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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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13 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Growth of ZnTe by Physical Vapor Transport and Traveling Heater Method

ZnTe crystals were grown by horizontal physical vapor transport (PVT) and a Te-solution vertical traveling heater method (THM). The grown crystals were examined by X-ray Laue diffraction technique and Hall measurements to determine the growth orientation and the electrical properties of the crystals. They were also characterized by low temperature infrared (IR) absorption measurements. Several sets of distinct peaks were observed in the IR absorption spectra for the THM samples and were identified as resulting from CU(2+) impurities. Similar measurements on vapor grown ZnTe showed featureless absorption spectra. Chemical analyses were carried out to measure the impurity content in various ZnTe samples and synchrotron radiation topography was used to Study crystalline microstructure of the (111) ZnTe single crystals grown by PVT.

Su, Ching-Hua↗
NASA NTRS1990

Experimental approaches for improving SiGe thermoelectric efficiency at JPL

Efforts to improve the thermoelectric efficiency of silicon-germanium alloys are discussed. These efforts are essentially focused on substantially enhancing carrier concentration levels and thus increasing the power factor values of n-type materials. With the help of thermodynamic phase diagram calculations, a combination of various crystal growth and dopant saturation techniques is used for this purpose. Bulk polycrystal growth of double-doped materials is achieved by zone leveling while a new method (the traveling heater method) for high-quality single-crystal growth of SiGe is being developed. Thin films of homogeneous single-crystalline multidoped Si80Ge20 have also been successfully grown from low-temperature melts to investigate combined dopant solid solubility variations. Very high carrier concentration levels were obtained by (P+As)-combined diffusion in zone-leveled and hot-pressed materials. The good overall understanding of doping mechanisms which has been achieved should enable optimization of the thermoelectric properties over this extended carrier concentration range. Reductions in thermal conductivity are being sought by introduction of very small phonon scattering centers (inert material) in the initial powders-precursors of Si-Ge alloys. This approach should benefit both n- and p-type materials.

Borshchevsky, Alex↗
NASA NTRS2001

Dynamic Magnetic Field Applications for Materials Processing

Magnetic fields, variable in time and space, can be used to control convection in electrically conducting melts. Flow induced by these fields has been found to be beneficial for crystal growth applications. It allows increased crystal growth rates, and improves homogeneity and quality. Particularly beneficial is the natural convection damping capability of alternating magnetic fields. One well-known example is the rotating magnetic field (RMF) configuration. RMF induces liquid motion consisting of a swirling basic flow and a meridional secondary flow. In addition to crystal growth applications, RMF can also be used for mixing non-homogeneous melts in continuous metal castings. These applied aspects have stimulated increasing research on RMF-induced fluid dynamics. A novel type of magnetic field configuration consisting of an axisymmetric magnetostatic wave, designated the traveling magnetic field (TMF), has been recently proposed. It induces a basic flow in the form of a single vortex. TMF may find use in crystal growth techniques such as the vertical Bridgman (VB), float zone (FZ), and the traveling heater method. In this review, both methods, RMF and TMF are presented. Our recent theoretical and experimental results include such topics as localized TMF, natural convection dumping using TMF in a vertical Bridgman configuration, the traveling heater method, and the Lorentz force induced by TMF as a function of frequency. Experimentally, alloy mixing results, with and without applied TMF, will be presented. Finally, advantages of the traveling magnetic field, in comparison to the more mature rotating magnetic field method, will be discussed.

Mazuruk, K.↗
NASA NTRS1996

The Universal Multizone Crystallizator (UMC) Furnace: An International Cooperative Agreement

The Universal Multizone Crystallizator (UMC) is a special apparatus for crystal growth under terrestrial and microgravity conditions. The use of twenty-five zones allows the UMC to be used for several normal freezing growth techniques. The thermal profile is electronically translated along the stationary sample by systematically reducing the power to the control zones. Elimination of mechanical translation devices increases the systems reliability while simultaneously reducing the size and weight. This paper addresses the UMC furnace design, sample cartridge and typical thermal profiles and corresponding power requirements necessary for the dynamic gradient freeze crystal growth technique. Results from physical vapor transport and traveling heater method crystal growth experiments are also discussed.

Watring, D. A.↗
NASA NTRS1998

Application of Rotating Magnetic Fields to THM Growth Process: Te-CdTe

The numerical simulation of ongoing traveling heater method (THM) solution growth experiments of CdTe from Te solvent and the influence of a Rotating Magnetic Field (RMF) on control of convection in the solution zone is presented. The application of RMF is pursued as a means to actively control thermo-solutal convection in the solution zone which otherwise would be dominated by buoyancy forces. Numerical simulation and scaling analysis are used to generate a flow-regime map demarcating the boundary separating the buoyancy- and RMF-driven convection in the solution zone. Results indicate that whereas at low gravity levels the application of RMF can completely overwhelm buoyancy-induced convection, at normal gravity levels the successful control of convection by RMF requires use of fairly thin solvent zones. Simulation results also indicate that field strengths required to dominate natural convection on earth may lead to instabilities and transition to turbulence, and an associated deleterious effect on the quality of grown crystals. These and other simulations results are discussed in reference to experimental evidence.

LeClair, Mark↗
NASA NTRS1998

Numerical Simulation of THM Growth of CdTe in Presence of Rotating Magnetic Fields

The influence of rotating magnetic fields (RMF) on the flow pattern and compositional uniformity in the solution zone of a traveling heater method (THM) system for growth of CdTe is numerically investigated. The analysis is conducted at the 10(exp -6) and 10(exp -1) g(sub 0) as representative of space and ground processing conditions. It is shown that under microgravity conditions, application of RMF can be used to overwhelm residual buoyancy-induced convection and to control the uniformity of solution-zone composition at the growth front without appreciable modification of the growth interface shape. At high gravity levels, RMF is found not to be able to completely dominate buoyancy-induced convection. In this regime, for the range of field strengths studied, RMF is found to result in a) complex flow structures in the solution zone, b) enhancement of compositional non-uniformities at the growth front, and c) increased convexity of the growth interface. A scaling analysis of convection in the solution zone is used to generate a non-dimensional map delineating the RMF- and gravity-dominated flow regimes.

Ghaddar, Chahid K.↗
NASA NTRS2000

Convection Induced by Traveling Magnetic Fields in Semiconductor Melts

Axisymmetric traveling magnetic fields (TMF) can be beneficial for crystal growth applications. such as the vertical Bridgman, float zone or traveling heater methods. TMF induces a basic flow in the form of a single roll. This type of flow can enhance mass and heat transfer to the growing crystal. More importantly, the TMF Lorentz body force induced in the system can counterbalance the buoyancy forces, so the resulting convection can be much smaller and even the direction of it can be changed. In this presentation, we display basic features of this novel technique. In particular, numerical calculations of the Lorentz force for arbitrary frequencies will be presented along with induced steady-state fluid flow profiles. Also, numerical modeling of the TMF counter-balancing natural convection in vertical Bridgman systems will be demonstrated.

Konstantin, Mazuruk↗
NASA NTRS2001

Traveling Magnetic Field Applications for Materials Processing in Space

Including the capability to induce a controlled fluid flow in the melt can significantly enrich research on solidification phenomena in a microgravity environment. The traveling magnetic field (TMF) is a promising technique to achieve this goal and is the aim of our ground-based project. In this presentation we will discuss new theoretical as well as experimental results recently obtained by our group. In particular, we experimentally demonstrated efficient mixing of metal alloys in long tubes subjected to TMF during processing. Application of this technique can be an elegant solution to ensure melt homogenization prior to solidification in a microgravity environment where natural convection is generally absent. Results of our theoretical work on TMF induced flows, such as convection control in Bridgman as well as in the Traveling Heater method, will be presented. Possible applications of TMF on board the ISS will also be discussed.

Motakef, S.↗
NASA NTRS2010

NASA Tech Briefs, April 2010

Topics covered include: Active and Passive Hybrid Sensor; Quick-Response Thermal Actuator for Use as a Heat Switch; System for Hydrogen Sensing; Method for Detecting Perlite Compaction in Large Cryogenic Tanks; Using Thin-Film Thermometers as Heaters in Thermal Control Applications; Directional Spherical Cherenkov Detector; AlGaN Ultraviolet Detectors for Dual-Band UV Detection; K-Band Traveling-Wave Tube Amplifier; Simplified Load-Following Control for a Fuel Cell System; Modified Phase-meter for a Heterodyne Laser Interferometer; Loosely Coupled GPS-Aided Inertial Navigation System for Range Safety; Sideband-Separating, Millimeter-Wave Heterodyne Receiver; Coaxial Propellant Injectors With Faceplate Annulus Control; Adaptable Diffraction Gratings With Wavefront Transformation; Optimizing a Laser Process for Making Carbon Nanotubes; Thermogravimetric Analysis of Single-Wall Carbon Nanotubes; Robotic Arm Comprising Two Bending Segments; Magnetostrictive Brake; Low-Friction, Low-Profile, High-Moment Two-Axis Joint; Foil Gas Thrust Bearings for High-Speed Turbomachinery; Miniature Multi-Axis Mechanism for Hand Controllers; Digitally Enhanced Heterodyne Interferometry; Focusing Light Beams To Improve Atomic-Vapor Optical Buffers; Landmark Detection in Orbital Images Using Salience Histograms; Efficient Bit-to-Symbol Likelihood Mappings; Capacity Maximizing Constellations; Natural-Language Parser for PBEM; Policy Process Editor for P(sup 3)BM Software; A Quality System Database; Trajectory Optimization: OTIS 4; and Computer Software Configuration Item-Specific Flight Software Image Transfer Script Generator.

Source record↗
NASA NTRS2002

Variable Specific Impulse Magnetoplasma Rocket Engine

An engine is disclosed, including a controllable output plasma generator, a controllable heater for selectably raising a temperature of the plasma connected to an outlet of the plasma generator, and a nozzle connected to an outlet of the heater, through which heated plasma is discharged to provide thrust. In one embodiment, the source of plasma is a helicon generator. In one embodiment, the heater is an ion cyclotron resonator. In one embodiment, the nozzle is a radially diverging magnetic field disposed on a discharge side of the heater so that helically travelling particles in the beater exit the heater at high axial velocity. A particular embodiment includes control circuits for selectably directing a portion of radio frequency power from an RF generator to the helicon generator and to the cyclotron resonator so that the thrust output and the specific impulse of the engine can be selectively controlled. A method of propelling a vehicle is also disclosed. The method includes generating a plasma, heating said plasma, and discharging the heated plasma through a nozzle. In one embodiment, the nozzle is a diverging magnetic field. In this embodiment, the heating is performed by applying a radio frequency electro magnetic field to the plasma at the ion cyclotron frequency in an axially polarized DC magnetic field.

Franklin R Chang-Diaz↗
NASA NTRS1989

Galileo Mission Science Briefing

The first of two tapes of the Galileo Mission Science press briefing is presented. The panel is moderated by George Diller from the Kennedy Space Center (KSC) Public Affairs Office. The participants are John Conway, the director of Payload and operations at Kennedy; Donald E. Williams, Commander of STS-43, the shuttle mission which will launch the Galileo mission; John Casani, the Deputy Assistant Director of Flight Projects at the Jet Propulsion Lab (JPL); Dick Spehalski, Galileo Project Manager at JPL; and Terrence Johnson, Galileo Project Scientist at JPL. The briefing begins with an announcement of the arrival of the Galileo Orbiter at KSC. The required steps prior to the launch are discussed. The mission trajectory and gravity assists from planetary and solar flybys are reviewed. Detailed designs of the orbiter are shown. The distance that Galileo will travel from the sun precludes the use of solar energy for heat. Therefore Radioisotope heater units are used to keep the equipment at operational temperature. A video of the arrival of the spacecraft at KSC and final tests and preparations is shown. Some of the many science goals of the mission are reviewed. Another video showing an overview of the Galileo mission is presented. During the question and answer period, the issue of the use of plutonium on the mission is broached, which engenders a review of the testing methods used to ensure the safety of the capsules containing the hazardous substance. This video has actual shots of the orbiter, as it is undergoing the final preparations and tests for the mission.

Source record↗
NASA NTRSDate not supplied

Experimental Capabilities and Achievements of the Space Environment Dynamometer (SED)

The Space Environment Dynamometer (SED) chamber was designed to conduct research in cryobotics; an area of study that focuses on robotic systems and rotating machinery operating in extreme cold environments including Earth, low Earth orbit, Mars, Moon, asteroids, Solar orbit, planetary orbit, or those encountered during travel among these destinations. The test chamber incorporates a modular dynamometer, consisting of a variety of brakes, torque sensors and motors to be easily interchanged between tests. Each test employs a unique test profile that incorporates different setpoints of applied torques and velocities for a given period or number of rev- olutions. The modularity of the dynamometer setup allows for any combination of motor, gearbox to be tested. This chamber is one of a kind and resides at the Swamp Works facility within the Granular Mechanics and Regolith Operations laboratory (GMRO) at NASA Kennedy Space Center. Other cold chambers exist, however they are project specific and do not simultaneously output real time torque, temperature and efficiency data. The modularity of this extreme cold environment test chamber, coupled with the custom software and instrumentation, makes it one of a kind. The chamber is capable of stabilizing cryogenic temperatures and pressures to commensurate moon environments. Tests have successfully been conducted on motors and gearboxes for various cryogenic temperature set points, torques, and angular velocities. Relevant internal temperatures of the test article and chamber were recorded using a variety of temperature sensors. The temperature setpoints, on the motors and gearboxes tested, were stabilized by using PID gain scheduling of the PWM signal for the various heaters. The heat removal for the motor was provided by creating a thermally conductive path from a cryohead directly to the test article using copper straps. A variety of strainwave gears (SWGs), also known as Harmonic drives, planetary gear systems and DC motor actuator configurations have been tested in the chamber. The experiments performed were for various projects including Bulk Metallic Glass Gears (BMGG), Volatiles Investigating Polar Exploration Rover (VIPER), In-Situ Resource Utilization Pilot Excavator (IPEX) . Various upgrades have been made to the extreme cold environment test chamber for the use of cryobotic research. These upgrades greatly increased the autonomous capabilities of the test set up by providing redundancies in the hardware and software. The redundancies were primarily added to protect the integrity of the cryohead. A new strapping and insulation method was performed to create the thermal conductive path from the actuators to the cryohead. The software was upgraded to include temperature setpoint control, further increasing the autonomous capabilities of the test. This paper goes into detail regarding the upgrades made to the extreme cold environment test chamber, as well as highlights the results from a COLDArm acceptance test.

Casey J. Clark↗