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All sourcesNASA NTRSDOE OSTI
NASA NTRS2014

Determining the Source of Water Vapor in a Cerium Oxide Electrochemical Oxygen Separator to Achieve Aviator Grade Oxygen

More than a metric ton of water is transported to the International Space Station (ISS) each year to provide breathing oxygen for the astronauts. Water is a safe and compact form of stored oxygen. The water is electrolyzed on ISS and ambient pressure oxygen is delivered to the cabin. A much smaller amount of oxygen is used each year in spacesuits to conduct Extra Vehicular Activities (EVAs). Space suits need high pressure (>1000 psia) high purity oxygen (must meet Aviator Breathing Oxygen "ABO" specifications, >99.5% O2). The water / water electrolysis system cannot directly provide high pressure, high purity oxygen, so oxygen for EVAs is transported to ISS in high pressure gas tanks. The tanks are relatively large and heavy, and the majority of the system launch weight is for the tanks and not the oxygen. Extracting high purity oxygen from cabin air and mechanically compressing the oxygen might enable on-board production of EVA grade oxygen using the existing water / water electrolysis system. This capability might also benefit human spaceflight missions, where oxygen for EVAs could be stored in the form of water, and converted into high pressure oxygen on-demand. Cerium oxide solid electrolyte-based ion transport membranes have been shown to separate oxygen from air, and a supported monolithic wafer form of the CeO2 electrolyte membrane has been shown to deliver oxygen at pressures greater than 300 psia. These supported monolithic wafers can withstand high pressure differentials even though the membrane is very thin, because the ion transport membrane is supported on both sides (Fig 1). The monolithic supported wafers have six distinct layers, each with matched coefficients of thermal expansion. The wafers are assembled into a cell stack which allows easy air flow across the wafers, uniform current distribution, and uniform current density (Fig 2). The oxygen separation is reported to be "infinitely selective" to oxygen [1] with reported purity of 99.99% [2]. Combined with a mechanical compressor, a Solid Electrolyte Oxygen Separator (SEOS) should be capable of producing ABO grade oxygen at pressures >2400 psia, on the space station. Feasibility tests using a SEOS integrated with a mechanical compressor identified an unexpected contaminant in the oxygen: water vapour was found in the oxygen product, sometimes at concentrations higher than 40 ppm (the ABO limit for water vapour is 7 ppm). If solid electrolyte membranes are really "infinitely selective" to oxygen as they are reported to be, where did the water come from? If water is getting into the oxygen, what other contaminants might get into the oxygen? Microscopic analyses of wafers, welds, and oxygen delivery tubes were performed in an attempt to find the source of the water vapour contamination. Hot and cold pressure decay tests were performed. Measurements of water vapour as a function of O2 delivery rate, O2 delivery pressure, and process air humidity levels were the most instructive in finding the source of water contamination (Fig 3). Water contamination was directly affected by oxygen delivery rate (doubling the oxygen production rate cut the water level in half). Water was affected by process air humidity levels and delivery pressure in a way that indicates the water was diffusing into the oxygen delivery system.

Graf, John↗
DOE OSTI2020

Transcritical diffuse-interface hydrodynamics of propellants in high-pressure combustors of chemical propulsion systems

Rocket engines and high-power new generations of gas-turbine jet engines and diesel engines oftentimes involve the injection of one or more reactants at subcritical temperatures into combustor environments at high pressures, and more particularly at pressures higher than those corresponding to the critical points of the individual components of the mixture, which typically range from 13 to 50 bars for most propellants. This class of trajectories in the thermodynamic space has been traditionally referred to as transcritical. However, the fundamental understanding of fuel atomization, vaporization, mixing, and combustion processes at such high pressures remains elusive. In particular, whereas fuel sprays are relatively well characterized at normal pressures, analyses of dispersion of fuel in high-pressure combustors are hindered by the limited experimental diagnostics and theoretical formulations available. The description of the thermodynamics of hydrocarbon-fueled mixtures employed in chemical propulsion systems is complex and involves mixing-induced phenomena, including an elevation of the critical point whereby the coexistence region of the mixture extends up to pressures much larger than the critical pressures of the individual components. As a result, interfaces subject to surface-tension forces may persist in multicomponent systems despite the high pressures, and may give rise to unexpected spray-like atomization dynamics that are otherwise absent in monocomponent systems above their critical point. In this article, the current understanding of this phenomenon is reviewed within the context of propulsion systems fueled by heavy hydrocarbons. Emphasis is made on analytical descriptions at mesoscopic scales of interest for computational fluid dynamics. In particular, a set of modifications of the constitutive laws in the Navier–Stokes equations for multicomponent flows, supplemented with a high-pressure equation of state and appropriate redefinitions of the thermodynamic potentials, are introduced in this work based on an extended version of the diffuse-interface theory of van der Waals. The resulting formulation involves revisited forms of the stress tensor and transport fluxes of heat and species, and enables a description of the mesoscopic volumetric effects induced by transcritical interfaces consistently with the thermodynamic phase diagram of the mixture at high pressures. Additionally, applications of the theory are illustrated in canonical problems, including dodecane/nitrogen transcritical interfaces in non-isothermal systems. The results indicate that a transcritical interface is formed between the propellant streams that persists downstream of the injection orifice over distances of the same order as the characteristic thermal-entrance length of the fuel stream. The transcritical interface vanishes at an edge that gives rise to a fully supercritical mixing layer.

02 PETROLEUM↗
NASA NTRSDate not supplied

Heterogeneity of Bulk Oxygen Isotopic Compositions in Anhydrous Interplanetary Dust Particles

Introduction: Anhydrous interplanetary dust particles are one of the least altered ancient solar systemmaterials. Their bulk chemical compositions match those of CI chondrites within a factor of 2-3, except for carbonwhich is enriched in both anhydrous and hydrated IDPs by ~4x CI [1]. Hydrous IDPs often show 16O-poor isotopiccompositions, likely due to the interaction with isotopically heavy H2O [2]. Anhydrous IDPs are interpreted tooriginate from comets from the outer solar system [3]. Oxygen isotopic data for these materials is scarce, but resultspoint to a wider range of compositions [4]. This heterogeneity might be a result of mixing between a 16O-rich and a16O-poor reservoir formed via self-shielding and photodissociation of CO [5]. Here, we report bulk oxygen isotopiccompositions of three anhydrous IDPs in context of their mineralogical composition and discuss possible origins ofisotopic heterogeneity. Experimental: Bulk chemical composition and mineralogy of 70 nm thin ultramicrotomed sections of threeanhydrous IDPs (L2099A7, L2099A8, and L2071AB1) were analyzed using a Thermo Scientific Titan Themis G360-300 TEM equipped with a four-quadrant energy-dispersive X-ray detector (Super-X G2) at University ofMünster. Bulk oxygen isotopic compositions were measured using a NanoSIMS 50 at the Max-Planck-Institut fürChemie in Mainz. A focused Cs+ ion beam (~1 pA, ~100 nm) was rastered over a field of view varying from 5 x 5 to6 x 6 μm2, depending on particle size for 15 layers. Negative secondary ions of 16O, 17O, 18O, 12C14N, and 28Si werecollected on electron multipliers. The 16OH contribution to the 17O peak was 1-2 ‰. As a standard, a matrix regionof meteorite CR2 Queen Alexandra Range (QUE) 99177 was used, whose oxygen isotopic composition wasmeasured by [6]. Results and Discussion: Particles A7 and A8 are both fine-grained, consisting mostly of small, 100 nm-sizedequilibrated aggregates (EA). Both particles exhibit discontinuous magnetite rims with thicknesses up to 50 nm inA7 and 100 nm in A8 on the outsides. In Particle AB1, the upper part of the particle consists of a few EAs, while thelower part contains lots of small GEMS grains with 100-200 nm diameter clustered together. Magnetite rims arenearly absent, the rare rims reaching maximum 20 nm thickness, indicating that AB1 is of more primitive naturethan the other two IDPs [1]. Furthermore, it contains several diffuse GEMS-like areas, identified by an amorphoussilicate groundmass with small nano-inclusions of Fe,Ni-metal and Fe-sulfides. All three particles are subsolar forall major element/Si ratios. Mean S/Si of particles A7 and A8 is 0.046 and 0.048, respectively, while it is an order ofmagnitude higher in AB1 (0.184). This reflects the higher degree of thermal alteration in A7 and A8, resulting in theloss of volatile S and oxidation of Fe-sulfides and FeNi-metal to magnetite as present in particle rims. A8 is rather16O-poor with δ17OSMOW = 7.8 ± 3.4 ‰ and δ18OSMOW = 9.5 ± 3.1 ‰ (1σ), followed by A7 with δ17OSMOW = − 0.8 ±4.6 ‰ and δ18OSMOW = −2.2 ± 3.4 ‰. In contrast to that, AB1 has the most 16O-rich bulk composition with δ17OSMOW= −24.2 ± 5.4 ‰ and δ18OSMOW = −25.3 ± 3.6 ‰. All investigated IDPs plot slightly above the CCAM line aspreviously reported for other anhydrous IDPs [4], maybe due to a contribution from circumstellar dust from AGBstars enriched in 17O [7]. The 16O-rich composition of AB1 is similar to the most 16O-rich anhydrous IDP U2015D21measured by [8] which is dominated by GEMS [9] and the GEMS-rich IDP GM4-2 reported by [10]. Nevertheless,it is unlikely that GEMS are the carrier for the 16O-rich composition of AB1 because most GEMS have O isotopiccompositions indistinguishable from terrestrial values, although errors on these analyses are large [11]. The isotopicheterogeneity is best explained by contribution of grains from different regions in the protoplanetary disk, samplingdifferent O isotope reservoirs, created by self-shielding and photodissociation of CO. This process resulted in 16O-rich CO gas and 16O-poor H2O that froze as ice-mantles onto dust grains [12]. Alternatively, the higher degree ofheating in A7 and A8 could have influenced isotopic fractionation, because higher δ17,18O values are reported fromthe regions of the atmosphere where small particles are heated and oxidized, as observed for the thermal alteration ofcosmic spherules [13]. Acknowledgements: We would like to thank NASA Astromaterials Acquisition & Curation Office for providing IDPsamples and DFG for funding this project (VO1816/5-1)

B Schulz↗