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Table 1. Full-scale injection rates employed to simulate metabolic challenge to the RCA test articles in this investigation. Metabolic Rate, Watts 103 152 249 293 366 469 586 CO2 Injection Rate, SLM 0.271 0.402 0.658 0.774 0.967 1.238 1.548 H2O Injection Rate, g/min. 0.60 1.02 1.13 1.44 1.59 1.36 1.29 to determine boundary velocities during vacuum swings, valve equations were employed, eq. 9 and eq. 10. Parameters for the model described in table 2 are summarized in table 3. Mass, heat, and dispersion coefficients were approximated according to heuristic relationships summarized elsewhere8 and further op- timized against experimental performance data. Isotherm parameters were determined from experimental data relating adsorbent loading to adsorbate concentration. Gas viscosity and heat capacity could either be determined from heuristic relationships reported elsewhere13 or through internal algorithms in the simulation software used to approximate a solution. The coupled system of partial differential equations was solved using finite difference techniques through the Aspen Custom Modeler software package. A second order central finite differencing scheme was applied in order to accurately model bi-directional flow that occurs during vacuum desorb. The Gear formulae were used for numerical integration as a result of the ability of the Gear formulae to simulate phenomena with dynamics on drastically different time-scales. The calculations were performed on a CPU with a 2.66 GHz Intel⃝R CoreTM2 Quad processor and 3.25 GB of RAM. For any specified metabolic rate, pressure, and flow rate, solution generally take several minutes to an hour. IV. Results & Discussion In order to maintain a safe environment within the PLSS during extra-vehiclar activity, the rapid cycle amine system is under aggressive developmental efforts for air revitalization. The process is achieved through cycling an interleaved system of thermally-coupled vacuum swing adsorption (VSA) reactors. This concept has been translated into a handful of function prototypes. The prototypes can be classified into either rectangular or cylindrical units. This manuscripts details the experimental results and the results of a correlated model for two such units. With respect to the model, the major difference is attributed to the ∇ operator which assumes different forms for either rectangular (i.e. Cartesian) or cylindrical geometry. In addition, the rectangular adsorbent layers maintain a constant cross-sectional area while the cylindrical devices has a change in cross-sectional area as gas flows from the inner to the outer radius. However, before considering the experimental results, it is worth exploring the sorption behavior of carbon dioxide and water on SA9T to develop intuition about the physics through which the RCA works. A. Sorption Behavior of SA9T An example solution for these equations is provided in fig. 3. It becomes immediately apparent that the sorption behavior of H2O and CO2 are significantly different. The experimental loading data collected for this analysis, along with the magnitude of the heats of adsorption, indicate that water undergoes type III adsorption while CO2 follows a type I process. In particular, type-I processes are generally represented as a Langmuir process where adsorbate molecules compete for surface sites in which non-covalent interactions result in molecules associating with a surface.10,14,15 Conversely, type-III processes demonstrate limited sorption at low concentrations followed by an exponential rise in sorption with increasing concentration. 5 of 15 American Institute of Aeronautics and AstronauticsPDF Image | Vacuum Swing Adsorption Units for Spacesuit Carbon Dioxide and Humidity Control
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