One-dimensional transient numerical model and characteristic analysis for a double helix tube of conical J-T cryocooler

•An efficient one-dimensional transient model is developed and validated for rapidly calculating the entire J-T cryocooler.•The heat mass distribution in the conical heat exchanger significantly influences the cool-down time.•The adiabatic discharge of a pressure vessel plays an indispensable role in the rapid cooling process.•An appropriate vessel pressure can be found for a fast cooling rate by optimal evaporator pressure. An open cycle miniature J-T cryocooler can provide a clear advantage over other cryocoolers in terms of the smaller size, faster cooling down, and no moving parts. In recent years, some experimental research has shown that the progress of heat exchanger technology promotes the application of miniature J-T cryocoolers in the field of infrared detection. Especially micro-finned double helix tube heat exchangers provide good performance for a conical J-T cryocooler. In order to study its rapid cooling mechanism, a one-dimensional numerical model is established for analyzing this unique flow and heat transfer characteristics in such a conical heat exchanger of J-T cryocooler, and the model algorithm is proved to be effective and efficient by the experiments for rapidly calculating entire J-T cryocooler. The simulated results show that the application of double layers conical helix tubes not only enhances heat transfer areas at the same mass flow rate but also optimizes the thermal mass distribution in the heat exchanger such that this part of thermal mass near the evaporator is reduced. Thus, the high-pressure working fluid can be cooled rapidly and throttled to a two-phase state, improving the heat transfer efficiency of the impact jet flow. On the other hand, excessively high vessel pressure will affect the saturation pressure in the evaporator, resulting in a cooling rate reduction. An appropriate vessel pressure can be found for a fast cooling rate by optimal evaporator pressure. In addition, studies revealed that the temperature drop resulting from the adiabatic discharge of the pressure vessel plays an indispensable role in the fast cooling process.