A Study of a Miniature In-Line Pulse Tube Cryocooler
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A miniature pulse tube cryocooler has been designed and tested in our laboratory. The main part of the cryocooler, consisting of an in-line assembly of aftercooler, regenerator, cold heat exchanger, buffer tube and hot heat exchanger has an overall length of 31 mm. The regenerator is filled with SS #635 mesh screen and has a length of 12 mm. Despite the miniature dimensions, all the aforementioned components of the cryocooler are connected by pressure-tight joints allowing easy disassembly and are easily replaceable. The modular arrangement allows separate testing of the components and additional experimental tuning. The oscillating pressure is supplied by an external Eydan® compressor, and the entire assembly is fitted with an inertance tube and reservoir. A theoretical SAGE® model estimated 305 mW of cooling at 110 K for operation at 100 Hz with a filling pressure of 40 bars and a pressure ratio of 1.3 at the aftercooler. As a result of the small dimensions, the actual performance of the cryocooler is strongly dependent on the uniform passage of gas between the cooler components, and in most cases differs from the theoretical assumptions. Nevertheless, experimental tuning of the components design and their interconnections in the cryocooler allowed us to reach the theoretical performance, and furthermore, to reach a higher cooling power than predicted by the SAGE® model. The actual cryocooler provides 400 mW of cooling at 110 K while operating at 103 Hz with the aforementioned fill pressure and pressure ratio. The cooler achieves a no-load temperature of 99 K, while the heat rejection temperature stabilizes at 305 K.