Study On High Frequency Pulse Tube Cryocooler With Precooling At Liquid Helium Temperature

The development and progress of science and technology requires the use of the cooling technology at liquid helium temperature. Cryocoolers near 4K with a long life is of particular interest for the application of space detectors. At present, the tipical 4 K cryocoolers are Gifford-McMahon (GM) cryocoolers and GM-type pulse tube cryocoolers (PTCs) operating at low frequency which have the problems of large volume, low efficiency and needs periodical maintenance.These features make them unsuitable for space applications. While the Stirling cryocooler and Stirling-type PTCs operating at high frequency have the advantages of compact structure, light weight and high efficiency. Furthermore, because of no moving part at cold end, the Stirling-type PTCs have the potential to have a long life and become very ideal candidate for space applications. Research on Stirling-type high frequency PTCs working at liquid helium temperature is very significant.In this paper, an overview of liquid helium temperature cryocoolers has been reviewed. The difficulties of reaching liquid helium temperature for high frequency PTCs have been demonstrated. And on the basis of the investigation and analysis of several phase shifters in PTCs, the cold inertance tube was used to solve the difficulty of shifting the phase between the mass flow and pressure to the ideal angle for a PTC with small acoustic power. The phase shift theory of the cold inertance tube was introduced. At the same time, based on the previous theoretical research, a precooled high frequency PTC was set up and the experiments were carried out. An important foundation was established for high frequency PTC to reach liquid helium temperature. The main work of the paper includes the following sections: 1) Theoretical model of inertance tube for the whole temperature was established.Based on the transmission line model and considered the real-gas properties of working fluid, a theoretical model of cold inertance tube was established. A programme for single inertance tube based on the software known as LabVIEW was developed. The influence of temperature, pressure ratio and reservoir volume on the performance of the inertance tube was studied. A phase graph of the cold inertance tube at different temperatures was obtained, which can provide some direct guidance for the design of the cold inertance tube and normal inertance tube at ambient temperature.2) A high frequency PTC with precooling at liquid helium temperature was set up.Based on previous theoretical design, a single-stage high frequency PTC precooled by a two-stage G-M type PTC was set up which is the foundation of the successful experiments for the next step.3) The liquid helium temperature was reached by the high frequency PTC with precooling.Experimental study shows that with an operating frequency of 30Hz, an average pressure of 0.5 MPa, the input power of 50W and the precooling temperature of 9.7 K, the high frequency PTC reached a no-load temperature of 5.2 K which verify the fact that a PTC with helium-4 as working fluid is capable of reaching helium temperature with high operating frequency. Meanwhile, the influence of operating parameters (operating frequency, average pressure, precooling temperature, and input power) and structural parameters on the performance of the high frequency PTC was also carried out, which provides the guidance of the way to increase the precooling temperature firstly, and finally achieve the totally high frequency PTC with no precooling working at liquid helium temperature.