Chemical compatibility of various working fluids with additively manufactured materials for two-phase thermal control systems

The chemical compatibility between container materials and their working fluid is a critical aspect for the long-term heat transfer performance of two-phase thermal management systems. With the recent emergence of additive manufacturing (AM), which has shown significant potential for the design of next generation thermal control devices, chemical compatibility between AM alloys and different working fluids must first be determined, however, before they can be successfully deployed. In this study, 30 different fluid–metal combinations were selected for experimental characterisation. Working fluids with high heat transport capacity such as water, acetone, methanol, toluene and ethylene glycol were included, as well as ammonia and propylene, which are particularly relevant for spacecraft applications. Selected AM materials comprised of a range of widely available metal alloys, including AlSi7Mg, AlSi10Mg, Invar, 316L stainless steel and Ti6Al4V. Thermosyphon devices were manufactured for experimental life-testing using the Gas Plug Test. Any corrosion or chemical reactions result in the generation of non-condensable gas (NCG) and a corresponding reduction in condenser temperature. At the end of 9000 h of testing, the majority of fluid–metal combinations demonstrated excellent chemical compatibility, with a number of notable exceptions. For the case of Invar–methanol, fluid decomposition took place with the metal acting as a catalyst for the reaction. Galvanic corrosion occurred at the interface between the bimetallic combination of aluminium and stainless steel with toluene as the electrolyte. Regardless of the metal used, ethylene glycol was found to undergo rapid decomposition at temperatures greater than 150 ◦C, leading to device failure. Results for water showed slow continuous NCG generation for the duration of testing. These findings provide important information to designers and engineers who wish to make use of the benefits of AM in the next generation of two-phase thermal control systems.