Operating Characteristics of Cryogenic Loop Heat Pipes at Different Filling Pressures

A cryogenic loop heat pipe (CLHP) is a two-phase heat transport device for cooling equipment in cryogenic operating temperature regions, such as infrared detectors. Long-distance heat transport using a CLHP can decouple the heat source from the cryocooler, reducing the effects of vibration from the cryocooler. It is expected to improve the attitude control of the satellite and enable high-precision observations using optical instruments. In this study, a gravity-assisted CLHP has been designed, and its operational characteristics have been determined. The transport distance of the CLHP was 2m. In this report, we investigate the operating characteristics of the CLHP by changing the filling pressure of the CLHP. In addition, a one-dimensional thermal-mathematical model simulating the gas reservoir specific to the CLHP was constructed to investigate the effect of the filling pressure on the operating characteristics. In this study, the filling pressure was varied between 2.9 MPa and 3.4 MPa in 0.1 MPa increments. As a result, the maximum heat transport capacity was 25 W at 2.9 MPa-3.2 MPa and 30 W at 3.3 MPa-3.4 MPa, indicating that the heat transport capacity tends to increase as the filling pressure increases. The operating temperature increased with increasing filling pressure, with a maximum difference of 4.2 K. The effect on the operating characteristics was confirmed.