Patent Application
20090173334
The present invention is in the technical field of composite materials. The present invention is in the technical field of heat transport, extraction, and cooling. The present invention is also related to heat transport, extraction, cooling, storage and management for solar thermal, photovoltaic and other solar electric power generation, as well as all types of cooling and heat management, including but not limited to the electronics industry in general.
In this specification where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date, publicly available, known to the public, part of common general knowledge, or otherwise constitutes prior art under the applicable statutory provisions; or is known to be relevant to an attempt to solve any problem with which this specification is concerned.
While there are many different structures, arrangements and techniques for heat transportation, extraction and cooling in the state of the art, there is a need for improved structures, arrangements and techniques for cooling and heat transportation which have improved efficiency. For example, there is a need for such improvements in the areas of solar thermal, photovoltaic and other solar electric power generation, nuclear power generation cooling, as well as in the electronics industry, in general.
Cooling of photovoltaic cells is one of the main concerns when designing concentrating photovoltaic systems. Cells may experience both short-term (efficiency loss) and long-term (irreversible damage) degradation due to excess temperatures. Concentrating solar energy maximizes the ability to derive other forms of output therefrom. However, very high heat densities are often produced by sun concentrations of more than 1,000 times the nominal concentration of the sun's energy. This concentration is sometimes referred to as “1,000×” or “1,000 suns.” Some or all parts of an arrangement that are exposed to these levels of heat density may be destroyed or are rendered ineffective or inefficient. Consequently, at least some commercially available solar cells specify that they are not intended for use above 1,000 suns.
Design considerations for cooling systems include low and uniform cell temperatures, system reliability, sufficient capacity for dealing with worst case scenarios, and minimal power consumption by the system. For instance, an active cooling system with a thermal resistance of less than 10−4 K m2/W is typically necessary for solar cells under high concentrations (>150 suns).
Conventional nuclear power generation cooling systems typically require large volumes of water. Thus, it is common to locate nuclear power plants in close proximity to large bodies of water, such as lakes. However, severe drought conditions, which may become more prevalent due to climate change, can diminish the availability of enough water to provide adequate cooling. This can result in a disruption of the generation of electrical power. Thus, there is a need to provide a way to enable adequate cooling of nuclear power generation operations with lower volumes of cooling media than is currently utilized.
The present invention provides materials, arrangements, systems, and methods for improved efficiency in heat transport, extraction, cooling, storage and management.
The invention can be utilized in a number of potential applications, including but not limited to solar thermal, photovoltaic and other solar electric power generation applications. The present invention includes materials, arrangements, systems and methods that may be used in applications with very high heat densities produced by sun concentrations of up to, for example, 10,000×.
Heat management for solar electric power generation involves efficient extraction and transportation of heat generated by the solar cell with an incident concentrated solar energy strength of up to, for example, 10,000×. There are at least two notable aspects of this system: cooling the solar cells and transporting the heat away for other utility applications such as hot water and/or steam. Heat management for solar thermal power generation involves efficient extraction and transportation the heat absorbed by the heat collector subsystem with an incident sunlight concentration of up to, for example, 10,000×. There are at least two notable aspects of this system: collection of heat and transporting the heat away for other utility applications such as hot water and/or steam.
According to one aspect of the present invention there is provided an arrangement comprising: a solar energy receiving device; and at least one heat transport device in thermal communication with the solar it energy receiving device, the least one heat transport device formed from a composite material, the composite material comprising a matrix of carbon fibers, the carbon fibers comprising one or more of: mesophase carbon, carbon nanotubes, graphite, graphene and pan carbon.
According to a further aspect, the present invention provides a heat transport device comprising: an internal passage; and at least a portion of the internal passage formed from a composite material, the composite material comprising a matrix of carbon fibers, the carbon fibers comprising one or more of: mesophase carbon, carbon nanotubes, graphite, graphene and pan carbon.
According to a further aspect, there is provided a solar energy receiving device comprising a first surface for receiving solar energy incident thereon, and a second opposing surface, the second surface being electrically conductive; at least one heat transport device in direct contact with at least a portion of the second surface, the at least one heat transport device comprises at least one internal passage and at least one duct; and a heat transport media flowing within the at least one internal passage and at least one duct.
Unless otherwise defined herein or below in the remainder of the specification, all technical and scientific terms used herein have meanings commonly understood by those of ordinary skill in the art to which the present invention belongs.
Before describing the present invention in detail, it is to be understood that the terminology used in the specification is for the purpose of describing particular embodiments, and is not necessarily intended to be limiting. As used in this specification and the appended claims, the singular forms “a”, “an” and “the” do not preclude plural referents, unless the content clearly dictates otherwise.
Although many methods, structures and materials similar, modified, or equivalent to those described herein can be used in the practice of the present invention without undue experimentation, the preferred methods, structures and materials are described herein. In describing and claiming the present invention, the following terminology will be used in accordance with the definitions set out below.
As used herein, the term “heat receiving device” or “electromagnetic energy receiving device” means one or more devices arranged for receiving one or more forms of electromagnetic energy, such as solar energy, infrared energy, far infrared energy, microwave energy, sound energy, phonon energy, or radio waves, and possibly converting the electromagnetic energy incident thereon to one or more forms of energy which differ than the form which is incident thereon. The converted energy may take the form of electrical current, heat, mechanical energy and/or fluid pressure. Such heat receiving devices include, but are not limited to, photovoltaic solar cells and passive solar devices. One example of a comprehended passive solar device is a tube or other structure for transporting a heated fluid.
As used herein, the term “heat transfer media” means a vapor, a single fluid, mixed fluids, or multiphase fluids. The heat transfer media may have any suitable pressure, including pressures equal to, less than, or higher than, atmospheric pressure. The heat transfer media may include, but is not limited to, one or a combination of: organic fluid, inorganic fluid, biological fluid, water, steam, oil, and particles or structures of organic, inorganic or biological materials. When present in the form of a mixture, the heat transfer media may take the form of a colloidal dispersion or emulsion.
As used herein, the term “duct” shall mean one or more structures capable of conducting the heat transfer media therethrough. The duct includes structures such as channels, canals, tubes, conduits, passageways, tubules and capillaries. The term “duct” is not limited to any particular material, cross-sectional geometry or dimension. For purposes of illustration, the duct can be provided with dimensions on the order of 1 nm to a few centimeters.
As used herein, the term “designer” or “designer material” refers to the ability to control physical and/or thermal properties in the X, Y, Z material indices. Designer materials have made-to-order properties in one or more of the three dimensions.
According to certain aspects of the present invention, a variety of anisotropic materials, composites, thin films and matrices having high thermal conductivity have been developed. These materials can be used in any number of different applications. For example, the materials of the present invention can be used to provide unexpectedly superior results as heat transport devices such as solar cell package substrate material, micro-channel heat transport devices and fluidic systems, component mounts, connectors, thermal interface materials, heat spreaders, heat sinks, heat pipes, vapor chambers, thermoelectric devices, cooling components in nuclear power generation operations and other cooling components.
The materials of the present invention can be characterized as designer materials. Generally, conventional composites are made simply by mixing materials of different physical properties, with no special ordering within the composite and can only demonstrate bulk properties. By contrast, the designer materials of the present invention demonstrate different physical properties, thermal conductivity being a very important physical property for cooling and heat transport applications, in different directions and parts of the composite. In addition to thermal conductivity, one or more of the following properties may be tailored: coefficient of thermal expansion (CTE); thermal spreading coefficient Ke; and isothermal morphing of heat flux.
Designer materials of the present invention are anisotropic composites and matrices that are thinner, lighter, and stronger, and have eccentric heat spreading. Eccentricity is an important and major property in the designer materials. Heat spreading behavior in the X, Y and Z dimensions can be custom designed based on the application needs. In addition, the thermal conductivity and heat spreading could be custom designed to vary even along X, Y and Z axes. For example, the thermal properties in X direction could change as the value of X changes, which is along its length. In addition, the thermal conductivity and heat spreading could be custom designed to vary even along X, Y and Z axes. For example, the thermal properties in X direction could change as the value of X changes, which is along its length. If the heat spreading in an isotropic material could be visualized as a spheroid, the designer techniques enable making the shape an ellipsoid or even any random shape. Another way to visualize the power of the designer paradigm is an onion made up of layers, in which each layer could have different thermal properties, and different even within the layer surface.
Generally speaking, the designer materials of the present invention may comprise an anisotropic carbon-based fiber component and at least one of a high thermal conductivity filler and a high thermal conductivity coating or cladding.
The anisotropic carbon-based fibers can comprise one or more of: mesophase carbon fiber, carbon nanotube (CNT) based carbon fiber, graphene-based carbon fiber, graphite-based carbon fiber, and polyacrylonitrile (PAN) based carbon fiber. The carbon fiber may be derived from pitches, as well known in the art. Optionally, according to alternative embodiments, the fibers may be formed from copper, or be clad with copper.
According to one embodiment of the present invention, the fiber component of the composite comprises mesophase carbon fiber. Many materials containing polymers can be converted at early stages of carbonization to a structurally ordered anisotropic liquid crystals called mesophase, which can in turn be used to produce an anisotropic high quality carbon fiber.
The molecular structure 10 of one of the carbon materials used in the composites of the present invention is illustrated in the
As illustrated in
The anisotropic carbon-based fibers can be embedded with an isotropic high thermal conductivity filler material. Suitable filler materials include CNTs and other high conductivity materials like silver, diamond, aluminum nitride and boron nitride. Boron nitride and aluminum nitride have the special property of high thermal conductivity with no electrical conductivity. The amount of filler embedded varies depending on the desired application and performance objectives. For example, filler can be present in amounts of 5% to 50% by volume. By embedding such fillers, the thermal conductivity of the carbon-based can be increased to around 2,000 watts per meter-Kelvin along its length. As used herein CNT includes Single Wall CNT (SWCNT) and Multi Wall CNT (MWCNT), and combinations thereof. SWCNT and MWCNT have different conductivity and structural properties, whereas the choice between the two can depend factors such as the amount of heat to be transferred.
The carbon-based fibers, whether embedded with filler or not, may also be coated or clad with a high thermal conductivity material 28. Suitable coating or cladding materials include aluminum, copper, silver boron nitride, diamond and CNTs. The thickness of the coating or cladding may vary depending on the application and performance objectives, and desired final density of the composite. For example, the coating or cladding may range in thickness from 100 nm-5 μm. According to on non-limiting example, the coating thickness is approximately 0.5 μm.
The anisotropic carbon-based fibers can be spun and aligned to form linear matrix, and then heated to sinter the clad or coated materials to fuse the fibers 28 together. The fibers adhere to each other and pull close together into a compacted or dense matrix. The process boosts the density of the matrix by 5 to 25 times. Other factors being equal, higher density results in better thermal conductivity. Several other factors may also affect the density of the resulting matrix, such as the fiber diameter, density, type and quality of the embedded high conductivity filler material, and the CNT type (single wall or multi-wall). When present, the manner in which the CNTs are grown can also be an important factor that impacts the resulting shape and density of the matrix.
The coating or cladding 28 deposited on the anisotropic carbon-based fibers 20 can be provided with any suitable thickness t. For example, in order to fill the voids between longitudinal fibers to obtain a theoretical packing density of the matrix of 89.7%. As shown in
According to an alternative embodiment, the composite of the present invention may comprise the abovementioned anisotropic carbon-based fiber, high thermal conductivity filler and a foam material. Foam composites are made by air blowing and foaming similar to the way all metal foam composites are manufactured. The foam composites of the present invention made from anisotropic carbon-based fiber will be lighter than metal foams made solely from aluminum.
According to a further embodiment, the embedded and/or clad anisotropic carbon-based fibers 20 can be woven in various patterns, thereby forming a woven matrix composite designer material 31. One such woven composite structure is shown in
The composite matrix of the present invention can be provided with any suitable size or dimension. For example, the composite matrix can have a thickness from 10 nm-1,000 μm, more specifically 10 nm-800 nm, or 1 μm-1,000 μm. According to an alternative embodiment, a plurality of layers of composite matrix material can be fused together to build a thicker composite matrix.
The composite matrix material and cooling or heat transport components formed therefrom can be made by any number of suitable techniques or methods. The following is an illustrative, non-limiting discussion of such techniques and methods.
There are many considerations to keep in mind for the manufacture of the anisotropic carbon-based fiber embedded with high thermal conductivity fillers of the type mentioned above, like CNT and other nano/micro materials. It may be advantageous to collocate different related and associated manufacturing, testing and quality control processes to minimize the total cost of production by making the whole manufacturing process continuous. It may also minimize the post manufacturing and shipping processes generally associated with distributed manufacturing processes.
The manufacturing process can be continuous starting from the mesophase or the liquid crystal phase of the carbon fiber precursor material, until and including the finished product line of a cooling or heat transport component. The different steps of the continuous processes may include one or more of the following, in any particular order.
One or more high thermal conductivity nano and micro filler materials, such as CNTs and diamond, are embedded into carbon fiber at the mesophase and during the drawing of the fiber through fiber-drawing dies and the fiber spinnerets. The amount filler materials used depend on the desired increase in thermal conductivity. The drawing orifice chosen depends on the amount and type of filler materials as well as the filament diameter that make up the spun carbon fiber. If the orifice is smaller than a micron, the filler material and the carbon fiber filament become few hundred to hundreds of nanometers as the fiber filament drops down due to gravity and joins the other filaments from the other orifices of the drawing tool, thus resulting in thinner spun fiber. If diamond is used as the filler, the conductivity in the Z direction is also higher, because diamond has much higher conductivity than carbon fiber in all the three directions. The spun fiber has much higher thermal conductivity than unfilled carbon fiber due to CNT and other embedded nano and micro materials.
The next steps may include heating, re-crystallization and cooling through a continuous microwave heating and cooling process. Depending on the desired thermal conductivity, heating up to the mesophase formation temperature is required. This temperature can be on the order of 2000° C. to 3000° C.
The heat treated fiber can be sent through a pretreatment process for coating or cladding. A variety of metals with high thermal conductivity, such as copper, is coated on the fiber. The coating thickness can be approximately 10 nm-5 μm, and is controlled by the speed at which the fibers pass through the plating cycle.
The coated or clad fibers may be sintered together, as described above, which allows the fibers to come together or densify.
The fiber can be spooled into an array of spools.
The fibers may be sent through a fiber line up and weave processes.
The composite matrix material may be layered and fused together by a continuous roll-to-roll heating process. The type and thickness of the layers are chosen to define the thermal conductivity of the final designer matrix.
The designer composite matrix layers or films can be spooled into a shippable array of spools for use in the subsequent manufacture of a variety of cooling or heat transport devices or components.
Some heat transport components may even be manufactured in collocated next steps. A full range of cooling or heat transport components and materials can be made at least in part from a composite material of the present invention. Components and materials to include thermal interface materials (TIM), heat sinks, heat pipes, microchannel heat transport components, heat spreaders, stiffeners, packaging materials, PC board laminates, substrate material, microprocessor lid and other specialty packaging materials.
The composite materials of the present invention can be utilized in the construction of the devices, systems, arrangements and methods disclosed in: U.S. Provisional Application No. 60/996,273 filed Nov. 8, 2007; U.S. Provisional Application No. 61/071,410 filed Apr. 28, 2008; U.S. Provisional Application No. 61/071,411 filed Apr. 28, 2008; and non-provisional U.S. patent application Ser. No. ______ entitled “Solar Concentration and Cooling Devices, Arrangements and Methods,” by inventors K R S Murthy, Robert S. Block and Allen J. Amaro filed on an even date herewith. Each of the abovementioned patent applications being incorporated herein by reference in their entirety.
According to a further embodiment of the present invention, a heat transport device is provided. A heat transport device of the present invention can be formed, at least in part, from the composite matrix designer material described above. An exemplary heat transport device 60 is illustrated in
A heat transfer media 72 may be provided within the internal passage 62 and in communication with the at least one duct 64. The heat transfer media 72 can contain CNTs and/or other nano or micro size particles 74 to help create the turbulence and break up laminar flow to enhance the convective heat transport efficiency. The CNTs and/or nano or micro particles 74 impinge on the walls of the ducts 64 and collect heat therefrom then bounce back into the heat transfer media 72 and quickly disperse and transfer the heat into the heat transfer media 72, thus acting as heat transfer agents between the ducts 64 and the heat transfer media 72. The particles 74 also break up laminar boundary layer flow and create or add to the turbulent flow of the heat transfer media 72. Only appropriate volumes of these high conductivity particles 74 should be added to the heat transfer media 72 to minimize any coagulation/lumping in the fluidics channel system, valves, filters, membranes and pumps which may be present in such systems. Alternatively, the heat transport device 60 may comprise a closed system containing a set volume of heat transfer media 72, that may circulate, if at all, only in a closed loop. Appropriate curvature is designed into the ducts 64 to enhance the fluid flow turbulence. The inside walls of the ducts 64 may be provided with CNTs and/or nano/micro fibers 70 are grown vertically from the surface protruding into the heat transfer media. These protrusions transfer the conducted heat into the heat transfer media, swaying back and forth in the flow thereof.
The heat transport device 60 can be manufactured by any suitable technique. For example, nano-imprint lithography (NIL) can be used as a low cost method for forming nanometer-scale features such as ducts, nano-grooves and/or spikes. This method also conforms to the International Technology Roadmap for Semiconductors. NIL may be the lithography solution at the 32 and 22 nm fabrication nodes.
According to an additional embodiment of the present invention, a heat transport device, of the type described above, is incorporated into an arrangement including one or more solar cells, and is used for cooling the solar cell and/or transporting heat for other uses. An exemplary arrangement 80 is illustrated in
Alternatively, the present invention can be combined directly with conventional packaged solar cell arrangements that include a standard solar cell soldered onto a 15 mil thick ceramic substrate having electrical connectors provided thereon, and still provide advantages and benefits due to the exceptional cooling and heat transport properties.
According to a further embodiment, the arrangement 80 additionally may comprise optics or other suitable means 90 for producing concentrated solar energy 92 incident upon the solar cell 82. An arrangement formed consistent with the principles of the present invention is capable of amplifying the concentration of sunlight up to, for example, 10,000 times the nominal solar intensity level (10,000×). Additional optional features of the arrangement include electrical connections 94 and a printed circuit board 96. In addition, as illustrated in
According to a further embodiment of the present invention, a heat transport device, of the type described above, is incorporated into the cooling system of a nuclear power generation operation. The heat transfer media described above may optionally be utilized with or without the heat transport device. The improved efficiencies of the heat transport device constructed according to the present invention and/or the use of the heat transfer media described herein should provide greater cooling while requiring lower volumes of coolant than conventional arrangements.
An arrangement formed according to the principles of the present invention may include a combination of heat transport devices and other heat transport and/or cooling system components.
As illustrated, for example, in
All numbers expressing quantities of ingredients, constituents, reaction conditions, and so forth used in the specification are to be understood as being modified in all instances by the term “about.” Notwithstanding that the numerical ranges and parameters set forth, the broad scope of the subject matter presented herein are approximations, the numerical values set forth are indicated as precisely as possible. Any numerical value, however, may inherently contain certain errors resulting, for example, from their respective measurement techniques, as evidenced by standard deviations associated therewith.
Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, deletions, modifications, and substitutions not specifically described may be made without departing from the spirit and scope of the invention. Terminology used herein should not be construed in accordance with 35 U.S.C. §112, ¶6 unless the term “means” is expressly used in association therewith.
This application claims the benefit, pursuant to 35 USC §119(e), of: U.S. Provisional Application No. 60/996,273 filed Nov. 8, 2007; U.S. Provisional Application No. 61/071,410 filed Apr. 28, 2008; U.S. Provisional Application No. 61/071,411 filed Apr. 28, 2008; and U.S. Provisional Application No. 61/071,412 filed Apr. 28, 2008. The contents of each of the aforementioned Applications is incorporated herein by reference, in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60996273 | Nov 2007 | US | |
| 61071410 | Apr 2008 | US | |
| 61071411 | Apr 2008 | US | |
| 61071412 | Apr 2008 | US |
