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currently have a valve and an ad hoc valving system was built from solenoid valves for this phase of testing. This decreased half-cycle time could be associated a significant increase in pressure drop through the solenoid valving system. Although the explanation is currently unclear, the correlated model has demonstrated the capacity to generate valid half-cycle time predictions for these test articles. As a result, the model might provide the key to determining whether the test article geometry significantly influences the performance of the RCA vacuum swing adsorption system. These results will be discussed in the latter portion of this manuscript. D. Variable Metabolic Challenge Although knowing the performance of the RCA unit during cyclic steady-state is insightful toward under- standing the capabilities of this technology; during extra-vehicular activity, the unit will most likely be subject to multiple metabolic rates that may change at a frequency in which cyclic steady-state is not achieved. As a result, tests were performed to characterize the performance of the RCA unit under non-steady state oper- ation. In particular, two variable metabolic rate experiments were considered. Both a 7 hour and an 8 hour metabolic simulations were designed to mimic the variable profile of an astronaut performing the respective duration of extra-vehicular activity (EVA). These experiments were designed to (A) establish whether or not the RCA unit could effectively mitigate carbon dioxide levels under non-cyclic steady state conditions and (B) to understand how quickly the RCA unit can transition between intermediate steady-state conditions to new constraints on the system. Although both 7 and 8 hour profiles were collected for 110 and 170 ALM flow rates for the rectangular HS-RCA, the results presented herein will focus on the 110 ALM 8 hour results. The other results not explicitly depicted in this report follow similar trends to those included below and can be found elsewhere for the intrigued reader.5 The 8-hour variable metabolic profile imposed on the test article is summarized in table 4. Table 4. 8-hour variable metabolic profile experiment for the HS-RCA. Sequence [No.] [Watts] 1 249 2 322 3 601 4 100 5 334 6 469 7 249 8 322 9 601 10 100 11 334 11 469 Flow Rate [ALM] 110 110 110 110 110 110 110 110 110 110 110 110 CO2 Injection [SLM] 0.658 0.851 1.586 0.263 0.882 1.238 0.658 0.851 1.586 0.263 0.882 1.238 Dew Point [◦ F] Duration [min.] Met. Rate 51.0 30 51.0 60 51.0 10 51.0 50 51.0 60 51.0 30 51.0 30 51.0 60 51.0 10 51.0 44 51.0 81 51.0 15 The results for the variable profile investigation are displayed in fig. 6. Both the experimental and sim- ulation results demonstrate the HS-RCA was capable of handling the metabolic challenge of the simulated 8-hour extra-vehicular activity. The higher metabolic rates forced the RCA to cycle more quickly in order to maintain CO2 concentration below the critical threshold. The shorter half-cycles were also associated with a decrease in the dew point. The model predicts comparable half-cycle times as were recorded experi- mentally although the inlet CO2 flow rates was somewhat lower in the model than recorded experimentally. With regard to dew point, both the model and experiment show that as half-cycle time is increased, water accumulates in the system leading to higher dew points. This trend reverses for the higher metabolic rates where the RCA valve cycles faster. Overall, these results are encouraging as they indicate that the RCA technology should be capable of handling a wide variety of metabolic rates and should also be capable of transitioning quickly between states as activity is either increased or decreased. 10 of 15 American Institute of Aeronautics and AstronauticsPDF Image | Vacuum Swing Adsorption Units for Spacesuit Carbon Dioxide and Humidity Control
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