Classifications

• • 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
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F24—HEATING; RANGES; VENTILATING
  • F24V—COLLECTION, PRODUCTION OR USE OF HEAT NOT OTHERWISE PROVIDED FOR
  • F24V99/00—Subject matter not provided for in other main groups of this subclass

Definitions

• the invention relates to the field of radiant energy devices, heat transfer devices and methods and more particularly heat pumps.
• the Kyoto Accord is the first international agreement intended to minimize the climate change impact of fossil fuel consumption by reducing the net emissions of carbon dioxide and other greenhouse gases (GHGs). To succeed, such initiatives must be supported by technologies which eliminate or significantly reduce the GHG emissions associated with fossil fuels.
• Alternative energy technologies such as wind, solar and nuclear have made and continue to make energy supply contributions at or near zero emissions. However, it will be decades before such alternative energy technologies displace fossil fuels sufficiently to tip the GHG balance. In the interim, measures to increase the efficiency of energy use and fossil fuel conversion can help reduce GHG emissions.
• Fossil fuels (primarily coal) are burned to generate a large fraction of the total electricity used worldwide. Consumption rates vary widely, but in North America, the monthly CO 2 emissions associated with domestic electricity use averages roughly three tonnes per household. Some geographic regions have coal reserves which are expected to last more than a century. Consequently, there is great incentive to continue burning coal despite its contribution to GHG emissions. Unfortunately, the steam cycles on which conventional coal-fired generating plants are based run at net efficiencies below 40%. Most of the energy is released as waste heat into the environment when the steam is condensed. As a result of trying to address these concerns and as a result of rising energy costs, consumers at the industrial, commercial and residential levels are seeking ways to reduce the quantities of energy they purchase and consume.
• the prior art teaches the recovery of waste heat using passive heat exchange, chemical heat pumps, and vapour compression heat pumps (open or closed cycle heat pumps).
• Chemical heat pumps are limited to applications involving temperature ranges at which certain chemical reactions proceed at favourable rates. This limits both the number of installations for which the technology is economic, and the flexibility of each installation to economically accommodate variations in operating conditions. Because of the nature of the chemicals used, chemical heat pumps are also undesirable for some applications. Perhaps the only advantage that chemical heat pumps enjoy over their vapour compression counte ⁇ arts is the fact that their requirement for motive (electrical) energy input is a very small fraction of the total energy input.
• vapour compression heat pumps By far the largest number of operating heat pumps in the world are vapour compression heat pumps. Almost all vapour compression heat pumps are closed cycle units which recirculate a refrigerant continuously around a closed loop. The most common example of a vapour compression heat pump is the refrigerator.
• vapour compression heat pumps lie in compressor technology (which is the heart of the vapour compression pump) and the availability of suitable refrigerants. More specifically, vapour compression heat pumps have historically been considered unreliable and are complex thereby requiring maintenance. Many manufacturing companies are preoccupied with production-related equipment and therefore do not readily accept peripheral equipment that might not work or cause operational problems to other operating industrial systems. Further, manufacturing companies do not want peripheral equipment which requires specialized maintenance skills.
• Open cycle heat pumps avoid the refrigerant problem associated with closed cycle units because they use the industrial process fluid as the refrigerant. This eliminates the need for heat exchange with a captive working fluid.
• process liquids are sometimes corrosive or otherwise difficult to handle, maintain and use which adds to the compressor cost.
• process liquids are frequently mixtures of liquids which evaporate at different temperatures and complicate the cycle.
• process liquids frequently contain dissolved or suspended solids, which complicates some installations or makes them unworkable.
• open systems are not well suited to heat recovery from waste liquids as contamination of the working vapour with air is difficult to avoid and thereby limits cycle efficiency and economic attractiveness.
• Open cycle heat pumps at high temperatures are subject to the same compressor problems as their closed cycle counte ⁇ arts. Both open and closed cycle systems are subject to the limitation that a substantial amount of high cost electrical energy is required for vapour compression.
• the electrical energy input can constitute up to one half of the total high temperature energy that the unit delivers.
• the electrical energy input can be as little as 7 or 8% of the delivered heat. The cost of electricity relative to the costs of other energy sources is a major factor in determining the economic viability of a vapour compression installation.
• the present invention is directed to a method and device for increasing energy efficiencies by recovering heat which would otherwise be lost, and by raising the temperature of the heat sufficiently to permit use of recovered energy.
• the present invention provides a method for exaggerating the nondiffuse emission pattern radiating from a surface by configuring the geometry of the surface.
• This method can result in radiant heat flux flowing in specific directions from the surface in a more concentrated or less concentrated pattern than for an ordinary surface having the same composition and temperature.
• Another result of the method is that the apparent temperature of the surface as perceived from specific directions is higher than or lower than the actual temperature of the surface. Accordingly, if a receiving surface or target surface is placed in a region where the apparent temperature of the surface is higher than the actual temperature of the surface then the result is a net flow of radiant heat from the surface (or emitting surface) to the target surface.
• the net flow of radiant heat transfer can be further realized by minimizing the convective and conductive heat flow between the surface and the target surface (such that the combined heat flow by conduction and convection between the surface and the target surface is a small fraction of the net heat flow by radiation between the surface and the target surface).
• the geometry of the surface or emitting surface can be configured in various ways.
• the geometry of the surface is configured to a V shape with the opening of the V facing the target surface.
• the surface can be made of various materials.
• the material is highly reflective and in a more specific embodiment the surface is a highly polished metallic surface.
• entirely surrounding or nearly entirely surrounding the target surface by a continuous surface or a plurality of surfaces further increases the effect of this method.
• the present invention by supplying heat to the emitting surface and removing heat from the target surface, the present invention provides a method for producing a useful radiant heat pump.
• the concept of the radiant heat pump is based on the fact that radiant heat exchange between two bodies involves an independent and quantifiable flow of energy in each direction. This distinguishes radiant heat transfer from both conduction and convection, since at least on a macroscopic scale, conductive and convective heat transfer are uni-directional along a gradient.
• the invention proposes to establish a net flow of radiant heat against a temperature differential.
• One method of producing the artificial environment is to modify the geometry of the emitting surface such that its apparent temperature, from the perspective of the receiving surface, is higher than its actual temperature. This may be achieved by modifying the geometry of the emitting surface such that its emissions are more focussed and less diffuse, and by orienting the emitting surface to emit a greater concentration of heat in the direction of the receiving surface.
• the artificial environment can be further enhanced by eliminating conductive and convective heat transfer by introducing a vacuum, for instance, which will also have the benefit of reducing scattering of the emissions and interference with the radiant energy flow.
• Radiant heat pumps overcome many of the major problems associated with other prior art systems since radiant heat pumps require no compressor or other complex machines, require no chemicals or refrigerants, can operate well over a wide temperature range, and can be assembled from a large number of identical components which can be mass produced at low cost. Another advantage of radiant heat pumps is that they require electrical energy input only for pumping of the heat transport fluids, and not for operation (as in thermoelectric devices) or compression. Pumping of ordinary liquids is a very mature technology that industry will have little difficulty implementing efficiently.
• the radiant heat pump involves no refrigerants or other complex chemicals. Therefore, the practical and economic operating temperature ranges are not limited by chemical properties.
• the performance of each pump is determined by its geometry, the characteristics of the emitter surfaces, and the quality of emitter surface preparation. It appears that a radiant heat pump will operate well over a far broader temperature range than prior art heat pumps.
• radiant heat pumps Perhaps the most important advantage of radiant heat pumps is the fact that radiant heat transfer is enhanced by increasing temperature. Since the rate of emission is proportional to the fourth power of absolute temperature, the attractiveness of the radiant heat pump over existing technologies will typically increase with increasing source temperature.
• the present invention provides a radiant heat pump device for transferring heat from a surface to a receiving or target surface where the target surface has a higher temperature than the emitting surface.
• the surface emits energy radiation towards the target surface.
• the surface is geometrically configured to project nondiffuse radiant emission patterns towards the target surface.
• the result as apparent from the methods described above, is a net heat flow from the emitting surface to the target surface against a temperature differential.
• a hollow emitter assembly defines a vacuum-sealed enclosure. Passing through the hollow emitter assembly is a hollow cylindrical target for collecting radiation and for transporting the radiation to the exterior of the emitter assembly.
• the emitter assembly includes a plurality of emitting plates on the emitter assembly's inner surface, the emitter plates facing the hollow cylindrical target and the emitter plates having a smooth surface for reflecting radiation emitted from the emitter assembly to the emitter plates to the hollow cylindrical target.
• Figure 1 is an emitter assembly including two emitter plates each having an emitting surface in accordance with the invention
• Figure 2 is a top view of the emitter assembly in Figure 1 which demonstrates the reflection of emissions between two adjacent plate-emitting surfaces in accordance with the invention
• Figure 3 is a perspective view of an emitter assembly in relation to a target in accordance with the invention
• Figure 4 is a graph which demonstrates the ratio of focussed flux from an emitting surface compared to a theoretical blackbody flux in accordance with the invention
• Figure 5 is an emitter assembly in relation to a cylindrical target in accordance with the invention
• Figure 6A is a side view of one embodiment of the radiant heat pump in accordance with the invention
• Figure 6B is a cross sectional view of the radiant heat pump in Figure 6A taken at line A-A in accordance with the invention
• Figure 6C is a cross sectional view of the radiant heat pump in Figure 6B taken at line B-B in accordance with the invention.
• Figure 6D is a cross sectional view of the radiant heat pump in Figure 6C taken at line C-C in accordance with the invention
• Figure 7 is a cross sectional view of one embodiment of a radiant heat pump in accordance with the invention.
• FIG. 8 is a system of radiant heat pumps in accordance with the invention.
• radiant heat transfer between two bodies involves an independent, quantifiable flow in each direction.
• Conventional theory on radiant heat transfer is based on an ideal surface, known as the blackbody.
• the blackbody has a total emissive power which is proportional to the fourth power of its absolute temperature, emits uniformly (diffusely) in all directions, emits with a characteristic, predictable wavelength distribution and absorbs all radiant energy which is incident upon it.
• a less idealized theoretical surface than a blackbody is termed a graybody which also emits diffusely and with a characteristic wavelength distribution.
• a graybody only emits a fraction of the power of a blackbody; that fraction (uniform for all wavelengths) is termed its emissivity.
• a graybody also absorbs only a fraction of the incident radiant energy; that fraction (uniform for all wavelengths) is defined as abso ⁇ tivity (any incident energy not absorbed is reflected diffusely). Further, for a graybody, abso ⁇ tivity is generally equal to emissivity.
• any two blackbodies or graybodies placed in line of sight contact with each other will exchange radiant energy such that their temperatures tend to converge. That is, if one body has a higher temperature than the other body, then the amount of radiant energy from the higher temperature body which is transmitted to the lower temperature body will be greater than the amount of radiant energy from the lower temperature body which is transmitted to the higher temperature body.
• real surfaces In contrast with blackbodies and graybodies, real surfaces have emissivities and abso ⁇ tivities which vary with wavelength, emit with distribution patterns that deviate to varying degrees from truly diffuse, and have reflections that are partly specular and partially diffuse. Accordingly, real surfaces will emit different amounts, generally less, radiant energy than blackbody or graybody surfaces.
• the present invention provides a method and a device for exaggerating the nondiffuse emission patterns of real surfaces by making radiant emissions from the surfaces less diffuse than the surfaces' normal emissions.
• the nondiffuse emission patterns can be concentrated onto a receiving surface.
• this method which is contrary to the "normal" pattern considering that the vast majority of surfaces radiate heat diffusely, facilitates the net transfer of radiant heat energy to the receiving surface against a temperature gradient, which has very valuable commercial uses.
• two emitter plates 16 which each have the same dimensions and emitting surfaces 18, are placed in contact along edges of equal length. Viewed in cross section ( Figure 2), the line of contact forms the apex for a narrow, elongated "V" shape.
• the emissions from either plate 16 flowing in the general direction of the opening at the top of the V are confined and reflected by the opposing emitting surface 18 of the plate 16 and are reflected back toward the opening of the V.
• the nature of the reflections of the emissions is of particular interest. As shown in
• each reflection is a sort of focussing event.
• an emission may undergo several more reflections before emerging from the opening of the N. If the plates 16 are sufficiently smooth, only a trivial amount of scattering takes place at each reflection. Consequently, a high percentage of the original emission is reflected.
• the cumulative effect of multiple reflections to numerous emissions from the emitting surfaces 18 of this formation is a roughly concentrated beam of radiant heat energy whose component emissions approach with varying degrees of accuracy towards a direction parallel to the axis of symmetry 30.
• metals Due to the unique emissivity characteristics of metals, a metal surface is preferable for the emitting surfaces 18. More specifically, metals exhibit inverted emissivity characteristics (which increase at low angles) and are far from diffuse. A highly polished metal surface will result in even less diffusion upon reflection of radiant heat energy.
• the combination of polished metal emitting surfaces 18 into certain geometries causes the combined emitting surfaces 18 to project nondiffuse radiant emission patterns.
• the total emission of radiant energy from the emitting surfaces 18 will naturally be equal to or less than the corresponding total for the ideal blackbody with the same projected area.
• the emitting surface 18 projects relatively higher concentrations of radiant heat energy to specific regions and lower concentrations to other regions. That is, the radiant flux density projected along the axis of symmetry 30 for each emitting plate 16 pair is significantly higher than it would be in the case of diffuse emission but the flux densities at large angles from the axis of symmetry 30 are correspondingly lower. Accordingly, the emitting surface 18 may achieve up to several times the equivalent blackbody emission level for a target region and even greater emissions when compared to a diffuse emitter.
• the emitter assembly 14 is constructed so that the maximum relative flux density from the emitter plates 16 is incident on or near the target 31. Consequently, from the target's perspective, the high radiant flux density makes the "apparent" temperature of the emitter plates 16 higher than the emitter plates' actual temperature. Since heat flow to the target 31 is based on the apparent temperature of the emitting surface as perceived by the target surface, the target 31 will absorb more heat emitted from the emitter plates 16 than if the target 31 was able to perceive the emitter plates' actual temperature. Accordingly, there will be a net flow of heat to the target 31, notwithstanding that the target 31 may be at a higher surface temperature than surface temperature of the emitter plates 16.
• One method of maximizing heat transfer to a cylindrical target is to increase the number of pairs of emitter plates 16 oriented to project focussed emissions on the cylindrical target. This method can be embodied in the radiant heat pump device discussed below.
• Another method to maximize the advantageous radiant transfer from the emitting surface 18 to the target 31 is to minimize the conductive and convective "back flows" that occur as a result of the Zeroth Law. Conduction is minimized by limiting the cross- sectional area available for transfer back from the target 31 to the emitter plates 16. Convection is minimized by maintaining a vacuum between the emitting and target surfaces.
• RAD is the rate of radiant emission from the target
• RAD e is the rate of radiant heat gain by the target
• CONV is the rate of convective heat removal.
• E t is the emissivity (abso ⁇ tivity) of the target
• S is the Stefan-Boltzmann constant
• a t is the surface area of the target
• T t is the absolute temperature of the target.
• R is the ratio of incident emissions to blackbody emissions
• T e is the temperature of the emitter plates.
• the V shape shown in the figures may have various alternate configurations. More specifically, the angle of the opening of the V shape (shown as approximately 30° in
• Figure 1 may be narrower or wider, the emitter plates 16 may have varying widths and the emitter plates 16 may not be planar. More generally, a V shape is not essential as other geometric configurations (having a plurality of surfaces where some surfaces may even emit diffusely) may achieve the same pu ⁇ ose of exaggerating nondiffuse emission patterns to produce concentrations of emitted energy toward a region or regions.
• the present invention provides a radiant heat pump 10 having a hollow shell assembly 14 defining a vacuum sealed recess 15 and a hollow cylindrical target 12 disposed through the emitter assembly 14 for collecting energy by radiation and for transporting the collected energy to the exterior of the shell assembly.
• the shell assembly 14 includes a plurality of emitting plates 16 on the shell assembly's inner surface 17, the emitter plates 16 facing the hollow cylindrical target 12 and the emitter plates 16 having a smooth active radiant surface or emitting surface 18 for reflecting radiation transferred from the shell assembly 14 to the emitter plates 16 and then by radiation to the hollow cylindrical target 12.
• the radiant heat pump 10 is designed to enclose a vacuum such that conductive and convective heat transfer effects are insignificant when compared to radiant heat transfer although any means of minimizing conductive and convective heat transfer will be effective.
• the emitter assembly 14 may be spherical and the emitter plates 16 may define conical recesses for radiating focused emissions on a target 12 which, in such an embodiment, may also be spherical.
• the emitter assembly 14 may be spherical and the emitter plates 16 may define conical recesses for radiating focused emissions on a target 12 which, in such an embodiment, may also be spherical.
• a worker skilled in the art will appreciate that other two-dimensional and three- dimensional shapes will be effective.
• the shell assembly 14 may be nested as shown in Figure 7. That is, concentric shell assemblies (such that the outer surface of one shell assembly forms the collector in another shell assembly, and so forth) may be provided around the hollow cylindrical (or spherical) target 12. Since emissive power is proportional to the fourth power of absolute temperature, higher source temperatures provided to the inner emitter assembly from the outer emitter assembly would make a radiant heat pump 10 more effective in terms of temperature lift to the target 12.
• the radiant heat pump 10 is installed in an environment such as a generating plant or other energy facility where heated liquid or steam is in contact with the outside of the radiant heat pump.
• the liquid or steam is not at a high enough temperature for further use in the generating plant without upgrading the temperature (that is, the heat is waste heat).
• the exterior of the shell assembly 14 absorbs the heat and transmits the heat to the interior surface 17 which includes emitter plates 16. Simultaneously, water or other heat energy removal means flows through the hollow cylindrical element 12.
• the apparent temperature of the emitter plates 16 from the perspective of the cylindrical element 12 is greater than the actual temperature of the emitter plates 16, resulting in the cylindrical element 12 absorbing more heat than if cylindrical element 12 perceived the actual (lower) temperature of the emitter plates 16. Accordingly, there is a net flow of energy by radiation to the cylindrical element 12 which can raise the temperature of the cylindrical element 12 to a useful temperature, notwithstanding that the cylindrical element 12 is at a higher temperature than emitter plates 16.
• the emitter plates 16 may be long thin components formed, for example, by machining, forging, stamping, die casting or investment casting.
• the material used is preferably strong, rigid, and economical, with a high thermal conductivity. In descending order of thermal conductivity, copper, aluminum and steel are among the best common options currently available. If plastics, or composites with sufficient strength and rigidity at high temperature exist in combination with adequate thermal conductivity, durability and very low gas permeability, they can also be used to construct the emitter plates 16. These composites may have a strength to weight advantage over metals.
• Suitable plastic forming techniques for forming the emitter plates include rotomolding, thermoforming, and if components are small enough, possibly also injection molding.
• the emitter plates 16 are preferably solid and designed to direct a substantial portion of emitted heat to the hollow cylindrical target 12. A worker skilled in the art will appreciate that the emitter plates 16 may be machined in one continuous piece thereby forming one continuous surface around the hollow cylindrical target 12.
• the active radiant surface or emitting surface 18 is preferably very smooth. Due to the advantageous properties of polished metal with respect to reflectivity described above, the emitter plates 16 are preferably comprised of or coated with a polished metal surface 18. Numerous design changes to the emitter plates 16 are conceivable. For instance, the emitter plates 16 may be curved and the emitter plates 16 may include combinations of diffuse emitting materials and polished metals or other highly reflective materials. As stated above, the particular shape and arrangement of emitting surfaces generally (and specifically the emitter plates 16 in this case) is variable.
• the radiant heat pump 10 may include reflecting surfaces at each end of the cylindrical or spherical or other emitter surface 14 made of either flat or curved highly reflective material.
• each end of the emitter assembly 14 may include emitting surfaces made of either flat or curved surfaces that emit diffusely.
• the end caps 22 may be composed of combinations of materials which emit diffusely and are highly reflective.
• the hollow cylindrical target 12 is used to transfer heat absorbed by the target outside of the shell assembly 14 and on to a heat delivery system (usually through fluid flowing through the hollow cylindrical element which is heated to a useful temperature by abso ⁇ tion from the collector's surface). This upgraded energy can then be reused in a system (such as in Figure 8) to achieve the objective of conserving energy, recovering waste energy and reducing costs.
• the hollow cylindrical target 12 is preferably not reflective (that is, the surface of the hollow cylindrical target 12 should be highly abso ⁇ tive to maximize the net heat flow to the hollow cylindrical target 12). To achieve useful results, the surface area of the hollow cylindrical target 12 should be smaller than the apparent or effective surface area of the emitter plates 16.
• the artificial environment between the emitter assembly 14 and the hollow cylindrical target 12 can help maximize the net flow of heat to the hollow cylindrical target 12 through the minimization of any back flow (from target to emitter) by conduction or convection. This may be done, for instance, by vacuum sealing the emitter assembly 14 and minimizing contact of emitter and target by (for instance) providing heat insulation between those elements where they necessarily contact each other or intermediate mounting means.
• the present invention can be used in thermal-electric generating stations which currently waste approximately 40% of the total energy input by rejecting the energy input as low temperature heat, usually to a nearby body of water. This waste is the result of a thermodynamic limitation of the cycle used to convert heat into mechanical energy. Steam is condensed at the outlet of each turbine and pumped back up to high pressure as water. To maximize the efficiency of the generating cycle, this heat is rejected at as low a temperature as possible and is not worth recovering. Radiant heat pumps could be used to recover some of this rejected waste heat for re-injection into the process to greatly increase the overall efficiency of the plant.
• the discharge temperature from the steam turbines would be increased from the normal ambient temperature to perhaps 300 degrees C.
• the resulting small loss in efficiency of the existing cycle would be more than offset by the recovered heat.
• none of the existing heat exchange technologies are capable of effectively dealing with a source at this high temperature.
• the availability of the present invention, particularly to industry may result in industry-specific applications that do not currently exist.
• in exchanging heat between two flows it might be advantageous to transfer up in temperature rather than down as is currently the case with passive heat exchange.
• the present invention may, for example, ultimately find application in building space heating (using ambient or very low temperature sources) or refrigeration.
• the mating surfaces that permit accurate relative positioning of adjacent emitter plates 16 are machined to high accuracy ( ⁇ + 0.005" or better). This precision is economical and practical with the current generation of computer numerically controlled (CNC) machining technology. Locating features such as tabs for position keying and grooves for vacuum sealing elements between emitter plates may be added during the machining operation. In the same machining operation, or in a separate machining or grinding operation, the surfaces of the emitter plates 16 that participate in the radiant exchange are finished to a high quality. The quality of surface finishing required for economical performance of the radiant heat pump, and the effect of directional surface markings left by machining or grinding on operation of the heat pump is determined empirically, and depends upon the material chosen and the method of manufacture. However, if a higher surface quality of the metal emitter plates 16 is required, it maybe produced by secondary operations such as lapping and/or electropolishing.
• the emitting surfaces 18 are coated with a thin film (likely ⁇ 0.002") of an appropriate material.
• the preferred materials are chromium or aluminum, however other materials that later prove to be more suitable are intended to be included herein.
• the coating technique depends upon economics, with a preference for the most economical coating method that provides acceptable radiant and reflective properties to the emitting surfaces 18. Electroplating, which would be used for metals only, and vapour deposition are among the most likely candidates for coating techniques.
• the molding processes may be designed to minimize the amount and cost of work required after forming the emitter plate 16.
• polished molds used with high performance release agents might deliver active surface qualities ready for the final coating.
• the emitter plates 16 Prior to assembly into the radiant heat pump 10, the emitter plates 16 are cleaned thoroughly and taken to an assembly area which meets clean room standards, not unlike those used for manufacture of microelectronics. Completed emitter plates 16 are then stacked into cylindrical assemblies by placing them next to each other one unit at a time, and engaging the locating features until groupings spanning 180° of arc are complete.
• the next step in the assembly of the emitter assembly 14 is to combine two half shells into a full cylindrical array of emitter plates 16.
• the final step is to strap the array together with external hoops of metal or composite material.
• Vacuum sealing elements may be placed between emitters individually during assembly, or pumped through the sealing grooves in the entire array during a single step after strapping. In the latter case, the sealing material will harden to a rigid state that provides additional mechanical stability to the emitter assembly 14, and helps to bond its components together. After bonding, straps may no longer be necessary.
• a sealing agent applied externally on the emitter assembly 14 may further limit gas diffusion.
• End caps 22 of machined metal or a composite material would complete each enclosure and its vacuum seals.
• the end cap 22 inner surfaces are preferably highly reflective to infrared wavelengths.
• the end caps 22 also provide the connection point for vacuum lines (not shown), and possibly for reducing gases that would be flushed through each chamber to accelerate the removal of surface oxide prior to startup.
• each end cap 22 would provide a barrier to minimize thermal conduction between the shell assembly 14 and the target 12 passing through its central port. At least one of the two end cap-to-target joints would be allowed to slip relatively freely so that differential thermal expansion of the target 12 would not place it in compression. Both would be thermally isolated such that the target 12 is thermally insulated (for conduction) from the shell (and thus the emitters).
• the hollow cylindrical target 12 may be a thin walled tube with a thickness to diameter ratio ⁇ 0.1 and with sufficient strength and rigidity to withstand the internal pressure of a fluid medium that flows through the target 12 and conducts high temperature heat away from the radiant heat pump.
• the target 12 must also be sufficiently rigid to maintain its concentricity in the assembly to an acceptable accuracy.
• Highly conductive metals, such as copper are potential materials from which the target 12 may be comprised, however other materials are not intended to be excluded if they function as required in this invention.
• the convective performance inside the targets 12 may be enhanced by providing the interior of the target 12 with turbulence inducing inserts, or by surface roughening of the interior wall of the target 12.
• the outside surface of each target 12 will be coated with a material having a very high infrared absorbtivity.
• the geometric parameters of the radiant heat pump 10 of this invention will preferably include:
• an emitter assembly 14 length to diameter ratio in the range of 2:1 to 6:1; and 3. a ratio of shell assembly 14 inner diameter/target 12 outer diameter of between 10:1 and 50:1. If the rigidity of a composite or metal emitter assembly 14 assembled according to the above methods proves inadequate, the emitter assembly 14 may be reinforced with an external metallic frame (not shown). This approach may prove to be more economical than the use of metallic emitter plates 16, particularly in the case of composite emitters.

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