-X; Figure 11 shows schematically a further improved mechanism as according to figures 9 and 10, wherein a compensation ring is used; Figure 12 shows a section of the tensioning device according to figure 11;

Figure 13 shows a device for performing the method for gradually applying an inward directed force distrib- uted uniformly over the rim, wherein a tensioning band is wound several times round the rim of the dish-like bodies during evacuation of the envelope;

Figure 14 shows a disposition with which a tension¬ ing band can be wrapped round the rim of the dish-like bodies and the envelope can be evacuated simultaneously; Figure 15 shows a variant of the disposition accord¬ ing to figure 14;

Figure 16 shows another variant of the disposition according to figure 14; Figure 17 shows a section of an envelope during performing of a variant of the method according to the invention;

Figure 18 shows in section a device for arranging a vessel filled with mains water or another liquid inside a vacuum envelope;

Figure 19 shows an enlargement of a detail relating to the passage of the cold and hot water conduit of the vessel shown in figure 18;

Figure 20 shows a variant of the passage according to figure 19;

Figure 21 shows the supporting of the vessel in the device according to figure 18;

Figure 22 shows a section of the vessel depicted in figure 21 along the line XXII-XXII in figure 21; Figure 23 shows a variant of the apparatus according to the invention;

Figure 24 shows another variant of the apparatus according to the invention;-and

Figure 25 shows an improved embodiment of the appa- ratus shown in figure 24.

Figures 1 and 2 show the known apparatus for inter¬ cepting solar heat according to the patent specifications GB-A-2005402 and US-A-4185616. The convex thin-walled glass dishes 1 and 2 enclose a vacuum space inside which is situated a light-absorbing body 3 which converts light into heat. The heat is transported by conduction to the heat transport conduit 4 through which a heat transport¬ ing liquid can be pumped.

The light-absorbing body is suspended with thin- walled stainless steel supports 5 against glass dish-like bodies in the form of dishes l and 2. The heat transport conduit is carried out of the vacuum envelope through a hole in the bottom dish. The tension ring 6 provides an inward directed force on the rim of dishes 1 and 2 where¬ by tensile stresses in the dishes are compensated.

Figure 3 shows an enlarged detail of figure 1 where- in the construction of the rim of the dishes is revealed. The dishes 1 and 2 are first flattened on the rims, that is, a flat edge is ground onto the rim of the dishes 1 and 2. The dishes are then mutually joined with the flat edges using adhesive or glass solder, whereafter the joined edge is ground to a round shape whereby a surface results against which a tension ring 6 can lie. In order to prevent the occurrence of high point loads a gasket 8 can be placed between the rim of the dishes 1 and 2 and the tension ring 6. The hole in the bottom dish is sealed with a thin-walled stainless steel sleeve 7 which is hermetically connected to the dish 2 and the heat trans¬ porting conduit 4. Because of the thin-walls and because of the low heat conduction coefficient of stainless steel the heat loss of conduits 4 to the dish 2 is low. Figure 4 shows a variant of the construction for laying the tension ring 6 against the rim of the dishes 1 and 2, wherein two dishes with flattened rims are mutual¬ ly joined and wherein a packing 8 is moulded or otherwise arranged round the rim and then ground to a round shape, whereby a surface results against which the tension ring lies.

Figures 5 and 6 show a known tensioning mechanism for bringing to tension the steel tension ring 6 which consists of two sleeves 9 and 10 connected to the tension ring 6, a tensioning bolt 11 and a nut 12. During evacua¬ tion the force on tension ring 6 can be gradually in- creased by gradually tightening tensioning bolt 11 or by gradually tightening the tensioning bolt 11 hydraulically or pneumatically or in other manner.

A first drawback to this construction is that the tension due to friction between tension ring 6 and gasket 8 is not distributed uniformly over the rim of the dishes 1 and 2, whereby the inward directed force is not uni¬ formly distributed over the periphery either. A second drawback to this construction is that a great deviation in the inward directed force is created at the position of the tensioning mechanism due to the local occurrence of deflection.

Figures 7 and 8 show a device which eliminates the second drawback by using two flanges 13 and 14 with two holes in each which are positioned adjacently of the axis of the tension ring and through which two tensioning bolts can be arranged. In such a construction no deflec¬ tion occurs in the tension ring, whereby no deviation is created in the inward directed force at the position of the tensioning mechanism. Figures 9 and 10 show a device for largely obviating the first drawback. Herein a path is cut or otherwise arranged in the steel tension ring 6, in which path a lubricant is arranged or a low friction otherwise effect¬ ed and through which the gasket 8 can move. The arrow in figure 10 indicates the slide surface. Owing to the reduced friction between tension ring 6 and gasket 8 the tension is distributed more uniformly over the rim of dishes 1 and 2, whereby the inward directed force of tension ring 6 is also distributed better over the rim of dishes 1 and 2.

A further improvement of the first drawback is achieved with the method according to figures 11 and 12. Figure 11 shows the method schematically. The arrow in figure 12 indicates the slide surface. Due to the remain¬ ing friction between gasket 8 and tension ring 6 in the method according to figures 9 and 10, there still occurs deviation in the tensioning of the tension ring 6 round the dishes 1 and 2. This deviation can be compensated with the broken compensation ring 15. During evacuation of the dish envelope and gradual tensioning of tension ring 6 the diameter of the dish envelope becomes a little smaller whereby the compensation ring 15 moves a little along the gasket 8, wherein the extremities of the ten¬ sion ring 6 move toward each other. Because the opening in the compensation ring 15 is situated directly opposite the opening in tension ring 6 the direction of the fric- tion force which the compensation ring 15 exerts on the gasket 8 is opposed to the direction of the friction force which the tension ring 6 exerts on compensation ring 15, whereby the two friction forces neutralize each other. A second device with which a uniform inward directed force can gradually be applied to the rim of dishes 1 and 2 during evacuation of the dish envelope is shown in figure 13. Herein during evacuation of the dish envelope a tension band 16 is wound from a roll 17 a number of times with a determined force round the mutually joined dishes 1 and 2 provided with a flat edge as according to figure 3 or 4. The inward directed force on the rim of dishes 1 and 2 is determined by the number of times the tensioning band 16 is wrapped therearound. Tensioning band 16 can be of steel or a glass fibre or other materi¬ al that can tolerate a high tensile stress. A wire or a cable can be applied instead of a band.

Figure 14 shows a disposition with which the simul¬ taneous evacuation and winding of the tensioning band can be performed. The dish envelope is placed with the lower dish 2 in a large suction cup 22. The latter is connected to a shaft 28 rotatable via the ball bearings 26. Via conduit 23 the suction cup can be evacuated through the hollow shaft 28 and the rotatable seal 21 whereby dish 2 is held fast owing to the resulting friction. The dish envelope is evacuated via the conduit 20 and via the rotatable seal 21. The motor 24 can turn the shaft 28 via the transmission 25 whereby the dish envelope is turned via suction cup 22. The tensioning band 16 is hereby wrapped round the rim of dishes 1 and 2, wherein the roll 17 which lies on table 18 is slowly unrolled. The force with which the tensioning band 16 is wound round the dish envelope can be adjusted with the friction mechanism 19. The whole is mounted on a frame 27. It is also possible to make the dish envelope stand still and to rotate the roll with tensioning band 17 around it. Figure 15 shows a variant of the disposition of figure 14, wherein a number of feet 29 connected via arms 30 to the hollow shaft 28 fixedly hold dish 2 relative to the rotatable hollow shaft 28. The feet 29 can be glued to the dish 2 or may be small suction cups. The dish envelope is now evacuated through the hollow shaft 28, through conduit 20 and through the rotating seal 21 while the dish envelope is rotated, wherein the tensioning band 16 is wound with a determined force round the dish enve¬ lope. Figure 16 shows a variant of the disposition of figure 14, wherein the dish 2 is not held fast by a large suction cup 22 but by two holders 34 and 35 which are pressed by a pneumatic cylinder 32 or by a hydraulic cylinder or in other manner against the respective dishes 1 and 2 with a determined force and whereby the dish envelope is held fixedly due to the resulting friction. The dish envelope is evacuated through the hollow shaft 28, through the conduit 20,-which runs through holder 35, and through the rotating seal 21 while the dish envelope is rotated, wherein the tensioning band 16 is wound with a determined force round the dish envelope.

A third method with which a uniform inward directed force is gradually applied during evacuation is shown in figure 17. In this method the dishes 1 and 2 are not flattened on the rims and not mutually joined. The dishes 1 and 2 are placed in the double wedge-shaped and closed annular tension ring 6 with the gaskets 8 therebetween. During evacuation dishes 1 and 2 are pressed toward each other due to the atmospheric pressure, and herein the dishes slide over the gaskets 8 or the gaskets 8 slide over the tension ring 6, wherein because of the wedge shape the tension ring is stretched whereby the tension ring gradually begins to exert an inward directed force on the dishes 1 and 2 via the gaskets 8.

A fourth method is to heat the tension ring 6 to a determined temperature whereby the tension ring 6 expands thermally and whereafter the ring is placed round dishes 1 and 2. During evacuation of the envelope the tension ring 6 is gradually lowered in temperature whereby due to thermal shrinkage the tension force of the tension ring on the rim of the dishes is gradually enlarged. Figure 18 shows in cross section a device with which it is possible to dispose a (pressure) vessel 36 filled with mains water inside a vacuum envelope. During heating the pressure vessel must be able to expand a number of millimetres owing to thermal expansion, and the device makes this expansion possible while nevertheless hardly any movement occurs in the position of the hot and cold water conduit 38 and 37 relative to the through-fed 40.

The arrangement of the support is elucidated in figures 21 and 22. Placed at 120° relative to the centre point of the vessel 36 are three supports 39 which each consist of two rods which are hingedly connected to the dish 2 and to the vessel 36. During expansion the vessel can move freely outward because of the hinged mounting. Owing to the placing of the supports every 120° the centre of the vessel remains in position during expan¬ sion. The passage through the dish 2 of the cold and hot •water conduit 38 and 37 can then be arranged in the centre. Figure 19 shows the construction of the passage 40. The cold and hot water conduit 38 and 37 are guided to the outside through a hole in dish 2. The hole is closed by passage 40 which consists of thin-walled stain- less steel plate and which is hermetically connected to the conduits 37 and 38 and to the dish 2. The middle piece of passage 40 consists of a thin-walled stainless steel bellows enabling the remaining thermal movement. A variant of the passage is shown in figure 20, wherein the passage is formed by a thin-walled steel sleeve 7 and wherein some movement is made possible by mounting two thin-walled stainless steel bellows 41 in the conduits 37 and 38.

Figure 23 shows a device with which it is possible to utilize efficiently a large part of the solar radia¬ tion falling through the transparent dish 1. For this purpose a fin 42 is connected to the vessel 36 running entirely round the vessel. The sunlight falling adjacent¬ ly of the vessel is absorbed to a very large extent by the fin and there converted into heat. The heat is trans¬ ferred from fin 42 to vessel 36 by heat conduction.

An alternative to this device is depicted in figure 24. Here the light falling through the transparent dish 1 and adjacently of vessel 36 is reflected by a reflecting layer 44 on dish 2 onto the vessel 36 and absorbed by the vessel as indicated by the light ray 43.

A better operation is obtained by eccentric placing of the vessel 36 in the direction of the dish 1 and by fixing a conical reflector 45 to dish 2 which ensures that a ray of light falling through the transparent dish 1 and adjacently of vessel 36 cannot be reflected along the bottom of vessel 36 but is reflected toward the vessel by the conical reflector 45 as indicated with light ray 43 in figure 25.

Claims

1. Apparatus for collecting and converting light into thermal energy, comprising:

- a collecting and converting member;

- a gas-tight envelope for the collecting and con- verting member which comprises two dish-like bodies, at least one of which is at least partially transparent, and a tension ring encircling both dish-like bodies on their periphery which exerts an inward directed force on the rim of the dish-like bodies; and - means for carrying the thermal energy out of the envelope, characterized in that the tension ring is adapted for distributing the force exerted on the rim of the dish-like bodies uniformly along the periphery.

2. Apparatus as claimed in claim 1, characterized in that between the dish-like bodies and the tension ring at least one layer is arranged which reduces the friction between the dish-like bodies and the tension ring.

3. Apparatus as claimed in claim 1 or 2, character- ized in that the tension ring is provided with a tension¬ ing device which transmits without bending the generated tension force onto the tensioning band.

4. Apparatus as claimed in claim 1, characterized in that the boundary surface between the tension ring and each of the dish-like surfaces has the form of a part of a cone surface and that the width of these boundary surfaces is greater than the width of the contact surfac¬ es of the dish-like bodies.

5. Apparatus as claimed -in claim 1, characterized in that a compensation ring is arranged between the tension ring and the rim of the dish-like bodies.

6. Apparatus as claimed in claim 1, characterized in that the tension ring is formed by a band wound in sever- al layers round the rims of the dishes.

7. Apparatus as claimed in any of the claims 1-6, characterized in that the collecting and converting member rests via at least two supports on one of the dish-like bodies.

8. Apparatus as claimed in any of the claims 1-7, wherein the means for carrying the thermal energy outside of the envelope are formed by at least one conduit which is connected to the collecting and converting member and which extends via a passage through one of the dish-like bodies, characterized in that the passage is formed by a thin-walled tube which is connected gas-tightly to the dish-like body and to the at least one conduit.

9. Apparatus as claimed in claim 8, characterized in that bellows are incorporated in the conduits.

10. Apparatus as claimed in any of the claims 1-9, characterized in that the collecting and converting member is formed by a vessel finable with liquid.

11. Apparatus as claimed in claim 10, characterized in that the vessel is supported on one of the dish-like bodies by at least three supports distributed regularly along the periphery, which supports are each joined rotatably to the vessel and to the dish-like bodies and that the passage is placed in the centre.

12. Apparatus as claimed in claim 10 or 11, charac¬ terized in that the vessel is connected to a fin enlarg¬ ing the surface area for incoming radiation.

13. Apparatus as claimed in claim 10 or 11, charac¬ terized in that the internal surface of at least one of the dishes is provided with a reflecting layer.

14. Apparatus as claimed in claim 10, characterized in that a reflector reflecting incident sunlight to the vessel is arranged inside the-dish-like body.

15. Apparatus as claimed in claim 14, characterized in that the vessel is arranged eccentrically in the envelope and that the reflecting surface of the reflector is conical.

16. Method for manufacturing an apparatus for con¬ verting light into thermal energy, characterized by the following steps of:

- arranging round a collecting and converting member an envelope for the collecting and converting member, which envelope comprises two dish-like bodies, at least one of which is at least partially transparent;

- arranging a tension ring round the rim of both dish-like bodies; and - increasing the tensioning force in the tension ring substantially in proportion to the applying of a vacuum in the interior of the dish-like bodies.

17. Method as claimed in claim 16, characterized in that simultaneously with applying of the vacuum the tension ring is wrapped round the rim from a band wound under tension for arranging in several layers round the rim.

18. Method as claimed in claim 16, characterized in that during wrapping the envelope is supported by a rotationally driven support.

19. Method as claimed in claim 16, characterized in that the tension ring is heated prior to arranging on the dish-like bodies.