Patent Application
20080251065
The invention is directed generally to supercritical solar collectors and supercritical heat exchangers, and more specifically to supercritical solar collectors and configurations for high efficiency energy conversion.
Solar collectors are well known in the art. A solar collector is simply a device for delivering solar energy, most often thermal energy as means to direct photons for energy conversion devices or to transfer heat into a heat transfer fluid. Throughout the application, the invention will be referred to as a supercritical flat panel collector with the understanding that the designation of flat panel represents a contiguous sheet that could be substituted for a shape modified and non-contiguous collector without changing the inventive objectives and operations of the device.
In absorption heat pumps, an absorbent such as water absorbs the refrigerant, typically ammonia, thus generating heat. When the combined solution is pressurized and heated further, the refrigerant is expelled. When the refrigerant is pre-cooled and expanded to a low pressure, it provides cooling. The low pressure refrigerant is then combined with the low pressure depleted solution to complete the cycle.
There are no patent or literature references that disclose the use of supercritical fluids within a flat panel collector, nor the utilization of fail-safe valves and/or thermal diodes as a means to provide thermal management for integral energy conversion devices including photovoltaic devices.
The art lacks a high efficiency and very cost effective flat panel collector that combines the benefits associated with evacuated, concentrator, and traditional flat panel solar collectors.
The present invention is a fail-safe flat panel collector that achieves superior energy conversion efficiency by maximizing the collection of both direct energy conversion device energy such as electricity and thermal energy from both non-transformed photons to phonons and waste heat resulting from inefficiencies in the energy conversion device. A fundamental benefit resulting from the inventive design is a significant reduction in thermal losses. A further advantage of the supercritical flat panel thermal collector is the high thermal flux rate with minimal pressure losses.
FIG. I—A cross-sectional view of the SFPC depicted with integral microchannels and coatings.
FIG. II—A cross-sectional view of the SFPC configured to combine the inherent benefits of falling film heat exchangers.
FIG. III—A cross-sectional view of the SFPC depicted with internal fluid separation layers.
FIG. IV—A cross-sectional view of the SFPC depicted with integral safe storage in a solar concentrator.
FIG. V—A cross-sectional view of the SFPC depicted with an integral energy conversion device.
FIG. VI—A cross-sectional view of the SFPC depicted with integral solar photovoltaic device.
The term fail-safe is defined as being capable of compensating automatically and safely for a failure, as of a mechanism or power source.
A supercritical flat panel thermal collector, also referred to as “SFPC” wherein the flat panel thermal collector is comprised of supercritical heat transfer fluids with at least one benefit selected from the group consisting of reduced pressure losses, reduced thermal losses, superior heat transfer, and elimination of heat transfer fluid freezing. The virtual, if not complete, elimination of freezing design and operation consideration yields both operational simplification and cost reduction of at least −40 degrees Fahrenheit. The SFPC heat transfer fluid has a maximum surface tension of 20 dynes/cm, which in part enables smaller diameter piping. A piping diameter reduction, at least a minimum of 50%, enables superior heat transfer fluid distribution across at least more of the surface of the SFPC and in most cases an increase in heat transfer surface exceeding 50% of the collector surface area. The increase in heat transfer surface area enables a significant reduction of collector peak surface collector temperature, which yields benefits including reduced thermal losses, and superior heat transfer.
The pressure losses for any heat transfer fluid operating at supercritical pressures will be lower than low pressure operations. The supercritical collector fluid chamber “pipe” diameter operating at a pressure of greater than 300 psi is a minimum of 50% smaller than the diameter having equivalent friction losses for the identical heat transfer fluid at an operating pressure of less than 100 psi. The diameter of fluid flow chamber “pipe” is less than a quarter of an inch. Significant reductions in friction losses are obtained at diameters of less than 3000 microns. The preferred diameter is less than 1,000 microns. The particularly preferred diameter is less than 100 microns. The specifically preferred diameter is less than 10 microns. The diameter is predominantly limited by the manufacturing processes utilized to produce the supercritical collector. Current manufacturing means, including semi-conductor processes, printed circuit technology have the ability to produce anticipated less than 10 microns. These diameters include diameters of 10 nanometers, 50 nanometers, 100 nanometers, 1 micron, 5 microns, and 10 microns. The specific selection of diameter is a function of manufacturing costs, molecular weight and viscosity of heat transfer fluid, operating pressure, and flow rates.
A supercritical flat panel thermal collector comprised of an integral fail-safe valve to limit heat transfer fluid losses in the event of a heat transfer fluid leak.
A supercritical flat panel thermal collector comprised of an integral fail-safe thermal diode to transfer thermal load to an alternative heat sink.
The supercritical flat panel thermal collector is utilized as a supercritical solar flat panel collector.
The supercritical flat panel collector is comprised of a thermal barrier coating on the non-solar facing side. The more preferred supercritical flat panel collector also has a solar absorber coating on the solar-facing side.
The preferred supercritical flat panel collector is configured to operate as a falling film heat exchanger. The falling film configuration maximizes heat transfer, which also leads to lower thermal losses.
The supercritical flat panel collector is further comprised of internal layers to separate heat transfer fluids consisting of at least two components into at least two distinct flows. The separation of the heat transfer fluid into its distinct components enables the fastest “evaporating” components to separate from the primary heat transfer surface, thus maintaining contact with the component having the higher thermal conductivity. The particularly preferred supercritical flat panel collector has integral microchannels. The specifically preferred collector has channel widths of less than 10 microns. The specifically preferred collector has the microchannels configured within the collector on the maximum collector surface area for the purpose including a surface temperature differential less than 10 degrees Fahrenheit across the entire surface. It is further desired to achieve the lowest temperature differential, such as a temperature differential of less than 5 degrees Fahrenheit across the entire surface. The desired results include at least a 10 percent reduction in radiation losses as compared to a non-supercritical (i.e., traditional) flat panel thermal collector.
There are numerous methods recognized in the art to separate at least two distinct flows. These methods include methods selected from the group consisting of density, molecular weight, and immiscibility variations. A preferred exemplary method includes the utilization of a nanoporous matrix to enable for example supercritical carbon dioxide to be desorbed from the at least binary heat transfer fluid consisting of at least one ionic liquid or ionic liquid polymer. It is recognized that any heat transfer fluid can be utilized where the fluid is comprised of at least two fluids having a significant difference in density, molecular weight and/or miscibility. The preferred heat transfer fluid is such that the fluid separates by moving the composite heat transfer fluid from a region of miscibility into immiscibility.
The preferred configuration within the supercritical flat panel thermal collector is for the heat transfer fluid to enter the top internal layer when the heat transfer fluid is being heated. Alternatively, the preferred configuration within the supercritical flat panel thermal collector is for the heat transfer fluid to enter the bottom internal layer when the heat transfer fluid is being cooled.
The pressures achieved during the operation of the supercritical flat panel thermal collector are sufficient to directly drive a mechanical pump, thus being a thermally driven mechanical pump. The collector operating as an integral component of an absorption system utilizes the thermal gains of the supercritical flat panel thermal collector to provide at least in part the thermal load required to drive a desorption cycle, which in turn drives a mechanical pump, followed by the concurrent absorption cycle that at least preheats or at best heats a secondary heat transfer fluid. The secondary heat transfer fluid is preferred to be a heat transfer fluid such as municipal water that will in turn be utilized as domestic hot water.
A key feature of the supercritical flat panel is the reduced pressure losses due to small “pipe” diameters. The optimal pressure range is above the supercritical pressure of the heat transfer fluid. Numerous benefits are still obtained when the operating pressure range is transcritical, meaning that the operating pressure on the low pressure side is below the supercritical pressure with the high pressure side rising to a pressure above the supercritical pressure (i.e., occurs when the temperature rises due to solar energy). The operating pressures anticipated are pressures above 100 psi. The preferred operating pressure is above 300 psi. The particularly preferred operating pressure is above 500 psi. The specifically preferred operating pressure is above 1000 psi.
The supercritical flat panel thermal collector is further comprised of at least one of a photon to electron and a phonon to electron conversion device. Such energy conversion devices, also referred to as “ECD” includes photovoltaic, thermionics, and thermoelectric devices transform either photons or phonons (i.e., thermal energy packets) into electricity. Photovoltaic devices in particular are temperature sensitive, thus they often achieve lower efficiencies at higher temperatures. This is of special importance when the energy conversion devices are coupled with solar concentrators. The preferred configuration is such that the supercritical flat panel thermal collector is on the backside of the energy conversion device being directly coupled with a high thermal conductivity “paste” having a matching thermal coefficient of expansion “TCE”. The flat panel collector thus serves at least two critical roles: 1) it increases overall efficiency by effectively utilizing the thermal energy resulting from thermal losses of the energy conversion process, and 2) meeting the thermal cooling requirements resulting from the high thermal fluxes in a high concentration ratio solar concentrator. This configuration is the ideal method to transform the energy conversion device into a concentrated energy conversion device.
Safe and long-term operation of the concentrated energy conversion device requires direct integration of an integral temperature sensor. The integral temperature sensor is at least one of the necessary inputs to achieve feedback in a dynamic system controller in order to vary the heat transfer fluid flow rate in order to maintain an exit temperature that is less than the maximum energy conversion safety temperature. This objective is balanced with the thermal objectives of achieving the maximum heat transfer fluid exit temperature higher than a minimum thermal demand temperature. A third control scheme is an overall optimal temperature that realizes the maximum total efficiency, which is the combination of the energy conversion device efficiency and the thermal energy conversion efficiency.
Maximizing the total energy efficiency requires the incorporation of integral thermal barrier layers to limit thermal heat losses. Thermal losses are attributed to convective, radiative, and conductive thermal losses, all of which can be minimized through the utilization of thermal barrier coatings or even thermal insulators including aerogels, insulation, and vacuum chambers. One exemplary configuration to reduce thermal losses is through the utilization of an integral mechanical vapor compression heat pump system. The mechanical vapor compression heat pump concurrently achieves temperature lift of heat transfer fluid and a reduction in supercritical flat panel thermal collector thermal losses. The thermal losses are reduced by reducing the temperature differential across the thermal collectors high surface area thus reducing the maximum operating temperature in the collector. The mechanical vapor compression heat pump achieves temperature lift within a significantly smaller surface area thus reducing thermal losses.
Minimizing temperature differential across the entire surface of the supercritical flat panel is a fundamental advantage to numerous applications outside of solar applications. These include radiant floor heating and cooling. In fact the utilization of supercritical fluids prevents the water or other liquid heat transfer fluids from creating extensive damage in the occurrence of a leak. The supercritical flat panel is especially a superior heat exchanger for applications of radiant cooling by minimizing the opportunity for condensation due in part to the decrease in temperature differential with the ambient air and the significant increase in surface area.
supercritical flat panel collector comprised of microchannels for heat transfer fluid (FIG. 1—30), a substrate (FIG. 1—40) that integrates the series of microchannel heat exchangers/radiators into one continuous radiant surface, and a thermal barrier coating on the backside (FIG. 1—50) maximizes heat transfer. This configuration referred to as a supercritical flat panel heat exchanger “SHX” is ideal for maximizing heat transfer within radiant heating and cooling as configured within floor panels, wall panels, fencing, roofing, ceiling tiles, or architectural elements and structures. Architectural elements include sculptures or simply design elements.
The flat panel heat exchanger is optimally comprised of a series of microchannel heat exchangers integrated into at least one flat surface to achieve a temperature differential across the entire surface of less than 10 degrees Fahrenheit. The resulting flat panel is operated as a device selected from the group consisting of structural elements, floor panels, wall panels, fencing, roofing, ceiling tiles, or architectural elements and structures. It is further anticipated that the benefits realized by the flat panel microchannel heat exchanger are achieved for non-supercritical fluids when sufficient surface area reduces heat transfer fluid friction losses (i.e., pressure losses) due to sufficiently low flow rates as having low Reynolds Number.
The most promising configuration of the inventive supercritical flat panel collector is in combination with linear concentrating flat reflective Fresnel lenses. The flat panel Fresnel lense achieves significant benefits including reduction of wind susceptibility, low cost production, and relatively low structure requirements. A linear concentrating zone focuses the solar energy into a significantly smaller physical area. Thus the supercritical flat panel collector is smaller and more cost effective. The supercritical flat panel collector is designed to survive extreme weather conditions, though these are very unusual in frequency and severity. The optimal method to reduce the engineering requirements to survive such extreme weather is to utilize the same active tracking motors to “park” the supercritical flat panel collector into an integral housing within the solar concentrator for the safe storage of the supercritical flat panel thermal collector. Thus the solar concentrator serves a secondary purpose of protecting the supercritical flat panel collector and it's embedded energy conversion device (which is often the single most costly component).
The very high concentration ratios achieved place significant thermal demands on the energy conversion device. Thus any loss in thermal management capability can yield permanent damage to the energy conversion device. Normal operation transfers the thermal energy to the heat transfer fluid, which is optimally a supercritical fluid. The high pressures of supercritical fluids does lead to an increased potential for leaks, though the preferred supercritical fluid of carbon dioxide does not represent any elevated greenhouse potential. In the event of a leak or loss of heat transfer fluid, the energy conversion device that is often the most expensive component within the energy conversion system, must be protected. The integration of an integral fail-safe thermal diode serves to transfer the thermal load to an alternative heat sink. The preferred configuration integrates an alternative heat sink into the solar concentrator. The particularly preferred configuration utilizes the solar concentrator structure as a fail-safe heat sink, thus maximizing the functionality of the concentrator structure.
Numerous methods known in the art are recognized as being applicable for a thermal diode. It is anticipated than essentially any device that is capable of “switching” from a normal heat sink to the alternative heat is applicable. This device is further anticipated that an external pressure sensor is the input to a normally open contact/switch. This normally open contact is able to drive an actuated motor that establishes a thermal pathway to the alternative heat sink. The particularly preferred thermal diode is a pressure actuated spring device that upon pressure loss moves a mechanical contact that establishes a thermal pathway to the alternative heat sink. The thermal pathway is particularly preferred to be comprised of low thermal resistance materials including materials selected from the group consisting of a nanotube thermal bus/conduit and heat pipe.
An additional safety feature is the inclusion of a fail-safe valve that is activated by a pressure drop, which is indicative of a heat transfer fluid leak, to cut-off the leaky section of the supercritical flat panel collector. The preferred configuration utilizes the fail-safe valve under normal operation to pulse the heat transfer fluid into the flat panel collector. Enabling a relatively low temperature heat transfer fluid into the flat panel collector occurs at reduced pressure relative to the higher pressures obtained at the increasing and elevated temperature achieved by solar gain. This reduces, or potentially under certain operating conditions, eliminates the requirement of a pump/compressor to increase the hydraulic pressure of the heat transfer fluid.
The supercritical flat panel thermal collector, when further comprised of a solar photovoltaic device and a solar concentrator experiences significant thermal flux. The solar photovoltaic device most often requires at least passive cooling in order to maximize photovoltaic to electricity conversion efficiency and system lifetime. The cost economics of solar photovoltaic is leading to an increased utilization of solar concentrator, in many cases reaching solar concentrations as high as 1000 and often reaching 500. The further utilization of supercritical fluids achieves both the high thermal flux dissipation from the solar photovoltaic device while enabling the efficient conversion of waste thermal energy into useful energy including electricity as a means to increase the overall efficiency. The direct integration of a supercritical flat panel collector comprised of a transcritical or supercritical fluid within a flow chamber having channel “pipe” diameters preferably less than 100 microns (and specifically preferred less than 10 microns) on the backside of a solar photovoltaic or thermionic device serves as both active cooling and enhanced energy conversion yielding a combined energy efficiency greater than each individual component.
Lastly, it is anticipated that the supercritical flat panel thermal collector is preferably configured into a shape that meets additional secondary purposes. One such benefit includes the ability to integrate the flat panel collector into a secondary structural element, thus less structural components are required for the flat panel collector. Another such benefit is the ease in which the flat panel collector can shape modified to match the shape of an integral architectural element. The integration of the flat panel collector into building/architectural components achieves benefits including reduced costs, superior architectural appearance, and higher thermal resistance of the building/architectural components. Exemplary building/architectural components include roofing elements, external walls, and garage/carport roofs. The preferred shape modified collector is an architectural solar tree/structure that in it's own is architecturally pleasing. The trunk of the so-called tree serves as both the piping for the heat transfer fluid, and structural support for the flat panel collectors. The particularly preferred solar tree has the inherent ability for the collectors to be retracted and/or collapsed to minimize exposure to severe weather.
The figures depicted within the specification of the invention provides exemplary configurations of the most critical components of the SFPC. A detailed description of the figures is provided in the following paragraphs.
FIG. I depicts the SFPC comprising a solar absorber coating (10) as a coating of the of the structural substrate (20). The thermal gain collected from the solar energy is transferred via microchannels (30) into the supercritical heat transfer fluid. The microchannels (30) are sandwiched between two structural substrates (20 and 40). Lastly, a thermal barrier coating (50) is coating the non-solar facing side of the substrate (40) to limit thermal losses.
FIG. II depicts the SFPC at a tilt angle to enable the supercritical fluid to operate in a falling film configuration to maximize heat transfer.
FIG. III depicts the further inclusion of an internal fluid separation layer (140) between both top and bottom substrate layers (120 and 150). The preferred configuration during solar gain is such that the internal fluid separation layer is adjacent to the bottom substrate layer (150) to enable the more gaseous component of the supercritical heat transfer fluid to follow a pathway further away from the most critical heat transfer surface substrate (120).
FIG. IV depicts the SFPC (200) in a position away from the solar concentrator (210). The SFPC can be moved by any methods known in the art to stabilize the SFPC from weather conditions and to track and/or optimize solar collection and concentration. The solar concentrator has a void (210) designed to enable the SFPC to be safely stored, especially during severe weather while the SFPC also hosts energy conversion devices. The optimal placement for the void is a balance between minimizing the cost of structure and moving of SFPC (200) into void (210), while keeping to a minimum the solar concentrator active surface side removed which reduces the amount of solar energy collected. It is within the scope of the invention that the void can occur on the side of the solar concentrator or the bottom side of the solar collector.
FIG. V depicts the SFPC (300) with an integral energy conversion device “ECD” (310), a valve assembly device “Valve” (370), and thermal diode assembly device “Thermal Diode” (350). The valve assembly serves the purpose of isolating the SFPC from both additional SFPC devices and other portions of the piping for the supercritical heat transfer fluid to limit any impact of a failed SFPC (i.e., leak, loss of vacuum, etc.) on total energy efficiency and/or loss of heat transfer fluid. The thermal diode assembly device serves the purpose of eliminating/reducing thermal losses into the alternative heat sink, which ideally is integrated into the solar concentrator (320) or is the solar concentrator structure/alternative heat sink (340) during normal operation. However, during a failure of the thermal management system or simply reaching a peak temperature that exceeds the safe operation of the ECD, the thermal diode assembly device maximizes heat transfer to the alternative heat sink. The combined devices ensure safe and efficient long-term operation of the SFPC.
Additional features and advantages of the present invention are described in and will be apparent from the detailed description of the presently preferred embodiments. It should be understood that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications can be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be covered by the appended claims.
This application claims priority from U.S. Provisional Patent Application Ser. No. 60/596,248 filed Sep. 11, 2005.
| Number | Date | Country | |
|---|---|---|---|
| 60596248 | Sep 2005 | US |
