This invention relates generally to low temperature refrigeration systems, and more particularly to closed cycle cryogenic cooling systems and apparatus.
Cooling apparatus and systems capable of producing very low (cryogenic) temperatures find applications in many different fields, such as in electronics. The proper operation of many electronic or electro-optical devices, such as infrared, X-ray and gamma ray detectors, solid state lasers, and low noise amplifiers, requires that the devices be cooled to cryogenic temperatures. Moreover, such devices and their associated cooling systems must often operate under remote or adverse environmental conditions, such as aboard spacecraft, aircraft or other vehicles, wherein space and weight are at a premium and where high reliability and long operating life are required. In order to satisfy these requirements, open cycle cooling systems commonly have been employed. One such open cycle cooling system stores refrigerant gas under high pressure in a pressure vessel. Upon initiation, the gas flows through a heat exchanger to a Joule-Thomson (J-T) expansion valve located within a dewar where expansion causes liquefaction of the refrigerant. The liquid refrigerant is puddled to cool the device. Cold refrigerant vapor is then routed back through the heat exchanger to cool the incoming gas and is then vented out of the system. The pressure vessel used for storing the refrigerant must be removed, refilled, and returned to the system quite frequently. Although this system has the advantage of being quite simple and, thus, has good reliability, it is not very cost-effective and possesses a number of other disadvantages. It has a rather low efficiency. It requires high maintenance, and there is a possibility of contamination entering the system, which can cause it to malfunction, because of the frequent handling of the pressure vessel that is required. Moreover, in some applications, e.g., aboard spacecraft, replenishment or replacement of the refrigerant pressure vessel may be impractical.
Closed cycle cooling systems, which recompress and reuse refrigerant gas rather than venting it, are capable of higher efficiency than open cycle systems and do not require the same type of maintenance. However, closed cycle cooling systems are generally more complicated than open cycle systems and, therefore, may have lower reliability and lower operating life. Moreover, most closed cycle cooling systems do not lend themselves to miniaturization, and heretofore there has not been available a small, lightweight closed cycle cooling system having the desired reliability, efficiency and operating life that is capable of replacing open cycle systems in the above-described applications, despite the long-standing recognition of the problems associated with open cycle systems and despite considerable efforts directed toward developing suitable closed cycle systems.