Development of a switchless sorption compressor for the cryogenic refrigeration within the METIS instrument: Part I. Theoretical design

•A switchless design of sorption compressor is proposed for METIS refrigerator.•Switchless design is compared to GGHS design with respect to efficiency and size.•The dimensions of the switchless compressors for the METIS refrigerator are optimized. Vibration-free cryogenic sorption refrigerator was proposed for the Mid-infrared E-ELT Imager and Spectrograph (METIS) instrument in the European Extremely Large Telescope. Sorption compressor is the most important part in the refrigerator due to its dominate size, cost and complexity. Generally, gas-gap heat switches are applied for efficiency consideration which is particularly essential for space applications. In METIS refrigerator as a terrestrial application, low input powers, however, should not be the major concern, whereas complexity and costs become more important as high refrigeration powers and thus large numbers of sorption cells are required. To reduce these, we developed an alternative switchless sorption-compressor design. This paper presents the theoretical design of the switchless METIS sorption compressors, including the comparison between the designs with and without heat switches. Based on the switchless design, critical parameters for the METIS sorption compressors are determined to enable further development such as mechanical design, fabrication and experimental demonstration.