Flat Vacuum Solar Collector Having Chamber-Type Heads

Abstract

The invention relates to a flat solar collector comprising individual vacuum chambers. The invention is formed by two heads and a series of parallel tubes having high transmittance in the solar spectrum, which is disposed between said heads. The opposite side of the heads is provided with vacuum chambers which closure the connections of the conducting tubes. One of the vacuum chambers is characterized in that it is fitted with a vacuum valve at one end thereof. In addition, conducting tubes are disposed inside the aforementioned tubes having high transmittance in the solar spectrum and said conducting tubes are in turn connected to collector plates, all under vacuum conditions which minimize convection energy losses. When the conducting tubes are configured in series, the collector can raise the temperature of the working fluid to above 200° C. All of the above is performed in a novel, simple and economical manner.

Description

FIELD OF INVENTION

This invention refers to a device which provides an improvement in solar energy collection and conservation, in thermal solar collectors. The device is formed by using conventional components, which allows guaranteeing a better efficiency and a reduction in manufacturing cost.

BACKGROUND

This invention is directly related with flat solar collectors, which are used to absorb solar energy and transferring it to a fluid. Moreover, it is linked with flat vacuum solar collectors which provide vacuum between a collection plate and a glass closure to obtain a better performance.

Since time ago it is known that flat vacuum solar collectors are the most reliable of its kind, due to simplicity in their structure and low operating temperatures. These low operating temperatures do not damage the commercial materials being used in their manufacturing. However, collectors which are able to transfer a higher amount of energy to a fluid have been demanded in recent times, and a number of promising technologies have been achieved.

A reason why flat solar collectors do not reach high temperatures is mainly due to the convection effect. In these collectors, the main energy loss is due to the produced convection since the collecting plate is at a different temperature than the glass plate (collector closure). A number of different methods have been proved with the passage of time to prevent this effect, such as plate panels (hexagonal shape surfaces), by assembling a double glass plate, and creating a vacuum between the collector plate and the glass plate. This last method is the most commonly used, but requires a more rough structure than the conventional flat collector to support the vacuum caused stresses. In order to provide the required structural support to withstand these efforts, the collector structure has been modified, but a device is not yet available to reach the desired temperature without requiring costly, specialized materials and a troublesome manufacturing process.

In order to get an outlet temperature in the collector higher than 200° C. using commercial parts and simple manufacturing processes, the present device has been developed. Said device comprises high transmittance in solar spectrum tubes (TATES) closed in the end sides by a pair of heads attached to small vacuum chambers. The only TATES which are not closed by the vacuum chambers, are those with working fluid inlet and outlet. Within these TATES conducting tubes (TUCS) made of any thermal conducting material are located, attached to collector plates and closed with a selective surface in the solar spectrum to absorb the largest possible amount of energy. These TUCS are arranged over low thermal conduction supports, preferably ceramics, in order to lose the least possible amount of energy by conduction. By means of a vacuum pump coupling, a vacuum is created within the high transmittance in solar spectrum tubes and the vacuum chambers, which allows reaching temperatures higher than 200° C. The present invention is different from previously designed devices due to several factors, most relevant of them disclosed below. The first difference is that flat vacuum solar collectors in the past (U.S. Pat. No. 4,038,965-Lyon, U.S. Pat. No. 4,281,642-Steinberg, U.S. Pat. No. 4,289,113-Whittemore, U.S. Pat. No. 5,653,222-Newman) were designed in such a way that they all have a base, and a glass plate which closes the collector at all. These have a severe technical problem, since stresses created by a pressure difference within the collector and the atmospheric pressure, distort the structure and make it to fail, which causes a loss in vacuum within the collector. Lyon and Whittemore use linear supports which are attached along the collector so that they prevent distortion of the collector containing box. Steinberg designed a complex support which is located within the box. This support is a series of semicircles, which provide support to the glass closure on one side, while providing box support on the other side. Finally, Newman proponed a less complex solution, which uses a glass closure for the top of collector but the bottom thereof is comprised of semicircles, the semicircle peaks serve as a support for the top portion. In present invention the problem of pressure difference is solved by using high transmittance in solar spectrum tubes, which provide a smoothly spread stress distribution between said tubes. Another important problem having the above mentioned collectors is that glass thermal expansion and that from the base is different, which causes vacuum losses. The expansion of one piece depends on both the thermal expansion coefficient and the piece size. This is not a problem under present invention, since the only expansion which produces significant differences is the one occurring along the high transmittance in solar spectrum tubes and the conducting tubes, but because of the collector assembly form, said expansion does not cause any vacuum losses since having enough space for conducting tube differential expansion. Newman proposes in his design that tempered glass is used on top closure and then a series of treatment is provided to improve the glass optical properties, while under present invention commercial tubes showing better optical and thermal properties are used without any need to subject them to any additional treatment.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a general view of a flat vacuum solar collector.

FIG. 2 is a top view of a collector.

FIG. 3 is a cross-sectional view A-A of FIG. 2.

FIG. 4 a is rear view of one of the heads.

FIG. 4 b is a top view of one of the heads.

FIG. 4 c is a front view of one of the heads.

DETAILED DESCRIPTION OF INVENTION

The present invention represented in FIGS. 1 and 3 is a flat solar collector comprising an arrangement of High Transmittance in Solar Spectrum Tubes, herein and forth “TATES” (2), aligned in parallel and closed in their end sides by a pair of heads (1) and attached to small vacuum chambers (3).

Within each TATES and longitudinally arranged is a conducting tube (TUCS) (9) with a lower diameter than TATE, which transport the working fluid, TUCS are composed of any thermal conducting material, and each TUCS has attached along its length, a collecting plate (8) covered with a selective surface in solar spectrum to absorb the most possible amount of solar energy. These TUCS are arranged on low thermal conduction supports, preferably ceramics (10) to minimize the energy losses by conduction.

Each TATES end is closed by a head (1); the heads are preferably rectangular, having small punctures aligned along the head, this punctures have a larger diameter than TUCS to allow passing them therein. The number of circular punctures coincides with the number of TUCS, and the head side which is attached to TATES is named front side and the opposite one, rear side; being through this side where these vacuum chambers are joined (3), being of an area such that covers the cross-sectional area of 2 TATES. Vacuum chambers cover and are grouping in pairs the head circular punctures, where TUCS (9) are introduced. TUCS are located in parallel and they are joined each other, within the vacuum chamber by 90° or 180° elbows. The only circular punctures which are not covered by vacuum chambers are the first circular puncture or inlet puncture (6) and the last circular puncture or outlet puncture (7) from conducting tubes (TUCS) (9) which carry the working fluid. These are the only two contact points, no matter what the amount of TUCS comprising the solar collector is, with the feature that in this and last circular puncture the thermal expansion coefficient is different from the remaining.

For vacuum control and generation, at least on vacuum generation pump (4), and a pressure level meter (5) are connected to one of the vacuum chambers (3), which allows to generate the vacuum within the TATES and vacuum chambers, that is, in case that the vacuum within the system is lost, it is possible to recover it without requiring a system replacement and allowing additionally to control vacuum levels to keep a determined temperature thus preventing a modification in fluid temperature and flow. Because of that, the vacuum level in turn allows that TUCS reach temperatures higher than 200° C.

It may be noted from FIGS. 1, 2, 4a, 4b and 4c that the collector is a sealed device and composed by a variety of conventional elements which when being integrated achieve a non-conventional thermal performance. For improving the TATES performance (2), these are preferably built from borosilicate glass since due to its high compression mechanical strength they may reach a high vacuum level, which was impossible in other flat vacuum solar collectors.

Heads (1) are more detailed shown in FIGS. 4a, 4b and 4c. In FIG. 4c it is noted that the head is preferably rectangular and a number of bores are aligned in its front side equivalent to the amount of TATES (2) forming the solar collector. Surrounding these bores, circular slots (11) with the same diameter than TATES (2) are located and having a depth about the same than the TATES wall width (provided that this depth does not weaken excessively the head wall (1). Upon assembling the TATES(2) in heads (1) these circular slots (11) are filled with a material which prevents vacuum leakages, where said material may be grease, silicone or structural glue, the last being preferable. Assembly should be carried out once glue is dried to guarantee a vacuum leakage free joint between TATES and heads.

In FIG. 4a, the head rear side is seen where other slots are noticed (12) for vacuum chambers (3), which gather the bores whereby TUCS are passed, in such a way that when the TUCS number is odd, one of the bores at edge does not carry a slot, while when the number of TATES connected to heads is pair, the end side bores are always surrounded by a slot (12). Slots (12) shall be of a similar area to vacuum chambers (3), and with a depth about the same than the chamber wall width provided it does not excessively weaken the head wall (1). In the assembly process, these slots (12) are preferably filled with a structural glue, and vacuum chambers are inserted (3) inside the heads (1) before the glue is dried, in such a way that a vacuum leakage free joint is achieved between the vacuum chambers (3) and the heads (1).

One of the most important elements of this invention are the high transmittance in solar spectrum tubes (TATES), which shall be preferably of borosilicate glass, since these tubes show high optical, thermal and mechanical properties beneficial for collector performance. For example a common borosilicate glass tube will transmit more than 92% of the energy received from the sun and would reflect a negligible percentage (a common glass cannot reach these properties unless subjected to several additional treatments after manufacturing). Another important property is that its thermal expansion coefficient is so low that allows a wide material selection for head manufacturing (1). These TATES (2) shall be preferably of an outer diameter higher than 50 mm to adjust internally the conducting tubes (TUCS) with its respective collecting plate, as well as the support means. TATES are an ideal element since their circular cross-sectional surface show a smooth stress distribution in vacuum and therefore a need to add additional supports is nonexistent. Another element is the vacuum chambers (3); which serve as head closures (1), these are preferably built of glass tubes with a depth larger than 5 mm, although the cross section of these chambers may be circular, elliptic and polygonal, provided that fulfills the function of covering with one of their cross-sectional ends two adjacent TUCS. The use of glass is recommended since in this way takes advantage of the joint and elbow collecting surface which connect among them the TUCS. These vacuum chambers (3) may be of regular or borosilicate glass. It is worth to mention that some of these chambers carry a coupling to connect a vacuum pump (4) in the opposite end to the one on contact with the head, which allows to generate an initial vacuum or to recover the vacuum in case that due to any event a loss may exist. It is advisable that in another one of the vacuum chambers (3), preferably in the opposite side of a vacuum chamber (3) with vacuum pump (4), a pressure indicator (5) is installed, with which the existing vacuum level may be measured and the type of leakage if any. Another important feature which may be noticed in FIG. 1 is the working fluid inlet which for operation in these collectors is generally water. This inlet as not being in a vacuum chamber includes a package which contains the vacuum within the collector.

In FIG. 2 the same previously disclosed features may be observed. The amount of TATES (2) shall be determined by the working fluid flow and temperature to be observed, but sometimes at least two serial or parallel vacuum chamber solar collectors will be required to achieve these goals, thus obtaining a flat solar collector system. Having this in mind, it should be considered that for an odd TATES number (2), the TUCS inlet (6) and outlet (7) carrying the working fluid are each in each head (1), while when the TATES (2) number is even, TUCS inlet (6) and outlet (7) carrying the working fluid are located in the same head (1).

In FIG. 3, a detail is shown of a cross-sectional view in point A-A represented by FIG. 2; the different elements comprising each TATES inner part in the solar collector may be observed. Beginning with the upper part, a collector plate (8) is firstly located, which is whether welded or attached to the conducting tube (TUCS) (9) carrying the working fluid and the TUCS (9) stand on low thermal transmission supports, preferably ceramics (10). Within the vacuum chambers (3) the joints among the TUCS (9) are located, depending on the arrangement to be used (serial or parallel).

Collector plates (8) are made of a thermal conducting material (preferably copper). These collector plates (8) shall be of a thickness not larger than 0.2 mm and their length shall be shorter than each TATES (2) on each end depending on the circular slot (11) depth. Their width shall be also a minimum of 95% from TATES (2) diameter, and the maximum dimension of these plates shall be only determined by the collector plate material thermal expansion (8), since in any time these will not touch the TATES (2) because that would cause heat losses by contact. Another important feature of collector plates (8) is that these are coated by a solar spectrum selective surface on both sides. Together with these collector plates (8) the TUCS (9) are located which carry the working fluid. The joint between these components is carried out by using any additive which allows a maximum possible heat transmission, such as silver welding. The TUCS (9) are also coated with a selective surface, preferably black chromium. This selective surface shall have a high solar spectrum monochromatic absorptivity and a low solar spectrum monochromatic emittance to be a candidate for use in a collector. All the thermal conducting material angles of this selective surface are coated since in special cases concentrators may be arranged together to the collector and directing their light beam to the concentrator bottom, since being the TATES (2) bottom would pass the same energy passing in the top portion (more than 92%). TUCS and collector plate assembly stands on support means (10) made of a thermal insulating material (e.g. ceramics) so that the largest possible amount of energy is transferred to the working fluid. These supports (10) may be substituted by designs having a lower contact surface with the TUCS (9) or with the TATES (2). In the vacuum chamber ends (3) is where the TUCS attachment is made. Materials within the vacuum chambers (3) generally form 180° elbows which are also coated with a solar spectrum selective surface, in order to take advantage as much as possible from solar energy.

A flat vacuum solar collector with chamber type heads is possible to operate by fulfilling with all previous disclosure, which may raise the working fluid temperature higher than 200° C. since vacuum prevents that convection is present, then conduction losses are only present. These losses are very small since the contact is with insulating materials. In addition, a 100% of the piping for solar energy absorption may be used since everything is enclosed within containers with high solar spectrum transmittance.

Claims

1. A flat solar collector with vacuum chambers characterized by comprising at least two high transmittance in solar spectrum tubes, arranged in parallel, with the same diameter and length; limited on each end side by a plate comprising in its whole length a number of aligned circular punctures, with a lower diameter than the high solar spectrum transmittance pipe diameter; the plate in one of its sides, having circular slots which diameter matches with the high transmittance tube diameter; and in the opposite side they have larger slots surrounding in pairs the circular punctures; a support of low thermal conduction is located inside each high transmittance tube with a conducting tube of lower diameter than the plate circular punctures being arranged longitudinally thereon; passing through them and protruding by the plate rear side; the protruding conducting tube end sides are located in the plate rear side and connected each other by means of elbows; at least a vacuum chamber over which means to generate and recover vacuum and means for measuring a pressure level are possible to be arranged, is located in the same plate rear side matching with the larger slot.

2. A flat solar collector with vacuum chambers according to claim 1, characterized in that heads are preferably rectangular, having 2 or more circular punctures aligned along the head; a “circular slot” surrounding each circular puncture is located in the head front side, the number of “circular slots” is equivalent to the amount of high transmittance in solar spectrum tubes used for the solar collector.

3. A flat solar collector with vacuum chambers according to claim 2, characterized in that the “circular slots” have the same diameter than the high transmittance in solar spectrum tubes and having a depth about the same than the high transmittance tube wall width.

4. A flat solar collector with vacuum chambers according to claim 3, characterized in that the high transmittance in solar spectrum tubes are optionally joined with grease, silicone and structural glue.

5. A flat solar collector with vacuum chambers according to claim 1, characterized in that the rear side heads have slots in larger amounts equivalent to the high transmittance in solar spectrum tubes less 1; said slots are inserted and joined with grease, silicone or preferably structural glue, the vacuum chambers grouping in pairs the end sides protruding from the conducting tubes and leaving without grouping the conducting tubes wherein the working fluid is entering and leaving; said vacuum chambers are arranged in a position where a set of 2 consecutive conducting tubes may be covered.

6. A flat solar collector with vacuum chambers according to claim 4, characterized in that the number of high transmittance tubes is odd in the rear side of both heads, one of the edge bores does not include a slot, while when the number of high transmittance tubes is even, the edge bores in one of the heads is always framed by a slot while in the other head, the edge bores are not framed by a slot. Slots shall be of a similar dimension to the vacuum chambers, and with a depth approximately the same than the chamber wall width.

7. A flat solar collector with vacuum chambers according to claim 4, characterized in that each conducting tube is covering a collector plate length and the conducting tubes stand on low or null thermal transmission supports, preferably ceramics, and said supports in turn stand on the high transmittance in solar spectrum tubes.

8. A flat solar collector device with vacuum chambers according to claim 6, characterized in that the collector plates are located in parallel to the head top portion and being covered by a selective surface in both sides, in addition the attachment means between collector plates and conducting tubes may be of a welded, pressed, glued base or any other attachment means which efficiently transmits energy therein.

9. A flat solar collector with vacuum chambers according to claim 1, characterized in that the high transmittance tubes have preferably an outer diameter of 50 mm.

10. A flat solar collector with vacuum chambers according to claim 1, characterized in that the vacuum chambers are preferably built with glass tubes and having a bottom larger than 5 mm, with a circular, elliptic, or polygonal cross-section, preferably elliptic.

11. A flat solar collector with vacuum chambers according to claim 1, characterized in that when the number of high transmittance tubes is odd, the conducting tube inlet and outlet transporting the working fluid are located one on each head, while when the number of high transmittance tubes is even, the conducting tube inlet and outlet transporting the working fluid are located in the same head.

12. A flat solar collector with vacuum chambers according to claim 1, characterized in that the high transmittance in solar spectrum tubes form a geometric structure providing a body to the solar collector device.

13. A flat solar collector device with vacuum chambers according to claim 1, characterized in that the conducting tubes y and the collector plates are coated with a high monochromatic absorptivity selective surface and a low monochromatic emittance in solar spectrum or they are painted with high temperature resistant reflection preventing black paint, which allows taking advantage of the solar energy.

14. A flat solar collector with vacuum chambers according to claim 1, characterized in that the conducting tubes are attached among them by means of elbows, and the elbows are coated with a high monochromatic absorptivity selective surface or they are painted with high temperature resistant reflection preventing black paint, which allows taking advantage of the solar energy.

15. A flat solar collector with vacuum chambers according to claim 1, characterized in that within each high transmittance in solar spectrum tube is located a conducting tube.

16. A flat solar collector with vacuum chambers according to claim 1, characterized in that the high transmittance in solar spectrum tubes are preferably of borosilicate glass but they may be of any material which efficiently transmits solar energy.

17. A flat solar collector with vacuum chambers according to claim 1, characterized in that there is sufficient space within the vacuum chamber for conducting tube thermal expansion.

18. A flat solar collector with vacuum chambers according to claim 1, characterized in that the joint within the vacuum chamber between the conducting tubes is carried out by means of 90° or 180° elbows.

19. A flat solar collector with vacuum chambers according to claim 1, characterized in that vacuum is generated by means of a vacuum generating pump and being able to recover and control as required.

20. A flat solar collector with vacuum chambers according to claims 1, characterized in that the collector device may increase the working fluid temperature up to more than 200° C.

21. A flat solar collector system with vacuum chambers, characterized in that at least two flat solar collectors with vacuum chambers are serially or parallel connected according to claims 1.

22. A flat solar collector system with vacuum chambers, characterized in that connection of flat solar collectors with vacuum chambers is performed by attaching the inlet and outlet conducting tubes.