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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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Space processing of directionally solidified eutectic-alloy type turbine blades is envisioned as a simple remelt operations in which precast blades are remelted in a preformed mold. Process systems based on induction melting, continuous resistance furnaces, and batch resistance furnaces were evaluated. The batch resistance furnace type process using a multiblade mold is considered to offer the best possibility for turbine blade processing.
A web furnace was constructed for pulling dendritic-web samples. The effect of changes in the furnace thermal geometry on the growth of dendritic-web was studied. Several attempts were made to grow primitive dendrites for use as the dendritic seed crystals for web growth and to determine the optimum twin spacing in the dendritic seed crystal for web growth. Mathematical models and computer programs were used to determine the thermal geometries in the susceptor, crucible melt, meniscus, and web. Several geometries were determined for particular furnace geometries and growth conditions. The information obtained was used in conjunction with results from the experimental growth investigations in order to achieve proper conditions for sustained pulling of two dendrite web ribbons. In addition, the facilities for obtaining the following data were constructed: twin spacing, dislocation density, web geometry, resistivity, majority charge carrier type, and minority carrier lifetime.
The long-term goal of this work is to produce silicon of solar-grade quality at 3 x 10 to the 6th kg/y for less than $10/kg by, or before 1986. The approach is to improve and expand upon the technology used today to commercially produce metallurgical-grade silicon (MG-Si). This is currently being accomplished by using purer raw materials in the arc furnace process for producing MG-Si, by upgrading the furnace itself, and by unidirectionally solidifying the molten silicon exiting the furnace. Solar cells fabricated from partially purified MG-Si have shown average AM0 efficiencies in the range of 9-11%. Since further MG-Si purification yet remains possible, fabrication of cells of considerably higher conversion efficiency is deemed feasible.
The article discusses the production of solar cells from high-purity silicon. The process consists of reducing the level of impurities in the raw materials, preventing material contamination before and after entering the furnace, and performing orders-of-magnitude reduction of metal impurity concentrations. The high-purity raw materials are considered with reference to carbon reductants, silica, and graphite electrodes. Attention is also given to smelting experiments used to demonstrate, in an experimental-scale furnace, the production of high-purity SoG-Si. It is found that high-purity silicon may be produced from high-purity quartz and chemically purified charcoal in a 50-kVA arc furnace. The major contamination source is shown to be impurities from the carbon reducing materials.
The design and development of equipment and processes to demonstrate continuous growth of crystals by the Czochralski method suitable for producing single silicon crystals for use in solar cells is presented. The growth of at least 150 kg of mono silicon crystal, 150 mm in diameter is continuous from one growth container. A furnace with continuous liquid replenishment of the growth crucible, accomplished by a meltdown system with a continuous solid silicon feed mechanism and a liquid transfer system, with associated automatic feedback controls is discussed. Due to the silicon monoxide build up in the furnace and its retarding effect on crystal growth the furnace conversion for operation in the low pressure range is described. Development of systems for continuous solid recharging of the meltdown chamber for various forms of poly silicon is described.
A unique, high temperature (1000-2000 K) continuously operating capacitive heat exchanger system is described. The system transfers heat from a combustion or solar furnace to a working gas by means of a circulating high temperature molten refractory. A uniform aggregate of beads of a glass-like refractory is injected into the furnace volume. The aggregate is melted and piped to a heat exchanger where it is sprayed through a counter-flowing, high pressure working gas. The refractory droplets transfer their heat to the gas, undergoing a phase change into the solid bead state. The resulting high temperature gas is used to drive a suitable high efficiency heat engine. The solidified refractory beads are delivered back to the furnace and melted to continue the cycle. This approach avoids the important temperature limitations of conventional tube-type heat exchangers, giving rise to the potential of converting heat energy into useful work at considerably higher efficiencies than currently attainable and of storing energy at high thermodynamic potential.
Work carried out on the JPL Flat Plate Solar Array Project, for the purpose of developing a method for silicon ribbon production by Edge-defined Film-fed Growth (EEG) for use as low-cost substrate material in terrestrial solar cell manufacture, is described. A multiple ribbon furnace unit that is designed to operate on a continuous basis for periods of at least one week, with melt replenishment and automatic ribbon width control, and to produce silicon sheet at a rate of one square meter per hour, was constructed. Program milestones set for single ribbon furnace operation to demonstrate basic EEG system capabilities with respect to growth speed, thickness and cell performance were achieved for 10 cm wide ribbon: steady-state growth at 4 cm/min and 200 micron thickness over periods of an hour and longer was made routine, and a small area cell efficiency of 13+% demonstrated. Large area cells of average efficiency of 10 to 11%, with peak values of 11 to 12% were also achieved. The integration of these individual performance levels into multiple ribbon furnace operation was not accomplished.
The purpose of this discussion is to report on the current materials research being done in micro-gravity solidification and future experimentation planned on-board a space shuttle mission. The Department of Engineering Mechanics at the USAF Academy is developing a micro-gravity furnace to be used on board the space shuttle. The micro-g furnace will be used to conduct materials research dealing with such topics as immiscible alloy solidification. The purpose behind this research project is three-fold: first, to develop a simple, inexpensive, an easy to use furnace to conduct space materials research; second, to conduct a solidification experiment on a lead-zinc alloy in space that macrosegregates due to gravity: and third, to provide a research mechanism for students to get involved with space materials research.
Commercial tube welders adapted to metallurgical research. Proposed furnace melts and resolidifies small metal samples during brief periods. In furnace, sample surrounded by large heat sinks and rapidly heated near midlength by intense source of heat. Furnace intended for use in experiments in microgravity: entire melting-and-freezing process requires less than 20 s of near weightlessness experienced in parabolic climb and dive of KC-135 airplane.
Efforts to demonstrate that the dendritic web technology is ready for commercial use by the end of 1986 continues. A commercial readiness goal involves improvements to crystal growth furnace throughput to demonstrate an area growth rate of greater than 15 sq cm/min while simultaneously growing 10 meters or more of ribbon under conditions of continuous melt replenishment. Continuous means that the silicon melt is being replenished at the same rate that it is being consumed by ribbon growth so that the melt level remains constant. Efforts continue on computer thermal modeling required to define high speed, low stress, continuous growth configurations; the study of convective effects in the molten silicon and growth furnace cover gas; on furnace component modifications; on web quality assessments; and on experimental growth activities.
In the Get Away Special 330 payload two germanium samples doped with gallium will be processed. The aim of the experiments is to create a planar solid/liquid interface, and to study the breakdown of this interface as the crystal growth rate increases. For the experiments a gradient furnace was designed which is heated by resistive heaters. Cooling is provided by circulating gas from the atmosphere in the cannister through cooling channels in the furnace. The temperature along the sample are measured by platinum/rhodium thermocouples. The furnace is controlled by a microcomputer system, based upon the processor 80C88. A data acquisition system is integrated into the system. In order to synchronize the different actions in time, a multitask manager is used.
Set of baffles just below exit duct of silicon-ribbon-growing furnace reduces thermal stresses in ribbons so wider ribbons grown. Productivity of furnace increased. Diverts plume of hot gas from ribbon and allows cooler gas from top of furnace to flow around. Also shields ribbon from thermal radiation from hot growth assembly. Ribbon cooled to lower temperature before reaching cooler exit duct, avoiding abrupt drop in temperature as entering duct.
A pilot plant scale furnace was designed and constructed for casting titanium alloy strips. The furnace combines plasma arc skull melting techniques with melt overflow rapid solidification technology. A mathematical model of the melting and casting process was developed. The furnace cast strip of a suitable length and width for use with honeycomb structures. Titanium alloys Ti-6Al-4V and Ti-14Al-21 Nb were successfully cast into strips. The strips were evaluated by optical metallography, microhardness measurements, chemical analysis, and cold rolling.
New facilities for high-temperature containerless processing in space are described, including the acoustic levitation furnace (ALF), the high-temperature acoustic levitator (HAL), and the high-pressure acoustic levitator (HPAL). In the current ALF development, the maximum temperature capabilities of the levitation furnaces are 1750 C, and in the HAL development with a cold wall furnace they will exceed 2000-2500 C. The HPAL demonstrated feasibility of precursor space flight experiments on the ground in a 1 g pressurized-gas environment. Testing of lower density materials up to 1300 C has also been accomplished. It is suggested that advances in acoustic levitation techniques will result in the production of new materials such as ceramics, alloys, and optical and electronic materials.
The effect of thermal convection on the shape of solid-liquid interface was investigated in experiments conducted in a transparent Bridgman-type directional solidification furnace. The relationship was numerically modeled using a standard 2D finite-difference approach, with the solid-liquid deformable interface approximated by a blocking-off technique. The directional solidification furnace was used with pure succinonitrile (which is also transparent) contained in a long square ampoule made of borosilicate glass. With the furnace in the vertical configuration, a flat interface was observed, in agreement with the model. On the other hand, a highly distorted interface was obtained in the horizontal configuration; the numerical results showed a strong recirculating cell in front of the interface due to natural thermal convection. The results indicate that thermal convection is responsible for the interface distortion.
Complicated, inexact calculations now unnecessary. Device called HTX used to simulate and measure transfer of heat between directional-solidification crystal-growth furnace and ampoule containing sample of crystalline to be grown. Yields measurement data used to calculate heat-transfer coefficients directly, without need for assumptions or prior knowledge of physical properties of furnace, furnace gas, or specimen. Determines not only total heat-transfer coefficients but also coefficients of transfer of heat in different modes.
The Crystals by Vapor Transport Experiment (CVTE) and Space Experiments Facility (SEF) are materials processing facilities designed and built for use on the Space Shuttle mid deck. The CVTE was built as a commercial facility owned by the Boeing Company. The SEF was built under contract to the UAH Center for Commercial Development of Space (CCDS). Both facilities include up to three furnaces capable of reaching 850 C minimum, stand-alone electronics and software, and independent cooling control. In addition, the CVTE includes a dedicated stowage locker for cameras, a laptop computer, and other ancillary equipment. Both systems are designed to fly in a Middeck Accommodations Rack (MAR), though the SEF is currently being integrated into a Spacehab rack. The CVTE hardware includes two transparent furnaces capable of achieving temperatures in the 850 to 870 C range. The transparent feature allows scientists/astronauts to directly observe and affect crystal growth both on the ground and in space. Cameras mounted to the rack provide photodocumentation of the crystal growth. The basic design of the furnace allows for modification to accommodate techniques other than vapor crystal growth. Early in the CVTE program, the decision was made to assign a principal scientist to develop the experiment plan, affect the hardware/software design, run the ground and flight research effort, and interface with the scientific community. The principal scientist is responsible to the program manager and is a critical member of the engineering development team. As a result of this decision, the hardware/experiment requirements were established in such a way as to balance the engineering and science demands on the equipment. Program schedules for hardware development, experiment definition and material selection, flight operations development and crew training, both ground support and astronauts, were all planned and carried out with the understanding that the success of the program science was as important as the hardware functionality. How the CVTE payload was designed and what it is capable of, the philosophy of including the scientists in design and operations decisions, and the lessons learned during the integration process are descussed.
An experiment was set up to evaluate the feasibility of using Rayleigh-Brillouin scattering as a diagnostic technique for measuring gas temperature in high pressure environments, such as the Space Shuttle Main Engine (SSME) Preburner. A high pressure furnace is used as the scattering chamber. Either nitrogen or hydrogen may be used. An argon ion laser beam is focused into the furnace. Light backscattering from the gas in the furnace is collected and analyzed with a 5-pass scanning Fabry-Perot interferometer and photon counting electronics. The multi-pass configuration provides the high frequency selectively needed to measure the Brillouin peaks in the presence of large amounts of spuriously scattered light at the laser frequency. Preliminary measurements were made at room temperature in nitrogen at pressures up to 2000 psia. The free spectral range of the interferometer and frequency separation of the Brillouin peaks are determined from measured spectra. Temperature measurements are then obtained using the simple continuum theory with low frequency values of specific heat ratio and shear viscosity. The measured temperatures are within 10 percent of the true value.