Development Status of a 2.5 K – 4 K Closed-Cycle Cooler Suitable for Space Use
Temperatures below 2.5 K have been reached in a continuously operating closed cycle cooler that has been engineered for space applications. This cooler is a modification of a 4 K cryocooler that consists of a two-stage Stirling cycle precooler with a closed cycle Joule-Thomson (JT) stage. The Stirling cycle precooler and the compressors for the JT system incorporate all the long life features of the Oxford/RAL single stage coolers which have been flown successfully. Some modifications have been made to the original development model 4 K refrigerator; this paper reports on the testing and performance of the cooler. Measurements of the change in performance of the two stage cooler with compressor-displacer separation distance are presented.
4He is used in the JT system for temperatures around 4 K and 3 He is used below 3 K. Different JT expansion orifices are used to optimise the cooler at 4 K and 2.5 K giving flow rates of about 3 mg/s and 1 mg/s respectively. For operation at the lower temperatures the reduced flow enables a lower pressure (and hence temperature) to be maintained on the low pressure side of the expansion orifice.
Under no-load conditions and with no gas in the JT system the precooler reaches a base temperature of 11.3 K. The JT system provided over 11 mW of cooling at 4.5 K. With the smaller orifice and using 3 He a temperature of 2.46 K was achieved with a heat load of over 3 mW. The input power to the cooler was approximately 126 W. The temperature stability of the system at about 2.5 K was better than 40 mK over a 72 hour period.
KeywordsHeat Load Base Temperature Cooling Power Thermodynamic Cycle Total Input Power
Unable to display preview. Download preview PDF.
- 1.under ESA contract 7198/MNL/MA(SC).Google Scholar
- 2.Bradshaw, T. W., Orlowska, A. H., “Mechanical cooling systems for use in space”. Proc. Instn Mech Engrs. vol.207 (1993) 21–25.Google Scholar
- 3.Bradshaw, T. W., Orlowska, A. H., and Hieatt, J. “Development status of a 2.5 K–4 K closed cycle cooler suitable for space use” Paper presented at the 24th International Conference on Environmental systems and 5th European Symposium on Space Environmental Control systems, Friedrichshafen, Germany 1994.Google Scholar