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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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Enriching Heavy Noble Gases in Titan Atmosphere by Cryogenic Condensation

Titan is an extraordinary moon belonging to Saturn. It presents a dense atmosphere with a surface pressure approximately 1.45 times that of Earth’s. The relative abundance of noble gases and their isotopes can elucidate extant geochemical processes and inform past and future planetary evolution. The GCMS on the Hyugens probe sampled the dense atmosphere of Saturn’s Titan in 2005 and did not detect Kr or Xe at ppb concentrations. Several chemical pathways have been considered as mechanisms to account for the depletion of these heavy nobles. However, our understanding remains incomplete without in situ detection. Thus, we investigate spaceflight cryogenic enrichment for Kr and Xe. The thermodynamic processes would be capable of substantially amplifying these gases at femtomole concentrations, in anticipation of future atmospheric surveys on Titan.

condensation↗
DOE OSTI2023

Metal-Free, Oxidative Condensation of Heteroaryl- and Aryl Carbaldehydes towards Functionalized Carbonitriles

Functionalization of pyridines with the carbonitrile group for advanced cyclization reactions routinely incorporates metals, toxic oxidants, and cyanide reagents, often in linear synthetic sequences. Here, motivated by the strategic need of a heteroaryl carbonitrile synthon for further elaboration, we disclose an efficient, metal-free, one-pot reaction sequence that uses ammonium acetate as the nitrogen source and bis-acetoxyiodobenzene as the oxidant with low loadings. The developed method tolerates a diverse substrate scope including heteroaryl, aryl, and alkyl substrates with similar efficiency and expands the practitioner's reaction. Method development, optimization, substrate scope, preliminary mechanistic observations, competition experiments, and a scale up reaction are delineated herein.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Efficient continuous Energy-Multigroup hybrid depletion scheme using the Shift Monte Carlo code. Part I: Energy condensation sensitivity analysis

Monte Carlo (MC) codes coupled to depletion solvers are increasingly used to provide high fidelity fuel cycle modeling capabilities. Here, these coupled depletion-MC tools produce accurate results in general but can experience nonphysical spatial oscillations when time steps are large or when a system’s dominance ratio approaches unity. Two substepping techniques have been developed previously to remedy and dampen these spatial oscillations without needing to reduce step sizes. The first approach relied on higher-order techniques to account for spectral changes within steps (extrapolation and interpolation techniques). The second approach used the first order perturbation (FOP) theory to account for the change in the one-group spatial flux distribution within steps. This paper develops a hybrid depletion methodology which, in a way, combines how the flux is handled in both substepping techniques. Specifically, the multigroup (MG) MC Shift code is used to update the flux distribution within steps rather than a one-group FOP solver. A fully reflected pincell is investigated, which is not spatially dependent in the MG representation. Thus, the analysis in this paper is an initial demonstration of hybrid depletion. An upcoming companion paper will focus on how the hybrid depletion dampens spatial oscillations. The hybrid depletion approach is verified to be consistent with previous constant extrapolation depletion (CED) methods. This paper finds that the hybrid CED exhibits some error in the eigenvalue and one group constants within macro steps. To address this discrepancy, a simple interpolation scheme (CELI) is investigated. This work found that CELI sufficiently addresses the discrepancy in spectrum for macro steps up to 100 days. Overall, this work demonstrates that the hybrid depletion method can significantly reduce the number of high fidelity MC executions in a MC-coupled depletion with an acceptable eigenvalue error.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
DOE OSTI2023

Theoretical estimates of flammability bounds for thin condensed fuel diffusion flames in microgravity using detailed models of chemistry and radiation

Recently, U-shape flammability maps have been constructed showing minimal oxygen vs. flame strain for opposed flame spread in micro-gravity by Olson and Ferkul. The U-shape defines the limiting flammability bounds from radiative extinction and flame blow-off. Here, the minimum of the U corresponds to the minimum possible oxidizer concentration where burning can occur, and is an important quantity of interest for fire safety. While high strain extinction bounds have been well analyzed, low strain radiative extinction has not. To estimate low strain extinction, in this study an analytical theory is developed based on thin flame theory coupled with a heat and mass transfer model for solid fuels. A reaction progress variable based on the Damköhler number is adapted in the theory to account for incomplete combustion at high strain rates and enable the capturing of the full flammability map. The analytical model is compared to a one dimensional numerical model w/ detailed chemical kinetics and coupled radiation heat transfer in planar and spherical geometries. The flammability maps are then qualitatively compared to experimental extinguishment data compiled by Olson and Ferkul for cylindrical rods of PMMA showing similar trends. The results show the newly developed analytics capture the radiative extinction bound compared to the numerical model and qualitatively agrees with microgravity data.

38 RADIATION CHEMISTRY, RADIOCHEMISTRY, AND NUCLEA↗