Browsing by Author "Navarro, Moses"
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Item Carbon Dioxide Washout Testing Using Various Inlet Vent Configurations in the Mark-III Space Suit(44th International Conference on Environmental Systems, 2014-07-13) Korona, F. Adam; Norcross, Jason; Conger, Bruce; Navarro, MosesRequirements for using a space suit during ground testing include providing adequate carbon dioxide (CO2) washout for the suited subject. Acute CO2 exposure can lead to symptoms including headache, dyspnea, lethargy, and eventually unconsciousness or even death. Symptoms depend on several factors including inspired partial pressure of CO2 (ppCO2), duration of exposure, metabolic rate of the subject, and physiological differences between subjects. Computational Fluid Dynamics (CFD) analysis has predicted that the configuration of the suit inlet vent has a significant effect on oronasal CO2 concentrations. The main objective of this test was to characterize inspired oronasal ppCO2 for a variety of inlet vent configurations in the Mark-III suit across a range of workload and flow rates. Data and trends observed during testing along with refined CFD models will be used to help design an inlet vent configuration for the Z-2 space suit. The testing methodology used in this test builds upon past CO2 washout testing performed on the Z-1 suit, Rear Entry I-Suit, and the Enhanced Mobility Advanced Crew Escape Suit. Three subjects performed two test sessions each in the Mark-III suit to allow for comparison between tests. Six different helmet inlet vent configurations were evaluated during each test session. Suit pressure was maintained at 4.3 psid. Suited test subjects walked on a treadmill to generate metabolic workloads of approximately 2000 and 3000 BTU/hr. Supply airflow rates of 6 and 4 actual cubic feet per minute were tested at each workload. Subjects wore an oronasal mask with an open port in front of the mouth and were allowed to breathe freely. Oronasal ppCO2 was monitored real-time via gas analyzers with sampling tubes connected to the oronasal mask. Metabolic rate was calculated from the CO2 production measured by an additional gas analyzer at the air outlet from the suit. Real-time metabolic rate measurements were used to adjust the treadmill workload to meet target metabolic rates. This paper provides detailed descriptions of the test hardware, methodology and results, as well as implications for future inlet vent designs and ground testing.Item Considerations for Thermal Modeling of Lithium-Ion Cells for Battery Analysis(46th International Conference on Environmental Systems, 2016-07-10) Rickman, Steven; Christie, Robert; White, Ralph; Drolen, Bruce; Navarro, Moses; Coman, Paul T.Recent events involving lithium-ion batteries on commercial aircraft have raised concerns regarding thermal runaway -- a phenomenon in which stored energy in a cell is rapidly released as heat along with vented effluents. If not properly managed, testing has shown that thermal runaway in a single cell can propagate to other cells in a battery and may lead to a potentially catastrophic event. Lithium-ion batteries are becoming more widely used in a number of human-rated extravehicular space applications on the International Space Station. Thermal modeling in support of thermal runaway propagation mitigation in the Lithium-ion Rechargeable EVA Battery Assembly (LREBA) and the Lithium-ion Pistol Grip Tool (LPGT) was pursued to inform design decisions and to understand the results of extensive development testing with the goal of enhancing safety. A correct representation of thermal runaway in battery-level thermal models requires an understanding of internal cell triggering mechanisms, heat transfer mechanisms through the cell wall, an accounting of energy transport through vented gases and effluents and proper consideration of heat transfer mechanisms within the battery. Development and refinement of internal cell multi-physics models provided heating profiles used for a simplified cell thermal network representation. A collection of simplified cells was used to formulate battery-level models of, both, the LREBA and LPGT battery configurations. Limited correlation of these models was performed using test data. An assessment of heat transport via vented gases was performed using computational fluid dynamics (CFD). Use of the models in conjunction with testing led to design enhancements for, both, the LREBA and LPGT configurations. These thermal-runaway severity-reduction measures are also being applied to other lithium-ion batteries being developed for the International Space Station, Extravehicular Mobility Unit and other programs. Modeling guidance and future efforts are discussed.Item EMU CO2 Washout Comparative Assessments for the HAB/HAP-E in Support of EVA 80(2023 International Conference on Environmental Systems, 2023-07-16) Navarro, Moses; Mah, Monica; Baukus, AbigailAfter water was reported in the Extravehicular Mobility Unit (EMU) helmet during ISS US EVA 80, mitigation strategies were created to attempt to arrest the motion of any droplets that enter the helmet for future Extravehicular Activities (EVAs). This included adding absorbent materials into the interior of the helmet. But before a mitigation strategy can be implemented, it must first be proven to be safe. Towards this aim, a computational fluid dynamics (CFD) model was developed to assess the effect that the absorbent material has on the concentration of carbon dioxide in the EMU helmet. Within a small, closed volume such as a helmet, some amount of the carbon dioxide produced by the suit-wearer will be re-inhaled before being cleared from the oral-nasal region. The ability of the suit to remove carbon dioxide is referred to as CO2 washout. Pathological levels of inhaled CO2 (hypercapnia) are associated with dizziness, fatigue, and headaches. The CFD model was built in ANSYS Fluent and adapted to assess CO2 washout in a variety of scenarios grouped into three categories: ventilation cases, varying metabolic rates, and varying sorbent material configurations. The presence of the sorbent material did not prove detrimental to CO2 washout in the helmet.Item Risk Analysis Associated with Loss of Toxic Gases during Orion Landing and Recovery Operations(49th International Conference on Environmental Systems, 2019-07-07) Swickrath, Mic; Navarro, Moses; Stambaugh, ImeldaMission, landing and recovery operations for the Orion crew module involve reentry into the Earth’s atmosphere and the deployment of three Nomex parachutes to slow the descent before landing along the west coast of the United States. Orion may have residual fuel (hydrazine, N2H4) or coolant (ammonia, NH3) on board which are both highly toxic to crew in the event of exposure. These risks were evaluated using a first principles analysis approach through fluid dynamics modeling. Plume calculations were first performed with the ANSYS Fluent computational fluid dynamics code. Data were then extracted at locations relevant to crew safety such as the snorkel fan inlet and the egress hatch. Mixing calculations were performed to quantify exposure concentrations within the crew bay before and during egress and departure. Finally, results included herein were used to inform the Orion post-landing Concept of Operations (ConOps) so that strategies could be formulated to maintain crew safety in the event of the loss of fuel or coolant.Item Water Phase Change Heat Exchanger System Level Analysis for Low Lunar Orbit(46th International Conference on Environmental Systems, 2016-07-10) Ungar, Eugene; Navarro, Moses; Hansen, Scott; Sheth, RubikIn low Lunar orbit (LLO) the thermal environment is cyclic – extremely cold in the eclipse and warmer than room temperature near the subsolar point. Phase change material heat exchangers (PCM HXs) are the best option for long term missions in these environments. The Orion spacecraft will use n pentadecane wax PCM HX for its envisioned mission to low Lunar orbit. Using water as a phase change material is attractive because its higher heat of fusion and greater density result in a lighter, more compact PCM HX. To assess the use of a water PCM HX for a human spacecraft in a circular LLO, a system level analysis was performed for the Orion spacecraft. Three cases were evaluated: a) A direct replacement of the wax PCM HX on the internal thermal control loop with a water PCM HX (including control modifications), b) a water PCM HX on the internal thermal control loop with a reduced radiator return setpoint temperature, c) locating the water PCM HX on the external loop with a controlled bypass. The model showed that the water PCM HX could not be used as a drop-in replacement for the wax PCM HX. It did not freeze fully during the eclipse owing to its lower freezing point. Even in the most advantageous location – on the external loop - at least 15% more radiator area than the Orion baseline was required to obtain equivalent performance. The study shows that, although water PCM HXs are attractive at a component level, system level effects mean that they are not a good choice for LLO.