Solar collector and solar heating system using same

A solar collector includes a substrate having a top surface and a bottom surface opposite to the upper surface, a sidewall, a transparent cover, and a heat-absorbing layer. The sidewall is arranged on the top surface of the substrate. The transparent cover is disposed on the sidewall opposite to the substrate to form a sealed chamber with the substrate together. The heat-absorbing layer is disposed on the upper surface of the substrate and includes a carbon nanotube structure.

This application is related to applications entitled, “SOLAR COLLECTOR AND SOLAR HEATING SYSTEM USING SAME”, filed Mar. 12, 2009 (Ser. No. 12/381,551); “SOLAR COLLECTOR AND SOLAR HEATING SYSTEM USING SAME”, filed Mar. 12, 2009 (Ser. No. 12/381,611); “SOLAR COLLECTOR AND SOLAR HEATING SYSTEM USING SAME”, filed Mar. 12, 2009 (Ser. No. 12/381,578); AND “SOLAR COLLECTOR AND SOLAR HEATING SYSTEM USING SAME”, filed Mar, 12, 2009 (Ser. No. 12/381,579). The disclosures of the above-identified applications are incorporated herein by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a solar collector and, particularly, to a solar collector incorporating carbon nanotubes.

2. Description of Related Art

Generally, solar collectors can be divided into two typical types: pipe solar collectors and flat plate solar collectors. For many applications, it has been demonstrated that the most efficient and least expensive type of solar collector is the flat plate collector. Referring toFIG. 8, a typical flat plate collector500, according to the prior art, includes a substrate52, a sidewall56arranged on the periphery of the substrate52, and a transparent cover50fixed on the sidewall56opposite to the substrate52. A sealed chamber60is formed between the substrate52and the transparent cover50. A number of supporters58are dispersed in the sealed chamber60at random. The transparent cover50is used for passage of light and is made of glass, plastic and other transparent materials. The substrate52is made of absorbing materials, such as copper, aluminum, or the likes. In use, the light enters the collector500through the cover50, and is absorbed by the substrate52. Thus, heat is generated by the substrate52and is transferred to a storage apparatus (not shown).

Actually, the traditional thin films made of absorbing materials have very high absorbing efficiency. The traditional solar collector500can't adopt the thin film technology because the film is difficult to evaporate on the large area substrate. As such, the heat absorbing efficiency of the solar collector500is limited by the material it used. Therefore, the efficiency of the collector500is limited accordingly.

What is needed, therefore, is to provide a solar collector and a solar heating system using the solar collector that can overcome the above-described shortcomings.

Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate at least one embodiment of the solar collector and the solar heating system using same, in at least one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

References will now be made to the drawings to describe, in detail, embodiments of the solar collector.

Referring toFIGS. 1-2, a solar heating system100according to a first embodiment is shown. The solar heating system100includes a solar collector10and a storage apparatus20connected to the solar collector10. The storage apparatus20is configured for storing heat generated by the solar collector10.

The solar collector10includes a substrate11, a sidewall12, a transparent cover13, a heat-absorbing layer14and a number of supporters15. The substrate11has a top surface111and a bottom surface112opposite to the top surface111. The transparent cover13has a bottom surface131. The sidewall12is mounted on the periphery of the top surface111of the substrate11. The transparent cover13is attached on the sidewall12opposite to the substrate11to form a sealed chamber16in cooperation with the sidewall12and the substrate11. The heat-absorbing layer14is disposed on the top surface111of the substrate11and received in the sealed chamber16.

The material of the substrate11can be selected from one of heat-conducting materials, such as metal, glass, polymer, and so on. A thickness of the substrate11can be in a range from about 100 μm to about 5 mm. The shape of the substrate11is not limited; and may be triangular, hexagonal, and so on.

The transparent cover13may be a solar radiation access window. The material of the transparent cover13can be selected from a group consisting of glass, plastic, transparent porcelain, polymer and other transparent materials. A thickness of the transparent cover13can be in a range from about 100 μm to about 5 mm. The shape of the transparent cover13is not limited, and may be triangle, hexagon, quadrangle, and so on.

The sidewall12is configured for supporting the transparent cover13, and then formed the sealed chamber16between the transparent cover13and the substrate11. The sidewall12is made of materials selected from glass, plastics, polymers, and the like. A height of the sidewall12is not limited. A thickness of the sidewall12can be in a range from about 100 μm to about 500 μm. In the present embodiment, the range is 150 μm to 250 μm.

The sealed chamber16may be a vacuum chamber or an atmospheric chamber filled with thermal-insulating materials. In the present embodiment, the sealed chamber16is an atmospheric chamber, and the thermal-insulating materials filled therein can be transparent foam materials, such as transparent foam rubber, transparent foam plastics, or the like. The sealed chamber16can also be filled with thermal-insulating gas, such as nitrogen, and/or inert gases.

The heat-absorbing layer14includes a carbon nanotube structure. The carbon nanotube structure includes a plurality of carbon nanotubes (CNT) dispersed uniformly therein. Further, the carbon nanotube structure includes at least a carbon nanotube film. A thickness of the carbon nanotube structure is in a range from about 0.2 μm to about 2 mm. The carbon nanotube films in the carbon nanotube structure can be arranged side by side. One or more carbon nanotube films can be overlapped or stacked with each other. The CNTs of the carbon nanotube structure can be arranged orderly, forming a ordered CNT film. Alternatively, the CNTs of the carbon nanotube structure can be arranged disorderly, forming a disordered CNT film. In the ordered CNT film, the carbon nanotubes are primarily oriented along a same direction in each film and substantially parallel to a surface of the carbon nanotube film. In the disordered CNT film, the carbon nanotubes are entangled with each other or arranged in an isotropic manner. The isotropic carbon nanotubes are substantially parallel to a surface of the carbon nanotube film. Different stratums/layers of films can have the carbon nanotubes offset from the carbon nanotubes in other films.

Referring toFIG. 3, according to a second embodiment the CNT film can be formed by been drawn from a CNT array, forming a drawn CNT film. The drawn carbon nanotube film includes a plurality of successive carbon nanotubes joined end to end and are aligned substantially in the same direction. The majority of carbon nanotubes are arranged along a primary direction. However, the orientation of some of the nanotubes may vary. Referring toFIG. 4, the drawing carbon nanotube film comprises a plurality of successively oriented carbon nanotube segments143joined end-to-end by van der Waals attractive force therebetween. Each carbon nanotube segment143includes a plurality of carbon nanotubes145parallel to each other, and combined by van der Waals attractive force therebetween. The carbon nanotube segments143can vary in width, thickness, uniformity and shape. The carbon nanotubes145in the carbon nanotube segment143are also oriented along a preferred orientation.

The drawing carbon nanotube film is drawn from a carbon nanotube array. The carbon nanotubes are combined by van der Waals attractive force. The drawing carbon nanotube film adhesive because the carbon nanotubes in the carbon nanotube array have relatively large specific areas. The thickness of the drawing carbon nanotube film ranges from about 0.5 nm to about 100 μm. The carbon nanotube structure16can include layers of drawing carbon nanotube film stacked on each other. The angle between the aligned directions of carbon nanotubes in two adjacent layers can be set as desired.

In a third embodiment, referring toFIG. 5, the CNT film is formed by a flocculation process, forming a flocculated CNT film. The flocculating carbon nanotube film is a carbon nanotube film with a plurality carbon nanotubes therein that are isotropic, uniformly arranged, disordered, and are entangled together. There is a plurality of micropores distributed in the flocculating carbon nanotube film, as such, a specific area of the flocculated carbon nanotube film is extremely large. The thickness of the flocculated carbon nanotube film is ranged from about 1 μm to about 1 mm.

In a fourth embodiment, the CNT film is formed by pressing a carbon nanotube array, forming a pressed CNT film. The pressed carbon nanotube film can be a free-standing carbon nanotube film. The carbon nanotubes in the pressed carbon nanotube film are arranged along a same direction or arranged along different directions. The carbon nanotubes in the pressed carbon nanotube film can rest upon each other. Adjacent carbon nanotubes are attracted to each other and combined by van der Waals attractive force. An angle between a primary alignment direction of the carbon nanotubes and a surface of the pressed carbon nanotube film is 0° to approximately 15°. The greater the pressure is, the smaller the angle. When the carbon nanotubes in the pressed carbon nanotube film are arranged along different directions, the carbon nanotube structure can be isotropic. The thickness of the pressed carbon nanotube film ranges from about 0.5 nm to about 1 mm.

The carbon nanotubes in the carbon nanotube structure can be selected from a group comprising of single-walled carbon nanotubes (SWCNT), double-walled carbon nanotubes (DWCNT), multi-walled carbon nanotubes (MWCNT), and their mixture. A diameter of the carbon nanotubes approximately ranges from 0.5 nm to 50 nm. A length of the carbon nanotubes is larger than about 10 μm. In the present embodiment, the length ranges from about 100 μm to about 1 millimeter.

A thickness of the carbon nanotube structure can vary according to the practice. Referring to theFIG. 6, the thicker the carbon nanotube structure is, the higher the light-absorbing ratio is. The light-absorbing ratio of the carbon nanotube structure can reach 96% when the thickness thereof is 10 microns. In the present embodiment, the thickness of the carbon nanotube structure is in a range of about 0.5 micron to about 2 millimeter. Referring toFIG. 7, the carbon nanotube structure has a high light-absorbing ratio in the wavelength ranged from 360 nm to 800 nm, and the light-absorbing can reach 93%-98% in the wavelength spectrum.

The supporters15are configured for increasing the strength of the solar collector10. The supporters15are dispersed in the sealed chamber16at random or in a desired pattern. The supporters15are spaced from each other and disposed between the substrate11and the transparent cover13. The supporters15are made of thermal-insulating materials, such as glass, plastics, rubber, and so on. A height of the supporters15is the same as that of the sidewall12for contacting with the transparent cover13. The shape of the supporters15is not limited, and may be, for example, rounded or bar-shaped.

The solar collector10further includes a reflection layer17. The reflection layer17is disposed on the bottom surface131of the transparent cover13. The reflection layer17is configured for allowing the visible light and near infrared light of the sunlight passing through the transparent cover13and reflecting the far infrared light radiated from the heat-absorbing layer14to prevent thermal radiation from escaping the sealed chamber16. Thus, the light absorbing efficiency of the solar collector10is improved. The reflection layer17may be an indium tin oxide (ITO) film or a titanium dioxide film and a thickness of the reflection layer17ranges from about 10 nm to about 1 μm.

The storage apparatus20is located on a bottom surface112of the substrate11and may include a number of pipes (not shown) filled with circulating fluid. The fluid may be selected from the group of water, glycol, or the like.

In use, since the carbon nanotube film is black and has a capability of absorbing most heat of the solar spectrum. The sunlight travels through the transparent cover13and reaches the heat-absorbing layer14. A good portion of the radiation of the sunlight is absorbed by the heat-absorbing layer14. Then, the heat absorbed by the heat-absorbing layer14is conducted to the storage apparatus20via the substrate11. Therefore, the solar collector10has a high efficiency because of the excellent light absorbing properties of the carbon nanotubes of the heat-absorbing layer14. The solar collector10is durable due to the toughness of the carbon nanotubes in the carbon nanotube film. The use of carbon nanotube, which does not oxidize easily, eliminated the need for a high vacuum. This significantly reduces the cost of the solar collector10.