Flow boiling of carbon dioxide at different channel orientations for the thermal management of future detector technologies at the High-Luminosity Large Hadron Collider

The global warming potential (GWP) of working fluids in thermodynamic cycles and their environmental impact have been gaining considerable attention within the recent years. The European Organization for Nuclear Research (CERN) supports the development of green technologies within the upgrades of their future accelerator facilities and Carbon Dioxide (CO₂) has been identified as an eco-friendly candidate with excellent heat transfer characteristics that has the potential for replacing detrimental refrigerants in future scientific and industrial cooling applications. Inspired by the positive experiences with several mid-scale refrigeration systems, the ATLAS and CMS experiments decided to use CO₂ as working fluid for the thermal management of their future Particle Tracker detectors requiring cooling capacities in the order of 0.5 MW. Pressure drop and heat transfer properties are key factors for designing thermodynamic cycles properly. Motivated by the lack of experimental data of flow boiling CO₂ in vertical directions, a comprehensive research program has been launched to investigate the two-phase flow behaviour of CO₂, in particular in vertical up- and downward direction.