Supercritical startup strategy of cryogenic loop heat pipe with different working fluids

Space infrared detectors of the next generation such as James Webb Space Telescope (JWST) have pressed requirement for cryogenic heat transport technology below 40 K. Cryogenic loop heat pipes (CLHP) could possess massive potential in an infrared detection system because it is developed from a loop heat pipe (LHP) as a highly efficient thermal control device for space application. This paper discusses the design procedure of CLHP and how to produce a CLHP prototype following design principles. The CLHP prototype had various working characters while adopting different working fluids such as nitrogen, neon, and hydrogen, with which the CLHP system could operate at 20-120 K. Both common and unique operating characteristics in its supercritical startup process were investigated. All three CLHPs could achieve a successful supercritical startup just with various periods. The effect of heat sink controlling measure is significant for CLHP especially for that with a narrower temperature range such as neon and hydrogen. Due to lower dynamic viscosity and more considerable latent heat of hydrogen, the automatic cooling characteristics of the primary evaporator was found in H-2-CLHP, which did not appear in the nitrogen or neon experiments.