Engineering topics

Hyers, Robert W.

Publications and source records attributed to Hyers, Robert W..

24 records · Page 2

NASA NTRS2002

Laminar-Turbulent Transition in an Electromagnetically-Levitated Droplet

During experiments on the MSL-1 (First Microgravity Science Laboratory) mission of the Space Shuttle (STS-83 and STS-94, April and July 1997), a droplet of palladium-silicon alloy was electromagnetically levitated for viscosity measurements. For the non-deforming droplet, the resultant MHD flow inside the drop can be inferred from motion of impurity particulates on the surface. In the experiments, subsequent to melting, Joule heating produces a continuous reduction of viscosity of the fluid resulting in an acceleration of the flow with time. These observations indicate formation of a pair of corotating toroidal flow structures inside the spheroidal drop that undergo flow instabilities. As the fluid temperature rises, the amplitude of the secondary flow increases; and beyond a point, the tracers exhibit non-coherent chaotic motion signifying emergence of turbulence inside the drop. Assuming that the observed laminar-turbulent transition is shear-layer type, the internal structure of the toroidal loops is used to develop a semi-empirical correlation for the onset of turbulence. Our calculations indicate that the suggested correlation is in modest agreement with the experimental data, with the transition occurring at a Reynolds number of 600.

Hyers, Robert W.↗

NASA NTRS2001

Studies of Nucleation, Growth, Specific Heat, and Viscosity of Undercooled Melts of Quasicrystals and Polytetrahedral-Phase-Forming Alloys

Undercooling experiments and thermal physical property measurements of metallic alloys on the International Space Station (ISS) are planned. This recently-funded research focuses on fundamental issues of the formation and structure of highly-ordered non-crystallographic phases (quasicrystals) and related crystal phases (crystal approximants), and the connections between the atomic structures of these phases and those of liquids and glasses. It extends studies made previously by us of the composition dependence of crystal nucleation processes in silicate and metallic glasses, to the case of nucleation from the liquid phase. Motivating results from rf-levitation and drop-tube measurements of the undercooling of Ti/Zr-based liquids that form quasicrystals and crystal approximants are discussed. Preliminary measurements by electrostatic levitation (ESL) are presented.

Kelton, K. F.↗

NASA NTRS2001

ISS-Crystal Growth of Photorefractive Materials (BSO): Critical Design Issues for Optimized Data Extraction from Space Experiments

Realization of the full potential of photorefractive materials in device technology is seriously impeded by our inability to achieve controlled formation of critical defects during single crystal growth and by difficulties in meeting the required degree of compositional uniformity on a micro-scale over macroscopic dimensions. The exact nature and origin of the critical defects which control photorefractivity could not as yet be identified because of gravitational interference. There exists, however, strong evidence that the density of defect formation and their spatial distribution are adversely affected by gravitational interference which precludes the establishment of quantifiable and controllable heat and mass transfer conditions during crystal growth. The current, NASA sponsored research at MIT is directed at establishing a basis for the development of a comprehensive approach to the optimization of property control during melt growth of photorefractive materials, making use of the m-g environment, provided in the International Space Station. The objectives to be pursued in m-g research on photorefractive BSO (Bi12SiO20) are: (a) identification of the x-level(s) responsible for photorefractivity in undoped BSO; (b) development of approaches leading to the control of x-level formation at uniform spatial distribution; (c) development of doping and processing procedures for optimization of the critical, application specific parameters, spectral response, sensitivity, response time and matrix stability. The presentation will focus on: the rationale for the justification of the space experiment, ground-based development efforts, design considerations for the space experiments, strategic plan of the space experiments, and approaches to the quantitative analysis of the space experiments.

Hyers, Robert W.↗

NASA NTRS2000

Solidification Studies from the Electrostatic Levitation System at the Marshall Space Flight Center

Electrostatic levitation (ESL) provides a means to study molten materials in a high-purity environment, free from contact with a container. Many phenomena important to materials science can be studied in the ESL. Solidification of metals, alloys and undercooled materials represent an important topic for research in the ESL. Recent studies of metals and alloys during solidification in the ESL are reported. Measurements include time, temperature and transformation of metallic glass-forming alloys, solidification velocities, and microstructure,

Rogers, Jan R.↗

NASA NTRS2000

The Electrostatic Levitation Facility at NASA's Marshall Space Flight Center

Containerless processing is an important area of research in materials science. Electrostatic levitation (ESL) represents an emerging technology which permits containerless processing in a vacuum environment. NASA's Marshall Space Flight Center (MSFC) established a levitation facility to provide a critical resource to the microgravity materials science research community to continue and enhance ground-based research in the support of the development of flight experiments during the transition to Space Station. During ESL processing, charged specimens are levitated in the electrostatic field produced by the system's electrodes. Three sets of positioning electrodes represent the heart of the MSFC system. Two dual-axis position sensitive detectors provide input for the PID control-loop computer. Sample position is maintained by adjusting the control voltages for the power supplies of the positioning electrodes. A UV source refreshes the charge on specimens during processing via the photoelectric effect. Lasers permit sample heating independent of positioning. The processing chamber typically operates under vacuum condition approximately = 10(exp -7) Torr. Electrostatic levitation provides a materials science research tool for investigations of refractory solids and melts. Topics of investigation include thermophysical properties, phase equilibria, metastable phase formation, undercooling and nucleation, time-temperature-transformation diagrams and other aspects of materials processing. Current capabilities and recent results of processing studies for metals, alloys and oxides will be reviewed.

Rogers, Jan R.↗

NASA NTRS2000

Turbulent Transition in Electromagnetically Levitated Drops

Electromagnetic levitation (EML) is an important tool in materials research. Because a sample can be processed without contact with a container, experiments may be performed on high temperature, highly reactive, and undercooled liquid metals. Many of these experiments are affected by fluid flow in the sample, driven by the electromagnetic positioning force. Despite the importance of convection in these experiments, the transition to turbulence is not well understood in this system. However, we have observed a transition from laminar to turbulent flow in EML droplets in the course of microgravity experiments in TEMPUS on the Space Shuttle (STS-94). The transition occurs repeatably and over a narrow range of conditions. These experimental observations are compared with two competing theories about the transition to turbulence. Also, the results of a particle tracking study of the instabilities leading up to the transition to turbulence are presented.

Hyers, Robert W.↗