Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D20/00—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00
  • F28D20/0056—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00 using solid heat storage material
• • 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
  • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
  • F25B9/14—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the cycle used, e.g. Stirling cycle
• • 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
  • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
• • 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
  • F25B9/00—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point
  • F25B9/10—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point with several cooling stages
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F28—HEAT EXCHANGE IN GENERAL
  • F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
  • F28D20/00—Heat storage plants or apparatus in general; Regenerative heat-exchange apparatus not covered by groups F28D17/00 or F28D19/00
• • 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
  • F25B2309/00—Gas cycle refrigeration machines
  • F25B2309/003—Gas cycle refrigeration machines characterised by construction or composition of the regenerator
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/14—Thermal energy storage

Definitions

• the invention relates to a heat storage medium for a low-temperature range, to a regenerator for low-temperature refrigerators and to a low-temperature refrigerator.
• Low-temperature refrigerators are generally multi-stage gas refrigerators that are used to generate temperatures in the range below 15 Kelvin.
• Such gas refrigeration machines work according to various methods, for example according to the Gifford-McMahon, Stirling or Pulse-Tube method.
• These refrigerators are independent of the working processes common that they have in the area of a so-called cold head between the hot side and the cold side a volume flowed through by the working fluid, which is filled with the heat storage agent and is called a regenerator.
• the regenerator is traversed alternately from a working fluid in both directions, and "serving as a buffer for received from the working fluid and at this released heat.
• the regenerator is a thermal.
• the regenerator It must have the highest possible heat capacity compared to the fluid flowing through. While temperatures of up to 15 Kelvin can be used as heat storage medium in the regenerator, stainless steel, bronze, lead or other metal bodies, this is not possible for significantly lower temperatures because the specific The heat capacity of these metals drastically decreases compared to that of helium from 30 Kelvin downwards and approaches zero in the range below 5 Kelvin.For very low temperature ranges, ie in the range below 15 Kelvin, are therefore used as heat sources in the rain Erator bulk material made of rare earth compounds used, as described for example in EP-A-0 411 591.
• rare earth connections A disadvantage of the use of rare earth connections is their magnetism, which is problematic in applications in strong magnetic fields, for example in magnetic resonance tomographs. Furthermore, rare earth compounds are sensitive to oxidation, tend to break due to their partial brittleness when vibrations occur, and are expensive. Helium and other low-boiling gases are also suitable as storage media for very low temperature ranges. For example, helium in the range below 15 Kelvin has a high specific heat capacity with a pressure-dependent maximum at approximately 9 Kelvin, which is thus far above the heat capacity of metals in this temperature range.
• regenerator in which helium is used as the heat storage medium, which, similar to a heat exchanger, is stationary in a spiral tube or a tube bundle in the regenerator housing.
• the regenerator housing can be filled with the helium storage medium, while the working fluid flows through the regenerator housing in pipes.
• regenerators constructed in this way showed, however, that a desired temperature of 4.2 Kelvin could not be reached, which is due to the high heat input due to the metallic spiral or tube material and the insufficient contact surface.
• the object of the invention is to provide a heat storage medium with a high heat capacity in a very low temperature range, a regenerator and a low-temperature refrigerator with a heat storage medium with a high heat capacity for very low temperatures. This object is achieved according to the invention by the features of claims 1, 10, 11 and 12 respectively.
• the heat storage medium according to the invention for ' a low temperature range i.e. for temperatures below 15 Kelvin, consists of a set of gas-tight hollow bodies that are permeable to the working fluid, and each hollow body has a filling of a low-boiling gas as a storage medium.
• Low-boiling gases are gases that have a boiling point below 30 Kelvin. This applies, for example, to the gases hydrogen, helium and neon, and to all of their isotopes. Low-boiling gases naturally have a relatively high specific heat capacity at low temperatures and are therefore well suited as a storage medium at temperatures below 30 Kelvin.
• Low-boiling gases are relatively inexpensive and can be enclosed in a hollow body with a hollow body wall made of non-magnetic, mechanically suitable, non-oxidizing and inexpensive material.
• the chemical, mechanical and magnetic properties of the heat storage medium can thus be adapted to the application.
• the gas-tight hollow bodies have a considerably larger surface than tubes or spirals, through which the heat exchange takes place. This significantly improves heat transfer.
• the storage medium is preferably a hollow body filling made of helium.
• a helium filling is a filling with a helium isotope, for example with 3 He or 4 He.
• the storage medium has helium at temperatures below 15 Kelvin has a relatively high specific heat capacity and is therefore well suited as a storage medium at temperatures down to the range of 2 Kelvin. Helium is also available inexpensively.
• the helium filling at a 'temperature of 4 Kelvin a pressure of about 0.5 bar, in particular a pressure above the critical pressure on.
• a helium filling pressure of more than 0.5 bar an absolute heat capacity is realized, which can store the heat that occurs in a relatively small regenerator.
• Such a regenerator is very compact compared to metallic heat accumulators.
• the material and the wall thickness of the hollow body wall are preferably selected such that the thermal penetration depth is at least one wall thickness.
• the thermal penetration depth ⁇ results from the equation
• a is the temperature conductivity of the selected hollow wall material at the working temperature (for example 2 Kelvin) and f mo ( _ is the modulation frequency with which the working gas flows through the heat storage medium in an alternating cycle.
• the working frequency f m ⁇ d is for low-temperature refrigerators at 1.0 to 10.0 Hz.
• the wall of the hollow body is made of metal. Metals and also metal alloys have good thermal conductivity and have good mechanical properties, which in turn can result in a low hollow body wall thickness.
• the hollow body wall can consist of copper, aluminum, silver, brass, steel or of other metals or metal alloys.
• the hollow body wall can alternatively also consist of ceramic.
• a heat storage medium can be used. Be made available that can be used without further measures for use in strong magnetic fields, e.g. for use in magnetic resonance tomographs etc. suitable is.
• each hollow body has a diameter of less than 3.0 mm. With diameters of less than 3.0 mm, a set of hollow bodies has such a large volume-specific surface that sufficient heat absorption or release is ensured. Typical diameters are 0.2 to 0.7 mm.
• Each hollow body preferably has approximately a spherical shape.
• a defined ratio between the surface of the hollow body, the total volume of the hollow body and the volume of the fill is approximately constant in the hollow body fill.
• a regenerator according to the invention has a housing which is filled with the heat storage medium described above.
• a low-temperature refrigerator according to the invention has the aforementioned regenerator and is designed as a regenerative circuit. process, preferably designed as a Gifford-McMahon, Stirling or Pulse-Tube refrigerator, helium being used as the working fluid. It is therefore used both as a storage medium helium and, separately, as a working fluid helium.
• FIG. 1 is a schematic representation of a refrigerator
• FIG. 2 shows a section through a refrigerator regenerator with a filling from a set of helium-filled hollow bodies
• Fig. 3 shows a section through a helium-filled hollow body.
• a refrigerator 10 is shown schematically in FIG. 1, the essential components of which are a compressor 12, a regenerator 14 and an expansion space 16 having a cold head.
• the compressor 12 and the regenerator 14 and the expansion space 16 are connected to one another by lines 18, 20.
• a working fluid preferably helium, is compressed by the compressor 12 and possibly pre-cooled.
• the compressed working fluid then runs through the gas line 18 and through the regenerator 14, in which it emits heat to a heat storage medium located in the regenerator 14.
• the working fluid flows further into the expansion space 16 and is subjected to a relaxation there.
• the working fluid that cools down in this way absorbs heat from the environment, in particular via a cold surface, and is then led back through line 20 to regenerator 14.
• the working fluid absorbs heat stored in the heat storage means and is fed back to the compressor 12 through the line 18.
• the regenerator 14 is used for thermal insulation between the compressor 12 and the expansion space 16.
• the refrigerator 10 can be designed as a Gifford-McMahon, Stirling or Pulse-Tube refrigerator, but can in principle also work according to another regenerative cycle, with a regenerator 14 being used for intermediate heat storage in a low-temperature range.
• a low temperature range means temperatures between 0 and 15 Kelvin.
• the regenerator 14 shown in longitudinal section in FIG. 2 is essentially formed by a cylindrical or oval housing 24, on the transverse housing walls 26, 27 of which the lines 18, 20 open.
• the regenerator housing 24 has, as heat storage means, a hollow body 30 that is pourable and gas-tight for the working fluid and closed gas-tight.
• the regenerator 14 can be filled homogeneously or in layers with different layers of different heat storage means.
• All hollow bodies 30 are approximately the same size and have approximately spherical shape.
• the bed can also consist of a mixture of hollow bodies of different diameters be formed.
• the hollow body wall 32 is made of copper or another metal or a metal alloy and has a thickness of approximately 0.2 mm. or less.
• the diameter of a hollow body 30 is 0.2 to 2.0 mm, but can also be larger, but not larger than 3.0 mm.
• the hollow body 30 is closed gas-tight and has a filling 34 made of helium.
• the helium filling 34 has a pressure of approximately 200 bar at room temperature and a pressure of several bar at a temperature of 4 Kelvin.
• the hollow bodies 30 filled with the helium filling 34 can be produced, for example, by a production method in which drops of the molten hollow wall material pass through a cooling chamber filled with helium gas.
• the filling of the hollow bodies can be formed from a single or a mixture of the different helium isotopes or from isotopes of hydrogen or neon or a mixture of the aforementioned elements.
• the choice of material for the hollow body wall, the modulation frequency with which the working gas flows through the regenerator alternately, and the wall thickness of the hollow body must be selected such that the depth of penetration ⁇ is at least one times the wall thickness. The depth of penetration ⁇ results from the equation
• a is the temperature conductivity of the selected hollow wall material at the working temperature (for example 4 Kelvin) and f mod is the modulation frequency with which the working gas cyclically alternates the heat storage medium flows through.
• the working frequency f mod can be assumed to be about 1.0 Hz for low-temperature refrigerators.
• the heat storage medium formed by the gas-tightly closed hollow bodies 30 having a helium filling has a high absolute heat storage capacity in a small volume, particularly in the very low temperature range of less than 15 Kelvin, due to the high specific heat capacity of helium in this temperature range.
• the heat storage means can be optimally adapted with regard to its electrical, mechanical and chemical requirements for each application, for example non-magnetic materials for the hollow body wall can be selected for cooling in magnetic resonance tomographs.
• heat storage elements can also be present in separate layers or mixed with the helium-filled hollow bodies 30 in the regenerator housing, for example heat storage elements made of rare earth alloys.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Mechanical Engineering (AREA)
• Thermal Sciences (AREA)
• General Engineering & Computer Science (AREA)
• Containers, Films, And Cooling For Superconductive Devices (AREA)
• Powder Metallurgy (AREA)

Applications Claiming Priority (2)

Publications (1)

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Family Applications (1)

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• 2003
  • 2003-04-24 DE DE10318510A patent/DE10318510A1/de not_active Withdrawn
• 2004
  • 2004-04-15 CN CNA2004800106551A patent/CN1777782A/zh active Pending
  • 2004-04-15 WO PCT/EP2004/003944 patent/WO2004094927A1/de not_active Application Discontinuation
  • 2004-04-15 JP JP2006505122A patent/JP2006524307A/ja active Pending
  • 2004-04-15 KR KR1020057020050A patent/KR20050113675A/ko not_active Application Discontinuation
  • 2004-04-15 EP EP04727558A patent/EP1616137A1/de not_active Withdrawn
  • 2004-04-15 US US10/553,487 patent/US20060201163A1/en not_active Abandoned
  • 2004-04-23 TW TW093111333A patent/TW200506296A/zh unknown

Non-Patent Citations (1)

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