Cryogenic heat exchanger

A microminiature heat exchanger for transferring heat from a high pressure gas stream to a low pressure gas stream within a cryogenic probe, said heat exchanger comprising:

• a laminated assembly of a plurality of plates of heat conductive material;
• a high pressure passageway through said laminated assembly, said high pressure passageway having an inlet port connectable to a cryogenic gas supply, said high pressure passageway having an outlet port connectable to an inlet of a gas expansion element;
• and
• a low pressure passageway through said laminated assembly, said low pressure passageway lying substantially alongside said high pressure passageway, said low pressure passageway having an inlet port connectable to an outlet of a gas expansion element, said low pressure passageway having an outlet port;
• wherein the direction of flow from said inlet port to said outlet port of said high pressure passageway is substantially opposite to the direction of flow from said inlet port to said outlet port of said low pressure passageway;
• wherein each said passageway is arranged to create a tortuous flow path, to ensure turbulent flow of cryogenic gas therethrough;
• and
• wherein:
• said plates are laminated together and then rolled about a longitudinal axis, to form a cylindrical laminated assembly;
• said high pressure passageway comprises a first channel formed in a first said plate;
• and
• said low pressure passageway comprises a second channel formed in a second said plate.

A microminiature heat exchanger for transferring heat from a high pressure gas stream to a low pressure gas stream within a cryogenic probe, said heat exchanger comprising:

• an axially stacked assembly of laminated flat plates and flat spacers, said plates being alternated with said spacers;
• a first plurality of holes formed through said plates to form a high pressure passageway through said laminated assembly, each said hole in said high pressure passageway in a said plate being transversely offset from a corresponding hole in each adjacent said plate, creating a tortuous high pressure flow path to cause turbulent flow of cryogenic gas;
• a second plurality of holes formed through said plates to form a low pressure passageway through said laminated assembly, each said hole in said low pressure passageway in a said plate being transversely offset from a corresponding hole in each adjacent said plate, creating a tortuous low pressure flow path to cause turbulent flow of cryogenic gas;
• and
• a substantially annular channel formed through each said plate and each said spacer to integrally form a substantially annular insulating jacket within said laminated assembly, said substantially annular channel being positioned radially outwardly from said high pressure passageway and said low pressure passageway, said annular insulating jacket being evacuated;
• wherein the direction of flow from said inlet port to said outlet port of said high pressure passageway is substantially opposite to the direction of flow from said inlet port to said outlet port of said low pressure passageway.

A microminiature heat exchanger for transferring heat from a high pressure gas stream to a low pressure gas stream within a cryogenic probe, said heat exchanger comprising:

• an axially stacked assembly of laminated flat plates and flat spacers, said plates being alternated with said spacers;
• a first plurality of holes formed through said plates, for turbulent flow of high pressure cryogenic gas, each said high pressure hole being transversely offset from a corresponding high pressure hole in each adjacent said plate;
• a second plurality of holes formed through said plates, for turbulent flow of low pressure cryogenic gas, each said low pressure hole being transversely offset from a corresponding low pressure hole in each adjacent said plate;
• an end plate laminated to an end of said stacked assembly, said end plate having an orifice therethrough in flow communication with said high pressure holes;
• and
• a substantially annular insulating jacket integrally formed within said heat exchanger by formation of substantially annular channels through said plates, said substantially annular channels being positioned radially outwardly from said high pressure passageway and said low pressure passageway, said annular insulating jacket being evacuated;
• wherein the direction of flow from said inlet port to said outlet port of said high pressure passageway is substantially opposite to the direction of flow from said inlet port to said outlet port of said low pressure passageway.

A microminiature heat exchanger for transferring heat from a high pressure gas stream to a low pressure gas stream within a cryogenic probe, said heat exchanger comprising:

• an axially stacked assembly of laminated flat plates and flat spacers, said plates being alternated with said spacers;
• a first plurality of holes formed through said plates, for turbulent flow of high pressure cryogenic gas, each said high pressure hole being transversely offset from a corresponding high pressure hole in each adjacent said plate;
• a second plurality of holes formed through said plates, for turbulent flow of low pressure cryogenic gas, each said low pressure hole being transversely offset from a corresponding low pressure hole in each adjacent said plate;
• a plurality of spacers laminated to an end of said stacked assembly, to create a manifold for connection of high pressure and low pressure gas lines to said heat exchanger;
• and
• a substantially annular insulating jacket integrally formed within said heat exchanger by formation of substantially annular channels through said plates, said substantially annular channels being positioned radially outwardly from said high pressure passageway and said low pressure passageway, said annular insulating jacket being evacuated;
• wherein the direction of flow from said inlet port to said outlet port of said high pressure passageway is substantially opposite to the direction of flow from said inlet port to said outlet port of said low pressure passageway.

A microminiature heat exchanger for transferring heat from a high pressure gas stream to a low pressure gas stream within a cryogenic probe, said heat exchanger comprising:

• an axially stacked assembly of laminated flat plates and flat spacers, said plates being alternated with said spacers;
• a first plurality of holes formed through said plates, for turbulent flow of high pressure cryogenic gas, each said high pressure hole being transversely offset from a corresponding high pressure hole in each adjacent said plate;
• a second plurality of holes formed through said plates, for turbulent flow of low pressure cryogenic gas, each said low pressure hole being transversely offset from a corresponding low pressure hole in each adjacent said plate;
• a substantially annular channel formed through each said plate and each said spacer to integrally form a substantially annular insulating jacket within said laminated assembly, said substantially annular channel being positioned radially outwardly from said high pressure and low pressure holes, said annular insulating jacket being evacuated;
• a plurality of spacers laminated to a first end of said stacked assembly, to create a manifold for connection of high pressure and low pressure gas lines to said heat exchanger;
• and
• an end plate laminated to a second end of said stacked assembly, said end plate having an orifice therethrough in flow communication with said high pressure holes;
• wherein the direction of flow from said inlet port to said outlet port of said high pressure passageway is substantially opposite to the direction of flow from said inlet port to said outlet port of said low pressure passageway.

A microminiature heat exchanger for transferring heat from a high pressure gas stream to a low pressure gas stream within a cryogenic probe, said heat exchanger comprising:

• a first sheet having a first flow channel etched therein to form a high pressure passageway, said high pressure passageway having an inlet port and an outlet port, said inlet high pressure port being formed at a first edge of said first sheet and said outlet high pressure port being formed at a second edge of said first sheet;
• and
• a second sheet having a second flow channel etched therein to form a low pressure passageway, said low pressure passageway having an inlet port and an outlet port, said outlet low pressure port being formed at a first edge of said second sheet and said inlet low pressure port being formed at a second edge of said second sheet;
• wherein said first and second sheets are laminated together, with said first edge of said first sheet aligned with said first edge of said second sheet, and with said second edge of said first sheet aligned with said second edge of said second sheet;
• and
• wherein said first and second sheets are rolled into a cylindrical shape having said inlet high pressure port and said outlet low pressure port at a first end, and having said outlet high pressure port and said inlet low pressure port at a second end.

A method of manufacturing a microminiature heat exchanger for use in a cryogenic probe, said method comprising:

• coating a plurality of sheets with a layer of photo resistive compound;
• creating a first design of a plurality of flat plates, each said plate having a first plurality of holes and a second plurality of holes and a substantially annular channel substantially surrounding said first plurality of holes and said second plurality of holes;
• creating a second design of a plurality of flat spacers, each said spacer having a first large opening and a second large opening divided by a partition and a substantially annular channel substantially surrounding said first large opening and said second large opening;
• transferring said first and second designs to said plurality of sheets by tracing said first and second designs with a laser to bond portions of said photo resistive compound to said plurality of sheets;
• washing said plurality of sheets in an etching compound to disintegrate non-bonded portions of said sheets to create said plurality of plates and said plurality of spacers arranged in said sheets;
• axially stacking said sheets to form a laminar assembly, said assembly comprising a plurality of laminar subassemblies, each said laminar subassembly comprising an axial stack of plates and spacers, said plates being alternated with said spacers, said first plurality of holes in each said plate being transversely offset from said first plurality of holes in adjacent said plates of said respective subassembly and aligned with said first large opening in said spacer therebetween, to form a high pressure passageway through said laminar subassembly, said second plurality of holes in each said plate being transversely offset from said second plurality of holes in adjacent said plates of said respective subassembly and aligned with said second large opening in said spacer therebetween, to form a low pressure passageway through said laminar subassembly, said annular channels in said plates and said spacers being aligned to form an insulating jacket surrounding said high pressure passageway and said low pressure passageway;
• placing said laminar assembly under a vacuum;
• diffusion bonding said laminated assembly together;
• maintaining said vacuum while performing said diffusion bonding to establish a vacuum in each said insulating jacket;
• and
• removing said plurality of laminar subassemblies from said laminar assembly, each said laminar subassembly comprising one said microminiature heat exchanger.

A method of manufacturing a microminiature heat exchanger for use in a cryogenic probe, said method comprising:

• coating at least one flexible substrate with a layer of photo resistive compound;
• creating at least two designs of serpentine flow channels, with one said design being a high pressure gas flow channel, and another said design being a low pressure gas flow channel, said high pressure flow channel having an inlet at a first end and an outlet at a second end, said low pressure flow channel having an outlet at a first end and an inlet at a second end;
• transferring said designs to said at least one substrate by tracing said designs with a laser to bond portions of said photo resistive compound to said at least one substrate;
• washing said at least one substrate in an etching compound to etch high pressure and low pressure flow channels into non-bonded portions of said at least one substrate to create a high pressure flow sheet containing said high pressure flow channel and to create a low pressure flow sheet containing said low pressure flow channel, said high pressure flow sheet having said high pressure inlet at a first edge and said high pressure outlet at a second edge, said low pressure flow sheet having said low pressure outlet at a first edge and said low pressure inlet at a second edge;
• laminating said high pressure flow sheet to said low pressure flow sheet, with said high pressure flow channel lying substantially parallel to said low pressure flow channel, and with said first edge of said high pressure flow sheet adjacent to said first edge of said low pressure flow sheet, and with said second edge of said high pressure flow sheet adjacent to said second edge of said low pressure flow sheet;
• and
• rolling said laminated flow sheets about a third edge of each said flow sheet to form a cylindrical heat exchanger, said high pressure inlet and said low pressure outlet being located at a first end of said heat exchanger, and said high pressure outlet and said low pressure inlet being located at a second end of said heat exchanger.