Ammonia two-phase mechanically pumped loop for geostationary application: Non-condensable gases factor

The two-phase mechanical pumped loop (2pMPL) is still a promising thermal control solution for spacecraft for different purposes. This paper describes some theoretical and experimental observations of non-condensable gases (NCG) impact on ammonia 2pMPL performances. It has been shown experimentally that NCG bubbles released under the condensation of two-phase ammonia can live in lines for a long time before completely dissolving. NCG bubbles in the pump, throttles or filters could impact overall system performances and reliability and, therefore, should be characterised. The evolution of the NCG bubble in subcooled liquid ammonia has been quantitatively analysed. A preliminary estimation of the NCG diffusion coefficient in liquid ammonia is provided.