Membrane Microgravity Air Conditioner

Membrane Microgravity Air Conditioner (MMAC) is a microgravity-compatible machine that removes particulates, heat, and humidity from air, and produces very clean humidity condensate. MMAC comprises, in pneumatic series, Particulate Filter (PF), Sensible Heat Exchanger (SHX), Latent Heat Exchanger (LHX), and air fan. MMAC cools and dries air with separate heat exchangers: a plate fin hydrophobic SHX using cool (13 °C) coolant, and a nanoporous-hydrophilic-membrane LHX using cold (4.4 °C) water in a pumped circuit at lower pressure than air flow through LHX. Humidity condenses into the LHX membrane pores, with condensate convecting through the membrane into the cold water circuit flow, driven by the air-to-water pressure difference (deltaP). Bubble-point deltaP of the LHX membrane is higher than its air-to-water deltaP, so air is excluded from the membrane pores. These pores are smaller (0.1-0.2 m diameter) than airborne microbiota, preventing biofilm growth in LHX pores and from entering the condensate circuit. MMAC has no two-phase air-water mixtures, hence is inherently microgravity compatible. A Proof-of-Concept (POC) MMAC produced condensate from humidity in unfiltered room air at undiminished rates continuously for over two months, indicating no performance decrease due to biofilm growth on the LHX membrane. Condensate production rates were positively correlated with air humidity levels; in a crewed spacecraft, this negative feedback keeps air humidity in a narrow range, with minimal engineering control required. Produced condensate was very clean, with total dissolved organic and inorganic contaminant concentrations in the single-digit part-per-million range. Conceptual design was performed of a full-scale spaceflight MMAC with a unique spatial configuration that minimizes air ducting for air conditioner functions. Based on POC MMAC test performance, it is estimated that a full-scale spaceflight MMAC will be significantly smaller and lighter than the International Space Station Condensing Heat Exchanger for the same sensible and latent heat transfer performance.