DE GRAEVE, Wim (Motte 22, Vloesberg, B-7880, BE)
| CLAIMS 1. A heat pump system for concentrating energy contained in infra red radiation produced by an emitting surface, comprising : • A passive concentrator package (4,5,14) comprising means to concentrate IR-radiation, said package comprising one or more IR-emitting surfaces, • A conversion means (6) for converting the IR radiation thus concentrated, into another form of energy, • Possibly one or more additional IR-emitting surfaces (3,11,12,13), arranged to produce IR radiation which can be concentrated by said concentrator package. 2. Heat pump according to claim 1, wherein none of said emitter surfaces is coupled to an external heating source. 3. Heat pump system according to claim 1, wherein said concentrator package comprises at least one lens (5) and/or at least one mirror (4,14) . 4. Heat pump according to any one of the preceding claims, wherein at least a portion of the emitting surfaces is provided in the form of a functionalized surface configured to produce, from said surface, infra red radiation, the energy of said radiation being higher in the direction perpendicular to the emitting surface, compared to the energy of radiation in the other directions . 5. Heat pump according to claim 4, wherein said concentrator package comprises at least one lens or mirror, and wherein furthermore at least a portion of the surfaces of said lens or mirror are provided with such a functionalized surface. 6. Heat pump according to any one of the preceding claims, wherein said heat pump comprises an enclosure (1,10), encircling a cavity (2,20), defined by at least a substantially flat surface (3) and a curved surface (4) facing said flat surface, wherein said flat surface forms at least a portion of said emitting surface, and wherein said curved surface (4) is a mirror. 7. Heat pump according to claim 6, further comprising a lens (5) arranged in proximity to said substantially flat surface (3) . 8. Heat pump according to claim 6 or 7, wherein said curved surface is a circumferential paraboloid (4) whose symmetry axis (7) is perpendicular to the substantially flat surface (3) . 9. Heat pump according to claim 6 or 7, wherein said curved surface (4) is a concave spherical surface (14) . 10. Heat pump according to claim 8, wherein said conversion means (6) is located in a position corresponding to the focal point of said paraboloid (4) . 11. Heat pump according to claim 9, wherein said conversion means (6) is located in a position corresponding to the centre of curvature of said spherical surface (14) . 12. Heat pump according to any one of claims 9 to 11, wherein said conversion means (6) is located in a position corresponding to a focal point of said lens (5) . 13. Heat pump according to any one of the preceding claims, further comprising an energy recuperating means (8,17) coupled to said conversion means (6), and configured to remove energy from said conversion means (6) . 14. Heat pump according to claim 13, wherein said conversion means (6) comprises a means for converting IR-radiation into thermal energy, and wherein said conversion means (6) further comprises or is connected to a heat exchanging means, and wherein said recuperation means comprises a conductor (8), arranged for allowing a fluid to flow therein, said fluid being heated in said heat exchanging means . 15. Heat pump according to claim 13, wherein said conversion means comprises a photovoltaic cell, and wherein said recuperation means comprises electrical network means configured to collect electrical energy generated by said photovoltaic cell. 16. Heat pump according to any one of the preceding claims, further comprising an external heat source (30,31), configured to heat up at least a portion of said emitting surfaces (4,14,3,11) . 17. Heat pump according to claim 16, wherein said external heat source is a heat exchanger means (31), arranged in contact with said portion of the emitting surfaces (4,14,3,11), and comprising conductors arranged to allow the flow of a heated fluid therein, to thereby heat up said portion of the emitting surfaces (4,14,3,11) . 18. Heat pump according to claim 17, wherein the conversion means (6) comprises or is connected to a further heat exchanging means, and wherein said recuperating means comprises a conductor (8,17), arranged for allowing a fluid to flow therein, said fluid being heated in said further heat exchanging means, and wherein said conductor (8) is coupled back via a feedback connection (32) to the heat exchanger means (31) coupled to said portion of the emitting surfaces (4,14,3,11) . |
Field of the Invention
[0001] The present invention is related to a heat pump configured to capture and concentrate energy contained in infra red radiation produced by an emitting surface.
State of the art
[0002] The purpose of a heat pump (energy pump) is to collect (massive, free or wasted) available low density energy that cannot be used in an economical /practical application (for instance outside air at 12°C) and compress it so to obtain high density energy that has a density level high enough to be used in economical/practical applications (for instance water at 50 0 C) . A typical example is the air to water heat pump used for domestic heating. It uses the outside air to collect & compress its energy content so that the water that comes out has a temperature high enough to be used for convection home heating systems. The energy we use for increasing the energy density should be lower than the total amount of compressed energy coming out. This ratio is well known and defined as the COP, Coefficient Of Performance. A typical air to water heat pump might attain a COP of 3 to 4 when working in ideal conditions.
[0003] Present heat pumps are typically based upon the well known Carnot cycle. Although we will not describe this cycle we do need to point out two essential elements of such a cycle. The first element is the use of an intermediate energy carrier (like Freon) which undergoes a phase change during the process. Typically it knows a phase change between gas and liquid state (and vice versa) . A second important element is a compression and expansion phase of the intermediate energy carrier. In a Carnot cycle this is typically a compressor and evaporator. [0004] The use of Carnot cycles in present heat pump systems has certain limitations. First of all : depending on the properties of the intermediate carrier, the in/out temperature band in which it can work at a good efficiency is limited. For instance present air to water pumps will have a good COP when outside air temp is above 10 0 C, lower outside air temps will make COP drop fast and below 0 0 C it often is no longer functioning. Secondly, the Carnot cycle uses a compressor, an intermediate energy carrier and a compressor/evaporator. These are mechanical and chemical elements that might fail or be toxic/environmentally unfriendly.
Summary of the invention
[0005] The present invention aims to overcome the above cited limitations. To this effect, the invention is related to a heat pump system as disclosed in the appended claims .
[0006] In particular, the invention is related to a heat pump system for concentrating energy contained in infra red radiation produced by an emitting surface, comprising :
• A passive concentrator package comprising means to concentrate IR-radiation, said package comprising one or more IR-emitting surfaces, • A conversion means for converting the IR radiation thus concentrated, into another form of energy,
• Possibly one or more additional IR-emitting surfaces, arranged to produce IR radiation which can be concentrated by said concentrator package.
The heat pump system preferably comprises an enclosure, which can be substantially sealed off from the environment, said enclosure comprising said concentrator package, said conversion means and said possible additional emitting surfaces.
[0007] According to an embodiment of the invention, none of said emitter surfaces is coupled to an external heating source. [0008] Said concentrator package may comprise at least one lens and/or at least one mirror.
[0009] In a heat pump of the invention, at least a portion of the emitting surfaces may be provided in the form of a functionalized surface configured to produce, from said surface, infra red radiation, the energy of said radiation being higher in the direction perpendicular to the emitting surface, compared to the energy of radiation in the other directions.
[0010] According to an embodiment, said concentrator package comprises at least one lens or mirror, and furthermore at least a portion of the surfaces of said lens or mirror are provided with such a functionalized surface. [0011] According to an embodiment, said heat pump comprises an enclosure, encircling a cavity, defined by at least a substantially flat surface and a curved surface facing said flat surface, wherein said flat surface forms at least a portion of said emitting surface, and wherein said curved surface is a mirror. Said heat pump according to the previous embodiment may further comprise a lens arranged in proximity to said substantially flat surface. [0012] Said curved surface may be a circumferential paraboloid whose symmetry axis is perpendicular to the substantially flat surface. Said curved surface may be a concave spherical surface.
[0013] Said conversion means may be located in a position corresponding to the focal point of said paraboloid. [0014] Said conversion means may be located in a position corresponding to the centre of curvature of said spherical surface.
[0015] Said conversion means may be located in a position corresponding to a focal point of said lens. [0016] A heat pump according to an embodiment of the invention may further comprise an energy recuperating means coupled to said conversion means, and configured to remove energy from said conversion means. [0017] In the latter embodiment, said conversion means may comprise a means for converting IR-radiation into thermal energy, and said conversion means may further comprise or be connected to a heat exchanging means, and wherein said recuperation means comprises a conductor, arranged for allowing a fluid to flow therein, said fluid being heated in said heat exchanging means.
[0018] Alternatively in said latter embodiment, said conversion means may comprise a photovoltaic cell, and said recuperation means may comprise electrical network means configured to collect electrical energy generated by said photovoltaic cell.
[0019] A heat pump according to the invention may further comprise an external heat source, configured to heat up at least a portion of said emitting surfaces. [0020] In the latter embodiment, said external heat source may be a heat exchanger means, arranged in contact with said portion of the emitting surfaces, and comprising conductors arranged to allow the flow of a heated fluid therein, to thereby heat up said portion of the emitting surfaces .
[0021] In the embodiment of the previous paragraph, the conversion means may comprise or be connected to a further heat exchanging means, and said recuperating means may comprise a conductor, arranged for allowing a fluid to flow therein, said fluid being heated in said further heat exchanging means, and wherein said conductor is coupled back via a feedback connection to the heat exchanger means coupled to said portion of the emitting surfaces. [0022] The present invention is a totally new concept of heat pump that eliminates mentioned limitations. In the new heat pump system we do not use a phase change of an intermediate energy carrier. Instead we do a double conversion of the energy state itself. We first convert mechanical energy (vibration of atoms) into electromagnetic radiation (for instance infrared light) . Later we will do the reverse and convert the electromagnetic radiation back into mechanical energy or even directly into electricity & mechanical energy. [0023] In between these two conversions we cannot use a compressor/evaporator to increase the energy density. Electromagnetic radiation is an energy state with no mass, pure energy. Instead we will use an optical system (like for example a concentrator lens or for example a parabolic mirror) to focus/bundle the infrared radiation. In a reverse way this optical packet may also be conceived to expand the infrared radiation. Brief description of the figures
[0024] Figure 1 describes a heat pump according to a first embodiment of the invention.
[0025] Figure 2 describes a heat pump according to a second embodiment.
[0026] Figures 3 and 4 show details of functional surfaces which can be applied in particular embodiments of the invention.
[0027] Figure 5 shows the embodiment of figure 2, further provided with an external heating means.
[0028] Figure 6 shows the embodiment of figure 5, further provided with a feedback connection.
[0029] Figure 7 shows the embodiment of figure 1, further provided with an external heating means. [0030] Figures 8a and 8b shows an experimental setup used as the basis for the exemplary data shown in the present description.
Detailed description of preferred embodiments [0031] The invention is related to a heat pump system arranged to capture and concentrate infra red thermal radiation produced by an emitting surface through the interaction of three basic elements :
1) An electromagnetic emitter surface Al, emitting infra red thermal radiation
2) A passive electromagnetic concentrator packet
3) An electromagnetic conversion surface A2
The emitter surface is at least partially included in the concentrator package, which itself comprises IR-emitting surfaces. Therefore, in more general terms, the heat pump of the invention comprises : 1) A passive concentrator package, comprising means to concentrate IR-radiation, said package comprising one or more IR-emitting surfaces,
2) A conversion means for converting the IR radiation thus concentrated, into another form of energy,
3) Possibly one or more additional IR-emitting surfaces, arranged to produce IR radiation which can be concentrated by said concentrator package,
[0032] The 'concentrator package' is defined as a means for optically concentrating IR radiation. The package primarily consists of lenses and/or curved mirrors, as will be explained on the basis of specific embodiments. These lenses and mirrors have themselves IR-emitting surfaces. The invention is related to a system wherein said IR-radiation emitted from these 'concentrator' surfaces, and possibly the IR-radiation emitted from further emitting surfaces in the system, and reflected by or transmitted through the concentrator package, is concentrated and converted into other forms of energy such as heat or electricity. This energy production can take place without requiring any added labour. Objects at room temperature or lower produce infra red radiation. As illustrated by test results obtained by the applicant, the present invention provides a system configured to capture and utilize this readily available energy.
[0033] Figure 1 shows a system according to a first embodiment of the invention. It shows an enclosure 10, encircling a cavity 20, a cross-section of which is shown from the top in figure 1. The enclosure is provided with a flat back wall 11 and flat side walls 12,13. The front wall 14 is a curved mirror. In the present description a 'mirror' is a surface which is at least partially reflective for IR-radiation. The surface of the mirror 14 may for example be a steel enamelled surface. The enclosure 10 is further closed off by a floor and ceiling surface. The curved surface of the front wall 14 may have the shape of a spherical concave dish. A radiation conversion means 16 is provided in a central location of the back wall 11. The conversion means 6 may comprise any known means to convert radiation energy into other forms of energy. The conversion taking place may for example be a radiation to heat conversion or a radiation to electricity (photovoltaic) conversion. Recuperation means 17 (e.g. a conductor wherein a fluid flows, said fluid being heated by a heat exchange means comprised within or in connection with the conversion means 6) may be provided to evacuate energy from the radiation conversion means. When the conductor 17 is not present, the system works as a cooling system for cooling the emitting surface 14.
[0034] In the embodiment of figure 1, the concentrator package consists only of the mirror surface 14. The surface of the mirror 14 is itself an IR-emitting surface, and is further configured to reflect and concentrate IR-radiation emitted by the flat walls 11,12 and 13, especially when walls 11, 12, 13 have high emissivity. However, walls 11,12,13 may have low emissivity, in which case the main emitting surface is the surface of the mirror 14 itself. The invention proves that the presence of a curved emitting surface, suitably shaped so that IR-radiation produced from said surface is concentrated, is capable of leading to a net energy production. According to preferred embodiments described further, this effect is enhanced when the emitting surface of the mirror 14 (and possibly of the walls 11-13) is provided with a funct ionali zed surface, configured to produce IR-radiation with higher intensity in the direction perpendicular to the emitting surface than in other directions. The conversion means 16 may be located in a point corresponding to the centre of curvature of the curved surface 14.
[0035] A second embodiment is shown in figure 2. The system according to the second embodiment comprises an enclosure 1, encircling an inner cavity 2, the shape of said cavity being defined by a flat surface 3 (of size Al) on one side, and a curved surface 4 on the other side, i.e. facing the flat surface 3. The curved surface has the shape of a circumferential paraboloid (i.e. surface obtained by rotation of a parabolic curve around a symmetry axis), with its symmetry axis 7 perpendicular to the flat surface 3. A lens 5 is arranged in proximity with the flat surface 3. An electromagnetic conversion means 6 is arranged in the focal point of the paraboloid, and preferably also in a focal point of the lens 5. The paraboloid surface 4 is a mirror (as defined above) . The conversion means 6 comprises the abovenamed conversion surface A2. Optionally, an energy recuperation means 8 is connected via a heat-exchanging connection to the conversion means 6.
[0036] Infra red radiation emitted from the paraboloid mirror 4 is concentrated in the conversion means 6, due to the paraboloid shape of the mirror and the location of the conversion means. Infra red radiation emitted from the emitter surface 3 is concentrated by the lens 5, so that a majority of the radiation produced at surface 3 is concentrated in conversion means 6. Radiation which does not impinge on conversion means 6 is reflected by the curved surface of the paraboloid 4, and equally concentrated in the conversion means 6, located in the paraboloid's focal point. This causes a net heating of the conversion means 6 with respect to the rest of the system. [0037] The heat recuperation means may comprise a conductor 8 provided for removing energy from the conversion means 6, via a fluid flowing in the conductor 8, said fluid being heated by a heat exchange means comprised within or in connection with the conversion means 6. The energy recuperation means may alternatively be an electrical network configured to receive electrical energy generated by a photovoltaic cell arranged within or in connection with the conversion means 6. The lens 5 may be omitted in the embodiment shown. Preferably in that case, the paraboloid mirror 4 is highly reflective for IR radiation.
[0038] According to a preferred embodiment, the emitter surface (3 or 11,12,13) and/or any surfaces of the concentration package (surface of the lens 5, mirror surface 4,14) is provided with a functionalized surface, e.g. to produce directional radiation, and thereby enhance the efficiency of the system (to be described further in more detail) .
[0039] In order to understand the functioning of the heat pump of the invention, the system of the invention is hereafter presented first at an ideal theoretical level. Looking in particular at the embodiment of figure 2, we assume that the heat pump is entirely isolated from the outside world, and no heat is removed from the conversion means 6. We also suppose that the concentrator packet (5,4) does not absorb any of the electromagnetic radiation. The mirror 4 reflects 100%, the lens 5 has a 100% transmittance . In this state we must arrive at an equilibrium between the emission/absorption of the emitter surface 3 and the emission/absorption of the conversion means 6. From Stephan Boltzmann we know the formula is
Qrad = AεσT 4 Wherein :
• A = surface m 2
• ε = emissivity of surface
• T = surface temperature 0 K (273+ t 0 C)
In our model this means that we can calculate T2 in case of given values of Al (surface area of emitting surface 3) , A2 (surface area of conversion means 6 and Tl (temperature of emitting surface 3) :
We notice that even at low temperature 273 K (0 C) for Im 2 of emitter surface and a relative low concentration factor of XlOO (A2/A1), we already achieve quite high T2 : 863°K (590 0 C) [0040] Now we leave the theoretical perfectly isolated box. If we now would start draining mechanical heat (Qdrain2) from surface A2 we would unbalance the enclosed system. We could drain this by for instance letting cold water flow through conductor 8, in heat- exchanging connection with the surface A2, and export this outside the system. By draining the surface A2 , it will become less hot. Thus it will emit less electromagnetic radiation back to surface Al. This means that surface Al will in turn become a little bit colder, until the system is in balance again. In this condition we could use an external heat source to heat up the emitting surface Al once again to its original temperature Tl (Qinjectl) . In this case we would return to the original state and Qinjectl would be equal to Qdrainl . This means that we have a passive (requires no external energy) solid-state (requires no moving parts) heat-pump from surface Al to surface A2. If we do not inject Qinjectl, the heat pump system will work as a cooling system at surface Al. [0041] The concentrator package might be a combination of well known lenses and mirrors. It may comprise lenses only, like Freznel lenses. Or it may comprise mirrors only, like a parabolic concentrator mirror with the absorber surface A2 placed in the focal point, as shown in figure 2. [0042] According to preferred embodiments of the invention, the concentration of energy is improved by the use of known optical techniques, applied in such a way that the emitted radiation from the emitting surface has a high degree of direction, or is enhanced in terms of the emitted energy.
[0043] For example, looking at the embodiment of figure 1 : when the mirror 14, the back wall 11 and side walls 12,13 are not provided with directional surfaces, the radiation emitted by the back wall and side walls is diffuse. This means that only a limited portion of the emitted energy is effectively reflected by the mirror 14. According to the invention, it is advantageous to provide at least the mirror wall 14 with a so-called Mirectional surface' i.e. a surface provided with means to obtain IR- radiation from said surface which has an increased intensity in a specific direction.
Reference is made to the following documents, incorporated herein by reference :
• Design and Fabrication of planar structures with coherent thermal emission characteristics, Lee&Zhang, Journal of Applied Sciences, 100, 063529 (2006) . • Coherent Thermal Emission From Modified Periodic Multilayer Structures, Lee&Zhang, Journal of Heat Transfer, vol. 129, January 2007.
• Extraordinary Coherent Thermal Emission From SiC due to Coupled Resonant Cavities, Dahan et al . , Journal of
Heat Transfer, vol. 130, November 2008.
• Angular and spectral peculiarities of the coherent thermal radiation of the magneto-optical Fabry-Perot resonator in a magnetic field, Morozhenko & Kollyukh, Journal of Optics A : Pure and Applied Optics, 11 (2009), 085503.
[0044] According to a preferred embodiment, at least a portion of the emitting surface (e.g. surfaces 14 and 4) in the heat pump of the invention is provided as a functionalized surface configured to produce, from said surface, infra red radiation, the energy of said radiation being higher in the direction perpendicular to the emitting surface, compared to the energy of radiation in the other directions. Said functionalized surface, hereafter referred to as λ directional surface' may consist of a surface which is provided with a pattern of microcavities, wherein the size and distribution of said cavities is configured to produce said directional radiation. Alternatively, the functionalized surface may be provided with Fabry-Perot resonator structures, configured to produce coherent thermal radiation. The material of the emitting surface and the dimensions of the microcavities or resonator structures may be executed in accordance with any of the abovenamed publications. For example, a silicon carbide surface or a polymer surface may be used, provided with a pattern of microcavities. [0045] Any other surface known in the art and capable of providing highly directional IR-radiation may be used as the emitting surface Al. Such a functionalized surface may also be used on the concentrator package, e.g. on the surface of the lens 5 and/or of the mirrors 4 and 14.
[0046] According to an embodiment , the functionalized surface may be obtained by applying a coating on the emitting surface 3, said coating having itself a functionalized (e.g. direction-enhancing) surface. This may for example be a SiC layer 21 provided with a pattern of microcavi t ies , as illustrated in figure 3. Instead of or in addition to such a coating, a directional grating 22 may be applied (see figure 4), which is another way of obtaining increased intensity in the direction perpendicular to the surface. Directional gratings can be used as described in the relevant literature, such as in the following document, incorportated herein by reference : Greenslade, Thomas B., "Wire Diffraction Gratings" The Physics Teacher, February 2004. Volume 42 Issue 2, pp. 76- 77. It is to be noted that when a coating and/or grating is applied to the emitting surface 3, it is in fact the outer surface of said coating or grating which effectively becomes the λ emitting surface' according to the invention. [0047] As mentioned above, certain embodiments of the invention comprise an external heat source, configured to heat up the emitting surface Al . Figures 5 and 6 show a number of practical ways of putting this into practice. In figure 3, a conductor 30 is provided in connection with a heat-exchanger 31, arranged in heat-conducting contact with the emitting surface 3, and configured to comprise a primary heated fluid flowing in said conductor 30. The heat-exchanger may be any known type of heat exchanger suitable for the purpose of heating up the emitting surface. The added heat enhances the IR-radiation emitted by the surface Al. Especially when a functionalized IR- directional surface is provided, the amount of heat produced and concentrated in the conversion means 6 is further increased. According to a specific embodiment, shown in figure 4, the conductors 8 and 30 are connected to form a feedback connection 32 from the conversion surface 6 to the emitting surface 3. [0048] Figure 7 shows an embodiment, wherein the conductor 30 and heat exchanger 31 is arranged in conjunction with the embodiment of figure 1. In the latter case, it is the emitting surface 14 of the curved mirror surface which is heated by the heat exchanger 31. [0049] In order to avoid absorption of the electromagnetic radiation in between the surface Al and the surface A2, the space in between can be made vacuum. Another solution is to use a gas that is transparent for the electromagnetic radiation emitted by surface Al and A2. [0050] The conversion means 6, 16 may comprise a photovoltaic concentrator cell. This cell might be tuned to the emission spectrum of the emitter surface Al. In such case only a certain percentage of the concentrated radiation will be converted into electricity (for example 30%) . This means that in our example 70% will be converted into mechanical heat. In our device we could cool this A2 PV cell by a cooling medium (like water) and drive this energy back to the emitter surface Al . Again in our heat- pump setting this would mean that almost no energy is lost. This variation on our passive (solid-state) heat-pump is to be seen as an optimized thermo voltaic heat pump.
[0051] When this device with an A2 PV cell is used as en electric power generator its overall efficiency will outperform that of typical Rankine based power plants. A coal fired Rankine power plant has an overall efficiency of about 45%. In this case we could suppose that the Qinjectl is steam coming from a steam boiler. The system could be dimensioned in such a way that the steam reaches a
(condensation) point after transferring its energy content through Al so that it can be reinjected in the steam boiler. As mentioned above in a single pass this way 30% would be converted to electrical power immediately and 70% would be lost through Qdrain2. However the energy density of Qdrain2 can be that high that it can be reinjected in the Al side. This would mean, except from some mechanical friction losses, that one could achieve power generation cycles with very high efficiency.
Example [0052] Measurements were done on an experimental set-up similar to the embodiment shown in figure 1. Figure 8a shows a top view of the specific set-up used in the experiment. Four side walls 40,41,42,43 and floor and ceiling portions, define an enclosure with the following (approximate) dimensions : Width W = 2m Length L = 2.6m Height H = 2.4m [0053] A steel spherical concave dish 44, of diameter 1.8m and radius of curvature 3.2m, is placed adjacent wall 43 and facing the opposite wall 40. The distance from the centre of the dish to the opposite wall is about 2m. The walls 40-41-42-43 are covered with black non-reflective paper. The enclosure is substantially sealed off from the environment and maintained during a given time, after which the temperature of the opposite wall 40 is measured with a heat-sensitive camera. [0054] Measurements revealed that after about 1.5hrs, the wall 40, facing the dish, exhibited a local temperature rise. In a circular zone 50 of about 800mm in diameter (see fig. 8b), located centrally in the wall 40, and directly facing the centre of the dish, a temperature rise was measured. In the centre of the zone 50, a temperature rise of about 1.5°C was measured with respect to the part of the wall 40 outside zone 50. This result proves the potential of a heat pump according to the invention .