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Comparison of Mixing and Displacement Ventilation under Limited Space Air Stability Conditions in a Space Capsule

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This study evaluated the performance of different ventilation methods under varying limited space air stability conditions with respect to air distribution and pollutant transport in a space capsule. Two ventilation methods were adopted: mixing ventilation (MV) and displacement ventilation (DV). A seated thermal manikin was centred in a computational domain representing the capsule in order to simulate the floating state of a crewmember. Carbon dioxide (CO2) was selected to represent the exhaled pollutant in the capsule macro-environment and the breathing micro-environment. The numerical results demonstrated that limited space air stability affects pollutant transport in the microgravity environment due to the gravitational sensitivity of capsule air. Moreover, the characteristics of the ventilation method depend on the limited space air stability condition. In the MV system, unstable conditions led to relatively stronger CO2 diffusion perpendicular to the exhaled mainstream, resulting in a less polluted breathing micro-environment. Conversely, stable conditions confined the exhaled CO2 to a limited layer near the level where it was released, resulting in a more polluted breathing micro-environment. Whereas in the DV system, very little difference was observed in the distribution of CO2 between stable and unstable conditions. In addition, the effect of ventilation rate on the distribution of CO2 was more obvious in the MV system than in the DV system. Under the same pollutant level in the MV system, the unstable condition consumed less energy than the stable condition. These results suggest that the unstable condition enables the more energy efficient removal of pollutants, and provides better air quality for crewmembers in a space capsule ventilated by MV. This study provides useful insights for ventilation design in space capsules.

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  1. ISS, International Space Station; ECLSS, Environmental Control and Life Support System; MV, mixing ventilation; DV, displacement ventilation; UDF, user defined function; ACH, air changes per hour


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Correspondence to Guangcai Gong.

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Deng, X., Gong, G. Comparison of Mixing and Displacement Ventilation under Limited Space Air Stability Conditions in a Space Capsule. Microgravity Sci. Technol. 32, 749–759 (2020).

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