Design and operation of water recovery systems for space stations
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The paper is based on the experience in the design and operation of “Salut”, “Mir” and International space stations water recovery systems and ground investigations. Due to energy, volume and mass limitations physical/chemical processes would be used in water recovery systems of space stations in the near future. The recovery methods are selected depend on the trace contaminant content in the feed liquid and the requirements for the water recovered: a sorption/catalytic and an ion-exchange processes for humidity condensate from the cabin and greenhouse atmosphere and for water from carbon dioxide reduction; membrane filtration (ultra filtration and reverse osmosis) with an ion-exchange post-treatment for hygiene water; the distillation method accompanied by sorption/catalytic purification for urine. The most important issues are minimal mass and power consumption and reliable decontamination of product water. The realization of these requirements is illustrated in the paper by the system for water recovery from humidity condensate design analysis. The systems use hydrodynamic, chemical and heat and mass transfer processes in single-phase and two-phase gas/liquid media. In the last case special methods for processes have to be used in space flight under microgravity conditions. The general principle of carrying out of the processes of gas/liquid separation and heat and mass transfer by condensation, evaporation, boiling, absorption, heterogeneous catalysis, etc. in microgravity is to provide the stable interface of phase separation. The molecular (capillary) surface tension forces and dynamic (centrifugal and friction) forces are therefore used. The paper reviews the selection of water recovery methods for different water products and hardware for performing hydrodynamic, chemical and heat and mass transfer processes in single-phase and two-phase gas/liquid media in microgravity conditions.