Study On A Novel Active Gas Distribution System And Utilization Of Excess Cooling Power Of G-M Type Pulse Tube Cryocoolers

G-M type pulse tube cryocooler has the advantages of low mechanical vibration, high reliability, high cooling power, which makes it competent for low temperature physics, superconductor magnet cooling, space temperature refrigeration and gas liquefaction.The developments of G-M type pulse tube cryocooler, especially the gas distribution systems and the excess cooling power at liquid helium temperatures are reviewed. Irreversible losses in regenerator and gas distribution system are main factors limiting the coefficient of performance of pulse tube cryocoolers. In view of these two factors, theoretical study on active gas distribution system and excess cooling power is carried out. And extensive experimental study is performed based on a single-stage G-M type pulse tube cryocooler and a two-stage G-M type pulse tube cryocooler. The present work focuses on the following sections:1,Theoretical and experimental research on a novel active gas distribution systemA novel active gas distribution system for G-M type pulse tube cryocoolers is proposed to overcome disadvantages of traditional gas distribution system, such as higher power consumption and irreversible losses. The active gas distribution system adds either one or some reservoirs connected to the compressor. The reservoir serves for storing part of exhaust gas with middle pressure and supplying the gas to cryocooler during intake process. Hence the new refrigeration cycle includes intake process from middle stage reservoir, intake process from compressor, exhaust process to middle stage reservoir and exhaust process to the compressor. Compared to the traditional gas distribution system, the irreversible losses during intake and exhaust processes decrease significantly due to the decreased pressure difference through the valves. The compression work may be also decreased because of less gas compressed by the compressor. Theoretical study shows that entropy generation of the active gas distribution system reduces 50% compared to that of the traditional gas distribution system.Experimental study is carried out based on a self-made single-stage G-M type pulse tube cryocooler. Experiments show that the active gas distribution system decreases the power consumption by 27% and entropy generation by 37% when the proportion of opening time of the middle stage reservoir is 30%. The cryocooler reaches a lower refrigeration temperature with minor decrease of cooling power. Comparison tests have also been done on the solenoid valve system and the rotary valve system. Reasons for the difference of coefficient of performance between two systems are revealed from a view of structure of solenoid valve and rotary valve.2,Theoretical and experimental research on excess cooling power at liquid helium temperaturesThe so-called excess cooling power is transformed from the enthalpy loss in regenerator and pulse tube with minor influence on cooling performance of the cold head. Simulation of excess cooling power at liquid helium temperature is performed with the regenerator software REGEN3.3. Models of single-stage and multi-stage excess cooling power are established. The influence of variation of hot end and cold end temperatures on excess cooling power is studied.Experiment on the distribution of excess cooling power in regenerator and pulse tube, influence of variation of hot end and cold end temperatures on excess cooling power, multi-stage excess cooling power and exergy efficiently of cryocooler is carried out based on a G-M type pulse tube cryocooler working at liquid helium temperature. Result shows that excess cooling power can increase the cold exergy of cryocoolers. Meanwhile, excess cooling power may lead to decrease of cooling capacity at the first stage and the temperature profiles in regenerator and pulse tube.