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the cylindrical and rectangular RCA designs. Consequently, conductance to vacuum, and all other factors, can be held constant within the model in order to gain insight about how the device geometry influences performance. This analysis was performed for both the cylindrical and rectangular geometries. In this analysis, dual-end vacuum was considered for desorption since experimental data existed for both test articles for correlation of the DEV model. The flow rate was set to 170 ALM while all metabolic profiles were explored as summarized by table 1. The conductance to vacuum for the model was more closely associated with the conductance for the cylindrical test article and associated solenoid valving. This was chosen as the basis for comparison as the cylindrical system ostensibly has increased pressure drop and serves as a more conservative estimate of RCA capabilities. 20 35 HS RCA Outlet Dew Point TA2 RCA Outlet Dew Point HS RCA Half-Cycle TA2 RCA Half-Cycle 15 10 5 0 -5 -10 -15 30 25 20 15 10 5 -20 0 50 150 250 350 450 550 650 Metabolic Rate, Watts 50 150 250 350 450 550 650 Metabolic Rate, Watts Figure 7. Simulation results for rectangular versus cylindrical designs with comparable vacuum conductance in dual-end vacuum desorb mode. The results for this analysis are depicted in fig. 7. The results demonstrate that the cylindrical geometry provides a slightly longer half cycle time than the rectangular unit. This result can be explained through considering the geometry. Since both theoretical units experience equal conductance to vacuum and the same starting pressure, the inlet side of both units will have similar de-pressurization profiles as they desorption occurs. Conversely, the cross sectional area of the cylindrical unit decreases radially while the rectangular has a constant cross-section. The increase in cross-section of the cylindrical unit results in a decrease in superficial velocity, and thereby pressure drop, to the outlet side improving the ability to de-pressurize and desorb from the back side of the cylindrical unit. This results in increased half-cycle time. With regard to mean outlet dew point, the cylindrical unit tends to have outlet dew points within a smaller band than the rectangular unit. This result is associated with the disparity in half-cycle times between the two units. For the cylindrical unit with the longer half-cycle time, the bed achieves a more loaded cyclic state. As a result, outlet dew points tend to be higher driving the mean outlet dew point to a higher value than the rectangular unit. These results suggest there could be a performance advantage for the cylindrical design pending pressure drop associated with valves, manifolds, and plenums are kept equal. However, the caveat may present a challenge a the cylindrical unit my need to consist of several more layers than a rectangular unit to maintain a small device diameter. This would presumably increase the pressure drop within the test article and will be investigated in future performance testing. 12 of 15 American Institute of Aeronautics and Astronautics Dewpoint, F Half-cycle time, min.PDF Image | Vacuum Swing Adsorption Units for Spacesuit Carbon Dioxide and Humidity Control
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