EP2162688A1 - An element for emission of thermal radiation - Google Patents

An element for emission of thermal radiation

Info

Publication number
EP2162688A1
EP2162688A1 EP08756972A EP08756972A EP2162688A1 EP 2162688 A1 EP2162688 A1 EP 2162688A1 EP 08756972 A EP08756972 A EP 08756972A EP 08756972 A EP08756972 A EP 08756972A EP 2162688 A1 EP2162688 A1 EP 2162688A1
Authority
EP
European Patent Office
Prior art keywords
wavelength range
radiation
layer
particles
wavelength
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP08756972A
Other languages
German (de)
French (fr)
Inventor
Geoffrey Burton Smith
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
University of Technology Sydney
Original Assignee
University of Technology Sydney
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Priority claimed from AU2007221733A external-priority patent/AU2007221733A1/en
Application filed by University of Technology Sydney filed Critical University of Technology Sydney
Publication of EP2162688A1 publication Critical patent/EP2162688A1/en
Withdrawn legal-status Critical Current

Links

Classifications

    • C—CHEMISTRY; METALLURGY
    • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
    • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
    • C09K5/00—Heat-transfer, heat-exchange or heat-storage materials, e.g. refrigerants; Materials for the production of heat or cold by chemical reactions other than by combustion
    • C09K5/08—Materials not undergoing a change of physical state when used
    • C09K5/14—Solid materials, e.g. powdery or granular
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25B—REFRIGERATION MACHINES, PLANTS OR SYSTEMS; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS
    • F25B23/00—Machines, plants or systems, with a single mode of operation not covered by groups F25B1/00 - F25B21/00, e.g. using selective radiation effect
    • F25B23/003—Machines, plants or systems, with a single mode of operation not covered by groups F25B1/00 - F25B21/00, e.g. using selective radiation effect using selective radiation effect
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D31/00—Other cooling or freezing apparatus
    • F25D31/006—Other cooling or freezing apparatus specially adapted for cooling receptacles, e.g. tanks
    • F25D31/007—Bottles or cans
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F13/00—Arrangements for modifying heat-transfer, e.g. increasing, decreasing
    • F28F13/18—Arrangements for modifying heat-transfer, e.g. increasing, decreasing by applying coatings, e.g. radiation-absorbing, radiation-reflecting; by surface treatment, e.g. polishing
    • G—PHYSICS
    • G02—OPTICS
    • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
    • G02B5/00—Optical elements other than lenses
    • G02B5/20—Filters
    • G02B5/26—Reflecting filters
    • E—FIXED CONSTRUCTIONS
    • E06—DOORS, WINDOWS, SHUTTERS, OR ROLLER BLINDS IN GENERAL; LADDERS
    • E06B—FIXED OR MOVABLE CLOSURES FOR OPENINGS IN BUILDINGS, VEHICLES, FENCES OR LIKE ENCLOSURES IN GENERAL, e.g. DOORS, WINDOWS, BLINDS, GATES
    • E06B9/00—Screening or protective devices for wall or similar openings, with or without operating or securing mechanisms; Closures of similar construction
    • E06B9/24—Screens or other constructions affording protection against light, especially against sunshine; Similar screens for privacy or appearance; Slat blinds
    • E06B2009/2411—Coloured fluid flow for light transmission control
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
    • F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
    • F25D2331/00—Details or arrangements of other cooling or freezing apparatus not provided for in other groups of this subclass
    • F25D2331/80—Type of cooled receptacles
    • F25D2331/805—Cans
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28F—DETAILS OF HEAT-EXCHANGE AND HEAT-TRANSFER APPARATUS, OF GENERAL APPLICATION
    • F28F2245/00—Coatings; Surface treatments
    • F28F2245/06—Coatings; Surface treatments having particular radiating, reflecting or absorbing features, e.g. for improving heat transfer by radiation

Definitions

  • the present invention broadly relates to an element for emission of thermal radiation.
  • the present invention provides an element for emission of thermal radiation, the element comprising particles arranged for receiving thermal energy and emitting at least a portion of the received thermal energy in the form of the thermal radiation, the thermal radiation predominantly having a wavelength or wavelength range within an atmospheric window wavelength range in which the atmosphere of the Earth has a reduced average absorption and emission compared with an average absorption and emission in an adjacent wavelength range whereby absorption by the element of radiation from the atmosphere is reduced.
  • the atmospheric window wavelength range typically includes a minimum of the average absorption of the atmosphere of the Earth.
  • the atmosphere has atmospheric windows within the wavelength ranges of 3 to 5 ⁇ m and 7.9 ⁇ m to 13 ⁇ m. Within these wavelength ranges the emission of the sun is also negligible and often regarded as zero, which has the added advantage that even during daytime the element only absorbs very little radiation from the sun within that wavelength range.
  • the element according to embodiments of the present invention and a medium that may be in thermal contact with the element typically is cooled or cooling is facilitated without the need for electrical energy. In particular during the night, or when irradiation by the sun is avoided, cooling well below ambient temperature is possible .
  • the particles may be distributed throughout the element, which in this case also comprises a material that is substantially transmissive for radiation having a wavelength within the atmospheric window range.
  • the element may comprise a surface portion, such as a coating, in which the particles are concentrated and which is arranged so that the thermal radiation can be emitted.
  • the element may also comprise a membrane which locates the particles.
  • the element may also comprise a cover that may be suspended over a body portion of the element or that may be provided in the form of a cover layer that is in direct contact with the body portion.
  • the cover typically is transmissive for the thermal radiation emitted by the particles and protects the particles from hot breezes and other external influences that could reduce the cooling efficiency.
  • the cover typically comprises a thermally insulating material.
  • the cover may comprise a polymeric material such as polyethylene.
  • the cover may comprise an oxide or sulphide material, which typically is arranged to block at least a portion of incident UV radiation. In one specific example the oxide or sulphide material is positioned on or over the polyethylene material and also protects the polyethylene.
  • This example combines the relative strength of typical polyethylene material with the UV protective function of the sulphide or oxide material, which also increases the lifespan of the polyethylene material.
  • the polymeric material and the oxide or sulphide material typically are - A - arranged so that relatively high transmittance for radiation having a wavelength within the atmospheric window is retained.
  • the oxide or sulphide material may be a layer that is positioned on or over the polymeric material .
  • the sulphide or oxide layer typically has a thickness that is selected so that in use at least the majority of incident UV radiation is blocked and the cover is substantially transmissive for radiation having a wavelength range within the atmospheric window wavelength range.
  • the thickness of the layer typically is within the range of 100 nm - lOOOnm, 150 nm - 300 nm and typically is of the order of 200 nm.
  • the element may further comprise wall portions that define an interior space within which a medium that is to be cooled is in use located.
  • the wall portions typically comprise a reflective material.
  • the element may include thermally insulating materials and may for example form an at least partially thermally insulated container.
  • the element may also comprise a structure that has projecting wall portions which are positioned so that, in use, incoming radiation from regions of the atmosphere, which are near the horizon, is substantially blocked off. It is known that for such radiation the atmospheric window is less transmissive, because the atmosphere is "thicker" for radiation traveling closer to the horizon. Being less transmissive, the atmosphere then also radiates more strongly at these wavelengths from directions close to the horizon. Consequently, avoiding that such radiation can reach the particles improves the cooling efficiency of the element.
  • the projecting wall portions typically are reflective for the thermal radiation emitted by the particles.
  • the structure may also comprise the above- described cover.
  • the projecting wall portions typically are reflective for the thermal radiation emitted by the particles and may be positioned so that, in use, thermal radiation emitted by the particles or reflected by the projecting wall portions is directed in a direction towards Space and in a direction away from the horizon.
  • the projecting wall portions typically are formed from a material that has low thermal emittance.
  • the element comprises a concentrator such as a "CPC" concentrator or a parabolic dish or trough concentrator.
  • the projecting wall portions typically form a portion of the concentrator.
  • the concentrator typically is arranged so that radiation emitted form substantially all regions of the conduit is directed towards the sky by the concentrator.
  • the projecting wall portion has the added advantage that heating of the particles, and/or of the medium that is to be cooled by the particles, by a hot breeze that may in use pass over the element is reduced.
  • the element forms a part of, or is provided in the form of, an object and is arranged for cooling of the object and/or a medium that is in thermal contact with the object.
  • the element may be in contact with the portion of the object and may also be adhered to, formed on or otherwise applied to the portion of the object.
  • the object includes a container, such as a can, in which for example food or a liquid may be located.
  • the object may be a container, such as a food container or a container for transportation or storage of medicine, organs, blood, or anything else that is to be cooled.
  • the object may be an electronic device and the element may be arranged for cooling of the electronic device or may form a part of any means for transportation including automobiles, trucks, train carriages and shipment containers and the like, which require cooling of an interior portion.
  • the element may also be a part of a structure, such as a building or a house.
  • the element may be provided in the form of a window, roof tile, roof sheet or skylight.
  • the element may comprise a substantially transparent polymeric material that comprises the particles for emission of the thermal radiation.
  • the element may in this embodiment also comprise a honeycomb-like structure that provides additional strength.
  • the element may further comprise a material, such as a further type of particles, that is arranged for absorbing incoming radiation in the near infrared wavelength range.
  • the element may be arranged so that the incoming near infrared radiation is absorbed and the resulting absorbed thermal energy is at least partially re-emitted in the form of thermal radiation by the particles arranged for emission of radiation having a wavelength within the atmospheric window wavelength range.
  • the element is arranged to enable cooling to temperatures that are 5°, 10° , 20° below an ambient temperature or even lower.
  • the element may also be arranged to extract heat at a finite rate at a temperature below ambient.
  • the element may be arranged so that cooling rates such as 40, 60, 80 W per m 2 of cooling material area are possible at temperatures that are 5°, 10° or more below ambient temperature.
  • the particles may be arranged for generation of ionic surface plasmon resonances having a wavelength or wavelength range within the atmospheric window wavelength range.
  • ionic surface plasmon is used for a surface plasmon excitation that involves movement of ions, such as that often referred to as “Fr ⁇ hlich resonance” .
  • the particles typically are arranged so that at least some, typically the majority or all, of the ionic surface plasmons have a wavelength within the wavelength range from 1 - 7 ⁇ m, 2 - 6 ⁇ m, or 3 - 5 ⁇ m, and/or any one of 5 - 16 ⁇ m, 7 - 14 ⁇ m, 8 - 13 ⁇ m and 7.9 - 13 ⁇ m.
  • the atmospheric window wavelength range may be one of a plurality of atmospheric window ranges, such as the wavelength range of 3 - 5 ⁇ m and 7.9 to 13 ⁇ m.
  • the particles comprise, or are entirely composed of, SiC or another suitable material .
  • At least a portion of the particles may also be arranged for emission of radiation by a physical mechanism other than that associated with the generation of ionic surface plasmons.
  • the particles may be composed of any suitable material that is arranged for emission of radiation having a wavelength within the atmospheric window wavelength range.
  • the element may comprise a material that is arranged for emission of radiation having a wavelength outside the atmospheric window range .
  • the element may comprise a polymeric material, such as a coating, that is transmissive for radiation of a predetermined range of wavelength.
  • the particles may be embedded in the polymeric material or may be located adjacent the polymeric material.
  • the element may also be arranged to reflect at least some incident radiation, such as radiation from the atmosphere and/or from the sun in the daytime.
  • the element may comprise a reflective material that is provided in the form of a layer positioned below the particles and may be arranged to reflect at least a portion of incident radiation.
  • the element may comprise reflective particles that are dispersed within an at least partially transparent material, such as the above-described polymeric material .
  • the element comprises at least one channel for a fluid whereby the element is arranged for cooling the fluid.
  • the element may not necessarily comprise particles that are arranged for emission of thermal radiation having a wavelength within the atmospheric window wavelength range, but the particles may be replaced by at least one layer that is arranged for emission of thermal radiation having a wavelength within the atmospheric window wavelength range.
  • the at least one layer may comprise a granular structure, a porous structure or may have a surface that is profiled so that the at least one layer is arranged for generation of ionic surface plasmon resonances having a wavelength or wavelength range within the atmospheric window wavelength range.
  • the at least one layer may be a part of a multi-layered structure that is arranged for generation of ionic surface plasmon resonances having a wavelength or wavelength range within the atmospheric window wavelength range.
  • the present invention provides in a second aspect an element for emission of thermal radiation, the element comprising at least one layer that is arranged for receiving thermal energy and emitting at least a portion of the received thermal energy in the form of the thermal radiation, the thermal radiation predominantly having a wavelength or wavelength range within an atmospheric window wavelength range in which the atmosphere of the Earth has a reduced average absorption and emission compared with an average absorption and emission in an adjacent wavelength range whereby absorption by the element of radiation from the atmosphere is reduced.
  • the atmospheric window wavelength range typically is a wavelength range from 3 to 5 ⁇ m and/or from 7.9 ⁇ m to 13 ⁇ m.
  • the at least one layer typically is arranged for generation of ionic surface plasmon resonances having a wavelength of wavelength range within the atmospheric window wavelength range.
  • the at least one layer may have a structural property that is selected so that the at least one layer is arranged for generation of ionic surface plasmon resonances having a wavelength or wavelength range within the atmospheric window wavelength range.
  • the at least one layer may comprise grains, or may at least in part be of a porous structure and the structural property may be associated with a grain size or a thickness of residual solid between pores, respectively.
  • the at least one layer may have a surface roughness and the structural property may be associated with thickness or width of surface features of the at least one layer.
  • the grain size, the thickness of residual solid between pores and - li the thickness or width of surface features of the at least one layer typically are within the range of 50nm - 150nm.
  • the at least one layer may be a part of a multi-layered structure having layer thicknesses that are selected so that the multi -layered structure is arranged for generation of ionic surface plasmon resonances having a wavelength or wavelength range within the atmospheric window wavelength range.
  • the present invention provides in a third aspect a cooling system comprising the above-described element in accordance with the first or second aspect of the present invention, the element forming a part of an object and the cooling system comprising a thermally insulating wall portion for reducing exchange of thermal energy between a portion of the object an environment of the cooling system.
  • the element may be in contact with the portion of the object and may also be adhered to, formed on or otherwise applied to the portion of the object.
  • the object may include a container, such as a can, in which for example food or a liquid may be located.
  • a container such as a can, in which for example food or a liquid may be located.
  • the thermally insulating wall portion typically is arranged so that the element of the object is in use enabled to emit thermal radiation in a direction away from the cooling system.
  • the cooling system typically is also arranged so that the object is positionable in, and removable from, an interior formed by the thermally insulating wall portion.
  • the cooling system may further comprise a removable lid- portion and a base portion that together with the thermally insulating wall portion form an enclosure in which in use the object is positioned, the lid-portion being formed from a material that is transmissive for thermal radiation emitted by the particles of the element
  • Figure 1 shows an a device incorporating an element for emission of thermal radiation according to an embodiment of the present invention
  • Figures 2, 3 (a), 3 (b) and 4 show objects incorporating an element for emission of thermal radiation according to an embodiment of the present invention
  • Figure 5 shows a transmission spectrum of the atmosphere of the Earth as a function of wavelength
  • FIGS. 6 - 8 show elements for emission of thermal radiation according to embodiments of the present invention.
  • Figure 9 shows a a cooling system according to a specific embodiment of the present invention.
  • the element comprises particles that are arranged for emission of radiation having a wavelength within a range referred to as the "atmospheric window wavelength range" .
  • the atmospheric window wavelength range is a wavelength range within which the absorption and emission of radiation by the atmosphere of the Earth is strongly reduced or zero. Radiation .emitted from the element within that wavelength range is largely transmitted through the atmosphere to Space where the average temperature is 4 Kelvin. Further, as within that wavelength range typically very little or no radiation is received by the element, the element functions as a pump of thermal energy.
  • the element comprises a cooling material that is disclosed in Australian provisional patent application No 2007903673 and US patent application No .11/765217. These patent applications are hereby incorporated by cross-reference.
  • Figure 1 shows a cooling element 10 in accordance with an embodiment of the present invention.
  • the element 10 may be arranged for cooling a medium that is in thermal contact with a portion of the element 10.
  • the element 10 is arranged so that thermal radiation can be emitted from surface portion 12 to the atmosphere either directly or indirectly.
  • the element 10 is arranged so that a portion of the thermal energy received from the medium is emitted by the element 10 in the form of thermal radiation so that cooling of the medium is facilitated by the element 10.
  • the cooling element 10 may form a part of an evaporative cooling device.
  • the element 10 typically is arranged to cool a liquid, typically water, prior to evaporation.
  • the element 10 may form a part of any other type of air-conditioning device and the element 10 may be arranged for facilitating cooling of a fluid that in use circulates though portions of the air- conditioning unit.
  • the element 10 may form a part of be a radiator, heat exchanger, or refrigerator or any other type of cooling device.
  • a person skilled in the art will appreciate that there are numerous examples of cooling devices in which the element 10 may be incorporated.
  • FIG. 2 shows an example of a structure 14 in which an element for emission of the thermal radiation according to embodiments of the present invention is incorporated.
  • the structure 14 is in this embodiment a house or building or the like and includes roof-covering and/or other external coverings that are provided in the form of objects 16.
  • each object 16 may be a roof tile or a roof- sheet which comprises a metallic, ceramic or polymeric material.
  • the object 16 comprises a surface portion that incorporates the particles for emission of the thermal radiation and is positioned over the metallic, ceramic or polymeric material.
  • the particles may be embedded in a coating material that is applied by painting or otherwise to the metallic, ceramic or polymeric material of the object 16.
  • the coating material is substantially transmissive for radiation having a wavelength within the atmospheric window wavelength range.
  • the particles may be positioned on a surface portion of the object 16 without being embedded in a coating material.
  • the object 16 is arranged so that thermal radiation is emitted which results in cooling of a roof space of the house or building 14.
  • This particular application has significant advantages in particular for warmer regions of the Earth.
  • roof spaces gain a substantial amount of thermal energy and often maintain a substantial portion of that thermal energy during the night.
  • the element 16 facilitates cooling of the roof space and thereby improves comfort of living in the house or building 14.
  • large portions of the external surface, such as the roof area of a house or building 14, are covered by the object 16.
  • the structure 14 may also include further objects that incorporate an element for emission of the thermal radiation and that are provided in the form of windows, such as window 18.
  • the window 18 is arranged so that a portion of near-infrared radiation is blocked.
  • the object 20 is in this example a container for containing food, medical articles, blood or organs and the like or any other objects or matter that requires cooling.
  • An external surface portion of the object 20 comprises the particles arranged for emission of thermal radiation. Emission of the thermal radiation results in cooling of the container 20 and an interior portion thereof.
  • Figure 3 (b) shows an example of a further variation of a container that includes the element 12.
  • the container 22 has wall portions 24 that are composed of a thermally insulating material.
  • the container 22 also comprises a top portion 26 that is composed of a material that is substantially transmissive for the thermal radiation having a wavelength range within the atmospheric window wavelength range.
  • the top portion may also have thermally insulating properties and may for example comprise iron oxide or ZnS.
  • a medium that is to be cooled is positioned adjacent the element 12.
  • This embodiment has the added advantage that the thermally insulating wall portions further increase the cooling efficiency. Further, the elememt lOand the medium that is to be cooled are protected from any hot breezes that may also reduce the cooling efficiency.
  • the element for emission of thermal radiation may form a portion of an electronic device, such as an integrated electronic device, and may be arranged for cooling of the electronic device.
  • Figure 4 shows a structure 28 that is largely transmissive for visible radiation and may be used as a roof-sheet, window or sky light and the like.
  • the structure 28 comprises a first layer 30 and a second layer 32.
  • the first layer 30 and the second layer 32 are connected by members 34 so that a honey-comb like structure is formed tat is relatively stabile.
  • the structure 28 comprises a polymeric material and has particles incorporated within that material so that the structure 28 has advantages analogous to those of the above-discussed element.
  • the cooling element has numerous applications for cooling objects, or fluids. If an object or fluid is to be cooled, the cooling element may be arranged to cool the object or fluid directly. Alternatively, the cooling element may be arranged for cooling the object or fluid indirectly by cooling another fluid of material, which then cools the fluid or object that is to be cooled.
  • Figure 5 shows a transmission spectrum 34 of the atmosphere of the Earth for substantially cloud free conditions.
  • the average transmission is increased to nearly 1 within the range of approximately 7.9 to 13 ⁇ m compared to adjacent wavelength ranges. Further, the average transmission of the atmosphere is increased within a wavelength range of 3 - 5 ⁇ m. Within these wavelength ranges the atmosphere of the Earth has "windows" .
  • Plot 36 is an estimation of the emission spectrum of a black body having a temperature of
  • Figure 6 shows a secondary electron microscopy micrograph of a surface portion of the element according to a specific embodiment of the present invention.
  • the element 40 comprises a reflective metallic layer 42, which in this embodiment is provided in the form of an aluminum layer positioned on a substrate. Further, the element 40 comprises SiC particles 44, which are positioned on the metallic layer 42. The SiC particles 44 have an average diameter of approximately 50 nm and are deposited using suitable spin coating procedures.
  • the SiC particles 44 are in this embodiment nano-particles and the majority of the surface of the particles 44 is exposed to air.
  • the particles 44 show resonantly enhanced absorption and emission of radiation at a wavelength range of 10 to 13 ⁇ m. Within that wavelength range ionic surface plasmons are generated.
  • the wavelength range of resonant ionic surface plasmon emission is within the above- described atmospheric window wavelength range. For that wavelength range the average absorption of the atmosphere of the Earth is very low and consequently very little radiation in this wavelength range is transferred from the atmosphere to the element 40.
  • the energy associated with the emitted radiation is largely drawn from the thermal energy of the particles 44 and/or from a medium that is in thermal contact with the particles 44. Due to the atmospheric window, the emitted radiation is largely transmitted through the atmosphere and directed to Space where the temperature typically is 4 Kelvin. Consequently, the element 40 functions as a pump of thermal energy even if the cooling material, or a medium that is in thermal contact with the cooling material, has a temperature below ambient temperature.
  • the reflective material 42 has the added advantage that a large portion of incident radiation is reflected away from the element 40 and consequently thermal absorption of radiation having a wavelength within or outside the atmospheric window is reduced, which increases cooling efficiency.
  • the particles 44 may be composed of other suitable materials that show ionic surface plasmon resonances, such as BN and BeO. Further, the particles 44 may also be composed of materials that are not arranged for ionic plasmon generation at a wavelength within the atmospheric window wavelength range, but may be arranged for emission of radiation within that wavelength range by any other possible mechanism. For example, SiO, silicon oxynitride particles exhibit relatively strong emissions within that wavelength range .
  • the reflective material 42 improves the cooling efficiency.
  • the element may not necessarily comprise a reflective material.
  • the particles 44 may be embedded in a transparent material, such as a suitable polymeric material that is positioned upon the reflective material 42.
  • the polymeric material may comprise polyethylene or a fluorinated material .
  • the element 50 also comprises the above-described particles 44.
  • the particles 44 are positioned within a matrix of a polymeric material 54 that is largely transparent to thermal radiation within a black body wavelength range, such as radiation having a wavelength within the range of 3 - 28 ⁇ m, or a wavelength range outside one or both of 3 - 5 and 7.9 - 13 ⁇ m, or most of solar spectral range in addition to the black body radiation range.
  • the polymeric material 54 may comprise polyethylene or a fluorinated polymeric material .
  • incident radiation is not reflected, but largely transmitted through the cooling material 50, which also reduces thermal absorption of radiation directed to the element 50 and thereby improves the cooling efficiency.
  • the element 50 comprises particles 56.
  • the particles 56 have a spectrally selective property that complements a spectrally selective property of the particles 44.
  • the particles 56 are arranged for generation of electronic surface plasmons in the near infrared (NIR) wavelength range. Within that wavelength range the particles 56 absorb radiation, such as radiation originating from the sun. This inhibits transmission of a portion of incident radiation, which facilitates the cooling.
  • the cooling material 50 is arranged so that the thermal energy, that is present as a consequence of the absorbed solar radiation, is emitted by the particles 44.
  • the element 50 may be provided in the form of a skylight or a window, such as window element 18.
  • the cooling material 50 typically is arranged so that a large portion of the visible light originating from the sun can penetrate through the element 50.
  • the particles 44 emit radiation within the atmospheric window wavelength range, which results in cooling, and the particles 56 partially "block" thermal radiation originating from the sun which facilitates the cooling.
  • the particles 56 may comprise indium tin oxide, tin oxide, LaB6, SbSn oxide, or aluminium doped ZnO.
  • the particles 56 may also be arranged for generation of electronic surface plasmons at any other suitable wavelength range.
  • the element 50 may comprise a layered structure of dielectric and/or metallic materials having layer thicknesses that are selected to effect reflection of thermal radiation, such as thermal radiation originating from the atmosphere, which further facilitates cooling .
  • the element 30 may also comprise a layer structured material that is arranged so that a portion of light within the visible wavelength range is reflected and light that is transmitted though the element 50 is of a particular colour, which has advantageous applications for aesthetic purposes.
  • the element 60 corresponds to the element 50 shown in Figure 7 and described above, but is in this embodiment positioned on a reflective layer 62.
  • the element 60 is particularly suited for cooling a medium that may be in thermal contact with the cooling material 60.
  • the reflective layer 62 is a metallic layer that is arranged to reflect radiation having a wide wavelength range and originating, for example, from the sun.
  • the reflective layer 62 may be arranged to reflect the majority of thermal radiation and visible radiation originating from the sun and from the atmosphere, which facilitates cooling of the cooling material 60.
  • the reflective material may comprise for example Al, Cu, Ag, Au, Ni, Cr, Mo, W or steel including stainless steel .
  • the reflective material may not be provided in form of a layer, but may be provided in form of reflective particles that are incorporated in the material 54.
  • FIG. 9 shows the cooling system 90 which comprises an object 92.
  • the object may be a container, such as a food container, or a can, such as a beverage can.
  • the object 92 includes a top portion 94 to which the above described element for emission of thermal radiation is applied.
  • the element may be provided in the form of a coating functioning in the same manner as the elements 40, 50 and 60 described with reference to Figures 6 to 8.
  • the cooling system 90 comprises a thermally insulating housing 96 in which the object 92 is positioned. Further, the cooling system 90 comprises a lid-portion 98 which is composed of material that is transmissive for thermal radiation emitted by the particles of the element 94. Further, the cooling system 90 comprises a base portion on which the housing portion 96 and the object 92 are positioned.
  • the housing portion 96 is taller than the object 92 so that in use the likelihood of incidence of direct sunlight on the object 92 is reduced. Further, the housing portion 96 is sufficiently tall so that in use incoming radiation from the atmosphere, which is incident at angles which are closer to the horizon than to the zenith , is substantially blocked off.
  • the housing portion 96 is reflective for the thermal radiation emitted by the particles and is in use positioned so that thermal radiation emitted by the particles is directed in a direction towards Space and in a direction away from the horizon.
  • Interior wall portions of the housing portion 96 comprise a material that has low thermal emittance.
  • the lid-portion 98 creates a barrier for transfer of heat by convection and, at the same time, is transmissive for thermal energy emitted by the particles of the element 94.
  • the particles of element 94 absorb thermal energy from an adjacent portion of the object 92 and emit the absorbed thermal energy in the form of thermal radiation having a wavelength range within the atmospheric wavelength range.
  • the housing portion 96 and the base portion 100 provide thermal insulation and consequently facilitate cooling of the object 92.
  • the cooling system 90 is arranged so that the object is removable from an interior of the housing portion 96.
  • the cooling system 90 may be provided in various different forms.
  • the object 92 may not necessarily be a container for food or liquid, but may alternatively be any other type of object.
  • the element 94 may be applied to any side portion of the object and may also be in indirect thermal contact to the object.
  • the housing portion 96 may have any suitable shape.
  • the particles of the element may also be positioned in a membrane that has openings which a suitably sized to locate one or more of the particles.
  • the element may also comprise projecting wall portions, which may or may not be reflective and which are arranged so that in use it is avoided that radiation that penetrated to atmospheres at regions near the horizon.
  • the element may not necessarily comprise particles that are arranged for emission of thermal radiation having a wavelength within the atmospheric window wavelength range, but the particles may be replaced by at least one layer, such as a multi- layered structure, that is arranged for emission of thermal radiation having a wavelength within the atmospheric window wavelength range.
  • the layers of the multi -layered structure typically have thicknesses that are selected so that in use ionic surface plasmon resonances are generated and the ionic surface plasmon resonances have a wavelength or wavelength range within the atmospheric window wavelength range.
  • the multi-layered structure may comprise SiO and SiC layers having a thickness of the order of 50 - 150nm.
  • the particles may be replaced by grains of a layer having a granular structure, such as a suitable
  • the average diameter of the grains is selected so that the layer is arranged for emission of thermal radiation having a wavelength within the atmospheric window wavelength range.
  • the particles may also be replaced by a porous layer or a layer having a rough surface, such as a suitable SiC layer.
  • an average pore spacing or surface profile, respectively, is selected so that the layer is arranged for emission of thermal radiation having a wavelength within the atmospheric window wavelength range.
  • the element may comprise the above-described particles in addition to the above-described at least one layer.
  • the at least one layer and the particles may both be arranged for emission of thermal radiation having a wavelength range within the atmospheric window wavelength range.

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Abstract

The present disclosure provides an element for emission of thermal radiation. The element comprises particles arranged for receiving thermal energy and emitting at least a portion of the received thermal energy in the form of the thermal radiation. The thermal radiation predominantly has a wavelength or wavelength range within an atmospheric window wavelength range in which the atmosphere of the Earth has a reduced average absorption and emission compared with an average absorption and emission in an adjacent wavelength range whereby absorption by the element of radiation from the atmosphere is reduced.

Description

AN ELEMENT FOR EMISSION OF THERMAL RADIATION
Field of the Invention
The present invention broadly relates to an element for emission of thermal radiation.
Background of the Invention
Various methods are used to cool interior spaces of buildings, refrigerate food, condense water or reduce the temperature of objects. These methods have in common that they require relatively large amounts of energy, which typically are provided in the form of electrical energy. For example, in countries which have a relatively warm climate the electrical energy required for cooling often exceeds the available electrical energy, which may result in a breakdown of a power grid. Further, electrical energy is at this time still at least partially generated using non-renewable energy resources, for example by burning coal, which is of concern for the environment and contributes to global warming. Consequently, it would be advantageous if cooling could be achieved in a manner that uses less energy. There is a need for technological advancement .
Summary of the Invention
The present invention provides an element for emission of thermal radiation, the element comprising particles arranged for receiving thermal energy and emitting at least a portion of the received thermal energy in the form of the thermal radiation, the thermal radiation predominantly having a wavelength or wavelength range within an atmospheric window wavelength range in which the atmosphere of the Earth has a reduced average absorption and emission compared with an average absorption and emission in an adjacent wavelength range whereby absorption by the element of radiation from the atmosphere is reduced.
Because the atmosphere of the Earth has very low absorption within the atmospheric window wavelength range, only a very small amount of radiation is returned from the atmosphere to the particles within that wavelength range and emitted radiation is largely directed through the atmosphere and into Space where the typical temperature is of the order of 4 Kelvin. As a consequence, thermal energy received by the element is "pumped" away by the element .
The atmospheric window wavelength range typically includes a minimum of the average absorption of the atmosphere of the Earth. The atmosphere has atmospheric windows within the wavelength ranges of 3 to 5 μm and 7.9 μm to 13 μm. Within these wavelength ranges the emission of the sun is also negligible and often regarded as zero, which has the added advantage that even during daytime the element only absorbs very little radiation from the sun within that wavelength range.
The element according to embodiments of the present invention and a medium that may be in thermal contact with the element typically is cooled or cooling is facilitated without the need for electrical energy. In particular during the night, or when irradiation by the sun is avoided, cooling well below ambient temperature is possible .
The particles may be distributed throughout the element, which in this case also comprises a material that is substantially transmissive for radiation having a wavelength within the atmospheric window range. Alternatively, the element may comprise a surface portion, such as a coating, in which the particles are concentrated and which is arranged so that the thermal radiation can be emitted. The element may also comprise a membrane which locates the particles.
The element may also comprise a cover that may be suspended over a body portion of the element or that may be provided in the form of a cover layer that is in direct contact with the body portion. The cover typically is transmissive for the thermal radiation emitted by the particles and protects the particles from hot breezes and other external influences that could reduce the cooling efficiency. The cover typically comprises a thermally insulating material. For example, the cover may comprise a polymeric material such as polyethylene. Further, the cover may comprise an oxide or sulphide material, which typically is arranged to block at least a portion of incident UV radiation. In one specific example the oxide or sulphide material is positioned on or over the polyethylene material and also protects the polyethylene. This example combines the relative strength of typical polyethylene material with the UV protective function of the sulphide or oxide material, which also increases the lifespan of the polyethylene material. The polymeric material and the oxide or sulphide material typically are - A - arranged so that relatively high transmittance for radiation having a wavelength within the atmospheric window is retained. For example, the oxide or sulphide material may be a layer that is positioned on or over the polymeric material . The sulphide or oxide layer typically has a thickness that is selected so that in use at least the majority of incident UV radiation is blocked and the cover is substantially transmissive for radiation having a wavelength range within the atmospheric window wavelength range. The thickness of the layer typically is within the range of 100 nm - lOOOnm, 150 nm - 300 nm and typically is of the order of 200 nm.
The element may further comprise wall portions that define an interior space within which a medium that is to be cooled is in use located. The wall portions typically comprise a reflective material. The element may include thermally insulating materials and may for example form an at least partially thermally insulated container.
The element may also comprise a structure that has projecting wall portions which are positioned so that, in use, incoming radiation from regions of the atmosphere, which are near the horizon, is substantially blocked off. It is known that for such radiation the atmospheric window is less transmissive, because the atmosphere is "thicker" for radiation traveling closer to the horizon. Being less transmissive, the atmosphere then also radiates more strongly at these wavelengths from directions close to the horizon. Consequently, avoiding that such radiation can reach the particles improves the cooling efficiency of the element. The projecting wall portions typically are reflective for the thermal radiation emitted by the particles. The structure may also comprise the above- described cover.
The projecting wall portions typically are reflective for the thermal radiation emitted by the particles and may be positioned so that, in use, thermal radiation emitted by the particles or reflected by the projecting wall portions is directed in a direction towards Space and in a direction away from the horizon. The projecting wall portions typically are formed from a material that has low thermal emittance.
In one specific embodiment the element comprises a concentrator such as a "CPC" concentrator or a parabolic dish or trough concentrator. In this case the projecting wall portions typically form a portion of the concentrator. The concentrator typically is arranged so that radiation emitted form substantially all regions of the conduit is directed towards the sky by the concentrator. Further, the projecting wall portion has the added advantage that heating of the particles, and/or of the medium that is to be cooled by the particles, by a hot breeze that may in use pass over the element is reduced.
In another specific embodiment the element forms a part of, or is provided in the form of, an object and is arranged for cooling of the object and/or a medium that is in thermal contact with the object.
The element may be in contact with the portion of the object and may also be adhered to, formed on or otherwise applied to the portion of the object. In one specific embodiment the object includes a container, such as a can, in which for example food or a liquid may be located.
For example, the object may be a container, such as a food container or a container for transportation or storage of medicine, organs, blood, or anything else that is to be cooled. Further, the object may be an electronic device and the element may be arranged for cooling of the electronic device or may form a part of any means for transportation including automobiles, trucks, train carriages and shipment containers and the like, which require cooling of an interior portion.
The element may also be a part of a structure, such as a building or a house. For example, the element may be provided in the form of a window, roof tile, roof sheet or skylight. For example if the element is provided in a form that is substantially transparent for visible light, the element may comprise a substantially transparent polymeric material that comprises the particles for emission of the thermal radiation. The element may in this embodiment also comprise a honeycomb-like structure that provides additional strength. The element may further comprise a material, such as a further type of particles, that is arranged for absorbing incoming radiation in the near infrared wavelength range. In this case the element may be arranged so that the incoming near infrared radiation is absorbed and the resulting absorbed thermal energy is at least partially re-emitted in the form of thermal radiation by the particles arranged for emission of radiation having a wavelength within the atmospheric window wavelength range. A person skilled in the art will appreciate that there are many additional examples of objects which may comprise the element or which the element may form.
In embodiments of the present invention the element is arranged to enable cooling to temperatures that are 5°, 10° , 20° below an ambient temperature or even lower.
The element may also be arranged to extract heat at a finite rate at a temperature below ambient. The element may be arranged so that cooling rates such as 40, 60, 80 W per m2 of cooling material area are possible at temperatures that are 5°, 10° or more below ambient temperature.
The particles may be arranged for generation of ionic surface plasmon resonances having a wavelength or wavelength range within the atmospheric window wavelength range.
Throughout this specification the term "ionic surface plasmon" is used for a surface plasmon excitation that involves movement of ions, such as that often referred to as "Frόhlich resonance" .
The particles typically are arranged so that at least some, typically the majority or all, of the ionic surface plasmons have a wavelength within the wavelength range from 1 - 7 μm, 2 - 6 μm, or 3 - 5 μm, and/or any one of 5 - 16 μm, 7 - 14 μm, 8 - 13 μm and 7.9 - 13 μm. However, it is to be appreciated that at least a portion of the particles may also be arranged so that the ionic surface plasmons are generated at a wavelength range that is partially outside the atmospheric window wavelength range. Further, the atmospheric window wavelength range may be one of a plurality of atmospheric window ranges, such as the wavelength range of 3 - 5 μm and 7.9 to 13 μm.
In one specific embodiment of the present invention the particles comprise, or are entirely composed of, SiC or another suitable material .
At least a portion of the particles may also be arranged for emission of radiation by a physical mechanism other than that associated with the generation of ionic surface plasmons. The particles may be composed of any suitable material that is arranged for emission of radiation having a wavelength within the atmospheric window wavelength range. Alternatively or additionally, the element may comprise a material that is arranged for emission of radiation having a wavelength outside the atmospheric window range .
The element may comprise a polymeric material, such as a coating, that is transmissive for radiation of a predetermined range of wavelength. For example, the particles may be embedded in the polymeric material or may be located adjacent the polymeric material.
The element may also be arranged to reflect at least some incident radiation, such as radiation from the atmosphere and/or from the sun in the daytime. The element may comprise a reflective material that is provided in the form of a layer positioned below the particles and may be arranged to reflect at least a portion of incident radiation. Alternatively or additionally, the element may comprise reflective particles that are dispersed within an at least partially transparent material, such as the above-described polymeric material .
In one embodiment the element comprises at least one channel for a fluid whereby the element is arranged for cooling the fluid.
It is to be appreciated that in variations of the above- described embodiments the element may not necessarily comprise particles that are arranged for emission of thermal radiation having a wavelength within the atmospheric window wavelength range, but the particles may be replaced by at least one layer that is arranged for emission of thermal radiation having a wavelength within the atmospheric window wavelength range. For example, the at least one layer may comprise a granular structure, a porous structure or may have a surface that is profiled so that the at least one layer is arranged for generation of ionic surface plasmon resonances having a wavelength or wavelength range within the atmospheric window wavelength range. Alternatively, the at least one layer may be a part of a multi-layered structure that is arranged for generation of ionic surface plasmon resonances having a wavelength or wavelength range within the atmospheric window wavelength range.
The present invention provides in a second aspect an element for emission of thermal radiation, the element comprising at least one layer that is arranged for receiving thermal energy and emitting at least a portion of the received thermal energy in the form of the thermal radiation, the thermal radiation predominantly having a wavelength or wavelength range within an atmospheric window wavelength range in which the atmosphere of the Earth has a reduced average absorption and emission compared with an average absorption and emission in an adjacent wavelength range whereby absorption by the element of radiation from the atmosphere is reduced.
The atmospheric window wavelength range typically is a wavelength range from 3 to 5 μm and/or from 7.9 μm to 13 μm.
The at least one layer typically is arranged for generation of ionic surface plasmon resonances having a wavelength of wavelength range within the atmospheric window wavelength range.
The at least one layer may have a structural property that is selected so that the at least one layer is arranged for generation of ionic surface plasmon resonances having a wavelength or wavelength range within the atmospheric window wavelength range. For example, the at least one layer may comprise grains, or may at least in part be of a porous structure and the structural property may be associated with a grain size or a thickness of residual solid between pores, respectively. Further, the at least one layer may have a surface roughness and the structural property may be associated with thickness or width of surface features of the at least one layer. The grain size, the thickness of residual solid between pores and - li the thickness or width of surface features of the at least one layer typically are within the range of 50nm - 150nm.
Alternatively, the at least one layer may be a part of a multi-layered structure having layer thicknesses that are selected so that the multi -layered structure is arranged for generation of ionic surface plasmon resonances having a wavelength or wavelength range within the atmospheric window wavelength range.
The present invention provides in a third aspect a cooling system comprising the above-described element in accordance with the first or second aspect of the present invention, the element forming a part of an object and the cooling system comprising a thermally insulating wall portion for reducing exchange of thermal energy between a portion of the object an environment of the cooling system.
The element may be in contact with the portion of the object and may also be adhered to, formed on or otherwise applied to the portion of the object.
The object may include a container, such as a can, in which for example food or a liquid may be located.
The thermally insulating wall portion typically is arranged so that the element of the object is in use enabled to emit thermal radiation in a direction away from the cooling system. The cooling system typically is also arranged so that the object is positionable in, and removable from, an interior formed by the thermally insulating wall portion. The cooling system may further comprise a removable lid- portion and a base portion that together with the thermally insulating wall portion form an enclosure in which in use the object is positioned, the lid-portion being formed from a material that is transmissive for thermal radiation emitted by the particles of the element
The invention will be more fully understood from the following description of specific embodiments of the invention. The description is provided with reference to the accompanying drawings .
Brief Description of the Drawings
Figure 1 shows an a device incorporating an element for emission of thermal radiation according to an embodiment of the present invention;
Figures 2, 3 (a), 3 (b) and 4 show objects incorporating an element for emission of thermal radiation according to an embodiment of the present invention;
Figure 5 shows a transmission spectrum of the atmosphere of the Earth as a function of wavelength;
Figures 6 - 8 show elements for emission of thermal radiation according to embodiments of the present invention; and
Figure 9 shows a a cooling system according to a specific embodiment of the present invention.
Detailed Description of Specific Embodiments
Generally, the element comprises particles that are arranged for emission of radiation having a wavelength within a range referred to as the "atmospheric window wavelength range" . The atmospheric window wavelength range is a wavelength range within which the absorption and emission of radiation by the atmosphere of the Earth is strongly reduced or zero. Radiation .emitted from the element within that wavelength range is largely transmitted through the atmosphere to Space where the average temperature is 4 Kelvin. Further, as within that wavelength range typically very little or no radiation is received by the element, the element functions as a pump of thermal energy.
The element comprises a cooling material that is disclosed in Australian provisional patent application No 2007903673 and US patent application No .11/765217. These patent applications are hereby incorporated by cross-reference.
Further details of the function of the element will be discussed with reference to Figures 4-7.
Referring initially to Figures 1-3, examples of elements and objects incorporating the element according to specific embodiments of the present invention are now described.
Figure 1 shows a cooling element 10 in accordance with an embodiment of the present invention. For example, the element 10 may be arranged for cooling a medium that is in thermal contact with a portion of the element 10. The element 10 is arranged so that thermal radiation can be emitted from surface portion 12 to the atmosphere either directly or indirectly. The element 10 is arranged so that a portion of the thermal energy received from the medium is emitted by the element 10 in the form of thermal radiation so that cooling of the medium is facilitated by the element 10.
The cooling element 10 may form a part of an evaporative cooling device. In this case the element 10 typically is arranged to cool a liquid, typically water, prior to evaporation. Alternatively, the element 10 may form a part of any other type of air-conditioning device and the element 10 may be arranged for facilitating cooling of a fluid that in use circulates though portions of the air- conditioning unit.
Further, the element 10 may form a part of be a radiator, heat exchanger, or refrigerator or any other type of cooling device. A person skilled in the art will appreciate that there are numerous examples of cooling devices in which the element 10 may be incorporated.
Figure 2 shows an example of a structure 14 in which an element for emission of the thermal radiation according to embodiments of the present invention is incorporated. The structure 14 is in this embodiment a house or building or the like and includes roof-covering and/or other external coverings that are provided in the form of objects 16.
For example, each object 16 may be a roof tile or a roof- sheet which comprises a metallic, ceramic or polymeric material. The object 16 comprises a surface portion that incorporates the particles for emission of the thermal radiation and is positioned over the metallic, ceramic or polymeric material. For example, the particles may be embedded in a coating material that is applied by painting or otherwise to the metallic, ceramic or polymeric material of the object 16. The coating material is substantially transmissive for radiation having a wavelength within the atmospheric window wavelength range. Alternatively, the particles may be positioned on a surface portion of the object 16 without being embedded in a coating material.
The object 16 is arranged so that thermal radiation is emitted which results in cooling of a roof space of the house or building 14. This particular application has significant advantages in particular for warmer regions of the Earth. During hot summer days roof spaces gain a substantial amount of thermal energy and often maintain a substantial portion of that thermal energy during the night. The element 16 facilitates cooling of the roof space and thereby improves comfort of living in the house or building 14. In one specific embodiment of the present invention large portions of the external surface, such as the roof area of a house or building 14, are covered by the object 16.
Referring again to Figure 2, the structure 14 may also include further objects that incorporate an element for emission of the thermal radiation and that are provided in the form of windows, such as window 18. The window 18 is arranged so that a portion of near-infrared radiation is blocked.
Referring now to Figure 3 (a) , a further example of an object that incorporates the element 10 for emission of thermal radiation is now described. The object 20 is in this example a container for containing food, medical articles, blood or organs and the like or any other objects or matter that requires cooling. An external surface portion of the object 20 comprises the particles arranged for emission of thermal radiation. Emission of the thermal radiation results in cooling of the container 20 and an interior portion thereof.
Figure 3 (b) shows an example of a further variation of a container that includes the element 12. In this case the container 22 has wall portions 24 that are composed of a thermally insulating material. The container 22 also comprises a top portion 26 that is composed of a material that is substantially transmissive for the thermal radiation having a wavelength range within the atmospheric window wavelength range. The top portion may also have thermally insulating properties and may for example comprise iron oxide or ZnS. A medium that is to be cooled is positioned adjacent the element 12. This embodiment has the added advantage that the thermally insulating wall portions further increase the cooling efficiency. Further, the elememt lOand the medium that is to be cooled are protected from any hot breezes that may also reduce the cooling efficiency.
A person skilled in the art will appreciate that there are numerous examples of objects in which the element for emission of thermal radiation maybe incorporated. For example, the element may form a portion of an electronic device, such as an integrated electronic device, and may be arranged for cooling of the electronic device.
Figure 4 shows a structure 28 that is largely transmissive for visible radiation and may be used as a roof-sheet, window or sky light and the like. The structure 28 comprises a first layer 30 and a second layer 32. The first layer 30 and the second layer 32 are connected by members 34 so that a honey-comb like structure is formed tat is relatively stabile. The structure 28 comprises a polymeric material and has particles incorporated within that material so that the structure 28 has advantages analogous to those of the above-discussed element.
A person skilled in the art will also appreciate that the cooling element has numerous applications for cooling objects, or fluids. If an object or fluid is to be cooled, the cooling element may be arranged to cool the object or fluid directly. Alternatively, the cooling element may be arranged for cooling the object or fluid indirectly by cooling another fluid of material, which then cools the fluid or object that is to be cooled.
Referring now to Figures 5 and 6, the function of the element for emission of thermal radiation according to a specific embodiment of the present invention are now described in further detail . Figure 5 shows a transmission spectrum 34 of the atmosphere of the Earth for substantially cloud free conditions. The average transmission is increased to nearly 1 within the range of approximately 7.9 to 13 μm compared to adjacent wavelength ranges. Further, the average transmission of the atmosphere is increased within a wavelength range of 3 - 5 μm. Within these wavelength ranges the atmosphere of the Earth has "windows" . Plot 36 is an estimation of the emission spectrum of a black body having a temperature of
1000C, which was calculated using Wein's law and gives an example of the emission spectrum for a medium that may be cooled using the cooling material according to embodiments of the present invention.
Figure 6 shows a secondary electron microscopy micrograph of a surface portion of the element according to a specific embodiment of the present invention.
The element 40 comprises a reflective metallic layer 42, which in this embodiment is provided in the form of an aluminum layer positioned on a substrate. Further, the element 40 comprises SiC particles 44, which are positioned on the metallic layer 42. The SiC particles 44 have an average diameter of approximately 50 nm and are deposited using suitable spin coating procedures.
The SiC particles 44 are in this embodiment nano-particles and the majority of the surface of the particles 44 is exposed to air. The particles 44 show resonantly enhanced absorption and emission of radiation at a wavelength range of 10 to 13 μm. Within that wavelength range ionic surface plasmons are generated. The wavelength range of resonant ionic surface plasmon emission is within the above- described atmospheric window wavelength range. For that wavelength range the average absorption of the atmosphere of the Earth is very low and consequently very little radiation in this wavelength range is transferred from the atmosphere to the element 40.
The energy associated with the emitted radiation is largely drawn from the thermal energy of the particles 44 and/or from a medium that is in thermal contact with the particles 44. Due to the atmospheric window, the emitted radiation is largely transmitted through the atmosphere and directed to Space where the temperature typically is 4 Kelvin. Consequently, the element 40 functions as a pump of thermal energy even if the cooling material, or a medium that is in thermal contact with the cooling material, has a temperature below ambient temperature.
The reflective material 42 has the added advantage that a large portion of incident radiation is reflected away from the element 40 and consequently thermal absorption of radiation having a wavelength within or outside the atmospheric window is reduced, which increases cooling efficiency.
In variations of the above-described embodiment the particles 44 may be composed of other suitable materials that show ionic surface plasmon resonances, such as BN and BeO. Further, the particles 44 may also be composed of materials that are not arranged for ionic plasmon generation at a wavelength within the atmospheric window wavelength range, but may be arranged for emission of radiation within that wavelength range by any other possible mechanism. For example, SiO, silicon oxynitride particles exhibit relatively strong emissions within that wavelength range .
The reflective material 42 improves the cooling efficiency. However, it is to be appreciated that the element may not necessarily comprise a reflective material. Further, the particles 44 may be embedded in a transparent material, such as a suitable polymeric material that is positioned upon the reflective material 42. For example, the polymeric material may comprise polyethylene or a fluorinated material . Referring now to Figure 7, an element according to a second specific embodiment of the present invention is now described.
In this embodiment the element 50 also comprises the above-described particles 44. In this example, however, the particles 44 are positioned within a matrix of a polymeric material 54 that is largely transparent to thermal radiation within a black body wavelength range, such as radiation having a wavelength within the range of 3 - 28 μm, or a wavelength range outside one or both of 3 - 5 and 7.9 - 13 μm, or most of solar spectral range in addition to the black body radiation range. For example, the polymeric material 54 may comprise polyethylene or a fluorinated polymeric material .
In contrast to the element 40, incident radiation is not reflected, but largely transmitted through the cooling material 50, which also reduces thermal absorption of radiation directed to the element 50 and thereby improves the cooling efficiency.
In addition, the element 50 comprises particles 56. In general, the particles 56 have a spectrally selective property that complements a spectrally selective property of the particles 44. In this example, the particles 56 are arranged for generation of electronic surface plasmons in the near infrared (NIR) wavelength range. Within that wavelength range the particles 56 absorb radiation, such as radiation originating from the sun. This inhibits transmission of a portion of incident radiation, which facilitates the cooling. In this embodiment the cooling material 50 is arranged so that the thermal energy, that is present as a consequence of the absorbed solar radiation, is emitted by the particles 44.
For example, the element 50 may be provided in the form of a skylight or a window, such as window element 18. In this case the cooling material 50 typically is arranged so that a large portion of the visible light originating from the sun can penetrate through the element 50. The particles 44 emit radiation within the atmospheric window wavelength range, which results in cooling, and the particles 56 partially "block" thermal radiation originating from the sun which facilitates the cooling.
For example, the particles 56 may comprise indium tin oxide, tin oxide, LaB6, SbSn oxide, or aluminium doped ZnO.
It is to be appreciated, however, that in variations of the above-described embodiment the particles 56 may also be arranged for generation of electronic surface plasmons at any other suitable wavelength range.
In addition, the element 50 may comprise a layered structure of dielectric and/or metallic materials having layer thicknesses that are selected to effect reflection of thermal radiation, such as thermal radiation originating from the atmosphere, which further facilitates cooling .
Further, the element 30 may also comprise a layer structured material that is arranged so that a portion of light within the visible wavelength range is reflected and light that is transmitted though the element 50 is of a particular colour, which has advantageous applications for aesthetic purposes.
With reference to Figure 8 an element 60 according to another specific embodiment of the present invention is now described. The element 60 corresponds to the element 50 shown in Figure 7 and described above, but is in this embodiment positioned on a reflective layer 62. The element 60 is particularly suited for cooling a medium that may be in thermal contact with the cooling material 60. In this embodiment the reflective layer 62 is a metallic layer that is arranged to reflect radiation having a wide wavelength range and originating, for example, from the sun.
For example, the reflective layer 62 may be arranged to reflect the majority of thermal radiation and visible radiation originating from the sun and from the atmosphere, which facilitates cooling of the cooling material 60. The reflective material may comprise for example Al, Cu, Ag, Au, Ni, Cr, Mo, W or steel including stainless steel .
In a variation of the embodiment shown in Figure 8, the reflective material may not be provided in form of a layer, but may be provided in form of reflective particles that are incorporated in the material 54.
The elements 50 and 60 may be incorporated into the cooling device 10 or objects 16 and 20. The element 60 has particularly advantageous applications as window or skylight, such as window 18. Referring now to Figure 9, a cooling system in accordance with an embodiment of the present invention is now described. Figure 9 shows the cooling system 90 which comprises an object 92. For example, the object may be a container, such as a food container, or a can, such as a beverage can. The object 92 includes a top portion 94 to which the above described element for emission of thermal radiation is applied. For example, the element may be provided in the form of a coating functioning in the same manner as the elements 40, 50 and 60 described with reference to Figures 6 to 8.
In this embodiment, the cooling system 90 comprises a thermally insulating housing 96 in which the object 92 is positioned. Further, the cooling system 90 comprises a lid-portion 98 which is composed of material that is transmissive for thermal radiation emitted by the particles of the element 94. Further, the cooling system 90 comprises a base portion on which the housing portion 96 and the object 92 are positioned. In this embodiment, the housing portion 96 is taller than the object 92 so that in use the likelihood of incidence of direct sunlight on the object 92 is reduced. Further, the housing portion 96 is sufficiently tall so that in use incoming radiation from the atmosphere, which is incident at angles which are closer to the horizon than to the zenith , is substantially blocked off. The housing portion 96 is reflective for the thermal radiation emitted by the particles and is in use positioned so that thermal radiation emitted by the particles is directed in a direction towards Space and in a direction away from the horizon. Interior wall portions of the housing portion 96 comprise a material that has low thermal emittance.
The lid-portion 98 creates a barrier for transfer of heat by convection and, at the same time, is transmissive for thermal energy emitted by the particles of the element 94.
In use, the particles of element 94 absorb thermal energy from an adjacent portion of the object 92 and emit the absorbed thermal energy in the form of thermal radiation having a wavelength range within the atmospheric wavelength range. The housing portion 96 and the base portion 100 provide thermal insulation and consequently facilitate cooling of the object 92. The cooling system 90 is arranged so that the object is removable from an interior of the housing portion 96.
It is to be appreciated, however, that the cooling system 90 may be provided in various different forms. For example, the object 92 may not necessarily be a container for food or liquid, but may alternatively be any other type of object. Further, the element 94 may be applied to any side portion of the object and may also be in indirect thermal contact to the object. In addition, the housing portion 96 may have any suitable shape.
Although the invention has been described with reference to particular examples, it will be appreciated by those skilled in the art that the invention may be embodied in many other forms. For example, the particles of the element, such as element 50 or 60 shown in Figures 7 and 8, may also be positioned in a membrane that has openings which a suitably sized to locate one or more of the particles. In addition, the element may also comprise projecting wall portions, which may or may not be reflective and which are arranged so that in use it is avoided that radiation that penetrated to atmospheres at regions near the horizon.
Further, it is to be appreciated that in variations of the above-described embodiments the element may not necessarily comprise particles that are arranged for emission of thermal radiation having a wavelength within the atmospheric window wavelength range, but the particles may be replaced by at least one layer, such as a multi- layered structure, that is arranged for emission of thermal radiation having a wavelength within the atmospheric window wavelength range. The layers of the multi -layered structure typically have thicknesses that are selected so that in use ionic surface plasmon resonances are generated and the ionic surface plasmon resonances have a wavelength or wavelength range within the atmospheric window wavelength range. For example, the multi-layered structure may comprise SiO and SiC layers having a thickness of the order of 50 - 150nm.
Alternatively, the particles may be replaced by grains of a layer having a granular structure, such as a suitable
SiC layer. In this case the average diameter of the grains is selected so that the layer is arranged for emission of thermal radiation having a wavelength within the atmospheric window wavelength range. The particles may also be replaced by a porous layer or a layer having a rough surface, such as a suitable SiC layer. In this case an average pore spacing or surface profile, respectively, is selected so that the layer is arranged for emission of thermal radiation having a wavelength within the atmospheric window wavelength range.
In addition, it is to be appreciated that the element may comprise the above-described particles in addition to the above-described at least one layer. The at least one layer and the particles may both be arranged for emission of thermal radiation having a wavelength range within the atmospheric window wavelength range.

Claims

Claims :
1. An element for emission of thermal radiation, the element comprising particles arranged for receiving thermal energy and emitting at least a portion of the received thermal energy in the form of the thermal radiation, the thermal radiation predominantly having a wavelength or wavelength range within an atmospheric window wavelength range in which the atmosphere of the Earth has a reduced average absorption and emission compared with an average absorption and emission in an adjacent wavelength range whereby absorption by the element of radiation from the atmosphere is reduced.
2. The element of claim 1 wherein the atmospheric window wavelength range includes a minimum of the average absorption of the atmosphere of the Earth.
3. The element of claim 1 or 2 wherein the atmospheric window wavelength range is a wavelength range from 3 to 5 μm and/or from 7.9 μm to 13 μm.
4. The element of any one of the preceding claims wherein the particles are distributed throughout the element and the element also comprises a material that is substantially transmissive for radiation having a wavelength within the atmospheric window range.
5. The element of any one of claims 1 - 3 comprising a surface portion in which the particles are concentrated and which is arranged so that the thermal radiation can be emitted.
6. The element of any one of claims 1 - 3 comprising a membrane which locates the particles.
7. The element of any one of the preceding claims comprising a cover that is substantially transmissive for the thermal radiation.
8. The element of claim 7 wherein the cover is provided in the form of a cover layer.
9. The element claim 7 wherein the cover is arranged for reduction of exchange of thermal energy by convection.
10. The element of any one of claims 7 to 9 wherein the cover comprises a polymeric material .
11. The element of claim 10 wherein the cover comprises polyethylene .
12. The element of anyone of claims 7 to 11 wherein the cover comprises an oxide or sulphide material .
13. The element of claim 12 when dependent on claim 10 or 11 wherein the oxide or sulphide material is positioned over the polyethylene material.
14. The element of claim 13 wherein the oxide or sulphide material is a layer that is positioned on the polymeric material .
15. The element of claim 14 wherein the layer of sulphide or oxide material has a thickness that is selected so that in use at least the majority of incident UV radiation is blocked and the cover is substantially transmissive for radiation having a wavelength range within the atmospheric window wavelength range.
16. The element of claim 15 wherein the thickness of the layer is within the range of lOOnm - lOOOnm.
17. The element of any one of the preceding claims further comprising wall portions that define an interior space within which a medium that is to be cooled is in use located.
18. The element of claim 17 wherein the wall portions comprise a reflective material.
19. The element of claim 17 or 18 wherein at least some of the wall portions are thermally insulating.
20. The element of any one of the preceding claims comprising a structure that has projecting wall portions which are positioned so that, in use, incoming radiation from regions of the atmosphere, which are near the horizon, is substantially blocked off.
21. The element of any one of the preceding claims comprising a structure that has projecting wall portions that are reflective for the thermal radiation emitted by the particles.
22. The element of any one of the preceding claims comprising a structure that has projecting wall portions which are positioned so that, in use, thermal radiation emitted by the particles or reflected by the projecting the walls is directed in a direction towards Space and in a direction away from the horizon.
23. The element of any one of the preceding claims comprising a structure that has projecting wall portions which are formed from a material that has low thermal emittance .
24. The element of any one of claims 1 to 19 comprising a concentrator.
25. The element of any one of the preceding claims wherein the particles are arranged for generation of ionic surface plasmon resonances having a wavelength or wavelength range within the atmospheric window wavelength range .
26. The element of claim 25 wherein the particles are arranged so that at least some of the ionic surface plasmons have a wavelength within the wavelength range from 7.9 - 13 μm.
27. The element of any one of the preceding claims wherein the element forms a part of, or is provided in the form, a window.
28. The element of any one of claims 1 to 26 wherein the element forms a part of, or is provided in the form, a roof tile.
29. The element of any one of claims 1 to 26 wherein the element forms a part of, or is provided in the form, a roof sheet .
30. The element of any one of claims 1 to 26 wherein the element forms a part of, or is provided in the form, a skylight .
31. The element of claim 27 to 30 wherein the element is substantially transparent for visible light, and wherein the element comprises a substantially transparent polymeric material that comprises the particles for emission of the thermal radiation.
32. The element of claim 31 being arranged so that in use at least a portion of the incoming near infrared radiation is absorbed and the resulting absorbed thermal energy is at least partially re-emitted in the form of thermal radiation by the particles arranged for emission of radiation having a wavelength within the atmospheric window wavelength range.
33. The element of any one of claims 1 - 26 wherein the element forms a part of an object.
34. The element of claim 33 wherein the element is applied to a portion of the object.
35. The element of claim 34 wherein the element is in contact with the portion of the object.
36. The element of claim 34 wherein the element is adhered to the portion of the object.
37. The element of claim 34 wherein the element is formed on the portion of the object.
38. The element of any one of claims 33 to 37 wherein the object includes a container.
39. The element of claim 38 wherein the object includes a can.
40. The element of claim 38 or 39 wherein the object includes food.
41. The element of claim 38 or 39 wherein the object includes a liquid.
42. A cooling system comprising the element of any one of claims 33 to 41, the cooling system comprising a thermally insulating wall portion for reducing exchange of thermal energy between a portion of the object and an environment of the cooling system.
43. The cooling system of claim 42 wherein the thermally insulating wall portion is arranged so that the element is in use enabled to emit thermal radiation in a direction away from the cooling system.
44. The cooling system of claim 42 or 43 wherein the cooling system is arranged so that the object is positionable in, and removable from, an interior formed by the thermally insulating wall portion.
45. The cooling system of claim 44 further comprising a removable lid-portion and a base portion that together with the thermally insulating wall portion form an enclosure in which in use the object is positioned, the lid-portion being formed from a material that is transmissive for thermal radiation emitted by the particles of the element.
46. An element for emission of thermal radiation, the element comprising at least one layer arranged for receiving thermal energy and emitting at least a portion of the received thermal energy in the form of the thermal radiation, the thermal radiation predominantly having a wavelength or wavelength range within an atmospheric window wavelength range in which the atmosphere of the Earth has a reduced average absorption and emission compared with an average absorption and emission in an adjacent wavelength range whereby absorption by the element of radiation from the atmosphere is reduced.
47. The element of claim 46 wherein the atmospheric window wavelength range is a wavelength range from 3 to 5 μm and/or from 7.9 μm to 13 μm.
48. The element of claim 46 or 47 wherein the at least one layer is arranged for generation of ionic surface plasmon resonances having a wavelength or wavelength range within the atmospheric window wavelength range.
49. The element of any one of claims 46 or 47 wherein the at least one layer has a structural property that is selected so that the at least one layer is arranged for generation of ionic surface plasmon resonances having a wavelength or wavelength range within the atmospheric window wavelength range.
50. The element of claim 49 wherein the at least one layer comprises grains and wherein the structural property is associated with a diameter of the grains and the grain diameter is selected so that the at least one layer is arranged for generation of ionic surface plasmon resonances having a wavelength or wavelength range within the atmospheric window wavelength range.
51. The element of claim 49 wherein the at least one layer comprises pores and wherein the structural property is associated with a thickness of residual solid the between the pores and wherein the thickness of the residual solid between the pores is selected so that the at least one layer is arranged for generation of ionic surface plasmon resonances having a wavelength or wavelength range within the atmospheric window wavelength range .
52. The element of claim 49 wherein the at least one layer has a surface roughness and the structural property is associated with a thickness or width of surface features of the surface of the at least one layer and wherein the thickness or width of the surface features is selected so that the at least one layer is arranged for generation of ionic surface plasmon resonances having a wavelength or wavelength range within the atmospheric window wavelength range.
53. The element of any one of claims 46 to 48 wherein the at least one layer is a part of a multi -layered structure having layer thicknesses that are selected so that the multi-layered structure is arranged for generation of ionic surface plasmon resonances having a wavelength or wavelength range within the atmospheric window wavelength range .
EP08756972A 2007-06-19 2008-06-19 An element for emission of thermal radiation Withdrawn EP2162688A1 (en)

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AU2007202832A AU2007202832A1 (en) 2007-06-19 2007-06-19 A cooling material
US97630607P 2007-09-28 2007-09-28
AU2007221733A AU2007221733A1 (en) 2007-06-19 2007-09-28 An element for emission of thermal radiation
PCT/AU2008/000892 WO2008154692A1 (en) 2007-06-19 2008-06-19 An element for emission of thermal radiation

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WO2008154692A1 (en) 2008-12-24
KR20100062993A (en) 2010-06-10
WO2008154693A1 (en) 2008-12-24
CN101784845A (en) 2010-07-21

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