Cryocooler with Magnetic Reciprocating Piston

Abstract

A cryocooler is described that can include a pressure wave generator, and a refrigeration device (for example, a coldhead), which can be used to liquefy a gas when the gas is exposed to a surface of the refrigeration device. The pressure wave generator can include one or more motors. Each motor can include a stator, and at least one electrical coil wound around a portion of the stator. The electrical coil can generate a reversing magnetic field when alternating electric current is passed through the electrical coil. The motor can further include a pressurized container that can be placed within the space enclosed by the stator, and a piston that can be placed inside the pressurized container. The stators can be placed external to the pressurized container. The piston is made by combining magnets that have opposite and transverse polarities, and are combined adjacently on a common reciprocating axis.

What is claimed is: 
     
         1 . A motor comprising:
 a stator defining a space;   an electrical coil configured to be wound around a portion of the stator, the electrical coil configured to generate a reversing magnetic field in the stator and in the space defined by the stator when alternating electric current is passed through the electrical coil;   a pressurized container configured to be placed within the space enclosed by the stator; and   a piston configured to be placed inside the pressurized container, the piston sliding within the pressurized container in response to the reversing magnetic field.   
     
     
         2 . The motor of  claim 1 , wherein the piston comprises a combination of a first magnet and a second magnet that have opposite and transverse polarities, the first magnet and the second magnet being combined on a common axis. 
     
     
         3 . The motor of  claim 2 , wherein:
 each of the first magnet and the second magnet are cylindrical;   a substantial portion of the pressurized container is cylindrical; and   a diameter of each of the first magnet and the second magnet is substantially equal to an inner diameter of the cylindrical portion of the pressurized container.   
     
     
         4 . The motor of  claim 3 , wherein a distance between a surface of the space defined by the stator and an outer surface of at least one of the first magnet and the second magnet is less than two millimeters. 
     
     
         5 . The motor of  claim 1 , wherein at least a circumferential portion of the piston is coated with a low friction material that minimizes friction between the outer surface of the piston and an inner surface of the pressurized container when the piston slides within the pressurized container. 
     
     
         6 . The motor of  claim 1 , wherein the sliding of the piston within the pressurized container is a resonant reciprocating motion. 
     
     
         7 . The motor of  claim 6 , wherein the pressurized container is configured to be connected to a coldhead including a phasing network, the resonant reciprocating motion of the piston within the pressurized container causing an oscillating flow of a working fluid within the pressurized container and the phasing network, the oscillating flow of the working fluid within the phasing network causing a lowering of temperature of at least some portion of the coldhead. 
     
     
         8 . The motor of  claim 7 , wherein the lowered temperature of the at least some portion of the coldhead causes a liquefaction of a gas exposed to an external surface of the coldhead. 
     
     
         9 . The motor of  claim 7 , wherein:
 the working fluid comprises at least one of: helium, hydrogen, ambient air, carbon dioxide, and argon; and   the gas that is liquefied by exposure to the external surface of the coldhead is oxygen.   
     
     
         10 . The motor of  claim 1 , wherein the pressurized container is made of a low-conductivity and non-ferromagnetic material. 
     
     
         11 . The motor of  claim 9 , wherein the low-conductivity and non-ferromagnetic material is one of: stainless steel, Inconel, glass, carbon, and titanium alloy. 
     
     
         12 . The motor of  claim 1 , wherein the piston comprises a plurality of magnets that link with the stator to generate a restoring force tending to return the piston to a mid-stroke position of the piston. 
     
     
         13 . The motor of  claim 1 , wherein the stator and the electrical coil are configured to be located in ambient air when the piston slides within the pressurized container due to the reversing magnetic field. 
     
     
         14 . The motor of  claim 1 , wherein the stator is configured to be removable and replaceable without opening or breaking the pressurized container. 
     
     
         15 . A system comprising:
 a pressure wave generator comprising one or more motors, at least one motor of the one or more motors comprising:
 a stator defining a space; 
 an electrical coil configured to be wound around a portion of the stator, the electrical coil configured to generate a reversing magnetic field in the stator and the space defined by the stator when alternating electric current is passed through the electrical coil; 
 a pressurized container configured to be placed within the space enclosed by the stator; and
 a piston configured to be placed inside the pressurized container, the piston reciprocating within the pressurized container in response to the reversing magnetic field; and 
 
   an acoustic load fluidically coupled with the pressure wave generator.   
     
     
         16 . The system of  claim 15 , wherein the acoustic load is at least one of: a Stirling cycle refrigerator and a pulse-tube acoustic-Stirling refrigerator. 
     
     
         17 . The system of  claim 15 , wherein the acoustic load is a compressor head. 
     
     
         18 . The system of  claim 15 , wherein:
 the one or more motors comprise at least two motors; and   the at least two motors are configured to be functionally combined to cancel mechanical vibration in the pressure wave generator.   
     
     
         19 . The system of  claim 15 , wherein the pressurized container is a part of a gas-tight enclosure open to only the acoustic load. 
     
     
         20 . The system of  claim 15 , wherein:
 the acoustic load comprises a phasing network;   the pressurized container is configured to be connected to the coldhead; and   the reciprocating motion of the piston within the pressurized container causes an oscillating flow of a working fluid within the pressurized container and the coldhead, the oscillating flow of the working fluid within the acoustic load causing a lowering of temperature of a portion of the acoustic load.   
     
     
         21 . The system of  claim 20 , wherein the lowered temperature of a portion of the acoustic load causes a liquefaction of a gas exposed to an external surface of the acoustic load. 
     
     
         22 . A system comprising:
 a gas source configured to separate a gas from a mixture of gases; and   a cryocooler configured to receive the separated gas from the gas source, the cryocooler configured to liquefy the gas, the cryocooler comprising a pressure wave generator and a refrigerating device that liquefies the gas when the gas is exposed to an outer surface of the refrigeration device, the pressure wave generator comprising at least one reciprocating motor, the at least one reciprocating motor comprising a stator defining a space, an electrical coil being wound around a portion of the stator, the electrical coil configured to generate a reversing magnetic field in the stator and in the space defined by the stator when alternating electric current is passed through the electrical coil, the at least one reciprocating motor further comprising a pressurized container configured to be placed within the space defined by the stator, the pressurized container enclosing a piston such that the piston reciprocates by sliding within the pressurized container in response to the reversing magnetic field.   
     
     
         23 . The system of  claim 22 , wherein:
 the refrigerating device comprises a phasing network; and   the reciprocating of the piston within the pressurized container causes an oscillating flow of a working fluid within the pressurized container and the refrigeration device, the oscillating flow of the working fluid within the refrigerating device causing a lowering of temperature of a portion of the refrigerating device.   
     
     
         24 . The system of  claim 23 , wherein the lowered temperature of the portion of the refrigerating device causes a liquefaction of a gas exposed to an external surface of an acoustic load that includes the phasing network. 
     
     
         25 . The system of  claim 22 , further comprising:
 a storage vessel configured to collect and store the liquefied gas.   
     
     
         26 . The system of  claim 22 , wherein the gas source is an air separation device that separates the gas from a mixture of gases, the air separation device including a molecular sieve. 
     
     
         27 . The system of  claim 22 , wherein the gas source is an air separation device that separates the gas from a mixture of gases, the air separation device comprising a heat exchanger comprising a plurality of heat exchanger channels. 
     
     
         28 . The system of  claim 22 , wherein the mixture of gases comprise gases compressed by a compressor, the gas source receiving the mixture of gases from the compressor. 
     
     
         29 . The system of  claim 22 , wherein:
 the mixture of gases is ambient air;   the separated gas is gaseous oxygen; and   the liquefied gas is liquid oxygen that is to be provided to at least one medical device used by one or more patients.