Supercritical Startup Experiment of Cryogenic Loop Heat Pipe for Deep Space Mission.

A cryogenic loop heat pipe (CLHP) is a two-phase heat transfer device for cooling devices in the cryogenic operating temperature range, such as infrared detectors. CLHPs have a longer heat transport capacity than other heat transfer devices, allowing for greater flexibility in the cryogenic detector and cryocooler layout. Furthermore, the heat source and the cryocooler can be decoupled, reducing the effects of vibrations from the compressor of the cryocooler. It is expected to lead to more accurate observations of optical instruments. The final goal of the research is to develop CLHP for deep space applications. For this purpose, it is necessary to properly understand the startup characteristics of CLHPs, whose initial state is supercritical. In this study, the CLHP was arranged in a gravity-assisted attitude to realize the startup from the supercritical state. (i.e., the condenser is arranged at a higher position than the evaporator.) Nitrogen was used as the working fluid, and a CLHP that can transfer more than 10 W for 2 m was designed. A 300 ml gas reservoir was installed in the CLHP, and the charge amount of nitrogen was 11.5 g. The charging pressure was 3.26 MPa at 300 K. The operating performance, such as the startup characteristics, stability of steady-state operation, and maximum heat transport capacity, was investigated in the tests.