Poisoning of Heat Pipes

Abstract. Thermal management is critical to space exploration efforts. In particular, efficient transfer and control of heat flow is essential when operating high energy sources such as nuclear reactors. Thermal energy must be transferred to various energy conversion devices, and to radiators for safe and efficient rejection of excess thermal energy. Applications for space power demand exceptionally long periods of time with equipment that is accessible for limited maintenance only. Equally critical is the hostile and alien environment which includes high radiation from the reactor and from space (galactic) radiation. In space or lunar applications high vacuum is an issue, while in Martian operations the systems will encounter a C02 atmosphere. The effect of contact at high temperature with local soil (regolith) in surface operations on the moon or other terrestrial bodies (Mars, asteroids) must be considered. Introduction Contamination, or poisoning, of the working fluid and variations in residual gas pressure can significantly alter the working fluid evaporation and heat transport rates. Possible sources of such contamination include dissolution of containment and wicking material by the working fluid, dission of low level impurities dissolved in the materials, penetration and solution of gases, and reaction with materials such as the regolith minerals from the surrounding environment. Such poisoning can change the surface tension properties of the working fluid. Long term extensive testing in well simulated space situations is needed prior to committing a final design for heat pipes for missions of several years in duration. In this work the intent is two-fold, namely (1) to initiate experiments to evaluate the diffusion of candidate gases through Inconel 625, a high temperature candidate containment material, and (2) to evaluate reactivity with a lunar regolith simulant. The composition of Inconel 625 is shown in Table 1.