Browsing by Author "Niehaus, Justin"
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Item Development and Validation of a Model to Account for Gaseous HCl and Aluminum Surface Interactions for Spacecraft Fire Safety Applications(49th International Conference on Environmental Systems, 2019-07-07) Niehaus, Justin; Gokoglu, Suleyman; Mazumder, Sandip; Berger, Gordon; Easton, JohnExperiments and modeling were performed to determine the surface kinetics of gaseous hydrogen chloride (HCl) with aluminum surfaces subjected to various treatments. HCl and other acid gases are a spacecraft fire safety concern as they are commonly found in products from electrical wire pyrolysis. Three types of aluminum surfaces were considered: surface with chromate conversion coating (iridite), anodized, and untreated. A test cell made of Teflon was used to measure the difference in HCl from the inlet to the outlet. Inlet and outlet sensors were used to measure HCl concentrations. A simple one-step global surface reaction model was proposed, and an Arrhenius surface kinetics expression that accounts for active surface sites was employed. The kinetic constants were determined (calibrated) using the measured data. The calibrated model was validated against experiments with different flow rates and HCl inlet concentrations. The results showed that anodized aluminum had the most HCl uptake, followed by the iridite and then the untreated aluminum. The amount of HCl uptake seems to correlate well with the thickness of the oxide layer on aluminum. The relevance of these findings are discussed with respect to the design of large-scale fire safety experiments in space and various fire safety application scenarios.Item Effect of Humidity on Surface Interactions of Gaseous HCl and Aluminum for Spacecraft Fire Safety Applications(2020 International Conference on Environmental Systems, 2020-07-31) Niehaus, Justin; Gokoglu, Suleyman; Mazumder, Sandip; Berger, Gordon; Easton, JohnExperiments were performed to understand the interaction of gaseous hydrogen chloride (HCl) with aluminum surfaces in the presence of water vapor. The results show that increasing levels of relative humidity, tested for 10, 25, and 50 percent in air, increase the capacity of HCl adsorption compared to results previously published with dry air flow. A series of tests were performed on individual aluminum samples after they had been saturated with a fixed concentration of HCl in dry air conditions with the goal of determining how their HCl uptake capacity change after various treatments with water relative to the original saturation run. HCl-saturated aluminum samples subjected to a second dry air flow at the same HCl concentration as the original test had an uptake of 23.5% of the original sample. Saturated aluminum samples subjected to an in-between clean-up relative humidity of 90% air flow had an uptake of 35.6% of the original. Saturated aluminum samples submerged in distilled water for 12 hours had an uptake of 82.2% of the original sample. Saturated aluminum subjected to 50% humid air resulted in similar uptake characteristics in multiple repeated tests. These small-scale tests were run in parallel to a large-scale ground duct test used to mimic the stand-off in the Cygnus spacecraft during a Saffire experiment. Conclusions of this testing will be used in the design of large-scale spacecraft fire safety experiments and to develop a model to account for the interactions of HCl and aluminum surfaces in the presence of water in those tests.Item Evaluation of Combustion Products from Large-Scale Spacecraft Fires during the Saffire-IV and Saffire-V Experiments(50th International Conference on Environmental Systems, 7/12/2021) Fortenberry, Claire; Casteel, Michael; Graf, John; Easton, John; Niehaus, Justin; Meyer, Marit; Urban, David; Ruff, GaryThe aim of the spacecraft fire safety series of experiments (Saffire) is to investigate the behavior of large-scale fires in microgravity. During these experiments, materials are ignited within the Northrop Grumman Cygnus resupply vehicle following its departure from the International Space Station. Saffire-IV and Saffire-V introduced a far-field diagnostics (FFD) unit to house sensors for smoke characterization, including gas monitors and particle detectors. The FFD also housed a prototype �smoke eater� device and a CO2 scrubber, which are designed to remove combustion products from a spacecraft atmosphere. Remote sensors installed at six locations throughout the Cygnus cabin measured CO2 concentrations and temperature, allowing evaluation of smoke plume transport. In this work, we report on gas and particle measurements from the Saffire-IV and Saffire-V experiments, presenting the first effort to comprehensively characterize combustion products from large-scale microgravity fires. We evaluate the transport of key species throughout the spacecraft cabin. Finally, we address post-fire cleanup methods and discuss remaining science questions to be targeted in future work.Item Model Development of Large-Scale Spacecraft Fires during the Saffire-IV Experiments(51st International Conference on Environmental Systems, 7/10/2022) Brooker, John; Niehaus, JustinAn accidental fire can pose dire consequences to crew safety and mission success. The Saffire Project aims to investigate large-scale fire behavior in microgravity in order to aid in the prediction of spacecraft fires. These series of experiments ignite solid materials within the Northrop Grumman Cygnus vehicle after it departs from a resupply mission to the International Space Station. A model of the Cygnus vehicle during the Saffire-IV experiment was developed using the commercial software PyroSim. The cargo arranged during the descent phase was used for the geometry of the model. In the model, cabin air flows into the Saffire payload while heat and combustion species flow out of the Saffire downstream through a standoff to a bed of sensors called the Far Field Diagnostic. The temperature sensors near the Saffire payload were used to determine the heat addition rate at the outlet of Saffire, while the details of the combustion and stoichiometry are used to determine the species flow at the outlet. Gas measurements previously reported for the Saffire-IV experiments are compared against the simulation results and sources of error are discussed.Item Modeling the Uptake of Hydrogen Chloride onto Interior Spacecraft Materials(50th International Conference on Environmental Systems, 7/12/2021) Niehaus, Justin; Mazumder, Sandip; Gokoglu, Suleyman; Berger, Gordon; Easton, JohnHydrogen chloride (HCl) is a major combustion product from the pyrolysis of polyvinyl chloride (PVC) insulated electrical wires, a common spacecraft fire safety concern. Models at two different scales were developed to predict HCl uptake on anodized, chromate conversion coated (Iridite), and bare aluminum surfaces, as well as on Nomex fabric: a macroscopic one-step global surface reaction model where all the active sites are on the exterior surface, and a pore model where the interior active sites deeper into the oxide layer can also be accessed by HCl. Experiments were performed to calibrate kinetic and diffusion constants in the models. A cast acrylic test cell was used to measure the differences between the inlet and outlet concentration of HCl after inserting a sample rod of the test material. For the materials with a thin (< 200 �m) or no oxide layer, the macroscopic surface reaction model adequately predicts the experimental measurements. For the anodized aluminum with a thicker oxide layer, the pore model provided a better match to experimental results. The results will be discussed with respect to the spacecraft fire safety project (Saffire).Item Vehicle Modeling during the Burning of Cotton Samples in the Saffire IV and V Experiments(2023 International Conference on Environmental Systems, 2023-07-16) Niehaus, Justin; Brooker, JohnPredicting the transport of combustion products and heat during a spacecraft fire can help design a safer vehicle and mission. The Saffire project has provided data on the spread of large fires in a microgravity environment within Northrup Grumman’s Cygnus vehicle after a resupply mission to the ISS. Solid materials, including cotton-based samples were ignited to study flame spread and the effect a fire has on a vehicle. Sensors were placed within Cygnus that measured carbon dioxide concentration and temperature. A model of the Cygnus vehicle was developed using inlet and outlet data of Saffire and the descent phase cargo configuration photos. The initial gas phase volume of the model did not match volume measurements provided by the release of CO2, likely due the porous nature of the trash and cargo in Cygnus. Holes were placed in the model cargo to match the experimental volume, providing a better prediction of species transport. Surface heat transfer was calibrated to match the closest remote sensor to the Saffire IV outlet, (RS3) in the forward port standoff, providing a better prediction of the temperature throughout the vehicle.