Speaker
Description
Open cycle Joule-Thomson (J-T) cryocoolers that operate with pure nitrogen and provide about 1 W of refrigeration effect at 80 K are used extensively in missiles. There is a worldwide interest in developing single-stage miniature J-T cryocoolers that operate with mixtures of refrigerants for cooling detector elements in space applications. Detector cooling enables noise reduction and thereby improves the signal-to-noise ratio. Heat exchangers of high effectiveness (typically greater than 97%) are required for these cryocoolers to function. The attainment of such high effectiveness in miniature heat exchangers makes designing these systems very challenging.
A miniature palm-sized variable speed compressor with a stroke volume of 1.4 cc is used to drive the cryocooler, and a mini-channel (∅<3 mm) multiple tubes in tube heat exchanger with a mean coil diameter of 90 mm and 160 mm long is used as an internal heat exchanger. A lowest temperature of 92 K is achieved with the cryocooler with 1 W of refrigeration effect at 99 K, and a maximum cooling capacity of 3 W is achieved at 104 K. The performance characteristics associated with the cryocooler, namely, the cooling capacity, exergy efficiency, effectiveness of the heat exchanger, and heat load characteristics, with three different nitrogen-neon-hydrocarbon refrigerant mixtures for achieving a few watts (1-3 W) of refrigeration effect in the temperature range of 90 – 100 K will be presented.
Keywords: Miniature Joule Thomson refrigerator, Multiple tubes in tube heat exchanger, Refrigerant mixtures.
