First principles analysis of heat exchanger concepts and designs for a closed CO₂ Brayton cycle with regeneration for a lunar fission to surface power system

The overall scope of this article is to develop and investigate different heat exchanger concepts for a closed CO₂ Brayton power cycle with regeneration that is part of the fission to surface power system (FSPS) concept from NASA, designed to function as a lunar outpost. The heat exchangers investigated are designed with the goal of utilizing 'off the shelf technology' and a sub-goal to ensure the heat exchangers designed are integrated into the FSPS as a whole. The FSP system utilizes two streams as the hot and cold sources: 850 K sodium and potassium eutectic (NaK) stream from a nuclear reactor and 375 K water stream cooled in titanium radiator piping as the cold source, which must be kept as a liquid. The thermodynamics and heat exchanger parameters were modelled and calculated using chemical process simulation software. The power delivered is 10 kW electric per power conversion unit. There are three heat exchangers investigated as possible options for the NaK-CO₂ hot side heat exchanger. When compared with a shell-and-tube heat exchanger, the compact heat exchangers are a better choice because they provide a lower mass system and a smaller footprint.