Air Circulation and Carbon Dioxide Concentration Study of International Space Station Node 2 with Attached Modules

Crew health is dependent on the concentration of carbon dioxide in the atmosphere breathed. Often, models used for concentration have used the assumption that each module of the space station is well mixed, i.e. that the CO₂ concentration is constant throughout the module. In this paper, Computational Fluid Dynamics (CFD) modeling is used to assess and validate the accuracy of that assumption. The concentration of carbon dioxide as calculated by CFD was compared to the concentration as calculated by a lumped parameter model. The assumption that the module is well mixed allows the use of relatively simple models, which can be developed and run quickly in order to support decisions for on-orbit analysis. CFD models generate more detailed information, such as CO₂ gradients within the modules and airflow and mixing characteristics. However, CFD models, particularly transient models, take longer to develop and use.