Stirling cycle cryocooler with optimized cold end design

Details Stirling cycle cryocooler with optimized cold end design Stirling cycle cryocooler with optimized cold end design

2000-04-26

2001-12-11

Capossela, Ronald (Department: 3744)

Refrigeration

Gas compression, heat regeneration and expansion, e.g.,...

C062S051200

Reexamination Certificate

active

06327862

ABSTRACT:

FIELD OF THE INVENTION
The field of the invention relates generally to cryocoolers. More particularly, the field of the invention relates to Stirling cycle cryocoolers.
BACKGROUND OF THE INVENTION
Recently, substantial attention has been directed to the field of superconductors and to systems and methods for using such products. Substantial attention also has been directed to systems and methods for providing a cold environment (e.g., 77° K. or lower) within which superconductor products such as superconducting filter systems may function.
One device that has been widely used to produce a cold environment within which superconductor devices may function is the Stirling cycle refrigeration unit or Stirling cycle cryocooler. Such units typically comprise a displacer assembly and a compressor assembly, wherein the two assemblies are in fluid communication and are driven by one or more linear or rotary motors. Conventional displacer assemblies generally have a “cold” end and a “hot” end, the hot end being in fluid communication with the compressor assembly. Displacer assemblies generally include a displacer having a regenerator mounted therein for displacing a fluid, such as helium, from one end, i.e., the cold end of the displacer assembly, to the other end, i.e., the hot end, of the displacer assembly. The piston assembly functions to apply additional pressure to the fluid, when the fluid is located substantially within the hot end of the displacer assembly, and to relieve pressure from the fluid, when the fluid is located substantially within the cold end of the displacer assembly. In this fashion, the cold end of the displacer assembly may be maintained, for example, at 77° K., while the hot end of the displacer assembly is maintained, for example, at 15° K. above ambient temperature. Devices such as superconducting filter systems are then typically placed in thermal contact with the cold end of the displacer assembly.
Current Stirling cycle cryocooler designs employ a heat acceptor positioned at the cold end of the displacer assembly. The heat acceptor is typically in thermal contact with the device that is to be cooled, such as a High Temperature Superconducting Filter (HTSF) system. Heat is transferred from the device and to the heat acceptor. The heat transferred to the heat acceptor then passes to the helium gas contained in the displace assembly. The transfer of heat from the heat acceptor to the helium gas typically is the most difficult since the resistance to heat transfer is greatest in this step.
In current cryocooler designs, the ineffective transfer of heat from the heat acceptor to the helium gas results in additional power requirements. In essence, a greater amount of input power is needed to achieve the desired refrigeration lift. The lower heat transfer rate is due, in large part, to the relatively small surface area and low convective heat transfer coefficient.
There is a need for a cryocooler design that decreases the heat transfer resistance between the heat acceptor and the helium gas. The cryocooler design would advantageously require less input power to provide an equivalent amount of refrigeration as compared to prior designs.
SUMMARY OF THE INVENTION
In a first aspect of the invention, a displacer unit for use in a Stirling cycle cryocooler is disclosed. The displacer includes a housing, a displacer liner adjacent to the inside of the housing, a displacer assembly, a regenerator unit, and a heat acceptor. The displacer assembly is located inside the displacer liner and is axially slidable with respect to the housing. The heat acceptor includes a radial component and an annular component. The heat acceptor is affixed to the cold end of the displacer unit.
In a second separate aspect of the invention, a heat acceptor for use on the cold end of a displacer unit is disclosed. The heat acceptor includes a radial component including a radially located inner face that is perpendicular to the long axis of the displacer unit. In addition, the heat acceptor includes an annular component including an inner circumferential face.
In a third aspect of the invention, the displacer unit according the first aspect of the invention further includes a plurality of radial holes in the displacer assembly.


REFERENCES:
patent: 3273356 (1966-09-01), Hoffman
patent: 3282064 (1966-11-01), Cowans et al.
patent: 3991585 (1976-11-01), Mulder
patent: 4078389 (1978-03-01), Bamberg
patent: 4359872 (1982-11-01), Goldowsky
patent: 4846861 (1989-07-01), Berry et al.

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