GB1575031A

GB1575031A - Solar energy collector

Info

Publication number: GB1575031A
Application number: GB2899/77A
Authority: GB
Original assignee: Owens Illinois Inc
Current assignee: OI Glass Inc
Priority date: 1976-01-26
Filing date: 1977-01-25
Publication date: 1980-09-17
Also published as: JPS57198959A; LU76608A1; FR2339819B1; IT1082665B; MX145456A; JPS6032092B2; FR2339819A1; IL50978A0; DK567276A; ZA7722B; BE850757A; IL50978A; IE44859L; IE44859B1; BR7700413A; NL7614466A; ES454627A1; JPS5292143A; CH620982A5

Abstract

In a glass jacket tube (40) which is transparent or translucent over its entire circumference and one end of which is closed, a glass absorption tube (41) is inserted, leaving an interspace, the closed end of which is adjacent to that of the jacket tube. At their ends opposite their closed ends, the two tubes are interconnected in a sealed manner by fusing together and a vacuum is created in the intermediate space. On the outer surface of the absorption tube, there is a coating which absorbs solar energy and has an absorption capacity of 0.8 or more and an emissive power of 0.1 or less. A conducting pipe (43) extends through the absorption tube to its closed end in such a manner that a fluid, on flowing back through the annular space between the two tubes, can carry the absorbed energy away. The design makes possible free mutual length changes of the two tubes in operation while avoiding sealing problems; it also makes possible economical manufacture. <IMAGE>

Description

(54) SOLAR ENERGY COLLECTOR (71) We, OWENS-ILLINOIS, INC., a Corporation organized under the laws of the State of Ohio, of Toledo, State of Ohio, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - The present invention relates to solar energy collectors.

In accordance with the present invention there is provided a solar energy collector comprising a substantially cylindrical circumferentially transparent glass outer tube having a closed end and an open end and, interiorly of said outer tube, a hollow, elongate substantially cylindrical glass absorber member of a lesser O.D. than the I.D. of said outer tube and having a closed end and an open end, said absorber member also having a solar energy absorbing surface disposed between said ends thereof, a glass-to-glass fusion seal closing the opening between said absorber member and the outer tube adjacent to the open end of the outer tube to thus provide a closed space therebetween, said space being evacuted, said absorbing surface comprising an opaque, wavelength selective coating embracing the external peripheral glass surface of said tubular absorber member and said coating having an absorptance of 0.80 or more and an emittance of 0.1 or less.

Preferably the construction of the collector is such that it comprises three coaxial glass tubes. The two outermost tubes are constructed from glass tubing to resemble oversized test tubes in that their one end is closed. The outer tube is sealed to the intermediate inner tube and the space therebetween evacuated, to a practical and efficient degree of vacuum to prevent heat loss through the space by convection and conduction heat loss. The intermediate inner tube is coated with an energy absorbing coating of high absorptance and low emittance. The third tube is placed inside the intermediate tube and is used to carry the fluid medium to the interior, closed end of the latter. The parts thus described, aside from the coatings, are of the same or similar composition of glass.

The thermal expansion characteristics are similar to allow a glass-to-glass flame seal rather than a glass-to-metal gradient seal used in this type of collector heretofore, thereby avoiding failure from thermal expansion differences during operation. Additionally, the glass parts may be sealed one to the other more readily and with less cost in manufacture.

The basic components of the energy collector unit for the system are made of glass of known tubular manufacture such as are prevalent today in the manufacture of glass tubing products, e.g. process glass pipe, or the like.

The tubular glass solar energy collectors are assembled onto a manifold such that the tubular collectors are detachably connected into a manifold. The manifold may be constructed for disposition of the collectors on either side thereof so as to extend laterally in rows along the manifold and provide an energy collecting system.

Advantageously, a manifold is provided for the fluid medium flow into and out of a plurality of the collector units connected thereto, and the collector units are provided with a quick disconnect and 0ring seal in a socket of the manifold for each collector unit.

A spring support means can be connected to the interior end of the coated, intermediate absorber tube holding that end of the tube in concentric position in the outer tube, the other end of the absorber tube being sealed to the wall of the outer tube for support.

The invention is described further hereinafter, by way of example, with reference to the accompanying drawings, in which: - FIGURE. 1 is a perspective view showing collector units in accordance with the invention in use on the roof slope of a dwelling; FIGURE 2 is a side view, partly broken away and in section, of one embodiment of a collector unit in accordance with the invention; FIGURE 3 is an exploded, perspective view, partly broken away and in section, showing a double manifold embodiment, wherein collector units extend on either side of the manifold; FIGURE 4 is a sectional plan view of a portion of the manifold of Fig. 3; FIGURE 5 is a perspective view of the end cap providing an inner end support means for the coated absorber tube of the collector inside the outer jacket tube;; FIGURE 6 is a staggered sectional end view of the collector taken along line 6-6 on Fig. 2; FIGURE 7 is a side elevational view, partly broken away and in. section, of a second embodiment of collector unit in accordance with the invention; and FIGURE 8 is a fragmentary, enlarged sectional view of a fusion assembly comprised by the glass absorber tube and the glass outer tube of the collector unit of Fig. 7.

Shown in Fig. 1 is a typical in-use setting for solar collectors in accordance with the invention. A dwelling 10, such as a house, has its roof section 11 located nearest the sun or most accessible to the sun, provided with a plurality of solar energy converter modules 12. The area selected for coverage by modules 12 may be left to the skill of the engineer and architect providing for the heating or cooling for the dwelling.

The Manifold The module of the solar energy converter is shown in detail in Fig. 3. Module 12 which appears in part on the exploded view, comprises a central longitudinal manifold section 13 that extends down the roof section (Fig. 1). Extending outwardly from either side of the manifold 13 are a plurality of collector units 14, to be described below. The collectors 14 are of a plug-in type of connection into side ports 15 spaced along opposite vertical side walls 16 and 17 of manifold 13. Internally of the manifold 13 are longitudinal passageways 18 and 19 running along the ports 15 on either side of the manifold. Sandwiched between passageways 18 and 19 is a central passageway 20 defined by the longitudinal interior vertical walls 21 and 22. Along walls 21 and 22 there are spaced apart ports 23.The ports 15 and 23 are matched as sets on the same central axis, i.e., the ports 15 and 23 in each such set are coaxial.

The manifold 13 connects into a fluid handling system illustrated by the duct 24 having an upper conduit passage 25 and a lower conduit passage 26. The duct 24 extends between the heating system (labelled "Fluid Heat Exchanger" on Fig. 3) and the solar converter module 12. The passage 25 carires the relatively cool fluid medium, such as water, air or the like, and introduces it through the matching aperture connection 39 in the vertical wall 24a of duct 24 and aperture 27 in the vertical end wall 28 of manifold 13. The aperture 27 leads into the central passageway 20 of manifold 13. The duct 24 and manifold 13 are connected and sealed together by the gasketed facing 29 held by cap screws 30 threaded into end wall 28 at 31. Gasket 29 may be any suitable compressible gasket material that will withstand elevated temperature service.Matching lower apertures 32 and 33 in wall 24a and 34 and 35 in wall 28 connect the respective passages 18 and 19 with the duct passage 26 for carrying the heated fluid medium coming from the collectors 14.

Manifold 13 is enclosed by top and bottom walls 36 and 37, respectively, and at its outer end by vertical wall 38.

The Collector Unit-First Embodiment The collectors 14 shown in Figs. 2 and 3 are all constructed alike, and each comprises an outer glass tube 40 that is of convenient length, say from 4 to 7 feet and of standard diameter, e.g. 2" O.D. A lower mirrored surface 45 may be employed to reflect radiant energy onto a portion of the absorber tube 41 of the collector.

The interior tube 41 is made of glass and is of somewhat lesser diameter and of slightly greater length. Tube 41 has its exterior surface precoated with an energy absorbing coating 42 having a high absorptance and low emittance. Examples of such wave length selective coatings are metallic undercoatings such as aluminum or silver deposited upon the glass surface, and with a semi-conductor type coating deposited over the metallic surface coating to provide the wavelength sensitivity desired. A high performance wavelength selective coating is used having 0.8 or greater absorptance and 0.1 or lower infra red emittance.

Inside tube 41 there is a fluid delivery glass tube 43 for conveying relatively cool fluid medium into the collector interiorly of tube 41 and adjacent the closed end wall 41a there of. The inner end 43a of delivery tube 43 is open (Fig. 2).

In assembly, the absorbing tube 41 already coated on the exterior with the wavelength selective coating 42, is further provided with a snap-on end support cap 46 (Fig. 5) which provides inner end support means for tube 41 in tube 40. Cap 46 comprises a semispherical shell and multiple (either 3 or 4) legs 47. The cap 46 is made of metal or plastics having some resiliency to maintain its force fit on the inner end of tube 41. Tube 41 is then inserted into the outer tube 40 and in this first embodiment of the invention is fastened to the outer tube 40 by fusing its open end onto tube 41 at the juncture 40a (Fig. 2).Thereafter, a vacuum is pulled through the opposite end of tube 40 at a tubulation 48 and sealed off at the tip of the tubulation in the manner known to those skilled in the art, the resultant sealed space 49 between the outer tube 40 and absorber tube 41- being highly evacuated; viz on the order of 10-4 torr of vacuum.

The delivery tube is then inserted interiorly of the absorber tube 41.

Each of the collector units 14 is detachably assembled into the manifold 13 as follows. The free end 43b of the delivery tube 43 is approximately the same O.D. as the diameter of the ports 23 in the interior walls 20 and 21 of the manifold. A rubber O-ring 50 is provided on free end 43b of the delivery tube to seal the latter in port 23. Similarly, free end 41b of the absorber tube is approximately the same O.D. as the port 15 in either of vertical side walls 16 or 17. A rubber O-ring 51 is provided on free end 41b of the absorber tube to seal it in port 15. The ports 15 and 23 are each provided with recess grooves 51 a and 50a respectively, to receive the gasket O-rings 51 and 50 therein.

The Collector Unit-Second Embodiment The collector construction shown on Figs. 7 and 8 has similar parts labelled with corresponding numerals marked by a prime designation.

The collector 14' comprises a glass outer tube 40' that is transparent or clear and is closed at its one outer end by means of a sealed tubulation 48'. The opposite end of tube 40' is open. The interior tube 41' is made of glass tubing of somewhat lesser diameter and length. The interior glass tube 41' has its exterior surface precoated over substantially its length and periphery with the high absorptance and low emittance wave length selective coating 42' as described earlier herein in connection with the first embodiment. Before the coating 42' is applied, preferably, the open end of glass tube 41' is worked to an outwardly flared end opening of the contour of the flared end 60 shown on Figs. 7 and 8.

The coating 42' is applied on the tube adjacent the flared end 60 to and inclusive of the closed end of tube 41'. -Next, tube 41' is inserted into glass- outer tube 40', a simple coil spring 61 being first assembled to fit on the closed end of tube 41' and bear against the closed end on the inside of outer tube 40'. At this stage of assembly, the tubulation 48' is still open. With the tubes 40', 41' in place, as shown on Fig. 7, and spring 61 somewhat compressed, the flared end 60 of tube 41' and the open end portion of tube 40' are heated and the glass fused together to form the integral end connection of the two tubes 40', 41', such as shown on Fig. 8.Thereafter, a vacuum is pulled through the opposite end tubulation 48' of the outer tube 40' and sealed off at the tip as shown, which seals the space 49' between the outer tube 40' and the inner absorber tube 41' at a vacuum, preferably on the order of 10-4 torr or greater of vacuum. The coating 42' is thus contained within the vacuum of space 49'. A delivery tube 43' is inserted through a wall member - 62 and annular rubber grommet 63 in a port 15' or 23' on one side or the other of the manifold 13, as described earlier herein. A rubber O-ring 51' is seated in a groove 51a' of the port 15' and compressed against the outer wall surface of tube 40' near the open end of the collector. The O-ring 51' forms the primary seal for the collector 14' in the manifold port.

Manifold 13 includes a layer of foamed insulation 64 around its exterior, exposed surfaces, and at locations corresponding to the collector ports in the manifold, the insulation layer includes formed ports 65 registering with the manifold ports. A thin washer-like seal 66' of flexible material is embedded in the insulation within the bore of each of the ports 65' which annularly engage the periphery of the tube 40' thereby providing an outer seal in the ports.

The outer tube 40' is made of high transmittance and preferably low iron transparent glass. The inner absorber tube 41' is preferably of substantially the same glass composition as tube 40' for ease in the joining process and to reduce the residual stress at the fusion seal between the outer and inner tubes near their open ends.

Regarding the wave length selective coating layer 42' on glass tube 41 and also the coating layer 42 on the tube 41 of the first embodiment, the coating comprises a sub -stance having 0.80 or greater absorptance and a sub-coat having -0.1 or less remittance; For high absorptance as indicated, metallic compounds such as oxides or sulphides of --chrome, nickel, copper or the like can be used with success; Sometimes a combination of metal and its compounds is best for -the solar energy absorption. For low emittance as indicated, aluminum, silver, cop per and gold are preferred as the sub-coat, the high absorption coating substances being superimposed thereover.

Any method of deposition of the coating substances selected must be capable of applying a controllable thin film. Such methods used with success are vacuum deposition, chemical vapor deposition, ionplating and sputtering.

In the invention, energy absorbing coatings not suitable in other types of collectors, such as flat plate collectors, may now be used because the coating is protected in the space 49' between the tubes in a hard vacuum environment. Chemical attack by air and moisture or lack of bonding integrality are alleviated and no longer detrimental factors in the tubular solar energy collector herein disclosed.

The spacing means used between the closed ends of the inner and outer tubes 41', 40' of the collector can be of any design or material. The design criterion is that it must provide a firm support of the inner tube end to minimize the stress created at the opposite fused ends, or open ends of the tubes. It must allow the inner tube to expand or shrink according to its ternperature without developing undue stress at the mentioned fused joint. Also, it must have preferably a minimum contact surface between the tubes and the spacing means to minimize heat loss by conduction, and it must also serve as a support during the sealing operation. As is disclosed herein, the spacing means may take the form of the snap-on clip 46 (Fig. 5) or the coil spring 61 (Fig. 7).

Because the spacer means is in the space to be evacuted to a hard vacuum, the material thereof used should not release gases after bake-out and tip-off of the outer tube 40 or 40' in the evacuating process. Also, the material of the spacer must -be free of oily substance and organic bonding material, which would not be eliminated at a bake-out temperature for evacuation. Stainless steel properly cleaned is the preferred material.

Operation of the Collector Module Utilizing the assembly shown on Fig. 3, and described - earlier herein, a fluid medium, for example air, is pumped in duct 25 into central passage 20 of the manifold.

The free ends 43b of the several collectors 14 communicate with passage 20 and are sealed therein so that the air flows lengthwise of the delivery tube 43 and exits at inner end 43a. Solar rays penetrate the upper glass of tube 40 and energy therefrom is absorbed by coating 42 of the ab absorber tube 41. The air circulated on the interior of tube 41 traverses the passage defined by a helical baffle 44 and heat exchange therewith increases the temperature of the air as it travels toward the free end 41b of tube 41.

When heated air reaches the free end 41b of the tube connected thereat into either passageway 18 or 19, as the case may be, the heated fluid medium flows into the lower duct 26 and is utilized to heat dwelling 10, or service hot water heating, or both.

One of the significant advantages of the system is that should any one of the collectors be damaged, break or malfunction, a replacement may be readily inserted and the defective unit removed, thereby maintaining the efficiency of the system.

The glass tubes of the unit are fabricated from known and standard glass shapes of either a soda-lime glass composition or a borosilicate glass composition. Both glasses are relatively inexpensive. The system and modules thereof may be assembled on the site of installation and need not be prefabricated at the factory and delivered to the site. The solar energy collector of this invention is simple to manufacture and assemble. Furthermore, it is lightweight; therefore, there is no need to further structure or reinforce the roof of the building where it is installed.

In use of the invention, the working fluid is deliverable from the collectors -at a temperature in excess of 250"F. The energy absorbing coating 42 or 42' is totally protected and will last the lifetime of usage of the collector unit.

The module concept illustrated herein includes the preferred embodiment whereby collectors extend on both sides of the manifold-a "double acting" system. It is also within the scope of the invention to fabricate a "single acting" system wherein collectors extend only along the one side of the manifold. Thins may have some specialized uses, but, as stated, the double acting system is the preferred embodiment.

In an alternative embodiment, the work -ing fluid is not passed through the absorber tubes 41 or 41' but rather the collector .includes means, such as a heat pipe device, located internally of the absorber tube for receiving as heat the solar energy absorbed by the absorber tube, and means coupling the working fluid to said first-mentioned means, for example within the manifold, for receiving heat energy from said firstmentioned means and conducting the heat away from the collector to a point of application.

WHAT WE CLAIM IS: - 1. A solar energy collector comprising a substantially cylindrical, circumferentially transparent glass outer tube having a closed end and an open end and, interiorly of said

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

per and gold are preferred as the sub-coat, the high absorption coating substances being superimposed thereover.

Any method of deposition of the coating substances selected must be capable of applying a controllable thin film. Such methods used with success are vacuum deposition, chemical vapor deposition, ionplating and sputtering.

In the invention, energy absorbing coatings not suitable in other types of collectors, such as flat plate collectors, may now be used because the coating is protected in the space 49' between the tubes in a hard vacuum environment. Chemical attack by air and moisture or lack of bonding integrality are alleviated and no longer detrimental factors in the tubular solar energy collector herein disclosed.

The spacing means used between the closed ends of the inner and outer tubes 41', 40' of the collector can be of any design or material. The design criterion is that it must provide a firm support of the inner tube end to minimize the stress created at the opposite fused ends, or open ends of the tubes. It must allow the inner tube to expand or shrink according to its ternperature without developing undue stress at the mentioned fused joint. Also, it must have preferably a minimum contact surface between the tubes and the spacing means to minimize heat loss by conduction, and it must also serve as a support during the sealing operation. As is disclosed herein, the spacing means may take the form of the snap-on clip 46 (Fig. 5) or the coil spring 61 (Fig. 7).

Because the spacer means is in the space to be evacuted to a hard vacuum, the material thereof used should not release gases after bake-out and tip-off of the outer tube 40 or 40' in the evacuating process. Also, the material of the spacer must -be free of oily substance and organic bonding material, which would not be eliminated at a bake-out temperature for evacuation. Stainless steel properly cleaned is the preferred material.

Operation of the Collector Module Utilizing the assembly shown on Fig. 3, and described - earlier herein, a fluid medium, for example air, is pumped in duct 25 into central passage 20 of the manifold.

The free ends 43b of the several collectors

14 communicate with passage 20 and are sealed therein so that the air flows lengthwise of the delivery tube 43 and exits at inner end 43a. Solar rays penetrate the upper glass of tube 40 and energy therefrom is absorbed by coating 42 of the ab absorber tube 41. The air circulated on the interior of tube 41 traverses the passage defined by a helical baffle 44 and heat exchange therewith increases the temperature of the air as it travels toward the free end 41b of tube 41.

When heated air reaches the free end 41b of the tube connected thereat into either passageway 18 or 19, as the case may be, the heated fluid medium flows into the lower duct 26 and is utilized to heat dwelling 10, or service hot water heating, or both.

One of the significant advantages of the system is that should any one of the collectors be damaged, break or malfunction, a replacement may be readily inserted and the defective unit removed, thereby maintaining the efficiency of the system.

The glass tubes of the unit are fabricated from known and standard glass shapes of either a soda-lime glass composition or a borosilicate glass composition. Both glasses are relatively inexpensive. The system and modules thereof may be assembled on the site of installation and need not be prefabricated at the factory and delivered to the site. The solar energy collector of this invention is simple to manufacture and assemble. Furthermore, it is lightweight; therefore, there is no need to further structure or reinforce the roof of the building where it is installed.

In use of the invention, the working fluid is deliverable from the collectors -at a temperature in excess of 250"F. The energy absorbing coating 42 or 42' is totally protected and will last the lifetime of usage of the collector unit.

The module concept illustrated herein includes the preferred embodiment whereby collectors extend on both sides of the manifold-a "double acting" system. It is also within the scope of the invention to fabricate a "single acting" system wherein collectors extend only along the one side of the manifold. Thins may have some specialized uses, but, as stated, the double acting system is the preferred embodiment.

In an alternative embodiment, the work -ing fluid is not passed through the absorber tubes 41 or 41' but rather the collector .includes means, such as a heat pipe device, located internally of the absorber tube for receiving as heat the solar energy absorbed by the absorber tube, and means coupling the working fluid to said first-mentioned means, for example within the manifold, for receiving heat energy from said firstmentioned means and conducting the heat away from the collector to a point of application.

WHAT WE CLAIM IS: - 1. A solar energy collector comprising a substantially cylindrical, circumferentially transparent glass outer tube having a closed end and an open end and, interiorly of said

outer tube, a hollow, elongate substantially cylindrical glass absorber member of a lesser O.D. than the I.D. of said outer tube and having a closed end and an open end, said absorber member also having a solar energy absorbing surface disposed between said ends thereof, a glass-to-glass fusion seal closing the opening between said absorber member and the outer tube adjacent to the open end of the outer tube to thus provide a closed space therebetween, said space being evacuated, said absorbing surface comprising an opaque, wavelength selective coating embracing the external peripheral glass surface of said absorber member and said coating having an absorptance of 0.80 or more and an emittance of 0.1 or less.
2. A solar energy collector as claimed in claim 1 wherein the open end of the absorber member includes an outwardly flared end portion, said flared end portion being fused onto the glass wall of said outer tube thereby sealing the space be tween the outer tube and the interior absorber member.
3. A solar energy collector as claimed in claim 1 or 2, including means for supplying a working fluid to the interior of the absorber member in heat exchange relation therewith and for withdrawing heated working fluid therefrom.
4. A solar energy collector as claimed in claim 3, wherein said means for supply ing working fluid comprises a manifold sealingly connected to the open end of the outer tube for receiving heated working fluid from the absorber tube, a source of the working fluid connected to the manifold, a fluid circulation tube communicating with said manifold and the working fluid supplied thereto and extending interiorly of said absorber member to a location spaced from and adjacent to its closed end.
5. A solar energy collector as claimed in claim 4, wherein said fluid circulation tube is comprised of glass.
6. A solar energy collector as claimed in claim 1 or 2 including a source of working fluid, means located internally of the absorber member for receiving as heat the solar energy absorbed by said absorber member, and means coupling the working fluid and said internal means for conducting the heat away from the collector.
7. A solar energy collector as claimed in any of claims 1 to 5, including a fluid handling member communicating with the hollow interior of said absorber member and providing for circulation of fluid medium throughout the interior of the absorber member, a fluid medium supply means, means connecting the supply means to the fluid handling member, and separate means connected with the open end of said absorber member to receive fluid medium therefrom, the fluid medium being arranged to flow from the fluid handling member through said absorber member in heat exchange relation with the energy absorbing surface thereof and into said separate means.
8. A solar energy collector as claimed in any of claims 1 to 7 wherein said wavelength selective coating comprises a subcoating layer of a metal selected from a group consisting of aluminium, silver, copper and gold and an over-layer of a metallic compound selected from a group consisting of oxides and sulphides of chrome, nickel and copper including combinations thereof.
9. A solar energy collector as claimed in any of claims 1 to 6, including resilient end support means engaging said closed end of the absorber member, supporting it firmly in spaced relation to the interior surface of said outer tube near the closed end of the latter and providing for expansion and contraction of the absorber member.
10. A solar energy collector as claimed in claim 9 wherein the resilient end support means comprises a coil spring axially compressed between said closed end of the absorber member and the closed end of the outer member.
11. A solar energy collector constructed substantially as hereinbefore particularly described with reference to and as illustrated in Figs. 1 to 6 of the accompanying drawings.
12. A solar energy collector constructed substantially as hereinbefore particularly described with reference to and as illustrated in Figs. 7 and 8 of the accompanying drawings.