A numerical cool-down analysis for Dewar-detector assemblies cooled with Joule-Thomson cryocoolers

Joule-Thomson (J-T) cryocoolers are commonly in use for rapid cool-down of Infra-Red (IR) detectors. The cool-down time is governed both by the J-T cryocooler performances and the Dewar structure, which is usually geometrically complicated. A finite-element model of the complete Dewar-Detector-Cooler Assembly (DDCA) is developed. The analysis calculates the heat transfer in the Dewar and the J-T cryocooler, the coolant flow rate, the pressure drop in the vessel that supplies the coolant to the J-T cryocooler, and the pressure drop in the low pressure stream of the heat exchanger that determines the pressure in the evaporator. A verification of the analysis is conducted against experimental results with a single cryocooler at a single scenario and the model is further validated against eleven other experimental results. A satisfactory agreement is obtained between the analysis and the experimental results.