A gas distributing system is proposed that curtails the time for attaining the normal operating condition, maintains maximum refrigeration over the whole operation temperature range, and increases reliability and operating life.Analysis of various designs of Gifford-MacMahon (GM) microrefrigerators (MR) shows that the most promising designs of this type of machines are MRs with free motion of the expulsor. The chief merits of the MRs are: adaptability to efficient manufacture, increased operating life and reliability because of a relatively smaller number of seals and moving parts, scope for reducing mass and size characteristics, and relatively low-duty electric drive. Furthermore, in the MRs there is a potential scope for manipulation of the gas distribution processes and the law of expulsor motion, which would allow maximum optimization of the processes of entry and exit of the working medium into and out of the chamber and would ensure stopping of the expulsor at the bottom and top dead centers (BDC and TDC) for increasing the area of the indicator diagram and, consequently, the efficiency of the RM.The GM MRs belong to gas cryogenic machines (GCM), among which can be distinguished two main most popular fundamentally different types, namely, Stirling and GM.In thermodynamic efficiency, Stirling GCMs are undoubtedly superior to other types of cryorefrigerators but have some shortcomings relative to GM GCMs: high vibration level, short overhaul life, and less freedom of mating with the object being cooled.For certain areas of application, refrigerators based on machines operating on Solvay cycle are of maximum interest. Refrigerators of this type are inferior to Stirling GCMs in thermodynamic efficiency but have important advantages: overhaul life more than 10000 h, low vibration level, and scope for locating the refrigerator at a considerable distance from the pressure source and in any spatial position.Because of these advantages, GM machines are used in several branches of the industry with virtually no alternative. This class of MRs ensures efficiency of such devices as cryopumps, IR detectors, thermal shields of cryostats, magnetic resonance imagers, etc.Recent developments of GM microrefrigerators (MRs) are aimed at expanding the sphere of their application, for example, for cooling superconductors having a high critical temperature, helium liquefaction and recondensation, etc. The major problems to be resolved by developers relate to raising reliability and efficiency of the MRs, ensuring ease of mat-
