CLOSED AND OPEN LOOP SOLAR AIR COLLECTORS
A solar thermal collector is disclosed. The collector comprises a body defining a housing; a solar absorber located, within the housing; a transparent insulating medium in proximity to the solar absorber; and a heat exchanger integrated, with the housing.
Embodiments of the invention relate to devices and methods to convert sunlight into heat.
BACKGROUNDSolar thermal collectors are devices which collect sunlight and convert it to heat. The resulting heat is then transferred to a fluid medium in the form of a gas or a liquid where it can be subsequently transported to a point of use. The transported heat can be exploited in a number of ways that are useful to human society and the many heat driven processes that support modern civilization.
SUMMARYAccording to one aspect of the invention, there is provided a solar thermal collector incorporating a transparent insulating medium comprising, a nano-porous matrix: which allows sunlight to pass into the solar thermal collector while reducing losses through the medium which occur via conduction and radiation by virtue of the properties of the transparent insulating medium; the heat from which is subsequently transported to the exterior of the collector via an integrated heat exchanger.
According to another aspect of the invention, there is provided a solar thermal system incorporating a transparent insulating, medium, comprising a nano-porous matrix: which allows sunlight to pass into the solar thermal system while reducing losses through the medium which occur via conduction and radiation by virtue of the way in which a heat transfer fluid interacts Within the transparent insulating medium; the heat from which is subsequently transported to the exterior of the collector via an integrated heat exchanger,
According to another aspect of the invention, there is provided a solar thermal system incorporating a transparent insulating medium, comprising a nano-porous matrix: which allows sunlight to pass into the solar thermal system while reducing losses through the medium which occur via conduction and radiation by virtue of the heat transfer fluid being a gas or combination of gasses; the heat transfer fluid passing through the matrix; and the heat from which is subsequently transported to the exterior of the collector via an integrated heat exchanger.
According to another of the invention, there is provided a solar thermal system incorporating a transparent insulating medium comprising a nano-porous matrix:
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- wherein, the heat transfer fluid is circulated within the collector via thermally driven buoyancy forces; the heat transfer fluid passing through the matrix;
- and the heat from which is subsequently transported to the exterior of the collector via an integrated heat exchanger.
According another aspect of the invention, there is provided a solar thermal system incorporating a transparent insulating medium comprising a nano-porous matrix:
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- wherein the heat transfer fluid is circulated within the collector via a pump;
- the heat transfer fluid passing through the matrix;
- and the heat from which is subsequently transported to the exterior of the collector via an integrated heat exchanger.
According another aspect of the invention, there is provided a solar thermal system incorporating a transparent insulating medium comprising a nano-porous matrix:
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- wherein the heat transfer fluid is circulated within the collector via thermal transpiration;
- the heat transfer fluid passing through the matrix;
- and the heat from which is subsequently transported to the exterior of the collector via an integrated heat exchanger.
According another aspect of the invention, there is provided a solar thermal system incorporating a transparent insulating medium comprising a nano-porous matrix:
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- wherein the heat transfer fluid is extracted from the ambient environment;
- the heat transfer fluid passing through the matrix;
- and the heat from which is subsequently transported to the exterior of the collector.
Other aspects of the invention will be apparent from the detailed description below.
In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will he apparent, however to one skilled in the art that the invention can be practiced without these specific details.
Reference in this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited b some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not others.
In one embodiment, a solar thermal collector is disclosed. The collector includes a light absorbing medium which converts incident sunlight into heat by raising the temperature of a heat transfer fluid, and fluidic pathways within the collector to allow for circulation of the heat transfer fluid to an integrated heat exchanger wherein the resulting heat can be transported to the exterior of the collector.
In general, the collector is nominally airtight, though some embodiments may allow for controlled exchange of air with the environment, and the interior under neutral pressure or below atmospheric pressure, in order to further minimize beat losses to the environment and enhance passive pumping mechanisms.
Heat losses 112 from the collector are limited to some extent by the inclusion of the nano-porous medium 108, which has several properties which, make it useful in this role. These include transparency to most of the spectrum of light emitted by the sun and some degree of absorptivity or reflectivity for light wavelengths longer than those emitted by the sun. The medium 108 may be in the form of a planar monolithic structure with a planar surface area ranging from fractions of a meter to a meter or greater and a thickness of fractions of a centimeter to a centimeter or greater, Or a similarly sized and shaped matrix comprised of an aggregate of smaller particulates which may have sizes ranging from hundreds of microns to several millimeters or more in diameter. The particulates in the matrix may be of a smooth distribution in size within this range, or may have several distinct sizes. The geometries may be uniform and regular in nature or completely random.
The material comprising the nano-porous medium 108 may be in the form of an aerogel or aerogel like material made from a metallic oxide or other organic or inorganic materials whose fundamental structure consists of open or closed cellular pores whose diameter may range from tens of nanometers to tens of microns or more. The porous structure is such that it impedes the flow of a gas or gasses through the medium and therefore impedes the loss of heat from the solar thermal system. Other materials with similar properties including but not limited to masses of woven organic, or inorganic, fibers may be utilized and/or incorporated as well as long as some combination of the requisite transparency transparent to the solar spectrum and absorbing and/or reflective for wavelengths longer than the solar spectrum) porosity and thermally insulating characteristics (i.e. less than 0.04 W/m.K) can be achieved with the resulting medium. In this way heat losses 112 from the solar absorber 110 are mitigated thereby improving the efficiency of the solar thermal system.
During operation a cold heat transfer fluid is pumped via interconnect path 120 into collector 102 where it comes into contact with the solar absorber 110. The heat transfer fluid is nominally a gas or some combination of gasses, such as air, which have been selected due to their low-cost, their positive characteristics with respect to specific heat and thermal conductivity, and their benign nature from the standpoint of chemical reactivity and human health. In the embodiment shown, heat transfer fluid (introduced via the interconnect path 120 as described above) can come into contact with the solar absorber 110 via a combination of flow paths 122, 124, and 128, with the latter two paths causing flow directly through the nano-porous medium 108. The total flows are combined as they come into contact with solar absorber 110 and extracted via interconnect pipe 116 so that their heat can be used elsewhere. External heat exchanger 118, is located near or at the point of use for the heat and serves to transfer the heat from the heat transfer fluid, represented by flows 122, 124, and 126, to another heat transfer fluid or to the point of use.
Referring now to
The heat exchanger 132 may be made from a variety of materials including, but not limited to metals, plastics, and ceramics. The overarching, requirements include that it can realize the requisite thermal conductivity to support heat transfer from the interior of the collector to the exterior, that it be environmentally rugged and be capable of supporting the hermeticity of the collector (if the collector is designed to be hermetically sealed), and that the surfaces of it which are to be exposed to internal and external heat transfer fluids be capable of being machined or fashioned in such a way as to achieve the requisite ratio of interior to exterior surface area ratio. For example, if the interior heat transfer fluid is to be a gas and the exterior heat transfer fluid is to be a liquid then the interior fluid will have a lower thermal conductivity than that of the exterior fluid. Crafting a heat exchanger with a high interior to exterior surface area ratio will facilitate the flow of heat from the interior to the exterior in this case by compensating for the differences in conductivity.
Referring back to
Variations on internal heat transfer flow configurations are disclosed in the aforementioned patent application U.S. patent application Ser. No. 14/292,702, and are essentially defined by the ratios between the flow rates of fluid flows 122, 124, and 128 any one or two of which could have a value of zero as defined during the manufacture of the collector or during its operation under a control mechanism. All of aforementioned internal heat flow configurations apply to this embodiment with the only difference being that the internal heat transfer fluid is physically separated from the exterior of the collector.
Various methods can be used to pump the fluid within the collector. Referring again to
Referring, now to
In general, internal fluid circulation within the collectors illustrated in
Another challenge to the design of this closed loop collector concerns changes in internal pressure as the collector undergoes heating. The consequence of a rise in temperature will mean an increase in the pressure. if the pressure in the non-operational state is near atmospheric it is doubtful that the collector an be easily designed to withstand the resulting increase thus some kind of expansion chamber will have to be incorporated into the collector. The expansion chamber is a component which is well known in the art of solar thermal systems as any heat transfer fluid in such systems will undergo expansion which results in an internal increase in pressure. In general, the expansion chamber is a metal container with a flexible membrane within that provides an airtight seal between openings on both sides of the membrane leading from the interior of the chamber to the exterior. If one of these opening is connected to a system which may undergo changes in pressure, then the membrane can expand within the chamber to accommodate the increased volume of the heat transfer fluid. if the collector is manufactured such that its internal pressure is below atmospheric then depending on the total increase in temperature during operation the interior pressure may not rise beyond atmospheric or not significantly past atmospheric. In such case an expansion chamber may not be necessary.
Referring now to
That is to say that the heated heat transfer fluid 514, in the form of hot air, can be provided directly to an application such as drying food or textiles, heating the product, food Of textiles in this case, by direct contact with the heat transfer fluid 514.
Referring now to
Overall, integrating the heat exchanger has the potential to make it easier to interface the collector to existing thermal piping and interconnect systems without the requirement of changing the heat transfer fluid within the piping system. Systems utilizing the collector design illustrated in
Claims
1. A solar thermal collector, comprising:
- a body defining a housing;
- a solar absorber located within the housing;
- a transparent insulating medium in proximity to the solar absorber; and
- a heat exchanger integrated with the housing.
2. The collector of claim wherein at least a portion of the heat exchanger resides within the housing.
3. The collector of claim 1, wherein the transparent insulating medium comprises a nano-porous matrix
4. The collector of claim 3, wherein the solar absorber is embedded within the nano-porous matrix.
5. The collector of claim 4, wherein the nano-porous matrix comprises aerogel,
6. The collector of claim 1, further comprising an inlet and outlet defined between the heat exchanger and the body defining the housing; wherein the inlet serves to introduce a cold heat transfer fluid into the housing, to undergo heating that coming into contact with the solar absorber, and the outlet serves to allow the heated heat transfer fluid to pass from the collective body two the heat exchanger.
7. The collector of claim 6, wherein the heat transfer fluid is circulated within the housing thermally-driven buoyancy forces.
8. The collector of claim 6, further comprising a pump located within the housing configured to facilitate circulation of the heat transfer fluid.
9. The collector of claim 1, wherein the body comprises a planar configuration including upper and lower faceplates.
10. The collector of claim 1, wherein the body has a cylindrical configuration.
11. The collector of claim 4, wherein the heat transfer fluid comprises air.
12. The collector of claim 1, wherein the heat exchanger is elevated relative to the solar absorber.
13. The collector of claim 1, which forms a closed loop system.
14. The collector of claim 1, which forms an open loop system.
Type: Application
Filed: Apr 18, 2016
Publication Date: Nov 24, 2016
Inventor: Mark W. MILES (Atlanta, GA)
Application Number: 15/132,180