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At least 973 records · Page 54

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NASA NTRS1989

Life sciences and space research XXIII(3): Natural and artificial ecosystems; Proceedings of the Topical Meetings of the 27th COSPAR Plenary Meeting, Espoo, Finland, July 18-29, 1988

The present conference discusses topics in the fields of higher plant growth under controlled environmental conditions, waste oxidation, carbon cycling, and biofermentor design and operation. Attention is given to CO2 and O2 effects on the development and fructification of wheat in closed systems, transpiration during life cycle in controlled wheat growth, sources and processing of CELSS wastes, waste-recycling in bioregenerative life support, and the effect of iodine disinfection products on higher plants. Also discussed are carbon cycling by cellulose-fermenting nitrogen-fixing bacteria, a bioreactor design with sunlight supply and operations systems for use in the space environment, gas bubble coalescence in reduced gravity conditions, and model system studies of a phase-separated membrane bioreactor.

Macelroy, R. D.↗

NASA NTRS1990

Solubility and partitioning of Ar in anorthite, diopside, forsterite, spinel, and synthetic basaltic liquids

The solubility and partitioning of Ar in natural anorthite, diopside, forsterite, spinel, and synthetic iron-free basaltic melts was investigated using a new technique that obviates the postquenching phase separation. It was found that the solubility of Ar in the minerals was surprisingly high. Moreover, the solubility of Ar in different samples of a particular mineral run in the same experiment varied more than the solubility in the same sample run in different experiments, suggesting that noble gases are held in lattice vacancy defects. Moreover, the results of TEM imaging revealed no anomalous microstructures, while EXAFS studies of some samples showed that Kr has no preferred site in the lattices, supporting the defect siting conclusion.

Broadhurst, C. Leigh↗

NASA NTRS1990

Convective heat flow in space cryogenics plugs - Critical and moderate He II heat flux densities

Plug flow rates of entropy, heat and normal fluid in phase separators and in zero net mass flow systems are, to some extent, quite similar. A simplified analysis of critical conditions is presented in agreement with data trends. A critical temperature gradient arises on the basis of the He II two-fluid model at the stability limit constraining the thermohydrodynamics of the system. Thus, the question of critical thermodynamic fluctuations associated with nucleation versus the possibility of critical gradients in externally imposed parameters is answered in favor of the latter route toward turbulence. Furthermore, a similarity equation is presented which incorporates size dependent rates for moderate heat flow densities observed in experiments.

Yuan, S. W. K.↗

NASA NTRS1990

Superfluid transport and its applications in space

Various transport modes in superfluid helium are discussed. They include zero net mass flow and finite mass flow for pure superfluid and normal fluid flow. An attempt is made to characterize these transport modes in a common frame of reference. Two dimensionless numbers are used, namely, the dimensionless heat flux number and the dimensionless driving force number. The equations are generalized by the use of a characteristic length so that they can be applied to the transport of HE II in any geometry. The theories are then extended to applications in space. In particular, fountain effect pumps and superfluid management at zero g by vapor-liquid phase separators are discussed in detail.

Yuan, S. W. K.↗

NASA NTRS1989

Testing of a controller for a hybrid capillary pumped loop thermal control system

A controller for a series hybrid capillary pumped loop (CPL) system that requires no moving parts does not resrict fluid flow has been tested and has demonstrated improved performance characteristics over a plain CPL system and simple hybrid CPL systems. These include heat load sharing, phase separation, self-regulated flow control and distribution, all independent of most system pressure drop. In addition, the controlled system demonstrated a greater heat transport capability than the simple CPL system but without the large fluid inventory requirement of the hybrid systems. A description of the testing is presented along with data that show the advantages of the system.

Schweickart, Russell↗

NASA NTRS1990

InAsSbBi, a direct band-gap, III-V, LWIR material

In the last several years Dr. Stringfellow's group at the University of Utah has reported success in incorporating over 3 percent Bi in InAs and 1.5 percent in InAsSb using Organometallic Vapor Phase Epitaxy (OMVPE) growth techniques. For InAs the lattice constant increase is linear with a=6.058+0.966x (InAs(1-x)Bi(x)), and a decrease in band gap energy of dEg / dx = -55meV / at a percentage Bi. Extrapolating this to the ternary minimum band gap at InAs(0.35)Sb(0.65), an addition of 1 to 2 percent Bi should drop the band gap to the 0.1 to 0.05eV range (10 to 20 microns). These alloys are direct band gap semiconductors making them candidates for far IR detectors. The current status of the InAsSbBi alloys is that good crystal morphology and x ray diffraction data has been obtained for up to 3.4 percent Bi. The Bi is metastable at these concentrations but the OMVPE grown material has been able to withstand the 400 C growth temperature for several hours without phase separation.

Stringfellow, G. B.↗

NASA NTRS1990

Dynamics of the interstellar medium

An extraordinarily rich assortment of electronic transitions of atoms and ions at ultraviolet wavelengths can be exploited to probe the behavior of interstellar gases in different contexts. The Copernicus and IUE (International Ultraviolet Explorer) satellites are used to investigate dynamical phenomena and important physical interactions which develop in separate phases of the medium. Insights on the establishment and overall properties of the mechanical energy created by stellar winds and supernova explosions at specific locations are outlined. Investigations of how multiple sources of energy move the gas and mold its structure over both small and large scales are outlined.

Jenkins, Edward B.↗

NASA NTRS1990

Oxygen production by electrolysis of molten lunar regolith

The goal of this study was threefold. First, the theoretical energy requirements of the process were to be defined. This includes studies of the relevant oxidation-reduction reactions in the melt, their kinetics and energies of reaction, and experimental determination of production efficiencies and melt resistivities as functions of melt composition and applied potential. Second, the product(s) of silicate electrolysis were to be characterized. This includes: (1) evaluating the phase relationships in the systems SiO2-TiO2-Al2O3-MgO-FeO-CaO and Fe-Si; (2) estimating the compositions of the metal products as a function of applied potential and feedstock composition based on phase equilibria in the Fe-Si system and free energy values for SiO2 and FeO reported in the literature; (3) definition of compositions of products in actual experiments; and (4) definition of the form the product takes (whether phases separate or remain fixed, whether crystals settle or float in the remaining melt, and how large crystals form). Third, materials for these highly corrosive high-temperature silicate melts were to be identified. This includes identifing materials that may be either inert or thermodynamically stable in these melts, and experimental testing of the materials to confirm that they do not deteriorate. The results are discussed within this framework.

Haskin, Larry A.↗

NASA NTRS1991

Variations in magmatic processes among igneous asteroids

Six asteroid classes (types V, E, A, R, M, S) are composed primarily of differentiated assemblages produced by igneous processes within their parent planetesimals. These are identified by surface materials which deviate from a chondritic composition to a degree that require igneous chemical fractionation processes. There are large variations among these igneous asteroids in the peak temperatures attained, in the efficiency of magmatic phase separation, and in the depth within the original parent body exposed at the present surface. These variations provide important constraints on the nature of asteroidal heating events, on the differentiation processes within small planetary bodies, and on the disruption of those parent bodies. Variations due to depth within the parent body and due to degree of magmatic differentiation are detailed.

Gaffey, M. J.↗

NASA NTRS1991

Stability of Y-Ba-Cu-oxide phases in salt flux

The results of an investigation into the possibility of growing YBa2Cu3O7 (or Y123) single crystals from a NaCl-KCl flux (salt flux) are presented. They are compared with results for Y123 crystals grown from a Ba-Cu-oxide flux system. The chosen salt flux composition was 1:1 (NaCl:KCl). The preparation method of the solutes is presented, with particular attention given to the compounds surrounding the Y123 phase, such as Y2BaCuO6 (Y211). Optical microscopy was introduced to study the morphology of the sample; X-ray diffraction was used for phase identification; and a chemical analysis was effected. The Y123, Y211, and BaCuO2 phases were shown to be dissociated in the NaCl-KCl flux, and could not be recrystallized. A small amount of the flux could be added to create large-grain Y123 crystals, but single-crystal growth was not possible in a top-seeded NaCl-KCl solution. This is attributed to significant differences in solubility of the crystal elements, and phase separation caused by CuO crystal formation.

Tao, Y. K.↗

NASA NTRS1991

Clathrate hydrate formation in amorphous cometary ice analogs in vacuo

Experiments conducted in clathrate hydrates with a modified electron microscope have demonstrated the possibility of such compounds' formation during the warming of vapor-deposited amorphous ices in vacuo, through rearrangements in the solid state. Subsolidus crystallization of compositionally complex amorphous ices may therefore be a general and ubiquitous process. Phase separations and microporous textures thus formed may be able to account for such anomalous cometary phenomena as the release of gas at large radial distances from the sun and the retention of volatiles to elevated temperatures.

Blake, David↗

NASA NTRS1990

The fountain effect in aerospace cryogenics

The theory of the fountain effect, also known as the thermomechanical effect, exhibited by superfluid helium is presented, and the application of this effect in space projects is described. Future uses of superfluid He in space are also discussed. These include the use of the fountain effect for liquid-vapor phase separation; for pumping superfluid helium from a storage vessel to a payload (as in the Superfluid Helium On-Orbit Transfer Flight Demonstration and the Superfluid Helium Tanker); for actuating a low-temperature refrigerator; and for circulating liquid helium within a cryostat (as in the Astromag dewar).

Castles, S. H.↗

NASA NTRS1990

Superfluid helium on-orbit resupply

The requirements for superfluid helium (SFHe) resupply were investigated, and the results were used to develop a conceptual design for a superfluid helium tanker (SFHT) which is designed to meet a 50-mission requirement. The SFHT design uses a conventional dewar approach with multiple vapor cooled shields, and a porous-plug phase separator for on-orbit temperature control. An open loop refrigeration approach is used for ground conversion of normal He to SFHe, allowing near-total fill of the supply tank. Design diagrams of the SFHT concept and of various SFHT subsystems are presented.

Eberhardt, Ralph N.↗

NASA NTRS1990

Experimental verification of a tank to tank He II transfer model with trade study results

A computer program has been developed to study the thermodynamics of tank to tank superfluid helium transfer. The model includes a supply and a receiver tank connected by a transfer line. The convey of He II from one tank to the other is controlled by a fountain effect pump (FEP). Phase separators are present in both the supply and receiver tank to regulate the bath temperature. Description of this model has been published elsewhere. In the present paper, data from a transfer experiment are used to verify the accuracy of this model. The experiment consisted of an FEP made of a 2-micron sintered stainless steel porous plug. Superfluid has been transferred from a liquid helium bath into a glass beaker. Bath temperatures, flowrate and heater power records are available. These results are compared to the predictions of the computer program and good agreement is found between the two. This model is very useful for the study and design of superfluid transfer systems, e.g., the Superfluid Helium Tanker (SFHT) and the Particle Astrophysics Magnet Facility (ASTROMAG).

Yuan, S. W. K.↗

NASA NTRS1990

JPL research to develop a He-3/He-4 dilution refrigerator for space applications

A research program to develop a He-3/He-4 solution refrigerator for space applications is underway. The results of the effort to use an electric field as a substitute for gravity to control the He-3/He-4 mixture interface that separates phases in terrestrial units are described. Further, experimental results obtained from an engineering model of a single-cycle dilution refrigerator with a mixing chamber capable of operating in a zero-gravity environment are described. Future research and development plans are outlined, in particular the need to test the operation of a single-cycle as well as a continuously operating dilution refrigerator in space.

Petrac, D.↗

NASA NTRS1992

Supercooling effects in Cu-10 wt pct Co alloys solidified at different cooling rates

Electromagnetic levitation and electron beam surface melting were employed to study the effects of supercooling and cooling rate on the solidification of Cu-10 wt pct Co alloys. Two major effects were observed in the supercooled alloys: the nucleation of a metastable copper-rich phase which contains 13 wt pct to 20 wt pct Co in samples supercooled between 105 and 150 K and liquid phase separation which occurs in samples supercooled 150 K or more. The microstructure of the electron beam melted surfaces consisted of very fine spheres which were similar to those of the sample supercooled more than 150 K but with a refined microstructure. The results indicate that a dynamic bulk supercooling of 150 K may exist in the molten pool during the solidification of electron beam melted surfaces.

Munitz, A.↗

NASA NTRS1992

Random-anisotropy Blume-Emery-Griffiths model

The results are described of studies of a random-anisotropy Blume-Emery-Griffiths spin-1 Ising model using mean-field theory, transfer-matrix calculations, and position-space renormalization-group calculations. The interplay between the quenched randomness of the anisotropy and the annealed disorder introduced by the spin-1 model leads to a rich phase diagram with a variety of phase transitions and reentrant behavior. The results may be relevant to the study of the phase separation of He-3 - He-4 mixtures in porous media in the vicinity of the superfluid transition.

Maritan, Amos↗

NASA NTRS1993

Freeze-Drying Makes Improved IPN And Semi-IPN Polymers

Novel process developed for production of interpenetrating polymer networks (IPN's) or semi-IPN's with greater fracture toughness and resistance to microcracks. Process controls degree of phase separation in IPN's. In experiment, IPN's and semi-IPN's formed by dissolving constituents in another common solvent in traditional method. Resins and composite materials produced were tested for both traditional and freeze-drying processes. Glass-transition temperatures and data from dynamic mechanical tests of freeze-dried IPN's and semi-IPN's demonstrated freeze-drying process provided much improved IPN's and semi-IPN's.

Pater, Ruth H.↗