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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 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1988

Experimental observation of electrochemical rate limitations affecting sodium ion-electron recombination at electrodes of the alkali metal thermoelectric converter at T about 1200 K

This paper considers a model of the internal impedances of thin porous Mo and W alkali metal thermoelectric converter (AMTEC), in which the kinetic parameters associated with the reaction of the beta-double-prime alumina solid electrolite (BASE)/porous metal/gas three-phase boundary can be evaluated. Impedance data in the frequency range 0.01-100,000 Hz were collected over a range of AMTEC cell operating voltages for small-area thin porous Mo and W electrodes, yielding apparent charge transfer resistances at a series of cell potentials/currents. The ohmic resistance in the AMTEC cell could be broken down and characterized with three parameters: the BASE ionic resistance, the electrode film sheet resistance, and the contact/lead resistance, all of which could be calculated or measured independently and used to calculate power curves in good agreement with observed power curves. It is shown that these calculations can be used to predict the properties of electrodes with optimized parameters or to detect enhanced transport modes.

Williams, R. M.↗
NASA NTRS1988

Radioisotope powered alkali metal thermoelectric converter design for space systems

The design concept of an alkali-metal thermoelectric converter (AMTEC) for 15-30-percent-efficient conversion of heat from the General Purpose (radioisotope) Heat Source (GPHS) on spacecraft is presented. The basic physical principles of the conversion cycle are outlined; a theoretical model is derived; a modular design is described and illustrated with drawings; and the overall AMTEC/GPHS system design is characterized. Predicted performance data are presented in extensive tables and graphs and discussed in detail.

Sievers, R. K.↗
NASA NTRS1989

High power density performance of WPt and WRh electrodes in the alkali metal thermoelectric converter

The properties of the alkali metal thermoelectric converter (AMTEC) are discussed together with those of an efficient AMTEC electrode. Three groups of electrodes were prepared and tested for their performance as AMTEC electrodes, including WPt-T3, WRh-B1, and WRh-B2. The best electrodes of both WPt and WRh types typically exhibited low porosity, and thickness greater than 0.8 micron, which indicated that transport in these electrodes does not occur by a purely free-molecular flow mode. The observed values of the exchange current were found to be within the range of those observed for oxide-free Mo electrodes under similar conditions.

Williams, R. M.↗
NASA NTRS1988

Effects of Na2MoO4 and Na2WO4 on molybdenum and tungsten electrodes for the alkali metal thermoelectric converter (AMTEC)

The effects of adding Na2MoO4 and Na2WO4 to porous Mo and W electrodes, respectively, on the performance and impedance characteristics of the electrodes in an alkali metal thermoelectric converter (AMTEC) were investigated. It was found that corrosion of the porous electrode by Na2MoO4 or Na2WO4 to form Na2MO3O6 and WO2, respectively, and recrystallization of the Mo or W as the salt evaporates, result in major morphological changes including a loss of columnar structure and a significant increase in porosity. This effect is more pronounced in Na2MoO4/Mo electrodes, due to the lower stability of Na2MoO4.

Williams, R. M.↗
NASA NTRS1989

Novel fabrication technique for improving the figure-of-merit of thermoelectric materials

Reduction of the thermal conductivity of thermoelectric materials in order to improve the figure of merit and, hence, the conversion efficiency is discussed. A novel fabrication technique that reduces the thermal conductivity without too adverse an effect on the electrical properties is reported. This is achieved by producing an oxygen-free, very-fine-grain SiGe alloy with very small (on the order of 50 A) precipitates.

Beaty, J. S.↗
NASA NTRS1989

Multiple doping of silicon-germanium alloys for thermoelectric applications

It is shown that heavy doping of n-type Si/Ge alloys with phosphorus and arsenic (V-V doping interaction) by diffusion leads to a significant enhancement of their carrier concentration and possible improvement of the thermoelectric figure of merit. High carrier concentrations were achieved by arsenic doping alone, but for a same doping level higher carrier mobilities and lower resistivities are obtained through phosphorus doping. By combining the two dopants with the proper diffusion treatments, it was possible to optimize the different properties, obtaining high carrier concentration, good carrier mobility and low electrical resistivity. Similar experiments, using the III-V doping interaction, were conducted on boron-doped p-type samples and showed the possibility of overcompensating the samples by diffusing arsenic, in order to get n-type behavior.

Fleurial, Jean-Pierre↗
NASA NTRS1989

SP-100 advanced radiator designs for thermoelectric and Stirling applications

Advanced radiator designs employing carbon-carbon liquid metal heat pipe technology, which significantly reduce the mass of the heat rejection subsystem for high temperature space technology systems such as the SP-100 are discussed. This technology is being developed to address the need for lightweight heat transfer components and structures for space applications. Heat pipe and subsystem designs were optimized for thermoelectric- and Stirling-engine-based SP-100 system designs. A multiple, deployed-petal radiator concept was selected for the heat rejection subsystem design as it provided minimum mass. Radiator stowage in the space transportation system cargo bay and deployment schemes were investigated for each of the optimized designs.

Moriarty, M. P.↗
NASA NTRS1991

Flexible thermal apparatus for mounting of thermoelectric cooler

A flexible heat transfer apparatus used to flexibly connect and thermally couple a thermoelectric cooler to an object to be cooled is disclosed. The flexible heat transfer apparatus consists of a pair of flexible corrugated sheets made from high thermal conductivity materials such as copper, aluminum, gold, or silver. The ridges of the corrugated sheets are oriented perpendicular to one another and bonded sandwich-fashion between three plates to define an upper section and a lower section. The upper section provides X flexure, the lower section provides Y flexure, and both sections together provide Z flexure.

Jones, Jack A.↗
NASA NTRS1991

Thermoelectric effects in decaying homogeneous magneto-gas turbulence

In the formulation of compressible MHD (i.e., magneto-gas dynamics), a 'generalized Ohm's law is required. In particular, an electron pressure term and a 'Hall effect' term may appear as non-negligible additions to the Ohm's law that is conventionally used for incompressible MHD. In 'high-beta' (i.e., relatively low magnetic energy) situations, the Hall term may be neglected (at least initially) but, as it turns out, the electron pressure term cannot be neglected. Here, three-dimensional, high-beta, homogeneous, decaying, magneto-gas turbulence is examined with regard to this additional term. Through numerical simulation, it is found that 'thermoelectric effects' are produced that significantly alter the evolution of the magnetic field and electric current strengths.

Shebalin, John V.↗
NASA NTRS1991

Effect of small scattering centers on the thermoelectric properties of p-type SiGe alloys

Theory predicts that the addition of ultra-fine, inert, phonon-scattering centers to thermoelectric materials will reduce their thermal conductivity. To investigate this prediction, ultrafine particulates (20 to 120 A) of silicon nitride have been added to boron-doped, p-type, 80/20 SiGe. All of the SiGe samples produced from ultrafine powder have lower thermal conductivities than standard SiGe, but high-temperature heat treatment increases the thermal conductivity back to the value for standard SiGe. However, the SiGe samples with silicon nitride, inert, phonon-scattering centers retained the lower thermal conductivity after several heat treatments. A reduction of approximately 25 percent in thermal conductivity has been achieved in these samples. The magnitude of the reduction agrees with theoretical predictions.

Beaty, John S.↗
NASA NTRS1991

Thermoelectric properties of hot pressed p-type SiGe alloys

This paper presents the results of measurements of electrical resistivity, Seebeck coefficient, thermal conductivity, as well as Hall carrier concentration, and mobility, for hot pressed SiGe 80 at. pct Si-20 at. pct Ge (SiGe) thermoelectric materials containing 0.24-3.0 at. pct boron. The carrier concentration was varied by annealing and quenching at different high temperatures. Figure-of-merit, Z, was found to be 0.60 +/- 0.03 x 10 exp -3/K over a carrier concentration range from 1.8- 3.5 x 10 exp -20/cu cm. This result is very encouraging from a production standpoint, since the dopant concentration is not critical.

Bajgar, Clara↗
NASA NTRS1991

Thermoelectric properties of hot-pressed fine particulate powder SiGe alloys

A novel material system and its fabrication technique have been defined and applied to the production of SiGe thermoelectric material through the hot pressing of 50-100 A ultrafine particulates into 80/20 SiGe. Relative to conventionally processed SiGe, a reduction of thermal conductivity of up to 40 percent is achieved in conjunction with an enhancement of material figure-of-merit of the order of 10-15 percent.

Beaty, John S.↗
NASA NTRS1991

A promising new thermoelectric material - Ruthenium silicide

Experimental and theoretical efforts directed toward increasing thermoelectric figure of merit values by a factor of 2 or 3 have been encouraging in several respects. An accurate and detailed theoretical model developed for n-type silicon-germanium (SiGe) indicates that ZT values several times higher than currently available are expected under certain conditions. These new, high ZT materials are expected to be significantly different from SiGe, but not unreasonably so. Several promising candidate materials have been identified which may meet the conditions required by theory. One such candidate, ruthenium silicide, currently under development at JPL, has been estimated to have the potential to exhibit figure of merit values 4 times higher than conventional SiGe materials. Recent results are summarized.

Vining, Cronin B.↗
NASA NTRS1992

Update to the safety program for the general-purpose heat source radioisotope thermoelectric generators for the Galileo and Ulysses missions

With the rescheduling of the Galileo and Ulysses launches and the use of new upper stages following the Challenger accident, the aerospace nuclear safety program for the general-purpose heat source radioisotope thermoelectric generators (GPHS-RTGs) was extended to accommodate the new mission scenarios. As in the original safety program, the objectives were to determine the response of the GPHS-RTG to the various postulated accident environments and to determine the risk (if any) associated with these postulated accidents. The extended GPHS-RTG safety program was successfully completed in sufficient time to prepare an updated Final Safety Analysis Report (FSAR) with revisions for the October 1989 launch of the Galileo spacecraft.

Bennett, Gary L.↗
NASA NTRS1993

Measurement of thermoelectric inhomogeneity of thermocouples

In a thermocouple probe that has significantly inhomogeneous legs, the relationship between emf and temperature is indefinite and depends on temperature distribution along the circuit. An inhomogeneous thermocouple cannot be calibrated to arbitrarily small uncertainty. Therefore, testing for inhomogeneities is a necessary preliminary to meaningful calibration. As most significant inhomogeneity that does occur is introduced during use (and sometimes during calibration) a post-test inhomogeneity measurement should also be employed to detect degradation that might have substantially affected the data. This paper presents a practical test method that is being developed for the observation, interpretation, and application of thermoelectric inhomogeneity as a routine quality assurance measurement that is an essential complement to traditional sheathed thermocouple calibration.

Reed, R. P.↗
NASA NTRS1954

Some Effects of Exposure to Exhaust-gas Streams on Emittance and Thermoelectric Power of Bare-wire Platinum Rhodium - Platinum Thermocouples

Thermocouples were exposed to exhaust gases from the combustion of propane, 72-octane gasoline, and JP-4 fuel. Exposure increased the emissivity of the thermocouple wire, which increased its radiation error. Two methods are presented for determining the emittance of the wires. The emissivity of a clean platinum rhodium-platinum thermocouple was approximately 0.2 in the temperature range investigated, while the emittance of an exposed thermocouple coated with exhaust residue was about 0.5. The exposure caused negligible change in the thermoelectric power of the thermocouples.

Glawe, George E↗
NASA NTRS1994

Improved Thermoelectrically Cooled Laser-Diode Assemblies

Cooling decreases wavelength and increases efficiency and lifetime. Two improved thermoelectrically cooled laser-diode assemblies incorporate commercial laser diodes providing combination of both high wavelength stability and broad wavelength tuning which are broadly tunable, highly stable devices for injection seeding of pulsed, high-power tunable alexandrite lasers used in lidar remote sensing of water vapor at wavelengths in vicinity of 727 nanometers. Provide temperature control needed to take advantage of tunability of commercial AlGaAs laser diodes in present injection-seeding application.

Glesne, Thomas R.↗