Theoretical And Experimental Research On A Two-Stage Stirling-Type Pulse Tube Cryocooler

Stirling-type pulse tube cryocooler has become more and more practical in many applications for its merit of low vibration, high efficiency, compact size and high reliability. Multi-stage Stirling-type pulse tube cryocooler is required, because the available refrigeration temperature about 60-80K of the single-stage pulse tube cryocooler is not low enough to meet the requirement of applications, such as cooling high temperature superconducting devices and IR detectors, or re-condensing hydrogen in hydrogen transportation and storage, etc.. Theoretical and experimental work on a two-stage Stirling-type pulse tube cryocooler is carried out to study the linear compressor technology and staged high-frequency pulse tube cryocooler technology. The research includes:1. Theoretical analysis is carried out on the two-stage high frequency pulse tube cryocooler. The U-shape thermal-coupled type two-stage pulse tube cryocooler, whose warm end of second pulse tube is connected to the ambient temperature, is chosen as the research object. By using the numerical analysis, the dimensions of the regenerator of both stages are optimized, and the operation parameters of the cryocooler and the output parameters of the compressor are determined. Then, the effects of the regenerative matrix, phase difference at cold end, mean pressure and operation frequency on the performance of the cryocooler are analyzed. Electrical circuit analysis method is used to optimize the inertance tube phase shifter.2. Theoretical analysis is carried out on the linear compressor, and a design approach was summarized. The linear motor of the compressor is analyzed by using finite element method, and its dimensions and operation parameters are optimized. The resonant system of the compressor is studied, and a flexure bearing is designed for keeping the compressor resonating and the piston suspending. The matching of the compressor to the pulse tube cryocooler is discussed, based on the required PV power and swept volume. A compressor with a swept volume of 60cm3 and a piston diameter of 39mm is designed. The output PV work of the compressor can vary within 1200W by adjusting the input electrical power.3. A moving-magnet linear compressor and a two-stage pulse tube cryocooler are manufactured, and a testing system is constructed. Experiment shows that the compressor can produce a pressure ratio of 1.3-1.5 with a maximum performance of about 50-55%, and its resonant frequency is about 33-38Hz.4. The performances of the compressor and the pulse tube cryocooler are improved by optimizing the coil of the linear motor, and redesigning the pre-cooler of the cold head. Both types of double inlet and inertance tube phase shifters are tested and optimized, the inertance tube phase shifter is capable of improving the performance of the first stage. Then, the effects of the parameters such as input electrical power, charging pressure and frequency on the cryocooler's performance are studied. Finally, a lowest temperature of 14.21K is reached by the cryocooler, under a operating condition of 1.3MPa mean pressure,32Hz frequency and 400W input electrical power. The temperature is just higher than 12.96K that was achieved by the university of Giessen recently. It's the first time that such a low temperature is obtained by a high frequency two-stage pulse tube cryocooler in China, and it is the first time that such a low temperature is obtained by this type of crycooler driven by a single compressor. The cryocooler can provide a cooling capacity of 1W at 35K, and the performance is stable whether a heat load is or not applied to the cold stage.