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NASA NTRS2020

Modeling Electrolytic Conversion of Metabolic CO2 and Optimizing a Macrofluidic Electrochemical Reactor for Advanced Closed Loop Life Support Systems

The International Space Station (ISS) is currently equipped with a complex, heavy, and power consuming system that recovers approximately 50% of O2 from metabolic CO2. Future long duration missions will require a sustainable and highly efficient system capable of yielding a minimum of 75% O2 recovery. A Macrofluidic Electrochemical Reactor (MFECR) technology development effort is currently underway at NASA Marshall Space Flight Center (MSFC) to significantly increase current O2 recovery efficiency and reduce complexity of the system. This paper presents a comprehensive multi-physic 3D model developed at MSFC on CO2 conversion to O2 and C2H4 at standard conditions via MFECR. The 3D spatial domain of the model is a replica of the actual MFECR’s 3D drawing generated for the MFECR fabrication and operated to recover O2 from CO2 yielding C2H4 as byproduct. Electrochemical (EC) physics that includes EC multicomponent reaction mechanisms, mass transport, and current density distributions is coupled in the model with all the other physics phenomena involved in the process, such as free and porous fluid flow, multicomponent mass transfer, heat transfer, and DC electrical current generation along with Joule heating effect. The authors plan to use experimental results to validate this comprehensive and rigorous model and build a reliable simulator that will not only assist the authors on the MFECR design but also optimize its operation.

Dominguez, Jesus A.↗

NASA NTRS1972

Evaluation of advanced bladder technology

Research conducted during this period is reported. Studies presented include: (1) diffusion and permeation of CO2, O2, N2, and NO2 through polytetra fluoroethylene; (2) diffusion, permeation and solubility of simple gases (CO2, O2, N2, CH4, C2H6, C3H8, and C2H4) through a copolymer of hexafluoro propylene and tetrafluoro ethylene (FEP); (3) viscous flow and diffusion of gases throug small apertures; (4) diffusion and permeation of O2, N2, CO2, CH4, C2H6, and C3H8 through nitroso rubber; and (5) results of gas transport studies with carborane siloxane, nitroso rubber, silicone membrane, krytox coating on teflon, and FEP coated glass cloth. Publications generated under this program are listed.

Christensen, M. V.↗

NASA NTRS1972

Simple technique for sequential Q-switching of molecular lasers.

A simple technique for sequentially Q-switching molecular lasers is discussed in which an optical scanner is used as an optical folding element in a laser cavity consisting of a stationary diffraction grating and partially reflecting mirror. Sequential Q-switching of a conventional CO2 laser is demonstrated in which over sixty-two transitions between 9.2 and 10.8 microns are observed. Rapid repetition rates (200 Hz) and narrow laser pulses (less than 5 microsec) allow conventional signal processing techniques to be used with this multiwavelength laser source which is a versatile tool for laser propagation studies, absorption spectroscopy, and gain measurements. Results of a preliminary experiment demonstrating the utility of measuring selective absorption of CO2 laser wavelengths by C2H4 are shown.

Lucht, R. A.↗

NASA NTRS1973

Carbon chemistry of Luna 16 and Luna 20 samples.

Luna 16 and Luna 20 samples were analyzed for volatilizable species using vacuum pyrolysis to 1400 C. The major gaseous products evolved (ranging from 10-650 micrograms/g) were H2O, CO, CO2, N2 and CH4. Minor components (all less than 10 micrograms/g) included NH3, HCN, NO, SO2, H2S, C2H2, C2H4, C2H6, C3H6 and higher hydrocarbons, benzene, toluene, and the polymeric contaminants Teflon and silicone oil. The total carbon and nitrogen contents (micrograms/g) for these sieved samples were: Luna 16 - C 418, N 134 and Luna 20 - C 380, N 80.

Simoneit, B. R.↗

NASA NTRS1976

Shear strength of metal-sapphire contacts

The shear strength of polycrystalline Ag, Cu, Ni, and Fe contacts on clean (0001) sapphire has been studied in ultrahigh vacuum. Both clean metal surfaces and surfaces exposed to O2, Cl2, and C2H4 were used. The results indicate that there are two sources of strength of Al2O3-metal contacts: an intrinsic one that depends on the particular clean metal in contact with Al2O3 and an additional one due to intermediate films. The shear strength of the clean metal contacts correlated directly with the free energy of oxide formation for the lowest metal oxide, in accord with the hypothesis that a chemical bond is formed between metal cations and oxygen anions in the sapphire surface. Contacts formed by metals exposed to chlorine exhibited uniformly low shear strength indicative of van der Waals bonding between chlorinated metal surfaces and sapphire. Contacts formed by metals exposed to oxygen exhibited enhanced shear strength, in accord with the hypothesis that an intermediate oxide layer increases interfacial strength.

Pepper, S. V.↗

NASA NTRS1977

Reforming of glucose and wood at the critical conditions of water

Reforming of organics in aqueous solutions is being investigated as a potential waste treatment process. Earlier studies showed that glucose in water reacts to form a gaseous mixture of CO, H2, CH4, CO2, C2H6, and C2H4 in the vicinity of the critical conditions of water (374 C, 22 MPa). The earlier work has been extended to determine the effect of variations in temperature and feed concentration on the extent of gasification. The percent gasification decreases with increasing feed concentration, indicating an overall kinetic order less than unity. Surprisingly, the percent gasification decreases with increasing temperature. A number of preliminary experiments were conducted with maple sawdust feed, which was thought to be representative of complex organic wastes from paper and vegetable matter. Once again, no solid products were found under the critical conditions; the percent gasification ranged from 16 to 88 percent, depending on the feed composition and residence time.

Modell, M.↗

NASA NTRS1978

Aeronomy of Saturn and Titan

The Saturn system presents exciting and unique objects for planetary aeronomy. The photochemistry of H2 and He leads to the formation of an ionosphere. Methane photolysis results in the formation of spectroscopically detectable amounts of C2H6 and C2H2 and in the case of Titan, C2H4. Density profiles of C2H6, C2H2, and PH3 should be indicative of the strength of atmospheric mixing processes.

Strobel, D. F.↗

NASA NTRS1978

Absolute rate of the reaction of atomic hydrogen with ethylene from 198 to 320 K at high pressure

The rate constant for the H+C2H4 reaction has been measured as a function of temperature. Experiments were performed with high pressures of Ar heat bath gas at seven temperatures from 198 to 320 K with the flash photolysis-resonance fluorescence (FP-RF) technique. Pressures were chosen so as to isolate the addition rate constant k1. The results are well represented by an Arrhenius expression. The results are compared with other studies and are theoretically discussed.

Lee, J. H.↗

NASA NTRS1979

Interstellar synthesis of the cyanopolyynes and related molecules

The cyanopolyynes HC2CN, HC4CN, HC6CN, and HC8CN, and the molecules CH3CHCN and CH3CH2CN, have recently been detected in the interstellar medium. It is shown that the observed abundances of these molecules can be obtained by gas-phase formation pathways if the reaction of H2CN(+) with C2H2 is rapid at low interstellar temperatures. The molecules CH2CHCN and C3N may be formed also by the reactions of H2CN(+) with C2H2, and CH3CH2CN may be formed by reaction of H2CN(+) with C2H4.

Mitchell, G. F.↗

NASA NTRS1979

Optoacoustic detection using Stark modulation

Stark modulation of the absorbed laser radiation in an optoacoustic detector (or spectrophone) is reported. Measurements were made over a range of total pressure between 760 Torr and 50 Torr. Greatly enhanced molecular discrimination is suggested due to the tuning ability of the Stark-shifted absorption. The background signal obtained by operating in this mode is more than 500 times smaller than that obtained by operating the same optoacoustic detector in the conventional chopped radiation mode. The responsivity of the optoacoustic detector and the absorption coefficient of C2H4 are presented as a function of total pressure.

Kavaya, M. J.↗

NASA NTRS1980

Pioneer Venus gas chromatography of the lower atmosphere of Venus

A gas chromatograph mounted in the Pioneer Venus sounder probe measured the chemical composition of the atmosphere of Venus at three altitudes. Ne, N2, O2, Ar, CO, H2O, SO2, and CO2 were measured, and upper limits set for H2, COS, H2S, CH4, Kr, N2O, C2H4, C2H6, and C3H8. Simulation studies have provided indirect evidence for sulfuric acid-like droplets and support the possibility of water vapor at altitudes of 42 and 24 km. The paper discusses the implications of these results for the origin, evolution, and present state of Venus' atmosphere.

Oyama, V. I.↗

NASA NTRS1981

Ethylene in IRC +10216

Ethylene has been detected in the circumstellar gas surrounding the supergiant star IRC +10216. Two lines of the nu sub 7 vibration-rotation band near 28 THz (949/cm) have been seen in absorption at an expansion velocity of 14 km/sec relative to the central star. The line intensities indicate a rotational temperature of T greater than 400 K and a radial C2H4 column density of 10 to the 16th to 10 to the 17th per sq cm.

Betz, A. L.↗

NASA NTRS1981

Atmospheric trace gases - Possibility of sources in the Southern Hemisphere

When measurements of globally distributed trace gases establish their existence in the Southern Hemisphere, it is not always clear whether their presence is due to transport from the Northern Hemisphere or partly from significant sources in the Southern Hemisphere. In this paper a simple criterion is developed whereby one can determine if significant Southern Hemisphere sources exist for a given trace gas. Despite the limitations of the model, there are strong indications that C2 hydrocarbons (C2H2, C2H4, C2H6), CO and CH4 have significant Southern Hemisphere sources.

Khalil, M. A. K.↗

NASA NTRS1981

Remote probing of the atmosphere using a CO2 DIAL system

An overview of our laser remote sensing effort is presented. Using both fundamental and frequency-doubled CO2 laser radiation in a differential absorption LIDAR (DIAL) system, background concentrations of CO, NO, and C2H4 in the atmosphere as well as increases due to localized emission sources have been measured. These species have been detected using the backscattered laser radiation from topographic targets at ranges to 2.7 km with a sensitivity of plus or minus 10 ppb. In addition, using a dual-laser DIAL system, the effect of induced correlation of the LIDAR returns due to atmospheric turbulence has been investigated. These results have been used to help quantify the accuracy of the DIAL measurements and are shown to be consistent with theory.

Killinger, D. K.↗

NASA NTRS1982

Photochemical processes in the inner coma

Models for the inner-coma chemistry of comets are reviewed. The physics relevant to the coma's chemistry is summarized, and the interaction of solar radiation with the coma is described, along with photolytic and chemical processes. The formation and destruction of several observed species are traced through a chemical reaction network, and model results are compared with observations. The species considered include CN, C2, C3, NH2, CH, CO, CO(+), OH, H2O, HCO, C2H4, and C2H3. The models most consistent with observations are shown to indicate that only trace amounts (2% in all) of molecules bearing CN, C2, C3, and NH2 can be present in the nucleus of a comet.

Huebner, W. F.↗

NASA NTRS1983

An analysis of the reflection spectrum of Jupiter from 1500 A to 1740 A

The Jovian reflection spectrum was modeled to determine the mixing ratios of C2H2, the upper limits to mixing ratios of C2H4, C4H2, and NH3, to detect the amount of dust in the stratosphere, and to measure the intensity of the H2 Lyman band dayglow emission. Data were gathered by the IUE spacecraft in the wavelength regions 1500 A to 1740 A, concentrating in the 10 mbar pressure region. Detailed Jupiter model parameters are provided. The mixing ratios of C2H2, C2H6, and C4H2 were found to be near 10 to the -7th, 6.6 x 10 to the -6th, and 2.9 x 10 to the -10th, respectively. Comparisons made with the Voyager 1 and 2 data indicated that the scale height of C2H2 in the 150-10 mbar region is double that of the bulk atmosphere. The data are significant for photochemical modeling of the upper Jovian atmosphere.

Gladstone, G. R.↗

NASA NTRS1983

The retrieval of atmospheric constituent mixing-ratio profiles from solar absorption spectra

Methods used to determine various atmospheric gas distributions are summarized. The experimentally determined mixing ratio profiles (the mixing ratio of a gas is the ratio of the number of gas molecules to the number of air molecules) of some atmospheric gases are shown. In most in situ experiments stratospheric gas samples are collected at several altitudes by balloon, aircraft, or rocket. These samples are then analyzed by various methods. Mixing ratio profiles of Ci, ClO, and OH were determined by laser induced fluorescence of samples. Others have analyzed gas samples by gas chromatography in order to determine the molecular abundances of CCl2F2, CCl4, CCl3F, CFCl3, CF2Cl2, CHClF2, CH3CCl3, CH4, CO, C2Cl3F3, C2Cl4, C2HCl3, C2H2, C2H4, C2H6, C3H8, C6H6, C7H8, H2, and N2O.

Shaffer, W. A.↗

NASA NTRS1984

The Jovian Stratosphere in the ultraviolet

The center-of-disk reflectivity of Jupiter in the wavelength range from 1500 A to 3000 A was computed from 31 low dispersion IUE spectra taken during solar maximum in 1979/80. The spectra were normalized to a reflectivity scale with the improved solar spectrum of July, 1980. Consideration of wavelength shifts between different IUE spectra and within the solar spectrum improved the apparent noise, especially longward of 2000 A. Six out of seven ammonia bands between 1900 A and 2200 A were detected. A vertically inhomogeneous radiative transfer program is used to compute model reflectivities for various stratospheric compositions. In addition to ammonia, the abundance of acetylene is also well determined because these molecules show narrow absorption bands in the ultraviolet. The abundances of the other molecules in the models (C3H4, C2H4, C4H2, C2H6, C3H6) are very uncertain and therefore are quoted only as upper limits. The best model fit is consistent with infrared observations by Voyager IRIS.

Wagener, R.↗