Engineering Papers⌕ Search

Engineering topics

Elleman, D. D.

Publications and source records attributed to Elleman, D. D..

At least 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Generation of a strong core centering force in a submillimeter compound droplet system

By amplitude-modulating the driving voltage of an acoustic levitating apparatus, a strong core centering force was generated in a submillimeter compound droplet system suspended by the radiation pressure in a gaseous medium. Depending on the acoustic characteristics of the droplet system, it was found that the technique can be utilized advantageously in the multiple-layer coating of an inertial confinement fusion pellet.

Lee, M. C.↗
NASA NTRS1982

Miniature J-T refrigators using adsorption compressors

More sophisticated cooling systems for the employed detectors will be needed to satisfy the demand for higher resolution and sensitivity of various detectors used in space missions. The design of the cooling system must take into consideration the unique environment of space vehicles. It is pointed out that a deep space vehicle usually has an ample supply of waste heat from a radioisotope thermoelectric generator (RTG) and has a heat sink near zero Kelvin. Passive radiative coolers have been used for cooling temperatures above 90 K. Cooling below 90 K is currently handled by phase changes of solid or liquid cryogens or mechanical refrigeration. However, the weight of the cryogen may be a problem in a long duration space mission. Refrigerators of small cooling capacity are required in many spacecraft applications. For some future NASA missions, a multistage Joule-Thomson refrigerator using adsorption compressors appears particularly attractive. A study is discussed of four different refrigeration stages which use charcoal as the adsorbent. The adsorbed gases are nitrogen, helium, hydrogen, and neon.

Chan, C. K.↗
NASA NTRS1982

Polymer coating of glass microballoons levitated in a focused acoustic field

Inertial confinement fusion (ICF) glass microballoons (GMBs) levitated in a focusing radiator acoustic device can be coated with liquid materials by deploying the liquid into the levitation field with a stepped-horn atomizer. The GMB can be forced to the center of the coating liquid with a strong acoustically generated centering force. Water solutions of organic polymers, UV-curable liquid organic monomers, and paraffin waxes have been used to prepare solid coatings on the surface of GMBs using this technique.

Young, A. T.↗
NASA NTRS1982

Application of microgravity and containerless environments to the investigation of fusion target fabrication technology

After the first observation of the core-centering force within a liquid shell in the KC-135 flight experiment, this force was successfully reproduced in terrestrial laboratories using two experimental techniques. The core-centering force generated for a compound drop system in the neutral buoyancy tank provides the first correlation between theoretical and experimental results. When this force was generated in a more realistic fusion-pellet system using the focusing-radiator levitating system, it was shown that this is a very strong force indeed in view of the fact that the ratio of specific gravities between the water and the core is approximately five. It is believed that this centering force will contribute significantly to an overall understanding of the fabrication physics of a fusion target system. Results from experiments in a vertical drag-free wind tunnel and in a 16-ft low pressure drop furnace suggest that eliminating or reducing the aerodynamic drag on fusion pellets during their formation stage will prevent the decentering of the bubble. Metallic and metallic glass fusion targets are seen as holding promise for improving and simplifying the fabrication process for ablative-type fusion targets.

Lee, M. C.↗
NASA NTRS1982

Development of electrostatic levitator at JPL

Preliminary results on the design and operation of electrostatic levitators developed at JPL are reported. Particular attention is given to the single-axis levitators for ground-based operation and for operation in the reduced gravity environment. Descriptions are given of the design principles and the performance of final products. A levitator designed for zero-g environment is shown. It is a single-axis system, so there is no active lateral damping. Two ring and two disk electrodes are included. The ring electrodes always maintain a constant voltage difference with respect to the central disk electrodes. This is to ensure that there is always a centering force that does not depend on the voltage difference between the top and bottom electrodes. As the ring-to-disk voltage increases, there is a proportionate increase in the centering force.

Rhim, W.-K.↗
NASA NTRS1981

Drop dynamics

The drop dynamics module is a Spacelab-compatible acoustic positioning and control system for conducting drop dynamics experiments in space. It consists basically of a chamber, a drop injector system, an acoustic positioning system, and a data collection system. The principal means of collecting data is by a cinegraphic camera. The drop is positioned in the center of the chamber by forces created by standing acoustic waves generated in the nearly cubical chamber (about 12 cm on a side). The drop can be spun or oscillated up to fission by varying the phse and amplitude of the acoustic waves. The system is designed to perform its experiments unattended, except for start-up and shutdown events and other unique events that require the attention of the Spacelab payload specialist.

Elleman, D. D.↗
NASA NTRS1981

Method and apparatus for producing concentric hollow spheres

Hollow spheres with precisely concentric inner and outer spherical surfaces are formed by applying vibrations to a nonconcentric hollow sphere while it is at an elevated temperature at which it is fluid or plastic, the vibrations producing internal flows which cause the inner and outer surfaces to become precisely concentric. Concentric spheres can be mass produced by extruding a material such as glass or metal while injecting a stream of gas into the center of the extrusion to form a gas-filled tube. Vibrations are applied to the extruded tube to help break it up into individual bodies of a desired uniform size, the bodies tending to form spherical inner and outer surfaces by reason of surface tension, and the continuing application of vibrations causing these surfaces to become concentric.

Wang, T. G.↗
NASA NTRS1981

Characterization of superfluid helium transfer

The friction factor and steady state flow rate of superfluid helium (He II) are measured, with the driving pressure difference generated by the saturated vapor pressure and a small hydrostatic pressure head. The temperature ranged from 1.5 K to the transition temperature of 2.17 K. Three different lengths and two different internal diameters were used for the stainless steel transfer tubes, and the transfer of liquid helium (He I) was investigated with the same apparatus for comparison. It was found that the friction factor of He II is greater than that of He I for pressure differences greater than 20 mm Hg, and smaller below that magnitude.

Yang, L. C.↗
NASA NTRS1979

Free oscillations of a large drop in space

In preparation for forthcoming studies on materials processing in space, techniques and equipment are being developed for the deployment and control of large globules of liquid in a zero-g environment. This paper first presents a theoretical analysis of the intense sound field within an enclosure by which positioning forces, torques, and temporal perturbations may be applied to a sample. Procedures for digital analysis of photographic records of the sample motion are described. Results on the mean and oscillatory motion of a 2.5 cm diameter water drop during the flight of a SPAR rocket are given. In particular, spectral analysis shows that the drop oscillates at several frequencies. Identification with theoretically expected modes is made for some of the spectral lines.

Jacobi, N.↗
NASA NTRS1978

Pulsed NMR spectroscopy

Method gives results approximating those of classical continuous-irradiation method but in less time. Method also makes it possible to measure chemical shifts and spin-lattice relaxation times with improved sensitivity. Equipment can be used for adiabatic demagnetization experiments, measurements of rotating-frame spin/lattice relaxation times, and accurate measurements of exact resonance points. When measuring relaxation times, pulse technique can be very effective since pulses may be limited in amplitude and length to prevent spin system from being driven into saturation.

Burum, D. P.↗
NASA NTRS1978

New technique for single-scan T1 measurements using solid echoes

A simple technique for single-scan T1 measurements in solids is proposed and analyzed for single exponential spin-lattice relaxation. In this technique, the direct spin heating caused by the sampling process is significantly reduced in comparison with conventional techniques by utilizing the 'solid echo' to refocus the magnetization. The applicability of this technique to both the solid and liquid phases is demonstrated.

Burum, D. P.↗
NASA NTRS1978

A multiple pulse zero crossing NMR technique, and its application to F-19 chemical shift measurements in solids

A simple multiple-pulse 'zero crossing technique' for accurately determining the first moment of a solid-state NMR spectrum is introduced. This technique was applied to obtain the F-19 chemical shift versus pressure curves up to 5 kbar for single crystals of CaF2 (0.29 + or - 0.02 ppm/kbar) and BaF2 (0.62 + or - 0.05 ppm/kbar). Results at ambient temperature and pressure are also reported for a number of other fluorine compounds. Because of its high data rate, this technique is potentially several orders of magnitude more sensitive than similar CW methods.

Burum, D. P.↗
NASA NTRS1978

Calculation of spin-lattice relaxation during pulsed spin locking in solids

The spin-lattice relaxation time has been calculated for dipolar solids in the case where the spins are locked by an RF pulse sequence with pulses of arbitrary angle and finite width. Expressions are given for the homonuclear case in general and for the heteronuclear case in the delta-function limit. The results for the homonuclear case are experimentally confirmed using solid C6F12. The analysis shows that for small pulse angles, at which the direct spin heating effect is known to be small, the relaxation behavior will be identical to the CW irradiation case.

Rhim, W.-K.↗
NASA NTRS1977

Acoustic energy shaping

A suspended mass is shaped by melting all or a selected portion of the mass and applying acoustic energy in varying amounts to different portions of the mass. In one technique for forming an optical waveguide slug, a mass of oval section is suspended and only a portion along the middle of the cross-section is heated to a largely fluid consistency. Acoustic energy is applied to opposite edges of the oval mass to press the unheated opposite edge portions together so as to form bulges at the middle of the mass. In another technique for forming a ribbon of silicon for constructing solar cells, a cylindrical thread of silicon is drawn from a molten mass of silicon, and acoustic energy is applied to opposite sides of the molten thread to flatten it into a ribbon.

Wang, T. G.↗
NASA NTRS1977

ADRF experiments using near n.pi pulse strings

Adiabatic demagnetization (ADRF) can be achieved in a dipolar coupled nuclear spin system in solids by applying a string of short RF pulses and gradually modulating the pulse amplitudes or pulse angles. This letter reports an adiabatic inverse polarization effect in solids and a rotary spin echo phenomenon observed in liquids when the pulse angle is gradually changed across integral multiples of pi during a string of RF pulses. The RF pulse sequence used is illustrated along with the NMR signal from a CaF2 single crystal as observed between the RF pulses and the rotary spin echo signal observed in liquid C6F6 for n = 2. The observed effects are explained qualitatively on the basis of average Hamiltonian theory.

Rhim, W. K.↗
NASA NTRS1977

Acoustic-energy shaping of meltable metals

Containerless shaping technique is applicable to machining metals technology. Process improves quality of melted metals by reducing introduction of impurities from container walls or floor.

Elleman, D. D.↗
NASA NTRS1977

Drop dynamics in space

Experiments to study the dynamics of liquid drops are being planned to be performed in the weightless environment of Spacelab. The liquids will range from superfluid helium through ordinary liquid to molten metals and glasses. The experiments will be conducted in a chamber now being developed which utilizes the forces and torques produced by acoustic waves excited within the chamber. None of the currently available facilities (drop towers, sounding rockets, or zero-g aircraft flights) can provide a sustained weightless environment, since the resulting zero-g periods are from 3 sec to 5 min. Spaceflight, however, will provide weightlessness for periods of one week, or more, allowing truly laboratory-like experiments to be conducted on free liquid drops and bubbles. In this paper we discuss both the drop dynamics experiments proposed for Spacelab and the acoustic chamber: its operation and current testing for these and other experiments.

Wang, T. G.↗