| Popis: |
The provision of atmospheric oxygen, removal of carbon dioxide and heat is essential to sustain crew health during human spaceflight missions. Microgravity and reduced gravity environments (such as a planetary surface) limit the use of bubble-forming technologies, since surface tension and inertial or viscous forces may dominate buoyancy, creating an adverse effect in the system. Gas-to-liquid contacting membranes would allow for non-bubbling mass transfer through solution-diffusion, with the potential for simultaneous heat transfer, as done in membrane distillation operations. Previously published work, with similar applications, have focused on characterizing microporous membranes. In this study, a commercially available, nonporous polydimethylsiloxane (PDMS) hollow fiber membrane separated carbon dioxide from an ambient gas stream (296 K) while deoxygenating a cooling-water feed (274 K). Control experiments were conducted with gas and water at ambient temperatures (296 K and 292 K, respectively). Results show that increasing water feed rate (0.5 to 1.5 LPM) reduced the percentage of oxygen transferred from the water to the gas stream (approximately 25% less). Also, a reduction in water temperature significantly reduced percent oxygen transferred (approximately 35% reduction). System heat transfer and carbon dioxide transfer rates were positively correlated to gas flow rates, showing gas-phase dependence. Coefficients derived from the experimental results were used to form semi-empirical mass transport models. Results of this study developed two findings, that a nonporous PDMS membrane could be used for simultaneous heat and mass transfer which could also be described from first-order principles. |
