Influence of frequency and pressure on entropy production characteristics of regenerator at 20 K pulse tube cryocooler

Highly sensitive very long band infrared detectors present the need for 2-stage pulse tube cryocoolers in the 20 K temperature region. The entropy production is closely related to the operating frequency and operating pressure of the cryocoolers, which limits the performance of cryocoolers. The entropy production characteristics with operating frequency at 35-45 Hz and the operating pressure at 2.4-3.2 MPa of a two-stage pulse tube cry-ocooler working at 20 K are studied. Active phase regulation is used to reduce the effect of impedance caused by pressure and frequency in the regenerator. The entropy production characteristics, acoustic power, and axial distribution of energy flow of the cold finger at different operating frequencies and operating pressures are compared theoretically. The results show that at a constant input acoustic power and an operating pressure of 2.8 MPa, the cooling capacity increases and the pre-cooling capacity decreases as the operating frequency de-creases. At the operating frequency of 40 Hz, the secondary cooling capacity and the required pre-cooling ca-pacity increased with the increase of operating pressure. Further, an experimental test platform is built to verify the simulation. Experimental phenomena are analyzed and interpreted in terms of the average temperature and impedance characteristics along the axial of the finger. This study provides a reference for the optimization of the entropy production and performance improvement of the regenerator of pulse tube cryocooler, especially the thermally coupled pulse tubes cryocooler working at the liquid hydrogen temperature for high-sensitivity infrared detection.