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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 739 records · Page 41
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

PHOTOPHORESIS IN A DILUTE, OPTICALLY THICK MEDIUM AND DUST MOTION IN PROTOPLANETARY DISKS

We derive expressions for the photophoretic force on opaque spherical particles in a dilute gas in the optically thick regime where the radiation field is in local thermal equilibrium. Under those conditions, the radiation field has a simple form, leading to well defined analytical approximations for the photophoretic force that also consider both the internal thermal conduction within the particle, and the effects of heat conduction and radiation to the surrounding gas. We derive these results for homogeneous spherical particles; and for the double layered spheres appropriate for modeling solid grains with porous aggregate mantles. Then, as a specific astrophysical application of these general physical results, we explore the parameter space relevant to the photophoresis driven drift of dust in protoplanetary disks. We show that highly porous silicate grains have sufficiently low thermal conductivities that photophoretic effects, such as significant relative velocities between particles with differing porosity or levitation above the midplane, are expected to occur.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2010

Spatial interference from well-separated split condensates

We use magnetic levitation and a variable-separation dual optical plug to obtain clear spatial interference between two condensates axially separated by up to 0.25 mm - the largest separation observed with this kind of interferometer. Clear planar fringes are observed using standard (i.e., nontomographic) resonant absorption imaging. The effect of a weak inverted parabola potential on fringe separation is observed and agrees well with theory.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2010

Constraints on Stable Equilibria with Fluctuation-Induced (Casimir) Forces

We examine whether fluctuation-induced forces can lead to stable levitation. First, we analyze a collection of classical objects at finite temperature that contain fixed and mobile charges and show that any arrangement in space is unstable to small perturbations in position. This extends Earnshaw's theorem for electrostatics by including thermal fluctuations of internal charges. Quantum fluctuations of the electromagnetic field are responsible for Casimir or van der Waals interactions. Neglecting permeabilities, we find that any equilibrium position of items subject to such forces is also unstable if the permittivities of all objects are higher or lower than that of the enveloping medium, the former being the generic case for ordinary materials in vacuum.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2010

Casimir Repulsion between Metallic Objects in Vacuum

We give an example of a geometry in which two metallic objects in vacuum experience a repulsive Casimir force. The geometry consists of an elongated metal particle centered above a metal plate with a hole. We prove that this geometry has a repulsive regime using a symmetry argument and confirm it with numerical calculations for both perfect and realistic metals. The system does not support stable levitation, as the particle is unstable to displacements away from the symmetry axis.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2012

Geometrical parameters of a water dropwise cluster

A dropwise cluster is obtained over the surface of water heated to 65-100 Degree-Sign C. The pair correlation function of drops in the cluster is constructed. The temperature dependences of the spacing between the drops, their diameter, and the altitude of their levitation over the water surface are measured.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Enthalpy of Mixing in Al–Tb Liquid

The liquid-phase enthalpy of mixing for Al$-$Tb alloys is measured for 3, 5, 8, 10, and 20 at% Tb at selected temperatures in the range from 1364 to 1439 K. Methods include isothermal solution calorimetry and isoperibolic electromagnetic levitation drop calorimetry. Mixing enthalpy is determined relative to the unmixed pure (Al and Tb) components. The required formation enthalpy for the Al3Tb phase is computed from first-principles calculations. Finally, based on our measurements, three different semi-empirical solution models are offered for the excess free energy of the liquid, including regular, subregular, and associate model formulations. These models are also compared with the Miedema model prediction of mixing enthalpy.

36 MATERIALS SCIENCE↗
DOE OSTI2016

LUNAR SURFACE AND DUST GRAIN POTENTIALS DURING THE EARTH’S MAGNETOSPHERE CROSSING

Interaction between the lunar surface and the solar UV radiation and surrounding plasma environment leads to its charging by different processes like photoemission, collection of charged particles, or secondary electron emission (SEE). Whereas the photoemission depends only on the angle between the surface and direction to the Sun and varies only slowly, plasma parameters can change rapidly as the Moon orbits around the Earth. This paper presents numerical simulations of one Moon pass through the magnetospheric tail including the real plasma parameters measured by THEMIS as an input. The calculations are concentrated on different charges of the lunar surface itself and a dust grain lifted above this surface. Our estimations show that (1) the SEE leads to a positive charging of parts of the lunar surface even in the magnetosphere, where a high negative potential is expected; (2) the SEE is generally more important for isolated dust grains than for the lunar surface covered by these grains; and (3) the time constant of charging of dust grains depends on their diameter being of the order of hours for sub-micrometer grains. In view of these results, we discuss the conditions under which and the areas where a levitation of the lifted dust grains could be observed.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Formation and Initiation of Erupting Flux Rope and Embedded Filament Driven by Photospheric Converging Motion

In this paper, we study how a flux rope (FR) is formed and evolves into the corresponding structure of a coronal mass ejection (CME) numerically driven by photospheric converging motion. A two-and-a-half-dimensional magnetohydrodynamics simulation is conducted in a chromosphere-transition-corona setup. The initial arcade-like linear force-free magnetic field is driven by an imposed slow motion converging toward the magnetic inversion line at the bottom boundary. The convergence brings opposite-polarity magnetic flux to the polarity inversion, giving rise to the formation of an FR by magnetic reconnection and eventually to the eruption of a CME. During the FR formation, an embedded prominence gets formed by the levitation of chromospheric material. We confirm that the converging flow is a potential mechanism for the formation of FRs and a possible triggering mechanism for CMEs. We investigate the thermal, dynamical, and magnetic properties of the FR and its embedded prominence by tracking their thermal evolution, analyzing their force balance, and measuring their kinematic quantities. The phase transition from the initiation phase to the acceleration phase of the kinematic evolution of the FR was observed in our simulation. The FR undergoes a series of quasi-static equilibrium states in the initiation phase; while in the acceleration phase the FR is driven by Lorentz force and the impulsive acceleration occurs. The underlying physical reason for the phase transition is the change of the reconnection mechanism from the Sweet–Parker to the unsteady bursty regime of reconnection in the evolving current sheet underneath the FR.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1995

(abstract) Determination of the Specific Heat and Total Hemispherical Total Emissivity of the Highly Undercooled Zr(sub 41.2)Ti(sub 13.8)Cu(sub 12.5)Ni(sub 10.0)Be(sub 22.5) Alloy

High temperature high vacuum electrostatic levitation was combined with DSC experiments to determine the specific heat C(sub p) of the undercooled Zr(sub 41.2)Ti(sub 13.8)Cu(sub 12.5)Ni(sub 10.0)Be(sub 22.5) liquid as a function of temperature. The containerless approach made it possible to undercool the melt to the glass transition temperature without inducing nucleation. Because the cooling process was purely radiative, noncontact temperature measurement techniques could be used to determine the specific heat to total hemispherical emissivity ratio, C(sub p)/epsilon(sub t), for the undercooled liquid region. Using C(sub p) values which were independently obtained by DSC, epsilon(sub t) could be determined. With knowledge of C(sub p) of the undercooled liquid it was possible to determine other thermodynamic properties such as Gibbs free energy and entropy as a function of undercooling.

levitation thermodynamic properties undercooled al↗
NASA NTRS1997

Thermoacoustic Streaming and Ultrasonic Processing of Low Melting Melts

Ultrasonic levitation allows the processing of low melting materials both in 1 G as well as in microgravity. The free suspension of the melts also facilitates undercooling, permitting the measurements of the physical properties of the metastable liquids.

ulotrasonic levitation microgravity low gravity lo↗
NASA NTRS1996

Faraday Wave Turbulence on a Spherical Liquid Shell

Millimeter-radius liquid shells are acoustically levitated in an ultrasonic field. Capillary waves are observed on the shells. At low energies (minimal acoustic amplitude, thick shell) a resonance is observed between the symmetric and antisymmetric thin film oscillation modes.

capillary↗
DOE OSTI2016

Accelerated Chemical Reactions and Organic Synthesis in Leidenfrost Droplets

Abstract Leidenfrost levitated droplets can be used to accelerate chemical reactions in processes that appear similar to reaction acceleration in charged microdroplets produced by electrospray ionization. Reaction acceleration in Leidenfrost droplets is demonstrated for a base‐catalyzed Claisen–Schmidt condensation, hydrazone formation from precharged and neutral ketones, and for the Katritzky pyrylium into pyridinium conversion under various reaction conditions. Comparisons with bulk reactions gave intermediate acceleration factors (2–50). By keeping the volume of the Leidenfrost droplets constant, it was shown that interfacial effects contribute to acceleration; this was confirmed by decreased reaction rates in the presence of a surfactant. The ability to multiplex Leidenfrost microreactors, to extract product into an immiscible solvent during reaction, and to use Leidenfrost droplets as reaction vessels to synthesize milligram quantities of product is also demonstrated.

Bain, Ryan M.↗
DOE OSTI2016

Accelerated Chemical Reactions and Organic Synthesis in Leidenfrost Droplets

Abstract Leidenfrost levitated droplets can be used to accelerate chemical reactions in processes that appear similar to reaction acceleration in charged microdroplets produced by electrospray ionization. Reaction acceleration in Leidenfrost droplets is demonstrated for a base‐catalyzed Claisen–Schmidt condensation, hydrazone formation from precharged and neutral ketones, and for the Katritzky pyrylium into pyridinium conversion under various reaction conditions. Comparisons with bulk reactions gave intermediate acceleration factors (2–50). By keeping the volume of the Leidenfrost droplets constant, it was shown that interfacial effects contribute to acceleration; this was confirmed by decreased reaction rates in the presence of a surfactant. The ability to multiplex Leidenfrost microreactors, to extract product into an immiscible solvent during reaction, and to use Leidenfrost droplets as reaction vessels to synthesize milligram quantities of product is also demonstrated.

Bain, Ryan M.↗
DOE OSTI2018

A Low-Cost Fabrication Technique for the Growth of Single-Domain GdBCO Bulk Superconductor from Raw Metal Oxides

A single-domain GdBCO bulk superconductor is usually fabricated using a mixture of pre-reacted precursor powders (including GdBa{sub 2}Cu{sub 3}O{sub 7−δ} and Gd{sub 2}BaCuO{sub 5}) by the top-seeded melt texture growth (TSMTG) process. However, the synthesis of pure-phase precursor powder by the solid-state sintering reaction can not only consume time for weeks but also prolong the fabrication process and can lead to a low-efficiency and high-cost process. In this paper, we reported the successful growth of single-domain GdBCO bulk superconductors by the top-seeded metallic oxide melt growth (TS-MOMG) process in which the raw materials of Gd{sub 2}O{sub 3}, BaO, and CuO, the three different metallic oxides, are just involved to fabricate the single-domain GdBCO bulk superconductors. After detailed investigations in the morphology, levitation force, trapped magnetic field, and critical temperature of the grown samples with different ratios, it was found that the simplified precursor-phase source can be used to fabricate the single-domain GdBCO bulk superconductors more efficiently, which can combine the crystal growth procedure and greatly economize the preparation cost and the time to the most extent.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Vibration Suppression of High-Temperature Superconducting Maglev System via Electromagnetic Shunt Damper

The high-temperature superconducting (HTS) maglev system is characterized with self-stable levitation, low energy consumption, and pollution-free operation, and it has been considered as a promising technology for implementing high-speed transport systems. But the previous studies have shown that the damping of such system is relatively low, which indicates the large-amplitude nonlinear vibration may occur easily under external disturbances and affect the long-term motion stability, operation safety, and comfort of HTS maglev in rail transit application. In order to suppress the harmful vibration, an electromagnetic shunt damper (EMSD) was designed and incorporated into the HTS maglev system. Compared with other systems which employ the EMSD to diminish the vibration, the HTS maglev system does not need to set up external devices to supply magnetic field for the damper, because the permanent magnet guideway (PMG) in this system is directly taken advantages of. The natural frequency of the damper is adjusted to a value close to that of the maglev system. In this way, the damper becomes most effective because the moving vehicle body and the circuit resonate simultaneously. The feasibility of the damper was demonstrated through systematic experiments, and the effects of different field cooling heights (FCHs) of the HTS maglev system on EMSD’s performance were experimentally studied as well. Also, how the change of resistors in the EMSD circuit affects its working efficiency was preliminarily explored in this work. The results show that under the definite external disturbance, the damper can effectively attenuate the acceleration of vibration, furthermore, and it is found that the damper works better in condition of lower FCH. Within the scope of our experiments, the EMSD with a resistor in lower resistance performs better as results have shown. This investigation indicates that the vehicle will run in a more smooth and comfortable way along the track with this damper. The work is important for the further practical application of the technology.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗