Models for Scalable Helium-Carnon Sorption Cryocoolers

We have developed models for the rapid design of helium-based Joule-Thomson cryocoolers using charcoal-pumped sorption compressors. The models take as inputs the number of compressors, desired heat-lift, cold tip temperature, and available precooling temperature and provide design parameters, optimized for low power, as outputs. The output parameters are the compressor dimensions, required charcoal mass, cycle temperatures and pressures, heat exchanger dimensions and J-T orifice characteristics. We predict that a helium/carbon cryocooler with 18 K precooling can be as efficient as 60 W/W. These models, which run in MathCad and Microsoft Excel can be coupled to similar models for hydrogen sorption coolers to give designs for 2-stage vibration-free cryocoolers that provide cooling from ∼50 K to 4 K. We present a preliminary design for a two-stage vibration-free cryocooler that is being proposed to support a mid-infrared camera on NASA's Next Generation Space Telescope.