Numerically investigated on the transient performance of fast cool-down J-T cryocoolers with non-isometric structure

Abstract

To achieve fast cool-down is important for the miniature Joule-Thomson (J-T) cryocooler in infrared detectors and other applications. A novel non-isometric helically coiled heat exchanger, with a first-sparse-then-dense type structure, was adopted in this study to improve the cool-down performance of miniature J-T cryocoolers. A transient model that takes real gas characteristics, heat leakage and compressible flow into account, was established and verified. The transient thermodynamic behaviors (temperature, internal heat load, mass flow rate and cooling capacity) of J-T cryocoolers with the typical, first-dense-then-sparse and first-sparse-then-dense type structure were analyzed and compared to obtain the better performance. It can be concluded that the first-sparse-then-dense structure can increase the cool-down rate by 13.4% with a smaller structural mass. Besides, different operating conditions with charging pressure and cylinder capacity were also simulated and analyzed. The results show that the first-sparse-then-dense structure always has the fastest cool-down rate in any operating condition. The simulation results can be used for the accurate prediction of system performance and structural design.