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NASA NTRS1989

Stress in dilute suspensions

Generally, two types of theory are used to describe the field equations for suspensions. The so-called postulated equations are based on the kinetic theory of mixtures, which logically should give reasonable equations for solutions. The basis for the use of such theory for suspensions is tenuous, though it at least gives a logical path for mathematical arguments. It has the disadvantage that it leads to a system of equations which is underdetermined, in a sense that can be made precise. On the other hand, the so-called averaging theory starts with a determined system, but the very process of averaging renders the resulting system underdetermined. A third type of theory is proposed in which the kinetic theory of gases is used to motivate continuum equations for the suspended particles. This entails an interpretation of the stress in the particles that is different from the usual one. Classical theory is used to describe the motion of the suspending medium. The result is a determined system for a dilute suspension. Extension of the theory to more concentrated systems is discussed.

Passman, Stephen L.↗

NASA NTRS1990

Dilution refrigeration for space applications

Dilution refrigerators are presently used routinely in ground based applications where temperatures below 0.3 K are required. The operation of a conventional dilution refrigerator depends critically on the presence of gravity. To operate a dilution refrigerator in space many technical difficulties must be overcome. Some of the anticipated difficulties are identified in this paper and possible solutions are described. A single cycle refrigerator is described conceptually that uses forces other than gravity to function and the stringent constraints imposed on the design by requiring the refrigerator to function on the earth without using gravity are elaborated upon.

Israelsson, U. E.↗

NASA NTRS1973

Dispersion and dilution of jet aircraft exhaust at high-altitude flight conditions

A method is presented for estimating the dispersion and dilution of jet aircraft exhaust from aircraft passage through times on the order of weeks thereafter. In the near wake of the aircraft, the solution is that for round turbulent jets in a parallel flow. More rapid dispersion due to atmospheric effects begins when the scale-dependent eddy viscosity becomes larger than the turbulent jet eddy viscosity. In the far wake region, the solution approaches that for scale-dependent dispersion from a point source moving with the aircraft. Calculations are presented for supersonic aircraft at high altitude flight conditions.

Holdeman, J. D.↗

NASA NTRS1974

Dispersion and dilution of jet aircraft exhaust at high-altitude flight conditions

Holdeman, J. D.↗

NASA NTRS1989

Magnetic particles

Magnetic polymer particles are formed by swelling porous, polymer particles and impregnating the particles with an aqueous solution of precursor magnetic metal salt such as an equimolar mixture of ferrous chloride and ferric chloride. On addition of a basic reagent such as dilute sodium hydroxide, the metal salts are converted to crystals of magnetite which are uniformly contained througout the pores of the polymer particle. The magnetite content can be increased and neutral buoyancy achieved by repetition of the impregnaton and neutralization steps to adjust the magnetite content to a desired level.

Chang, Manchium↗

NASA NTRS2000

Acetylated Lysozyme as Impurity in Lysozyme Crystals: Constant Distribution Coefficient

Hen egg white lysozyme (HEWL) was acetylated to modify molecular charge keeping the molecular size and weight nearly constant. Two derivatives, A and B, more and less acetylated, respectively, were obtained, separated, purified and added to the solution from which crystals of tetragonal HEWL crystals were grown. Amounts of the A or B impurities added were 0.76, 0.38 and 0.1 milligram per millimeter while HEWL concentration were 20, 30 and 40 milligram per milliliter. The crystals grown in 18 experiments for each impurity were dissolved and quantities of A or B additives in these crystals were analyzed by cation exchange high performance liquid chromatography. All the data for each set of 18 samples with the different impurity and regular HEWL concentrations is well described by one distribution coefficient K = 2.15 plus or minus 0.13 for A and K = 3.42 plus or minus 0.25 for B. The observed independence of the distribution coefficient on both the impurity concentration and supersaturation is explained by the dilution model described in this paper. It shows that impurity adsorption and incorporation rate is proportional to the impurity concentration and that the growth rate is proportional to the crystallizing protein in solution. With the kinetic coefficient for crystallization, beta = 5.10(exp -7) centimeters per second, the frequency at which an impurity molecule near the growing interface irreversibly joins a molecular site on the crystal was found to be 3 1 per second, much higher than the average frequency for crystal molecules. For best quality protein crystals it is better to have low microheterogeneous protein impurity concentration and high supers aturation.

Thomas, B. R.↗

NASA NTRS1985

High temperature oxidation of propene

An ignition delay correlation is established for propene-oxygen-argon mixtures on the basis of over 100 experiments with component concentrations being in the ranges of 0.6-1.6 percent for propene and 2.7-14.4 percent for oxygen diluted in argon. Temperatures in the range of 1274-1840 K were achieved, with average initial pressures ranging from 50 to 133 torr. Furthermore, standard numerical solutions were obtained using LSODE and CHEMEQ integration techniques, covering 59 reactions and 29 species. The partial agreement between the results indicates that the scheme used is adequate but incomplete. Two possible oxidative path-determining loops were identified, though neither was found conclusively superior to the other.

Burcat, A.↗

NASA NTRS2008

Transient Effects in Planar Solidification of Dilute Binary Alloys

The initial transient during planar solidification of dilute binary alloys is studied in the framework of the boundary integral method that leads to the non-linear Volterra integral governing equation. An analytical solution of this equation is obtained for the case of a constant growth rate which constitutes the well-known Tiller's formula for the solute transient. The more physically relevant, constant ramping down temperature case has been studied both numerically and analytically. In particular, an asymptotic analytical solution is obtained for the initial transient behavior. A numerical technique to solve the non-linear Volterra equation is developed and the solution is obtained for a family of the governing parameters. For the rapid solidification condition, growth rate spikes have been observed even for the infinite kinetics model. When recirculating fluid flow is included into the analysis, the spike feature is dramatically diminished. Finally, we have investigated planar solidification with a fluctuating temperature field as a possible mechanism for frequently observed solute trapping bands.

Mazuruk, K.↗

NASA NTRS2008

Transient Effects in Planar Solidification of Dilute Binary Alloys

Mazuruk, Konstantin↗

NASA NTRS1983

Anomalous bulk viscosity of two-phase fluids and implications for planetary interiors

The irreversible entropy production is calculated for the imposition of a pressure perturbation on a two-phase medium composed of a dilute suspension of droplets (or snowflakes) and a liquid phase of other materials. An absence of metastability is assumed, allowing the relaxation to be dominated by the solute finite diffusivity. The fluid medium was found to display a behavior suggestive of a bulk viscosity near 10 trillion P, a finding that is significant for studies of dissipation in planetary cores for tidal or seismic disturbances. A minimum quality factor for acoustic or tidal pressure oscillations and the accompanying frequency are calculated. An example is provided in terms of helium rain clouds in the deep interiors of giant planets. Additionally, a tidal quality factor of 10 to the 15th is found necessary to account for Io volcanism and resurfacing on Enceladus.

Stevenson, D. J.↗

NASA NTRS2006

Protein Crystallization Using Room Temperature Ionic Fluids

The ionic liquids (ILs) 1-butyl-3-methylimidizolium chloride (C4mim-C1), 1-butyl-3- methylimidizolium diethyleneglycol monomethylethersulfate ([C4mim]DEMGS), and 1-butyl-1 -methylpyrollidinium dihydrogenphosphate ([p1,4]dhp) were tested for their effects on the crystallization of the proteins canavalin, beta-lactoglobulin B, xylanase, and glucose isomerase, using a standard high throughput screen. The crystallization experiments were set up with the ILs added to the protein solutions at 0.2 and 0.4 M final concentrations. Crystallization droplets were set up at three proteixprecipitant ratios (1:1, 2:1, and 4:l), which served to progressively dilute the effects of the screen components while increasing the equilibrium protein and IL concentrations. Crystals were obtained for all four proteins at a number of conditions where they were not obtained from the IL-free control experiment. Over half of the protein-IL combinations tested had more successful outcomes than negative, where the IL-free crystallization was better than the corresponding IL-containing outcome, relative to the control. One of the most common causes of a negative outcome was solubilization of the protein by the IL, resulting in a clear drop. In one instance, we were able to use the IL-induced solubilizing to obtain beta-lactoglobulin B crystals from conditions that gave precipitated protein in the absence of IL. The results suggest that it may be feasible to develop ILs specifically for the task of macromolecule crystallization.

Pusey, Marc L.↗

NASA NTRS2003

In Situ Raman Microscopy of a Single Graphite Microflake Electrode in a Li(+)-containing Electrolyte

Highly detailed Raman spectra from a single KS-44 graphite microflake electrode as a function of the applied potential have been collected in situ using a Raman microscope and a sealed spectroelectrochemical cell isolated from the laboratory environment. Correlations were found between the Raman spectral features and the various Li(+) intercalation stages while recording in real time Raman spectra during a linear potential scan from 0.7 down ca. 0.0V vs Li/Li(+) at a rate of 0.1 mV/s in a 1M LiClO4 solution in a 1:l (by volume) ethylene carbonate (EC):diethyl carbonate (DEC) mixture. In particular, clearly defined isosbestic points were observed for data collected in the potential range where the transition between dilute phase 1 and phase 4 of lithiated graphite is known to occur, i.e. 0.157 < E < 0.215 vs Li/Li(+). Statistical analysis of the spectroscopic data within this region made it possible to determine independently the fraction of each of the two phases present as a function of potential without relying on coulometric information and then predict, based on the proposed stoichiometry for the transition, a spectrally-derived voltammetric feature.

Shi, Qing-Fang↗

NASA NTRS1999

Numerical Simulations of Crystal Growth of an Alloy Under Microgravity Conditions

The directional solidification of a dilute binary alloy (Bi-1.0 at.%Sn)is investigated. Results are obtained at a gravity level of I pg. Computations are performed in two dimensions with a fixed, non-uniform grid. The simulation involves a solution of the species concentration equation (modified to account for solute rejection at the interface) and energy equation (modified to account for phase-change) for both the solid and liquid phases, in addition to the constitutive equations for describing convective flow in the melt. The effects of conductive heat transfer in the ampoule and in a capillary tube in the sample are included. To gauge the effects of including this growth capillary tube in the apparatus, simulations both with and without the capillary tube are presented and compared. Fully transient simulations have been performed; no simplifying steady-state approximations are used, however, the influence of solute on the melting temperature at the interface is not included. Both thermal and solutal convective cells are seen to form. Convective velocities are significantly damped inside the capillary, causing less segregation due to convection. As solidification proceeds beyond the capillary tube, longitudinal segregation arises as a result of the change in cross-sectional area of solidifying material. The magnitudes of the velocities in this cell increase significantly once the solid/liquid front passes beyond the end of the capillary tube; this causes a corresponding increase in the level of radial solute segregation in the solidified material.

Simpson, James E.↗

NASA NTRS1973

Mechanical properties of electron-beam-melted molybdenum and dilute Mo-Re alloys.

Study of Mo-Re alloys aimed at examining the effects of small rhenium additions on the low-temperature ductility of molybdenum and determining the mechanical properties of dilute Mo-Re alloys. The results obtained indicate that high-purity Mo-Re alloys have ductile-brittle transition temperatures considerably lower than those for unalloyed molybdenum and that rhenium promotes normal solid-solution strengthening in molybdenum at elevated temperatures.

Klopp, W. D.↗

NASA NTRS1993

Characterization of Minnesota lunar simulant for plant growth

Processing of lunar regolith into a plant growth medium is crucial in the development of a regenerative life support system for a lunar base. Plants, which are the core of such a system, produce food and oxygen for humans and, at the same time, consume carbon dioxide. Because of the scarcity of lunar regolith, simulants must be used to infer its properties and to develop procedures for weathering and chemical analyses. The Minnesota Lunar Simulant (MLS) has been identified to date as the best available simulant for lunar regolith. Results of the dissolution studies reveal that appropriately fertilized MLS can be a suitable medium for plant growth. The techniques used in conducting these studies can be extended to investigate the suitability of actual lunar regolith as a plant growth medium. Dissolution experiments were conducted using the MLS to determine its nutritional and toxicity characteristics for plant growth and to develop weathering and chemical analysis techniques. Two weathering regimes, one with water and one with dilute organic acids simulating the root rhizosphere microenvironment, were investigated. Elemental concentrations were measured using inductively-coupled-plasma (ICP) emission spectrometry and ion chromatography (IC). The geochemical speciation model, MINTEQA2, was used to determine the major solution species and the minerals controlling them. Acidification was found to be a useful method for increasing cation concentrations to meaningful levels. Initial results indicate that MLS weathers to give neutral to slightly basic solutions which contain acceptable amounts of the essential elements required for plant nutrition (i.e., potassium, calcium, magnesium, sulfur, zinc, sodium, silicon, manganese, copper, chlorine, boron, molybdenum, and cobalt). Elements that need to be supplemented include carbon, nitrogen, and perhaps phosphorus and iron. Trace metals in solution were present at nontoxic levels.

Oglesby, James P.↗

NASA NTRS1996

On the Retrieval of Lightning Radio Sources from Time-of-Arrival Data

We examine the problem of retrieving three-dimensional lightning locations from radio frequency Time-Of-Arrival (TOA) measurements. Arbitrary antenna locations are considered. By judiciously differencing measurements that are related to the location of the antennas and their excitation times, the problem is converted from the initial spherical nonlinear form to a system of linear equations. In the linear formalism, the source location and time-of-occurrence is viewed geometrically as an intersection of hyperplanes in the four-dimensional Minkowski space (x,y,z,t). The linear equations are solved to obtain explicit analytic expressions for the location and time variables. Retrieval errors are not interpreted with conventional Geometrical Dilution of Precision (GDOP) arguments as discussed by Holmes and Reedy (1951), but with more recent inversion analyses considered by Twomey (1977). Measurement errors are propagated analytically so that the specific effect of these errors on the solution is clarified. The sensitivity of the solution on the number of antennas used, antenna network geometry, source position, and measurement differencing schemes are discussed in terms of the eigenvalues of the linear system.

Koshak, William J.↗

NASA NTRS2001

A Realistic Accretion Disk Model for AGNs

We present a new relativistic accretion disk model of AGNs, based on alpha modified accretion disk theory, where alpha is a parameter that characterizes the efficiency of the mechanism of angular momentum transport. In this model we have considered a geometrically-thin, high-luminosity (alpha-accretion disk, around a supermassive black hole. The geometrically thin limit assumes a local energy balance within the accretion disk, which has been used to derive the plasma temperature of the disk. The energy balance equation has three solutions: low, medium and high temperature, depending on the heating rate of the accretion disk. We predict that the inner part of a high luminosity accretion disk is in the high- temperature (10(exp 7) to 10(exp 9) K) state and for this we obtain the high temperature solution of the energy balance equation using a Comptonization process. We find the local spectrum of each ring of the disk (we have divided the high temperature region of the disk into 50 rings) to be a diluted Wien spectrum. However, the emergent integral spectrum of the high temperature region is a power-law with a high-energy cutoff that depends on the basic parameters of AGNs (the accretion rate, the incidence angle, and the mass and the angular momentum of the central black hole). We have fitted the observed spectra of 28 AGNs using the present model and have derived the values of the basic parameters of these AGNs. Results of these spectral fittings have been discussed in the framework of the unification model of AGNs.

Suleimanov, V.↗

NASA NTRS2004

Analysis of Fuel Vaporization, Fuel-Air Mixing, and Combustion in Integrated Mixer-Flame Holders

Requirements to limit pollutant emissions from the gas turbine engines for the future High-Speed Civil Transport (HSCT) have led to consideration of various low-emission combustor concepts. One such concept is the Integrated Mixer-Flame Holder (IMFH). This report describes a series of IMFH analyses performed with KIVA-II, a multi-dimensional CFD code for problems involving sprays, turbulence, and combustion. To meet the needs of this study, KIVA-II's boundary condition and chemistry treatments are modified. The study itself examines the relationships between fuel vaporization, fuel-air mixing, and combustion. Parameters being considered include: mixer tube diameter, mixer tube length, mixer tube geometry (converging-diverging versus straight walls), air inlet velocity, air inlet swirl angle, secondary air injection (dilution holes), fuel injection velocity, fuel injection angle, number of fuel injection ports, fuel spray cone angle, and fuel droplet size. Cases are run with and without combustion to examine the variations in fuel-air mixing and potential for flashback due to the above parameters. The degree of fuel-air mixing is judged by comparing average, minimum, and maximum fuel/air ratios at the exit of the mixer tube, while flame stability is monitored by following the location of the flame front as the solution progresses from ignition to steady state. Results indicate that fuel-air mixing can be enhanced by a variety of means, the best being a combination of air inlet swirl and a converging-diverging mixer tube geometry. With the IMFH configuration utilized in the present study, flashback becomes more common as the mixer tube diameter is increased and is instigated by disturbances associated with the dilution hole flow.

Deur, J. M.↗