Investigation On Loss Mechanism Of High Frequency Regenerator At 4K And Staging Configuration Of Multi-stage Pulse Tube Cryocooler

Cryocoolers working at liquid helium have important applications in the field of low temperature superconductivity (LTS), space exploration, military detection, medical examination and low temperature physics. Stirling type pulse tube cryocoolers have the advantage of high reliability, long life, light weight and have potentially high efficiency which makes them very appealing for 4 K applications. However, compared with the relatively efficient 80 K Stirling type pulse tube cryocoolers, both theoretical and experimental investigation on 4 K Stirling type pulse tube cryocoolers is only at the preliminary stage which limits their application in the liquid helium temperatures. In order to further understand the loss mechanism of 4 K regenerators at high frequency and explore the effective way of reaching 4 K with helium-4 as the working fluid, research work is carried out which focuses on the following sections:1. Thermodynamic analysis of pulse tube cryocooler and investigation on the loss mechanism of 4 K regenerator at high frequencyBased on the first law and second law of thermodynamics, analysis is carried out on the thermodynamic characteristic of the components of a pulse tube cryocooler and the various losses in a pulse tube cryocooler are given. Effect of temperature region, working fluid, average pressure and pressure ratio on the losses of 4 K regenerator at high frequency is studied which can provide guidance for better understanding the loss mechanism of high frequency 4 K regenerators.2. Staging configuration diagram of multi-stage Stirling type pulse tube cryocooler working at liquid helium temperatures is drawn.The staging configuration of pulse tube cryocoolers has great influence both on the performance of the cryocooler and the compactness of the system. The possible staging configuration of 4 K Stirling type pulse tube cryocoolers is explored and the configuration diagram is drawn for the first time. In order to determine the loss caused by staging configuration, effect of warm end temperature of pulse tube on the performance of the cryocooler with different acoustic power is investigated which is helpful for the optimization of multi-stage 4 K Stirling type pulse tube cryocooler.3. Theoretical investigation on cold inertance tubeThe conventional inertance tube located at the ambient temperature as the phase shifter for 4 K Stirling type pulse tube cryocooler with small acoustic power and relatively low operating frequency is not able to shift the mass flow and pressure to the ideal phase angle efficiently. As a result, the effect of temperature on the phase shifting ability of inertance tube is investigated and the use of cold inertance tube as the phase shifter for the precooled 4 K Stirling type pulse tube cryocooler is proposed. Modification of real gas behavior at low temperatures is made and effect of average pressure, pressure ratio and reservoir volume on phase angle of inertance tube is studied.4. Design and fabrication of a 4 K single-stage Stirling type pulse tube cryocooler precooled by a two-stage G-M type pulse tube cryocoolerIn order to focus on the behavior of the high frequency regenerator at liquid helium temperatures, a precooled 4 K Stirling type pulse tube cryocooler is designed based on the regenerator simulation model known as REGEN 3.3. The precooling requirement including the precooling temperature and the precooling power for the Stirling type pulse tube cryocooler to reach 4 K is given. And the thermal coupling component between the G-M type pulse tube cryocooler and the Stirling type pulse tube cryocooler is designed. Experimental setup of the precooled pulse tube cryocooler and the dynamic parameters measuring system was built up which lays the foundation for the experimental investigation of the 4 K Stirling type pulse tube cryocooler.5 Experimental investigation of the 4 K precooled Stirling type pulse tube cryocoolerIn order to verify the theoretical calculation and explore the possibility of reaching 4 K with helium-4 as the working fluid for a Stirling type pulse tube cryocooler, the effect of operating parameters which includes operating frequency, average pressure, input power and precooling temperature, regenerator matrix and regenerator geometry on the performance of the 4 K Stirling type pulse tube cryocooler and the precooling condition for the precooler is carried out. Liquid helium temperature was obtained with helium-4 as the working fluid for a Stirling type pulse tube cryocooler for the first time.