Refrigeration – Gas compression – heat regeneration and expansion – e.g.,...
Utility Patent
1999-04-16
2001-01-02
Capossela, Ronald (Department: 3744)
Refrigeration
Gas compression, heat regeneration and expansion, e.g.,...
C060S520000
Utility Patent
active
06167707
ABSTRACT:
BACKGROUND
The present invention relates generally to cryocoolers, and more particularly, to a two stage cryocooler having a hybrid configuration employing a Stirling first stage expander and a pulse tube second stage expander.
Low temperature refrigeration needs can often be met more efficiently with multi-stage refrigerators than with traditional single stage devices. For applications requiring closed-cycle refrigeration where multiple stages have been deemed advantageous, previous designs have typically implemented two or more expander stages of the same type. Examples of these expanders include those of the Stirling, Gifford-McMahon, pulse tube, and Joule-Thomson designs.
It would therefore be an advantage to have an improved cryocooler that improves upon conventional single and multi-stage designs. Accordingly, it is an objective of the present invention to provide for a two stage cryocooler having a hybrid configuration that uses a Stirling first stage expander and a pulse tube second stage expander.
SUMMARY OF THE INVENTION
To meet the above and other objectives, the present invention provides for a two stage expander having a hybrid configuration that combines a first stage Stirling expander with a second stage pulse tube expander. Both stages are pneumatically driven by a common reciprocating compressor or motor. The two stage cryocooler is designed for long, highly reliable life and is sufficiently small and light weight to permit its use in spacecraft applications.
The use of the first stage Stirling expander provides high thermodynamic efficiency in that it removes a majority of the heat load from gas within the cryocooler. The use of the second stage pulse tube expander provides additional refrigeration capacity and improved power efficiency with little additional manufacturing complexity due to the simplicity of the pulse tube expander, which has no moving parts. One of the major refrigeration losses in a traditional single-stage pulse tube expander, regenerator pressure drop, is relatively small in the present hybrid two stage cryocooler since the pulse tube regenerator operates at a reduced temperature (higher density yields lower gas velocity, which results in a lower pressure drop).
The use of the second stage pulse tube expander enables the incorporation of a low-through heat exchanger at an interface between first and second stage expanders. This feature significantly improves first stage efficiency (relative to conventional single stage Stirling expanders) by virtue of the improved heat transfer coefficient at the thermal interface between the first and second stage expanders. Use of the first stage Stirling expander also reduces the total dead volume of the hybrid cryocooler compared to a pulse tube cooler (either one or two stage cooler having equivalent thermodynamic power). This reduces mass flow requirements, which in turn reduces the swept volume requirements of the compressor. This enables refrigeration to be accomplished with a smaller compressor.
The present invention may be adapted for use with cryogenic refrigerators used in military and commercial applications where the application demands high efficiency refrigeration at one or two temperatures, small size, low weight, long life, high reliability, and cost effective producibility. The primary intended use for the present invention is in space-based infrared sensors for civil and defense applications.
The present invention improves upon or displaces existing conventional cryocooler expanders including single and multi-stage Stirling expanders and single and multi-stage pulse tube expanders. The present hybrid expander achieves better performance at the same or lower manufacturing cost than either Stirling or pulse tube technology can deliver separately.
REFERENCES:
patent: 4711650 (1987-12-01), Faria et al.
patent: 5519999 (1996-05-01), Harpole et al.
patent: 5613365 (1997-03-01), Mastrup et al.
patent: 5647219 (1997-07-01), Rattray et al.
patent: 5920133 (1999-07-01), Penswick et al.
Kirkconnell Carl S.
Neville Stephen C.
Price Kenneth D.
Alkov Leonard A.
Capossela Ronald
Lenzen, Jr. Glenn H.
Raufer Colin M.
Raytheon Company
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