Effects of non condensable gas in an ammonia loop heat pipe operating up to 125 °C

A Loop Heat Pipe (LHP) able to operate efficiently up to 125 °C has been developed, which is in line with the current tendency of satellite on-board equipment to increase their operating temperatures. In selecting the optimal LHP design for the elevated temperature application, the compatibility between the materials and working fluid has been identified as one of the main drivers. Incompatibility is linked to Non Condensable Gas (NCG) generation. In this paper, the behavior of the LHP developed with different amounts of nitrogen injected in its compensation chamber to simulate NCG generation, is analyzed. The LHP performance is studied by analysis of the test results at different temperatures and power levels. The test results are also compared to simulation in EcosimPro. Two main conclusions can be drawn from the study. The first is that the effects of an amount of more than two times the expected NCG at the End of Life of a typical telecommunications satellite (15 years) is almost negligible on the LHP operation. The second is that the main effect of the NCG is a decrease in the LHP thermal conductance, especially at low temperatures and low power levels. This decrease is more significant with the progressive addition of NCG.