Improving adsorption cryocoolers by multi-stage compression and reducing void volume

Adsorption cryocoolers offer the potential of operating reliably in space for > 10 years, far longer than present mechanical systems. They have no wear-related moving parts, are relatively simple and quiet, generate negligible mechanical vibration and electromagnetic interference, are easily scalable by combining additional compressor modules, can be combined in cascade refrigeration systems to produce temperatures < 4 K, and can be powered by waste heat from a nuclear or solar thermal energy source. This Paper describes how the performance of gas adsorption cryocoolers can be greatly improved by using adsorbents with low void volume within and between individual adsorbent particles, reducing void volumes in plumbing lines, and by compressing the working fluid in more than one stage. An analytical model was used to determine refrigerator specific power requirements and compressor volumetric efficiencies in terms of adsorbent and plumbing line void volumes and operating pressures for various charcoal adsorbents. Operating pressure optimization curves for 80 and 117.5 K charcoal/nitrogen adsorption cryocoolers are also presented, for both single stage and multi-stage compressor systems.