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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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At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Gravitational Instability in Suspension Flows

The gravity-driven flow of non-neutrally buoyant suspensions is shown to be unstable to spanwise perturbations when the shearing motion generates a density profile that increases with height. The instability is simply due to having heavier material over light. The wavelength of the perturbation is found to be on the order of the thickness of the suspension layer. The parameters important to the problem are the angle of inclination of the layer relative to gravity, the relative density difference between the particles and fluid, the ratio of the particle size to the suspension layer, and the bulk volume fraction of particles. An example showing the growth rate as a function of wave number is shown.

Carpen, Ileana C.↗
NASA NTRS2001

Aerospace Structural Materials Handbook Supplement GRCop-84

GRCop-84 is a high strength-high conductivity copper-based alloy developed at NASA Glenn Research Center for combustion chamber liners of regeneratively cooled rocket engines. It also has promise for other high heat flux applications operating at temperatures up to 700 C (1292 F) and potentially higher. The alloy must be made by powder metallurgy techniques such as gas atomization. Slower cooling rates such as those experienced during casting do not develop a proper microstructure. Once made into powder, the alloy exhibits excellent processability using conventional consolidation and forming techniques, e.g., extrusion and rolling. GRCop-84 is strengthened by a combination of dispersion and precipitation strengthening by fine (50-500 nanometer (2-20 microinch)) Cr2Nb particles and Hall-Petch strengthening from a fine copper grain size. The presence of a high volume fraction of particles prevents grain boundary sliding at high temperatures and contributes to the alloy's overall good high temperature mechanical properties. Maximum thermal conductivity is obtained by using two alloying elements (Cr, Nb) with limited solubility in solid Cu that form a high temperature intermetallic compound with an even lower solid solubility. The resulting matrix of the alloy is nearly pure copper. The limited solubility also minimizes Cr2Nb particle coarsening at elevated temperatures and enhances microstructural and mechanical property stability. Further enhancement of the microstructural stability is obtained by using a high volume fraction (approx. 14 vol.%) of Cr2Nb particles that effectively pin grain growth.

Ellis, David L.↗
NASA NTRS1973

Relative motion of orbiting particles under the influence of perturbing forces. Volume 3: Construction of relative motion traces

Geometric traces can be simply constructed to illustrate the relative motions experienced by particles in a number of problem situations. These diagrams describe the displacements and hodographs which arise as a consequence of initial value inputs and selected disturbance (force) conditions. Due to the linearization which is imposed on the mathematical formulation there is a separation of the in-plane and out-of-plane coordinate solutions. The construction of in-plane traces is easier to represent and to visualize. The out-of-plane geometries are the more complicated cases and generally need some added specializations in order to acquire figures which have some degree of symmetry and simplicity.

Eades, J. B., Jr.↗
NASA NTRS2003

Model of Fluidized Bed Containing Reacting Solids and Gases

A mathematical model has been developed for describing the thermofluid dynamics of a dense, chemically reacting mixture of solid particles and gases. As used here, "dense" signifies having a large volume fraction of particles, as for example in a bubbling fluidized bed. The model is intended especially for application to fluidized beds that contain mixtures of carrier gases, biomass undergoing pyrolysis, and sand. So far, the design of fluidized beds and other gas/solid industrial processing equipment has been based on empirical correlations derived from laboratory- and pilot-scale units. The present mathematical model is a product of continuing efforts to develop a computational capability for optimizing the designs of fluidized beds and related equipment on the basis of first principles. Such a capability could eliminate the need for expensive, time-consuming predesign testing.

Bellan, Josette↗
NASA NTRS1993

Low-gravity electrodeposition and growth of polymer thin films with large third-order optical nonlinearities by electrochemical processes for devices: Thiophene-based polymers

It has been proposed that NLO thin film properties may be improved by low-gravity processing. Strong candidates for NLO thin film applications are the polythiophenes. Polymeric thiophenes are attractive materials due to their ease of preparation, stability, and high X(exp 3). A simple and convenient method for preparation of polythiophenes is electrochemical oxidation. We will apply some of our experience and lessons learned in low-gravity metal, metal/cermet electrode position to improve the quality of polythiophene(s) thin films. In low gravity electrode position of Ni at a high rate on an Au substrate often results in the production of an x-ray non diffracting surface. Cobalt metal deposition does not give this result nor does Ni when deposited similarly on a glassy carbon substrate. Co/Ni alloy composition produced during electrode position is strongly dependent upon the amount of convection. Code position of neutral inert cermets with metals is influenced significantly by the presence of gravity and the size of the cermets. Tracks left in the 1-g surfaces by unsuccessful particle occlusion indicate suspension of the large particles is not the only reason for poor volume percentages of the larger particles in the deposits. All size particles are more homogeneously distributed in the deposits in low-gravity electrocodeposition than in 1-g. Low gravity gives larger volume percentages for the larger particles in the deposits, while 1-g gives larger volume percentages for the smaller particles. Intermediate size particles give mixed results. The experimental cells were constructed with flat electrode end plates such that 1-g bench reference electrode positions could be carried out at various orientations with respect to gravity. A series of bench studies using similar designed cells are suggested so that convection modification can be applied to electrochemical thin film preparation. Convection effects can then be coupled with other parameter variations in current, temperature, concentration, solvent, electrolyte, and anode substrates to optimize the properties of NLO thin films before resorting to low-gravity processing.

Penn, Benjamin G.↗
NASA NTRS1973

Fundamental equations of a mixture of gas and small spherical solid particles from simple kinetic theory.

The fundamental equations of a mixture of a gas and pseudofluid of small spherical solid particles are derived from the Boltzmann equation of two-fluid theory. The distribution function of the gas molecules is defined in the same manner as in the ordinary kinetic theory of gases, but the distribution function for the solid particles is different from that of the gas molecules, because it is necessary to take into account the different size and physical properties of solid particles. In the proposed simple kinetic theory, two additional parameters are introduced: one is the radius of the spheres and the other is the instantaneous temperature of the solid particles in the distribution of the solid particles. The Boltzmann equation for each species of the mixture is formally written, and the transfer equations of these Boltzmann equations are derived and compared to the well-known fundamental equations of the mixture of a gas and small solid particles from continuum theory. The equations obtained reveal some insight into various terms in the fundamental equations. For instance, the partial pressure of the pseudofluid of solid particles is not negligible if the volume fraction of solid particles is not negligible as in the case of lunar ash flow.

Pai, S. I.↗
NASA NTRS1980

Coordinated ionospheric and magnetospheric observations from the ISIS 2 satellite by the ISIS 2 experimenters. Volume 3: High-latitude charged particle, magnetic field and ionospheric plasma observations during northern summer

A list of ISIS 2 experiments and a description of the satellite are presented. Instrumentation of the satellite included an auroral scanning photometer, a red line photometer, a swept frequency sounder, an ion mass spectrometer, and triaxial fluxgate magnetometer. Data format descriptions are provided. Included with the geophysical data set is a list of all passes.

Source record↗
NASA NTRS1995

Full field gas phase velocity measurements in microgravity

Measurement of full-field velocities via Particle Imaging Velocimetry (PIV) is common in research efforts involving fluid motion. While such measurements have been successfully performed in the liquid phase in a microgravity environment, gas-phase measurements have been beset by difficulties with seeding and laser strength. A synthesis of techniques developed at NASA LeRC exhibits promise in overcoming these difficulties. Typical implementation of PIV involves forming the light from a pulsed laser into a sheet that is some fraction of a millimeter thick and 50 or more millimeters wide. When a particle enters this sheet during a pulse, light scattered from the particle is recorded by a detector, which may be a film plane or a CCD array. Assuming that the particle remains within the boundaries of the sheet for the second pulse and can be distinguished from neighboring particles, comparison of the two images produces an average velocity vector for the time between the pulses. If the concentration of particles in the sampling volume is sufficiently large but the particles remain discrete, a full field map may be generated.

Griffin, Devon W.↗
NASA NTRSDate not supplied

Particle Size Distribution Parameters from SAGE III/ISS Extinction Spectra

Stratospheric aerosols play key roles in the chemistry and radiation balance of the atmosphere and are a key input parameter for global chemistry and climate models. The degree to which aerosols impact chemistry and radiation balance depends primarily on the relative abundance of different sized particles within the sample volume, often referred to as the particle size distribution (PSD). If the PSD is accurately known then other key modeling parameters (e.g., surface area density and effective radius) can be derived. Historically, occultation observations from orbital instruments such as SAGE III/ISS have been used to infer these PSD parameters by inverting the extinction coefficient spectra. However, past efforts routinely failed to account for measurement uncertainty and lacked a rigorous estimate of the inferred PSD uncertainty. We carried out a series of simulations to evaluate the accuracy of these inferences and, for every valid SAGE III/ISS extinction spectrum, determined the range of PSD parameters that fell withing the bounds of the extinction error bars. Special application of this method was applied to estimate the impact of the 2022 Hunga Tonga eruption had on particle size distributions.

Travis N Knepp↗
NASA NTRSDate not supplied

Sage III/ISS Stratospheric Aerosols and Gas Experiment An Earth Science Mission on the International Space Station

Stratospheric aerosols play key roles in the chemistry and radiation balance of the atmosphere and are a key input parameter for global chemistry and climate models. The degree to which aerosols impact chemistry and radiation balance depends primarily on the relative abundance of different sized particles within the sample volume, often referred to as the particle size distribution (PSD). If the PSD is accurately known then other key modeling parameters (e.g., surface area density and effective radius) can be derived. Historically, occultation observations from orbital instruments such as SAGE III/ISS have been used to infer these PSD parameters by inverting the extinction coefficient spectra. However, past efforts routinely failed to account for measurement uncertainty and lacked a rigorous estimate of the inferred PSD uncertainty. We developed a PSD solution algorithm that infers single mode and bimodal distribution parameters and applied this algorithm to the SAGE II and SAGE III/ISS data record. Herein we describe the algorithm, evaluate its performance, and show results from the 2022 Hunga Tonga eruption.

Travis N. Knepp↗
NASA NTRS1977

Application of modified Twomey techniques to invert lidar angular scatter and solar extinction data for determining aerosol size distributions

Polarization properties of the angularly scattered laser light from a volume of air are used to determine the size distribution of the aerosol particles within the volume by the use of appropriate inversion techniques. Similar techniques are employed to determine a mean size distribution of the particulates within a vertical column through the atmosphere from determinations of the aerosol optical depth as a function of wavelength. In both of these examples, a modification of an inversion technique originally described by Twomey has been employed. Details of this method are presented as well as results from actual measurements employing bistatic lidar and solar radiometer.

Herman, B. M.↗
NASA NTRS2013

Data Compression Algorithm Architecture for Large Depth-of-Field Particle Image Velocimeters

A large depth-of-field particle image velocimeter (PIV) is designed to characterize dynamic dust environments on planetary surfaces. This instrument detects lofted dust particles, and senses the number of particles per unit volume, measuring their sizes, velocities (both speed and direction), and shape factors when the particles are large. To measure these particle characteristics in-flight, the instrument gathers two-dimensional image data at a high frame rate, typically >4,000 Hz, generating large amounts of data for every second of operation, approximately 6 GB/s. To characterize a planetary dust environment that is dynamic, the instrument would have to operate for at least several minutes during an observation period, easily producing more than a terabyte of data per observation. Given current technology, this amount of data would be very difficult to store onboard a spacecraft, and downlink to Earth. Since 2007, innovators have been developing an autonomous image analysis algorithm architecture for the PIV instrument to greatly reduce the amount of data that it has to store and downlink. The algorithm analyzes PIV images and automatically reduces the image information down to only the particle measurement data that is of interest, reducing the amount of data that is handled by more than 10(exp 3). The state of development for this innovation is now fairly mature, with a functional algorithm architecture, along with several key pieces of algorithm logic, that has been proven through field test data acquired with a proof-of-concept PIV instrument.

Bos, Brent↗
NASA NTRS1988

Optical measurements of soot and temperature profiles in premixed propane-oxygen flames

Two laser diagnostic techniques were used to measure soot volume fractions, number densities and soot particle radii in premixed propane/oxygen flat flames. The two techniques used were two wavelength extinction, using 514.5 nm to 632.8 nm and 457.9 nm to 632.8 nm wavelength combinations, and extinction/scattering using 514.5 nm light. The flames wre fuel-rich (equivalence ratios from 2.1 to 2.8) and had cold gas velocities varying from 3.4 to 5.5 cm/s. Measurements were made at various heights above the sintered-bronze, water-cooled flat flame burner with the equivalence ratio and cold gas velocity fixed. Also, measurements were made at a fixed height above the burner and fixed cold gas velocity while varying the equivalence ratio. Both laser techniques are based on the same underlying assumptions of particle size distribution and soot optical properties. Full Mie theory was used to determine the extinction coefficients K sub ext, and the scattering efficiencies, Q sub vv. Temperature measurements in the flames were made using infrared radiometry. Good agreement between the two techniques in terms of soot particle radii, number density and volume fraction was found for intensity ratios (I/I sub o) between 0.1 and 0.8. For intensity ratios higher or lower than this range, the differences in extinction coefficients at the wavelengths chosen for the two-wavelength method are too small to give accurate results for comparing particle radii and number densities. However, when comparing only soot volume fractions, the agreement between the two techniques continued to be good for intensity ratios up to 0.95.

Lyons, Valerie J.↗
NASA NTRS1988

Optical measurements of soot and temperature profiles in premixed propane-oxygen flames

Two laser diagnostic techniques were used to measure soot volume fractions, number densities and soot particle radii in premixed propane/oxygen flat flames. The two techniques used were two wavelength extinction, using 514.5 nm to 632.8 nm and 457.9 nm to 632.8 nm wavelength combinations, and extinction/scattering using 514.5 nm light. The flames were fuel-rich (equivalence ratios from 2.1 to 2.8) and had cold gas velocities varying from 3.4 to 5.5 cm/s. Measurements were made at various heights above the sintered-bronze, water-cooled flat flame burner with the equivalence ratio and cold gas velocity fixed. Also, measurements were made at a fixed height above the burner and fixed cold gas velocity while varying the equivalence ratio. Both laser techniques are based on the same underlying assumptions of particle size distribution and soot optical properties. Full Mie theory was used to determine the extinction coefficients K sub ext, and the scattering efficiencies, Q sub vv. Temperature measurements in the flames were made using infrared radiometry. Good agreement between the two techniques in terms of soot particle radii, number density and volume fraction was found for intensity ratios (I/I sub o) between 0.1 and 0.8. For intensity ratios higher or lower than this range, the differences in extinction coefficients at the wavelengths chosen for the two-wavelength method are too small to give accurate results for comparing particle radii and number densities. However, when comparing only soot volume fractions, the agreement between the two techniques continued to be good for intensity ratios up to 0.95.

Lyons, V. J.↗
NASA NTRS2004

History of Thermally Processed Solids in the Protoplanetary Disk: Reconciling Theoretical Models and Meteoritical Evidence

In this talk we assess theoretical models of the radial, temporal, and thermal evolution of nebula solids, and their ultimate accretion into planetesimals such as we see today, using meteorite evidence as a guide. Each class of chondrites contains a characteristic suite of chondrules and CAIs that may have formed over a period of several Myr during which planetesimals were accreting in the disk. Details of the various models for transient melting of chondrules and igneous CAIs will be left to others. However, high-temperature processes of different kinds evaporation, alteration, etc did affect these constituents and their environment over this time span. Here we describe evolutionary scenarios consistent with a large time gap between CAI and chondrule formation and the presence of distinctive suites of chondrules and CAIs in each chondrite class. Particle-gas dynamical processes transport particles of all relevant sizes (microns to many meters) within the nebula and affect their evolution in a variety of important ways. Turbulent radial diffusion spreads particles radially down their concentration gradients - as one example, it can prevent CAIs from being lost into the sun on several Myr timescales [1]. Vertical diffusion spreads the dense midplane particle layer, determining its volume density, which in turn affects the particle growth rate and even the dominant growth process [2-4]. Turbulent concentration selects aerodynamically sorted particles for orders-of-magnitude density enhancement, and is applicable to porous, fluffy particles of appropriate size as well as to solid chondrules [5]. Inward radial drift under gas drag brings a surprisingly large amount of material to regions where it evaporates; these evaporation fronts cause significant chemical modification of the nebula gas over a wide range of radii [6]. Radial transport by stellar winds can be important for small particles [7].

Cuzzi, J. N.↗
NASA NTRS1999

Coarsening in Solid-Liquid Mixtures Studied on the Space Shuttle

Ostwald ripening, or coarsening, is a process in which large particles in a two-phase mixture grow at the expense of small particles. It is a ubiquitous natural phenomena occurring in the late stages of virtually all phase separation processes. In addition, a large number of commercially important alloys undergo coarsening because they are composed of particles embedded in a matrix. Many of them, such as high-temperature superalloys used for turbine blade materials and low-temperature aluminum alloys, coarsen in the solid state. In addition, many alloys, such as the tungsten-heavy metal systems, coarsen in the solid-liquid state during liquid phase sintering. Numerous theories have been proposed that predict the rate at which the coarsening process occurs and the shape of the particle size distribution. Unfortunately, these theories have never been tested using a system that satisfies all the assumptions of the theory. In an effort to test these theories, NASA studied the coarsening process in a solid-liquid mixture composed of solid tin particles in a liquid lead-tin matrix. On Earth, the solid tin particles float to the surface of the sample, like ice in water. In contrast, in a microgravity environment this does not occur. The microstructures in the ground- and space-processed samples (see the photos) show clearly the effects of gravity on the coarsening process. The STS-83-processed sample (right image) shows nearly spherical uniformly dispersed solid tin particles. In contrast, the identically processed, ground-based sample (left image) shows significant density-driven, nonspherical particles, and because of the higher effective solid volume fraction, a larger particle size after the same coarsening time. The "Coarsening in Solid-Liquid Mixtures" (CSLM) experiment was conducted in the Middeck Glovebox facility (MGBX) flown aboard the shuttle in the Microgravity Science Laboratory (MSL-1/1R) on STS-83/94. The primary objective of CSLM is to measure the temporal evolution of the solid particles during coarsening.

Caruso, John J.↗