Classifications

• • 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
  • F25B9/06—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point using expanders
• • 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
  • F25B25/00—Machines, plants or systems, using a combination of modes of operation covered by two or more of the groups F25B1/00 - F25B23/00
• • 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
  • F25B40/00—Subcoolers, desuperheaters or superheaters
• • 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
  • F25B7/00—Compression machines, plants or systems, with cascade operation, i.e. with two or more circuits, the heat from the condenser of one circuit being absorbed by the evaporator of the next circuit
• • 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
  • F25B9/002—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point characterised by the refrigerant
• • 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
  • F25B9/02—Compression machines, plants or systems, in which the refrigerant is air or other gas of low boiling point using Joule-Thompson effect; using vortex 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
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
  • F25J1/003—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production
  • F25J1/0047—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle
  • F25J1/005—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the kind of cold generation within the liquefaction unit for compensating heat leaks and liquid production using an "external" refrigerant stream in a closed vapor compression cycle by expansion of a gaseous refrigerant stream with extraction of work
• • 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
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
  • F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
  • F25J1/0062—Light or noble gases, mixtures thereof
• • 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
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
  • F25J1/006—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures characterised by the refrigerant fluid used
  • F25J1/0062—Light or noble gases, mixtures thereof
  • F25J1/0065—Helium
• • 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
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
  • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
  • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
  • F25J1/0244—Operation; Control and regulation; Instrumentation
• • 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
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J1/00—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures
  • F25J1/02—Processes or apparatus for liquefying or solidifying gases or gaseous mixtures requiring the use of refrigeration, e.g. of helium or hydrogen ; Details and kind of the refrigeration system used; Integration with other units or processes; Controlling aspects of the process
  • F25J1/0243—Start-up or control of the process; Details of the apparatus used; Details of the refrigerant compression system used
  • F25J1/0257—Construction and layout of liquefaction equipments, e.g. valves, machines
  • F25J1/0275—Construction and layout of liquefaction equipments, e.g. valves, machines adapted for special use of the liquefaction unit, e.g. portable or transportable devices
  • F25J1/0276—Laboratory or other miniature devices
• • 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
  • F25B19/00—Machines, plants or systems, using evaporation of a refrigerant but without recovery of the vapour
  • F25B19/005—Machines, plants or systems, using evaporation of a refrigerant but without recovery of the vapour the refrigerant being a liquefied gas
• • 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
  • F25B2309/004—Gas cycle refrigeration machines using a compressor of the rotary type
• • 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
  • F25B2309/005—Gas cycle refrigeration machines using an expander of the rotary type
• • 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
  • F25B2309/02—Gas cycle refrigeration machines using the Joule-Thompson effect
  • F25B2309/023—Gas cycle refrigeration machines using the Joule-Thompson effect with two stage expansion
• • 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
  • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
  • F25B2400/04—Refrigeration circuit bypassing means
  • F25B2400/0411—Refrigeration circuit bypassing means for the expansion valve or capillary tube
• • 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
  • F25B2400/00—General features or devices for refrigeration machines, plants or systems, combined heating and refrigeration systems or heat-pump systems, i.e. not limited to a particular subgroup of F25B
  • F25B2400/05—Compression system with heat exchange between particular parts of the system
• • 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
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2245/00—Processes or apparatus involving steps for recycling of process streams
  • F25J2245/02—Recycle of a stream in general, e.g. a by-pass stream
• • 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
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2270/00—Refrigeration techniques used
  • F25J2270/14—External refrigeration with work-producing gas expansion loop
  • F25J2270/16—External refrigeration with work-producing gas expansion loop with mutliple gas expansion loops of the same refrigerant
• • 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
  • F25J—LIQUEFACTION, SOLIDIFICATION OR SEPARATION OF GASES OR GASEOUS OR LIQUEFIED GASEOUS MIXTURES BY PRESSURE AND COLD TREATMENT OR BY BRINGING THEM INTO THE SUPERCRITICAL STATE
  • F25J2270/00—Refrigeration techniques used
  • F25J2270/90—External refrigeration, e.g. conventional closed-loop mechanical refrigeration unit using Freon or NH3, unspecified external refrigeration
  • F25J2270/912—Liquefaction cycle of a low-boiling (feed) gas in a cryocooler, i.e. in a closed-loop refrigerator

Definitions

• the invention relates to a system and a method for cryogenic refrigeration.
• the invention relates to a heat exchanger configuration to recycle a cryogenic refrigerant to improve the refrigeration efficiency, e.g. for a thermally coupled load such as a refrigeration circuit for high temperature superconductors.
• Superconductive cables are commonly cooled using a thermally coupled liquid nitrogen circuitry, wherein the liquid nitrogen absorbs excess heat produced in said cables during normal operation and is accordingly evaporated.
• the evaporated nitrogen often leaves the system without being recycled and is accordingly lost, e.g. in open configurations.
• Such solutions are generally only economically viable at low to medium cooling capacity requirements. At higher cooling capacities, e.g. above 10-20 kW, operating costs become predominant in such open systems.
• closed loop refrigeration systems become favorable despite their high capital expenses.
• the temperature range is generally limited as the capacity of high temperature superconductors, e.g. cables, is reduced with a dropping temperature while at the same time the triple point of nitrogen is at 63 K. Accordingly, the temperature range is generally predefined by the required temperature for superconductive properties of a used load and the lower temperature limit of the used refrigerant for avoiding said refrigerant to attain a solid phase.
• Helium is therefore typically compressed in oil injected screw compressors, which generally results in a total system isentropic efficiency of below 20 percent. Accordingly, a need exists to further increase the isentropic efficiency of cryogenic refrigeration systems without significantly increasing the complexity and/or the control of such systems.
• a cryogenic refrigeration system which comprises a supply means for providing a supply flow of a cryogenic refrigerant, a compressor fluidly coupled to said supply means and configured to compress the supplied cryogenic refrigerant, and a cold box fluidly coupled to the compressor.
• the cold box comprises a first expansion device and a first heat exchanger, wherein the first expansion device is configured to receive the compressed cryogenic refrigerant from the compressor and expand it and provide the expanded refrigerant to the first heat exchanger, and wherein the first heat exchanger is configured to be thermally coupled to a load.
• the system comprises a second heat exchanger arranged in the cold box, which comprises at least a first and second heat exchanging section.
• the first heat exchanging section is configured to receive the expanded refrigerant from the expansion device and to subsequently provide the received expanded refrigerant to the first heat exchanger and the second heat exchanging section is configured to receive the expanded refrigerant from the first heat exchanger and to subsequently provide the expanded heated refrigerant to the first heat exchanger, wherein the first and second heat exchanger sections are thermally coupled.
• the first heat exchanger is configured to provide the received expanded refrigerant to the supply means and/or the compressor.
• Such configuration has the advantage that instead of directly providing a cooling medium to the first heat exchanger after the expansion stage the expanded or cooled refrigerant is first warmed up by the received expanded refrigerant from the first heat exchanger, i.e. the expanded refrigerant is recycled after a first round of cooling provided in the first heat exchanger.
• This allows expanding the cryogenic refrigerant to a much colder temperature according to the required and allowable cryogenic refrigeration capacity of the first heat exchanger.
• the received expanded refrigerant which may hence be a warmed cooled refrigerant, from the first heat exchanging section, and the received expanded refrigerant, i.e. from the second heat exchanging section, to the first heat exchanger, this allows to transfer double the cooling capacity without increasing the mass flow.
• the isentropic efficiency of the first heat exchanger is increased without requiring a coupled compressor and expansion device and corresponding control system.
• the adversary effect of a loss of refrigerant in common compressors is not enhanced since the mass flow is not required to be increased.
• the various features of the system may be connected to each other either directly or by means of at least one conduit or tube section.
• the cold box may furthermore be fluidly coupled with the compressor and/or supply means by means of valves, e.g. check valves, arranged outside or at the junction of the cold box.
• the compressor and/or the supply means may hence be connected to the cold box via said valves either directly or by means of a conduit, wherein an outlet of the compressor is connected to an inlet of a valve of the cold box, i.e. to provide a supply flow to the cold box, and an inlet of the compressor and/or supply means is connected to an outlet of a valve of the cold box, i.e. to provide a return supply flow from the first heat exchanger.
• the first and second heat exchanger may comprise inlets and outlets to provide a fluid coupling between each other and the expansion device, supply means, and/or compressor, where applicable.
• the first expansion device may be configured to provide the expanded refrigerant to a first inlet of the first heat exchanger for providing an expanded and/or cooled refrigerant to the first heat exchanger, wherein the first heat exchanging section of the second heat exchanger is fluidly coupled with the first expansion device via a first inlet of the second heat exchanger to receive the expanded refrigerant and is fluidly coupled with the first inlet of the first heat exchanger via a first outlet of the second heat exchanger to provide the expanded refrigerant to the first heat exchanger.
• the second heat exchanging section may be fluidly coupled to the first outlet of the first heat exchanger via a second inlet of the second heat exchanger to receive the expanded refrigerant and is configured to provide the received expanded refrigerant to the first heat exchanger via a second outlet of the second heat exchanger and a second inlet of the first heat exchanger.
• the first heat exchanger may then be configured to provide the received expanded refrigerant to the supply means and/or the compressor via a second outlet of the first heat exchanger.
• the system comprises a supply means and a compressor to provide a compressed cryogenic refrigerant to the cold box.
• the supply means may comprise e.g. a large vessel or any other means providing a sufficient supply flow of the cryogenic refrigerant, e.g. a coupling to a process medium flow of a refrigeration plant or refrigerant producing means.
• the supply means and the compressor may be fluidly coupled and arranged separately from each other, but may also be combined at an inlet of the system to provide a more compact arrangement.
• the expansion device may be configured as an expansion valve, expansion vessel or expansion turbine, with or without an additional pressure regulator and/or pressure control valve.
• the expansion device comprises a constant pressure, which is lower than the pressure upstream of the expansion device. Accordingly, the expansion device is configured to reduce the pressure of the compressed cryogenic refrigerant to such an extent that due to a sudden volume increase in the expansion device, e.g. by correspondingly sizing and dimensioning, the compressed refrigerant is relaxed resulting in a rapid pressure reduction of the refrigerant, such that preferably a gas phase is generated.
• the temperature of the relaxed refrigerant may remain constant or be reduced, the latent heat of the refrigerant is reduced, such that an amount of heat may be absorbed.
• all features of the system are preferably thermally isolated, such that the amount of heat entering and leaving the system is considered to be zero or negligible.
• the cold box may further comprise a second expansion device, wherein the second heat exchanger further may comprise a third and fourth heat exchanging section.
• the second expansion device may be fluidly coupled to the first heat exchanger and the second heat exchanger and be configured to receive the expanded refrigerant received by the first heat exchanger from the second heat exchanging section, provide an expansion of said refrigerant, and subsequently provide the secondary expanded refrigerant to the first heat exchanger via the third heat exchanging section.
• the fourth heat exchanging section may accordingly be configured to receive the secondary expanded refrigerant from the first heat exchanger and to subsequently provide the received secondary expanded refrigerant to the first heat exchanger.
• at least the third and fourth heat exchanging section may be thermally coupled.
• heat may be exchanged between the third and fourth heat exchanger sections, such that the secondary expanded refrigerant may be warmed by the received secondary expanded refrigerant from the first heat exchanger before being provided to the first heat exchanger.
• the third and/or fourth heat exchanging sections may be thermally coupled to the first and/or second heat exchanging sections, such that an even further improved heat exchange may be provided and an even colder expanded refrigerant may be provided by the first expansion device.
• the refrigerant exiting the first heat exchanger may hence be recycled twice, such that a quadruple cooling capacity is provided without increasing the mass flow.
• the recycling of the refrigerant by means of an expansion device and the heat exchanger may be repeated by including further expansion devices and heat exchanging sections.
• the recycling may be repeated a third or more time.
• the first and/or second heat exchanger may be configured as a series of heat exchangers.
• one or more additional heat exchangers may be provided that are arranged in the cold box and upstream of the expansion device.
• Such heat exchangers may hence receive both the compressed refrigerant from the compressor and the expanded refrigerant from the first heat exchanger, such that the compressed refrigerant is preheated before expansion and the expanded refrigerant that is returned to the supply means and/or compressor is pre-cooled before compression.
• the compressor of the cryogenic refrigeration system is a screw compressor or a turbo compressor.
• the compressor furthermore preferably comprises magnetic couplings and/or comprises or is configured as a serial compressor.
• the compressor may be configured to compress the refrigerant at ambient temperature.
• the implementation of a screw compressor provides a cost efficient compression while at the same time this increases the isentropic efficiency to about 31 percent.
• the implementation of a screw compressor is advantageous for refrigerants having a higher density, e.g. neon, which may hence be compressed at higher efficiencies.
• the implementation of a turbo compressor may be advantageous for refrigerants having a lower density, e.g. helium, and further improves the isentropic efficiency to over 42 percent.
• This furthermore allows a configuration of the compressor with magnetic couplings to ensure that only a minimum of refrigerants is lost.
• one or more serial turbo compressors may be used, as known from e.g. climatization or buildings.
• the use of a turbo compressor furthermore has the advantage that a hermetic sealing is provided, which is free of oil lubrication. Accordingly, an oil removal system, which may be required in a helium-based cryogenic refrigeration system, may be omitted.
• a compression at ambient temperature does not require any pre-cooling or temperature control and hence provides a cost efficient compression.
• the compressor and the expansion device are controlled separately and operated independently, e.g. the expansion device does not drive the compressor and vice versa. Accordingly, a control system may be provided, which independently regulates the compression pressure by controlling the compressor and the constant pressure of the expansion device.
• control system may be provided with a feedback mechanism, e.g. one or more sensors, in particular pressure sensors that are in fluid communication with the refrigerant and/or temperature sensors, to ensure that the system provides the cryogenic refrigeration according to predefined or set values and parameters.
• a feedback mechanism e.g. one or more sensors, in particular pressure sensors that are in fluid communication with the refrigerant and/or temperature sensors, to ensure that the system provides the cryogenic refrigeration according to predefined or set values and parameters.
• the first heat exchanger of the cryogenic refrigeration system is thermally coupled to a load.
• the load may comprise a refrigeration circuit for a high temperature
• superconductor e.g. a cable system.
• the load may be a refrigeration circuit or circuitry, which enters a warm end of the first heat exchanger and exits the first heat exchanger at a cold end.
• the term“warm end” is to be understood as the end of the first heat exchanger, where the expanded or cooled refrigerant has been heated for at least a first cycle and exits the first heat exchanger as an expanded or heated refrigerant.
• the term“cold end” is to be understood as the end of the first heat exchanger, where the expanded refrigerant provided via the second heat exchanger enters the first heat exchanger.
• the load comprises a second cryogenic refrigerant, wherein said second cryogenic refrigerant preferably comprises liquid nitrogen.
• the use of liquid nitrogen may be advantageous for a variety of loads with superconductor characteristics at relatively high temperatures.
• other circulating liquids or gases at different temperatures may be efficiently refrigerated with the proposed configuration.
• other cooling circuits may be provided.
• the load instead of traversing the first heat exchanger, the load may be thermally coupled by means of an adjacent arrangement.
• the first heat exchanger, or a series of first heat exchangers may be arranged to provide cryogenic refrigeration for a plurality of loads or refrigeration circuits.
• the second refrigerant in the refrigeration circuit may be compressed before entering the first heat exchanger.
• a further or alternative compression of the second refrigerant may be provided downstream of the first heat exchanger and upstream of the load to be cooled.
• the load is preferably provided us as a constant load and/or the cryogenic refrigeration is preferably provided at a constant mass flow, temperature, and physical state of the cryogenic refrigerant.
• the system preferably comprises fixed process conditions, which hence may be compatible with refrigeration plants and/or supply flows of a process medium.
• At least the first and second heat exchanging sections and/or the third and fourth heat exchanging sections may be arranged to each other to provide counter flow, cross flow, or equal flow heat exchanging sections.
• This also applies to the first heat exchanger, such that heat exchanging sections of the first heat exchanger may be similarly arranged to each other and/or with respect to a thermally coupled load, such as a refrigeration circuit.
• the compressor and/or the supply means may be configured to provide the refrigerant to the first expansion device as a gaseous refrigerant.
• said configuration also ensures that a gaseous refrigerant is provided to the second expansion device.
• the first heat exchanger does not require e.g. a vessel or phase separator at the lower temperature range to collect a liquid phase of the refrigerant and at the same time an evaporated gas flow with low specific enthalpy may be provided.
• smaller equipment such as compressors and heat exchangers may be provided, such that the dimensions of the system may be reduced.
• the first expansion device may also be configured to provide a two-phase or gas phase refrigerant, wherein the first heat exchanger is configured as a cold gas heat exchanger and to receive a gas phase from the cooled refrigerant.
• the expansion device may hence also provide a liquid and a gas phase, wherein preferably the first heat exchanger comprises a vessel, which collects the liquid phase and provides the gas phase as a cryogenic refrigerant.
• the use of a cold gas heat exchanger in comparison to an evaporating gas exchanger, has the advantage that no recirculation of flash gas or evaporated helium on the atmospheric pressure occurs.
• the cryogenic refrigerant comprises helium and/or neon.
• the used cryogenic refrigerant may be chosen according to the required cooling.
• the cooling may be dependent on the required temperature of a thermally coupled high temperature superconductor, which is known to reduce the capacity with decreasing temperature.
• the cryogenic refrigerant needs to be maintained and a pressure and temperature above the respective triple point.
• the triple point of nitrogen is at 63 K, such that for lower temperature ranges the use of nitrogen may not be applicable and hence other refrigerants, such as e.g. helium and/or neon may be used.
• the choice of cryogenic refrigerant may depend on the implemented compressor type, as outlined in the above.
• other refrigerants such as hydrogen or mixtures or compositions may be used.
• the cryogenic refrigeration system may further comprise an evaporating heat exchanger arranged outside of the cold box and upstream of the first expansion device and which is thermally coupled to the provided compressed cryogenic refrigerant supply flow.
• the expanded refrigerant or cooled refrigerant may hence be provided at a lower temperature to the second heat exchanger, thereby further improving the cooling efficiency of the first heat exchanger.
• the evaporating heat exchanger preferably comprises a liquid water or hydrogen circuit as a refrigerant to be evaporated.
• gaseous hydrogen may be provided as a cold gas heat exchanger.
• the implementation of water or hydrogen has the advantage that this forms a cost-effective cooling and the evaporated refrigerant may be simply released into the atmosphere after exiting the evaporating heat exchanger.
• the system may further comprise an evaporating heat exchanger arranged in the cold box and upstream of the first expansion device and which is thermally coupled to the provided compressed cryogenic refrigerant supply flow to pre-cool said refrigerant.
• the evaporating heat exchanger comprises a liquid nitrogen circuit as a refrigerant to be evaporated.
• the arrangement within the cold box has the advantage that the pre-cooling efficiency is increased while simultaneously reducing the dimensions of the system. Furthermore, a part of or excess second refrigerant being used in a load, e.g. in a refrigeration circuit, such as liquid nitrogen, may be provided to pre-cool the compressed cryogenic refrigerant prior to expansion.
• a refrigeration circuit such as liquid nitrogen
• a method for providing a cryogenic refrigeration comprising the steps of providing a supply flow of a cryogenic refrigerant by a supply means, compressing the supplied cryogenic refrigerant by a compressor, expanding the compressed cryogenic refrigerant by a first expansion device in a cold box, and providing the expanded refrigerant to a first heat exchanger in the cold box, wherein the first heat exchanger is configured to be thermally coupled to a load.
• the expanded refrigerant is received from the expansion device by a first heat exchanging section of a second heat exchanger in the cold box is subsequently provided to the first heat exchanger.
• the expanded refrigerant from the first heat exchanger is received by a second heat exchanging section of the second heat exchanger and is subsequently provided to the first heat exchanger, wherein heat is exchanged between the first and second heat exchanger section.
• the expanded refrigerant received by the first heat exchanger from the second heat exchanging section is furthermore provided to the supply means and/or the compressor.
• providing the expanded refrigerant from the first heat exchanger to the second heat exchanger and allowing a heat exchange through a thermal coupling with the expanded refrigerant received from the expansion device has the advantage that the expanded refrigerant is first warmed up before being used as a cryogenic refrigerant for, which allows expanding the cryogenic refrigerant to a much colder temperature according to the required and allowable cryogenic refrigeration capacity of the first heat exchanger.
• the received expanded refrigerant which may hence be a pre-warmed cooled or expanded refrigerant, from the first heat exchanging section, and the received expanded refrigerant, i.e.
• the method also comprises that the expanded refrigerant received by the first heat exchanger from the second heat exchanging section is received and expanded by a second expansion device, wherein the secondary expanded refrigerant is provided to the first heat exchanger via a third heat exchanging section of the second heat exchanger.
• the secondary expanded refrigerant from the first heat exchanger is furthermore received by a fourth heat exchanging section of the second heat exchanger and subsequently provided via the fourth heat exchanging section to the first heat exchanger, wherein heat is exchanged between at least the third and fourth heat exchanger section.
• the method may provide that the refrigerant exiting the first heat exchanger is hence recycled twice, such that a quadruple cooling capacity is provided without increasing the mass flow.
• going through a second expansion device and the second heat exchanger enables to transfer even four times the cooling capacity with the same mass flow at the same temperature range.
• the compression of the supplied first cryogenic refrigerant may furthermore be provided by a screw compressor, a turbo compressor, and/or at ambient temperature.
• the cryogenic refrigerant preferably comprises helium and/or neon.
• the method may furthermore comprise that the first heat exchanger provides a cryogenic refrigeration of a thermally coupled load, wherein said load preferably comprises a refrigeration circuit for a high temperature superconductor.
• a load preferably comprises liquid nitrogen as a second cryogenic refrigerant.
• the first heat exchanger may provide cryogenic refrigeration to e.g. a liquid nitrogen-based refrigeration circuit, which provides refrigeration to a high temperature superconductor at a supercritical temperature and pressure, wherein the provided recycling of the cryogenic refrigerant provides an improved cooling efficiency compared with known systems without requiring a complex control system or increasing the mass flow.
• Figure 1 is a schematic view of a first and second heat exchanger in a cryogenic system with a single recycling of the first cryogenic refrigerant
• Figure 2 is a schematic view of the embodiment according to Figure 1 with a double recycling of the first cryogenic refrigerant;
• Figure 3 is a schematic view of a first and second heat exchanger in a cryogenic system with a double recycling of the first cryogenic refrigerant and additional evaporating heat exchangers; and
• Figure 4 is a schematic view of a first and second heat exchanger in a further cryogenic system with a double recycling of the first cryogenic refrigerant and additional evaporating heat exchangers.
• a cryogenic refrigeration system 1 is schematically shown in operation using liquid helium as a cryogenic refrigerant and thermally coupled to a load 7. Accordingly, a supply flow of the liquid helium is provided by a supply means 2, which is fluidly coupled to a compressor 3.
• the supply means 2 according to the embodiment of Figure 1 is configured as a coupling to a refrigeration plant, which provides a continuous supply flow of liquid helium.
• the supply means 2 may also comprise e.g. a larger vessel providing the required amount and flow of liquid helium to the system 1 .
• the supply means 2 provides the supply flow of liquid helium as a cryogenic refrigerant to the fluidly coupled compressor 3, which is arranged downstream thereof and is configured as a screw compressor. Accordingly, the liquid helium is pressurized and provided as a compressed cryogenic refrigerant 20.
• the use of a screw compressor may require the implementation of a downstream oil removal system (not shown), depending on the used refrigerant and specifications of the compressor.
• the compressed cryogenic refrigerant 20, i.e. the pressurized liquid helium is then provided to the cold box 10 by means of a fluid coupling or valve at the junction of the cold box 10. This configuration ensures that the cold box 10 is essentially thermally isolated and only connected to the outside components via a said fluid coupling.
• the compressed cryogenic refrigerant 20 is received by a first expansion device 4, which is depicted as a pressure regulator and an expansion valve.
• a first expansion device 4 depicted as a pressure regulator and an expansion valve.
• other configurations including only an expansion valve, an expansion turbine, or a combined expansion valve and pressure regulator may be provided.
• the cryogenic refrigeration system 1 requires a normalization and stabilization of the temperatures in the system 1 during start up or an initial phase of operation, the temperature and pressure of the cryogenic refrigerant at various points or locations in the system 1 is considered to be constant and predictable during normal operation.
• the expansion device 4 comprises a constant pressure, which is lower than the pressure upstream of the expansion device 4, and is configured to provide a gas phase from the compressed cryogenic refrigerant 20.
• the compressed cryogenic refrigerant 20 is hence expanded, such that a relaxation of the pressurized liquid helium occurs, thereby increasing the volume of the first cryogenic refrigerant. Accordingly, the latent heat of the compressed cryogenic refrigerant 20 is reduced, thereby allowing the liquid helium to further absorb heat.
• the expansion device 4 hence provides an expanded refrigerant 22, which may have a lower temperature compared with the compressed cryogenic refrigerant 20 and which is received by a first heat exchanging section 6A of a second heat exchanger 6.
• the expanded refrigerant 22 is then passed to a first heat exchanger 5 via a respective inlet.
• the expansion device 4 may be configured to provide the expanded refrigerant 22 as a liquid or two-phase refrigerant
• the expansion device 4 according to Figure 1 is configured to provide the expanded refrigerant 22 in a gaseous state, such that the first heat exchanger 5 is configured as a cold gas heat exchanger.
• the cooled helium absorbs heat from the thermally coupled load 7, such that the cooled helium exits the first heat exchanger 5 via a respective outlet as an expanded refrigerant 24, which may be a heated refrigerant compared with the expanded refrigerant 22 exiting the expansion device.
• the load 7 is provided with cryogenic refrigeration, such that e.g. a high temperature superconductor may be accordingly cooled.
• the expanded refrigerant 24 from the first heat exchanger is provided to a second heat exchanger section 6B of the second heat exchanger 6, which is thermally coupled to the first heat exchanging section 6A.
• the received expanded refrigerant 24 hence traverses the second heat exchanging section 6B and is then passed to the first heat exchanger 5 via a respective inlet.
• the expanded refrigerant 24 received from the second heat exchanging section 6B absorbs heat within the first heat exchanger 5.
• the received expanded refrigerant 24 then exits the first heat exchanger 5 via a respective outlet and returns the expanded refrigerant 24 to the supply means 2, such that it can be re-used in the system 1 .
• the cryogenic refrigerant is recycled once before being returned to the compressor 3. Since the first and second heat exchanging sections 6A, 6B are thermally coupled, the expanded refrigerant 22 is provided to the first heat exchanger 5 in a relatively warmed state compared with the expanded refrigerant 22 exiting the expansion device 4 while at the same time the expanded refrigerant 24 from the first heat exchanger 5 exiting the second heat exchanger 6 is provided to the first heat exchanger 5. Not only does this allow a further expansion and the provision of a corresponding lower temperature of the compressed first cryogenic refrigerant 20, this also provides a doubling of the cooling capacity of the first heat exchanger 5 without increasing the mass flow. Accordingly, the isentropic efficiency is improved by this configuration.
• the compressor 3 and the expansion device 4 may be controlled separately and independently without requiring complex control systems or a mechanical coupling, i.e. without having the output of the compressor linked to the expansion device and vice versa.
• the embodiment according to Figure 1 schematically depicts that he first heat exchanger 5 is configured to provide all of the expanded refrigerant 24 received from the first heat exchanging section 6A to the second heat exchanging section 6B, it may also be provided that only a branch of the expanded refrigerant 24 is provided to the second heat exchanging section 6B, while the rest of the expanded refrigerant 24 is returned to the supply means 2.
• the embodiment according to Figure 1 is described with respect to liquid helium as a first cryogenic refrigerant, other refrigerants, such as e.g. neon, may be used.
• Figure 1 schematically depicts the first and second heat exchanger 5, 6 as equal flow heat exchangers.
• Flowever other configurations, such as a counter flow or cross flow heat exchanger may be provided instead of or in addition to an equal flow heat exchanger.
• the embodiment according to Figure 2 generally resembles the embodiment according to Figure 1 .
• the embodiment according to Figure 2 comprises a double recycling of the cryogenic refrigerant, as depicted by the additional return loop of the expanded refrigerant 24 from the first heat exchanger 5.
• the cryogenic refrigeration system 1 comprises a second expansion device 40 in the cold box 10 and the second heat exchanger 6 comprises an additional third and fourth heat exchanging section 6C, 6D.
• the second expansion device 40 is fluidly coupled to an outlet of the first heat exchanger 5 to accordingly receive the expanded refrigerant 24 received by the first heat exchanger 5 to expand said refrigerant 24 for providing a secondary expanded refrigerant 26 to the first heat exchanger 5 via the third heat exchanging section 6C.
• the fourth heat exchanging section 6D is configured to receive a secondary expanded refrigerant 28 from a respective outlet of the first heat exchanger 5 and to provide the received secondary expanded refrigerant 28 to the first heat exchanger 5.
• the third and fourth heat exchanger sections 6C, 6D are thermally coupled, such that heat is exchanged between said sections and the secondary expanded refrigerant 26 may hence be warmed by the secondary expanded refrigerant 28 before entering the first heat exchanger 5. Therefore, the expanded refrigerant 22 may be provided at an even lower temperature.
• the received secondary expanded refrigerant 28 from the first heat exchanger may be pre-cooled before entering the first heat exchanger 5, such that the overall cooling capacity is quadrupled without increasing the mass flow.
• the compressor 3 according to the embodiment is provided as a turbo compressor having magnetic couplings. Hence, no oil removal system is required and the energetic efficiency is even further increased. Alternatively, however, a screw compressor and, optionally, an oil removal system, may also be used.
• the first and second expansion devices 4, 40 are configured to provide a gas phase of the liquid helium, such that the first and second heat exchangers 5, 6 are configured as cold gas heat exchangers.
• the heat exchangers may also be configured to receive both a gas phase and a liquid phase, e.g. from a two-phase expanded refrigerant 22 and/or secondary expanded refrigerant 26, for example, by means of a phase separator or a vessel.
• the thermally coupled load 7 is configured as a refrigeration circuit 70 for a high temperature superconductor, e.g. a cable.
• the refrigeration circuit 70 enters the cold box 10 and is configured in a counter flow arrangement with respect to the first heat exchanger 5. Accordingly, the refrigeration circuit 70 is configured to enter the first heat exchanger 5 at a warm end and to exit the first heat exchanger 5 at a respective cold end, such that a second cryogenic refrigerant in the refrigeration circuit 70 may be efficiently cooled by the first heat exchanger 5.
• the second cryogenic refrigerant e.g. liquid nitrogen, then leaves the cold box 10 and is provided to e.g. a cable to provide the required cooling.
• the cold box 10 comprises an evaporating heat exchanger 8B, which is arranged upstream of the expansion device 4 and ensures that the compressed cryogenic refrigerant 20 is cooled down before being expanded by the expansion device 4.
• the evaporating heat exchanger 8B comprises a liquid nitrogen circuit 82, which enters the evaporating heat exchanger at a warm end of the evaporating heat exchanger 8B and is thermally coupled to the provided compressed cryogenic refrigerant 20, such that heat from the compressed cryogenic refrigerant 20 may be absorbed by the liquid nitrogen.
• the liquid nitrogen thereby evaporates into a gas phase, which exits the evaporating heat exchanger 8B and may be either released into the atmosphere or be received by e.g. a liquefaction plant.
• liquid nitrogen circuit 82 is depicted in the embodiment to be provided within the cold box 10, e.g. by a respective branch of the refrigeration circuit 70, the liquid nitrogen circuit 82, may also be partly provided outside of the cold box 10 via a respective coupling. By the same token, the evaporated liquid nitrogen may also be retained within the cold box 10 instead of being released outside of the cold box 10, e.g. into the atmosphere.
• the system 1 furthermore comprises an evaporating heat exchanger 8A, which is arranged outside of the cold box 10, upstream of the evaporating heat exchanger 8B, and downstream of the compressor 3.
• the evaporating heat exchanger 8A comprises a water circuit 80 and is thermally coupled to the supplied compressed cryogenic refrigerant 20, such that heat may be exchanged between the compressed cryogenic refrigerant 20 and the water of the water circuit 80. Accordingly, the water absorbs heat and is evaporated, such that the water exits the evaporating heat exchanger 8A in a gas phase.
• the evaporated water may be released into the atmosphere or may be e.g. re-used after a
• refrigeration circuit 70 the water circuit 80, and the liquid nitrogen circuit 82 are schematically depicted in a counter flow arrangement, other configurations, such as equal flow or cross flow arrangements may also be provided.
• the embodiment according to Figure 4 generally corresponds to the embodiment according to Figure 3, such that like features are denoted by identical reference numerals and repeated description thereof is omitted in order to avoid redundancies.
• the cold box 10 according to the embodiment of Figure 4 comprises further cold gas heat exchangers 8C, 8D, which are arranged upstream of the expansion device 4.
• the cold gas heat exchanger 8C is arranged upstream of the evaporating heat exchanger 8B, wherein the compressed cryogenic refrigerant 20 is thermally coupled both with the liquid nitrogen circuit 82 and the secondary expanded refrigerant 28 being returned to the supply means 2 from the first heat exchanger 5.
• the compressed cryogenic refrigerant 20 is pre-cooled by the evaporating gas from the liquid nitrogen exiting the evaporating heat exchanger 8B and the returning gas in the secondary expanded refrigerant 28.
• the returning gas in the secondary expanded refrigerant 28 may be pre-cooled due to the evaporating heat exchanger 8A, depending on the system conditions.
• the cold gas heat exchanger 8D is arranged upstream of the first expansion device 4 and downstream of both the evaporating heat exchanger 8B and the cold gas heat exchanger 8C.
• the compressed cryogenic refrigerant 20 is thermally coupled to the secondary expanded refrigerant 28 from the first heat exchanger 5, such that the compressed cryogenic refrigerant 20 is further cooled due to heat exchange with the returning gas in the secondary expanded refrigerant 28.
• further evaporating heat exchangers 8A, 8B and cold gas heat exchangers 8C, 8D provides a system with an even further improved energetic efficiency.
• the refrigeration circuit 70 may comprise a compressor 72 upstream of the first heat exchanger 5.
• the compressor 72 is schematically depicted in the cold box 10, a compressor 72 may also be arranged outside of the cold box 10, depending on the requirements of the system 1 .
• the liquid nitrogen being returned to the first heat exchanger 5 may be compressed before being cooled by the first heat exchanger 5 and before being returned to e.g. a cable.
• the refrigeration circuit 70 may furthermore comprise an expansion device arranged downstream of the first heat exchanger 5 (not shown) to further improve the cryogenic refrigeration capacity of the load 7.
• the system 1 comprises control units 9A, 9C 2, respectively control the compressor 3 and the first expansion device 4. Both control units 9A, 9C are connected to a main controller 9, which is generally configured to monitor the respective control units 9A, 9C.
• the system 1 may furthermore comprise one or more sensors, e.g., temperature and/or pressure sensors, which provide measurement signals to the respective control unit.
• the system 1 comprises further control units 9B,
• control units 9D to respectively control the second expansion device 40 and the compressor 72 of the refrigeration circuit 70.
• Said control units 9B, 9D are furthermore in communication with the main controller 9, such that these may also be monitored by the controller 9.
• the provision of the independent control units 9A, 9B, 9C, 9D and the controller 9 generally improves the controllability, predictability, and stability of the system 1 .
• said one or more control units 9A, 9B, 9C, 9D may also be merely optional.
• the second expansion device 40 and/or the compressor 72 may be e.g. not adjustable in a dynamic range and hence be configured to provide a constant pressure independently of a measured system parameter, which may be unproblematic with constant system conditions, e.g. a constant supply flow of the cryogenic refrigerant and a constant load 7.

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• 2018
  • 2018-07-30 GB GB1812376.0A patent/GB2575980A/en not_active Withdrawn
• 2019
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  • 2019-07-24 US US17/261,400 patent/US20210341182A1/en not_active Abandoned
  • 2019-07-24 EP EP19745564.5A patent/EP3830498A1/de not_active Withdrawn
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