Browsing by Author "Chen, Thomas T."
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Item Integrated Simulations of the Sabatier and Carbon Vapor Deposition Reactor to Understand Its Impacts to Operations and Performance(2024 International Conference on Environmnetal Systems, 2024-07-21) Chen, Thomas T.The Carbon Vapor Deposition (CVD) reactor is a technology developed by Honeywell Aerospace to convert methane, at high temperatures, into hydrogen and solid carbon. This element is coupled with a Sabatier reactor to support a closed loop environmental control and life support system with the aim of achieving nearly complete oxygen recovery (> 95%). Initial open loop, brassboard CVD reactor tests and simulations have shown its ability to achieve moderately high methane conversion and high hydrogen selectivity. However, in an integrated system, additional deficiencies are expected due to recycling of unreacted or extraneous species from the Sabatier reactor (e.g., carbon dioxide, hydrogen, water) and CVD reactor (e.g., hydrocarbons, methane, etc.). Sabatier and CVD reactor models were integrated and simulated to predict potential impacts to individual reactors� and overall system�s performance. The simulations showed that increasing the recycle of the CVD effluent hydrogen combined with decreasing the system inlet hydrogen flow rate (i.e., drawing a stoichiometric flow rate from an electrolyzer) can lead to an oxygen recovery of > 95%. However, system integration comes at a detriment to the individual reactors. The simulations show the initial conversion from the integrated system (Sabatier = 87% and CVD = 63%) to be lower than the standalone systems (Sabatier = 91% and CVD = 68%). Furthermore, transient simulations show substrate densification leading to worsening methane conversion coupled with increasing acetylene production, which is commensurate with soot formation. Simulations predict a shortening of the maintenance interval (i.e., time until CVD methane conversion drops below 50%) in the integrated system (Integrated = 110 hours vs Standalone = 275 hours), which would increase in the consumable substrate mass by ~2.5�. These analyses highlight the importance of long duration, integrated tests to corroborate these findings as well as suggest potential modifications (e.g., intermediate gas separations) to improve performance.Item Integrated Waste Trade Study: Lunar Surface to Deep Space(2024 International Conference on Environmnetal Systems, 2024-07-21) Rini,Emily; Ewert, Michael K.; Chen, Thomas T.The Logistics Reduction Project is one of NASA's technology development projects that is preparing humanity for deep space missions. Reducing the mass and volume of logistical supplies that must be carried from Earth to support the missions and their crews is the primary goal of the project. Effective ways to achieve this goal include reducing, reusing, or recycling wastes generated throughout the mission. Due to the goal of the project, waste processing technologies were analyzed for Lunar surface missions at various lengths and an 850-day Mars transit mission to evaluate the potential benefits of waste processing pertaining to each mission. The technologies assessed include trash compaction, trash-to-gas and human metabolic waste processing technologies, integrated with the baseline architectures of each mission�s habitat. The fully integrated systems were analyzed using an equivalent system mass, which is a metric that encompasses the mass, volume, power and cooling of a system, resulting in an estimate of launch mass and serving as a proxy for cost. Each system�s equivalent system mass was compared to that of the baseline waste processing system of the respective habitat, hand compaction with storage for Lunar surface missions and hand compaction with jettisoning for Mars transit, to evaluate whether the traded waste processing technology was beneficial. This analysis identifies a general trend that more sophisticated waste processing can be beneficial depending on the mission duration. For Lunar surface missions, the water recovery from waste processing can pay off over consecutive missions, due to offsetting the losses from the system via extravehicular activities. In contrast for Mars transit, the primary objective is mass removal from the spacecraft, so technologies like trash-to-gas are competitive with the baseline. Furthermore, the technologies which can recover resources from waste, such as water, may present additional advantages to an ever-changing Mars mission architecture.Item Kinetic Model Development of the Carbon Vapor Deposition Reactor to Predict Performance versus Design(2024 International Conference on Environmnetal Systems, 2024-07-21) Chen, Thomas T.; Barta, Daniel J.; Yates, Stephen F.; Triezenberg, MarkTo enable complete closure of a Sabatier-based atmosphere revitalization system where oxygen recovery is predicated by carbon dioxide reduction to methane and water, there must be a means of recovering the hydrogen from the byproduct methane. Honeywell�s Carbon Vapor Deposition (CVD) reactor is a potential technology that provides a thermochemical means where methane decomposes at high temperatures (> 1,000 �C) into hydrogen, solid carbon, and a small percentage of hydrocarbons. This advanced methane pyrolysis reactor utilizes a carbon fiber substrate to capture and immobilize the solid pyrolytic carbon rather than allowing continuation towards undesirable soot. The CVD reactor is a highly dynamic system whose characteristic geometry changes while operating. The reactor model was developed to provide predictive performance assessment capabilities at different operating conditions, geometries, and configurations to aid in technology development. Modeling of the CVD reactor considered the multitude of simultaneous and interdependent physicochemical processes that are entailed including: (1) the homogeneous gas-phase pyrolysis reactions, (2) the heterogeneous deposition reactions, and (3) the transport of gaseous species in the reactor domains. A 1-D CVD reactor model was developed based on a general packed bed axial dispersion plug flow reactor model with a solid substrate balance to account for carbon deposition. The model includes 59 species and 243 reactions constituting the methane pyrolysis reaction network, carbon deposition, and interconversions of oxygenate species. The reactor model was compared to brassboard test data where it was shown to be able to capture the pertinent physicochemical phenomena as evidenced by its agreement with short duration run data (i.e., looking at different temperature and flow rate conditions), as well as trend agreement with the brassboard reactor�s long duration test data. Recommendations are provided on further model development steps as well as its uses cases.