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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 703 records · Page 39

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NASA NTRS1995

Microrefrigeration by a pair of normal metal/insulator/superconductor junctions

We suggest and demonstrate experimentally that two normal metal/insulator/superconductor (NIS) tunnel junctions combined in series to form a symmetric SINIS structure can operate as an efficient Peltier refrigerator. Specifically, it is shown that the SINIS structure with normal-state junction resistences of 1.0 and 1.1 kOmega is capable of reaching a temperature of about 100 mK starting from 300 mK. We estimate the corresponding cooling power to be 1.5 pW per total junction area of 0.8 micrometers(exp 2) at T = 300 mK. This cooling power density implies that scaling of junction area up to about 1 mm(exp 2) should bring the cooling power into the microW range.

Leivo, M. M.↗

NASA NTRS2002

34% Efficient InGaP/GaAs/GaSb Cell-Interconnected-Circuits for Line-Focus Concentrator Arrays

While monolithic multi-junction cells are preferred for flat plate arrays, mechanically stacked multi-junction cells are superior for solar concentrator applications. Reasons for this are that the mechanical stacked configuration with high efficiency Gallium Antimonide cells allows utilization of a much wider range of the solar energy spectrum, and the ability to use voltage matched interconnects results in full use of low bandgap cell currents. Herein, data are presented for simple two terminal voltage-matched circuits using InGaP/GaAs/GaSb stacked cells showing 34% average circuit efficiency for a lot of 12 circuits given prismatic covers. These circuits have been designed to fit into the ultralight Stretched Lens Array being developed by NASA. With these new cell-interconnected-circuits, we project that the power density at GEO operating temperature can be increased from 296 W/m2 to 350 W/m2 while maintaining the specific power at 190 W/kg at the full wing level.

Fraas, L. M.↗

NASA NTRS2010

Miniature Low-Mass Drill Actuated by Flextensional Piezo Stack

Recent experiments with a flextensional piezoelectric actuator have led to the development of a sampler with a bit that is designed to produce and capture a full set of sample forms including volatiles, powdered cuttings, and core fragments. The flextensional piezoelectric actuator is a part of a series of devices used to amplify the generated strain from piezoelectric actuators. Other examples include stacks, bimorphs, benders, and cantilevers. These devices combine geometric and resonance amplifications to produce large stroke at high power density. The operation of this sampler/drill was demonstrated using a 3x2x1-cm actuator weighing 12 g using power of about 10-W and a preload of about 10 N. A limestone block was drilled to a depth of about 1 cm in five minutes to produce powdered cuttings. It is generally hard to collect volatiles from random surface profiles found in rocks and sediment, powdered cuttings, and core fragments. Toward the end of collecting volatiles, the actuator and the bit are covered with bellows-shaped shrouds to prevent fines and other debris from reaching the analyzer. A tube with a miniature bellows (to provide flexibility) is connected to the bit and directs the flow of the volatiles to the analyzer. Another modality was conceived where the hose is connected to the bellows wall directly to allow the capture of volatiles generated both inside and outside the bit. A wide variety of commercial bellows used in the vacuum and microwave industries can be used to design the volatiles capture mechanism. The piezoelectric drilling mechanism can potentially be operated in a broad temperature range from about-200 to less than 450 C. The actuators used here are similar to the actuators that are currently baselined to fly as part of the inlet funnel shaking mechanism design of MSL (Mars Science Laboratory). The space qualification of these parts gives this drill a higher potential for inclusion in a future mission, especially when considering its characteristics of low mass, small size, low power, and low axial loads for sampling.

Sherrit, Stewart↗

NASA NTRS2012

New Technology for Microfabrication and Testing of a Thermoelectric Device for Generating Mobile Electrical Power

Thermoelectric (TE) power generation is an increasingly important power generation technology. Major advantages include: no moving parts, low-weight, modularity, covertness/silence, high power density, low amortized cost, and long service life with minimum or no required maintenance. Despite low efficiency of power generation, there are many specialized needs for electrical power that TE technologies can uniquely and successfully address. Recent advances in thermoelectric materials technology have rekindled acute interest in thermoelectric power generation. We have developed single crystalline n- and p- type PbTe crystals and are also, developing PbTe bulk nanocomposites using PbTe nano powders and emerging filed assisted sintering technology (FAST). We will discuss the materials requirements for efficient thermoelectric power generation using waste heat at intermediate temperature range (6500 to 8500 K). We will present our recent results on production of n- and p- type PbTe crystals and their thermoelectric characterization. Relative characteristics and performance of PbTe bulk single crystals and nano composites for thermoelectric power generation will be discussed.

Prasad, Narasimha S.↗

NASA NTRS2014

Material Challenges and Opportunities for Commercial Electric Aircraft

Significant reduction in carbon dioxide emission for future air transportation system will require adoption of electric propulsion system and more electric architectures. Various options for aircraft electric propulsion include hybrid electric, turboelectric, and full electric system. Realization of electric propulsion system for commercial aircraft applications will require significant increases in power density of electric motors and energy density of energy storage system, such as the batteries and fuel cells. In addition, transmission of MW of power in the aircraft will require high voltage power transmission system to reduce the weight of the power transmission system. Finally, there will be significant thermal management challenges. Significant advances in material technologies will be required to meet these challenges. Technologies of interest include materials with higher electrical conductivity than Cu, high thermal conductivity materials, and lightweight electrically insulating materials with high breakdown voltage, high temperature magnets, advanced battery and fuel cell materials, and multifunctional materials. The presentation will include various challenges for commercial electric aircraft and provide an overview of material improvements that will be required to meet these challenges.

materials↗

NASA NTRSDate not supplied

Selecting an Encapsulant for an Aerospace Superconducting Machine

Achieving larger benefits from electrified propulsion in single aisle aircraft (the largest commercial aircraft market segment) necessitates that a significant fraction of their 20 MW or greater propulsion system be electrified. 5 to possibly 20 of the MW-scale electric machines investigated by NASA would be required to meet this need. Approximately 10-20 of NASA’s MW-scale electric machines would be required to reach the necessary power levels. Therefore, electric machines of 5 MW or greater are of interest. However, conventionally cooled high power density MW-scale electric machines still produce a significant amount of waste heat, which makes obtaining these power levels problematic. Highly efficient fully superconducting electric machines (or those with a cryogenically cooled, high purity copper or aluminum stator) are a possible solution but have multiple barriers to be overcome. One such barrier is the durability of superconducting windings. Superconductors are typically brittle, and encapsulants used to hold windings in place are a significant source of stress because of the mismatches in coefficient of thermal expansion at temperatures between room temperature and operational temperatures (20 to 77 K). These encapsulants also form a thermal barrier that can be detrimental to cooling the superconductors. This paper describes an initial study of commercially available encapsulants as it relates to superconducting machine applications along with initial modeling of thermal stress in superconducting windings for a superconducting or cryogenically cooled stator in a 5 MW electric machine.

encapsulant↗

DOE OSTI2022

Unraveling the Effects of Hierarchical Bimodal Microscale Porosity on Thick Electrodes

The thick electrode design is preferential in high-energy lithium-ion batteries (LIBs) systems. However, the sluggish ionic transport in homogeneous porous thick electrodes severely limits the areal capacity at high charging/discharging rates. The hierarchical porous design is a promising approach to mitigate kinetic limitations because it can distribute mass effectively in natural systems. In this study, the effects of bimodal microscale pores are fully investigated in thick electrodes from both architectural and electrochemical perspectives. Notably, by introduction of the bimodal microscale porous structure, the rate capability improves remarkably in thick electrodes with a low porosity (39%). Herein, by combining experimental results with simulations, this work presents a rational design guideline for preparing thick electrodes with a porosity at the commercial level, as well as simultaneous high energy and power densities, which brings new insights into the advanced electrode architecture design in scalable high-energy and high-power energy storage systems for practical applications.

25 ENERGY STORAGE↗

NASA NTRS1971

Reactor core length, externally configured thermionic converter.

Results of testing a converter having an external emitter configuration for 190 hours using RF induction heating. The converter was assembled with a rhenium emitter, 25.4 cm long, having a 91.2 sq cm emitting area, and a niobium collector with a molybdenum coating to improve its electronic property. The collector was water-cooled. The test included: static power output measurements, dynamic characteristics, and the effects of the temperature distribution along the emitter. The maximum power output achieved from the converter at an emitter temperature of 1942 K was 178 W at 0.48 V output, with a power density of 1.95 W/sq cm and an efficiency of 5.5%. The static characteristics also indicated that, with a constant power input, the converter power output does not vary with the output voltage as a result of self-adjustment of the emitter temperature. An investigation of the effects of the temperature distribution along the emitter length showed a 33% improvement in the converter output power with a flattening of the emitter temperature.

Shimada, K.↗

NASA NTRS1988

Recent advances in Alkali Metal Thermoelectric Converter (AMTEC) electrode performance and modeling

The Alkali Metal Thermoelectric Converter (AMTEC) is a direct energy conversion device, utilizing a high sodium vapor pressure or activity ratio across a beta-double prime-alumina solid electrolyte (BASE). This paper describes progress on the remaining scientific issue which must be resolved to demonstrate AMTEC feasibility for space power systems: a stable, high power density electrode. Two electrode systems have recently been discovered at JPL that now have the potential to meet space power requirements. One of these is a very thin sputtered molybdenum film, less than 0.5 micron thick, with overlying current collection grids. This electrode has experimentally demonstrated stable performance at 0.4-0.5 W/sq cm for hundreds of hours. Recent modeling results show that at least 0.7 W/sq cm can be achieved. The model of electrode performance now includes all loss mechanisms, including charge transfer resistances at the electrode/electrolyte interface. A second electrode composition, cosputtered platinum/tungsten, has demonstrated 0.8 W/sq cm for 160 hours. Systems studies show that a stable electrode performance of 0.6 W/sq cm will enable high efficiency space power systems.

Bankston, C. P.↗

NASA NTRS1991

Radioisotope thermal photovoltaic application of the GaSb solar cell

An examination of a RTVP (radioisotopic thermophotovoltaic) conceptual design has shown a high potential for power densities well above those achievable with radioisotopic thermoelectric generator (RTG) systems. An efficiency of 14.4 percent and system specific power of 9.25 watts/kg were predicted for a system with sixteen GPHS (general purpose heat source) sources operating at 1100 C. The models also showed a 500 watt system power by the strontium-90 isotope at 1200 C at an efficiency of 17.0 percent and a system specific power of 11.8 watts/kg. The key to this level of performance is a high-quality photovoltaic cell with narrow bandgap and a reflective rear contact. Recent work at Boeing on GaSb cells and transparent back GaAs cells indicate that such a cell is well within reach.

Morgan, M. D.↗

NASA NTRS2015

Thermal Analysis of Iodine Satellite (iSAT)

This paper presents the progress of the thermal analysis and design of the Iodine Satellite (iSAT). The purpose of the iSAT spacecraft (SC) is to demonstrate the ability of the iodine Hall Thruster propulsion system throughout a one year mission in an effort to mature the system for use on future satellites. The benefit of this propulsion system is that it uses a propellant, iodine, that is easy to store and provides a high thrust-to-mass ratio. The spacecraft will also act as a bus for an earth observation payload, the Long Wave Infrared (LWIR) Camera. Four phases of the mission, determined to either be critical to achieving requirements or phases of thermal concern, are modeled. The phases are the Right Ascension of the Ascending Node (RAAN) Change, Altitude Reduction, De-Orbit, and Science Phases. Each phase was modeled in a worst case hot environment and the coldest phase, the Science Phase, was also modeled in a worst case cold environment. The thermal environments of the spacecraft are especially important to model because iSAT has a very high power density. The satellite is the size of a 12 unit cubesat, and dissipates slightly more than 75 Watts of power as heat at times. The maximum temperatures for several components are above their maximum operational limit for one or more cases. The analysis done for the first Design and Analysis Cycle (DAC1) showed that many components were above or within 5 degrees Centigrade of their maximum operation limit. The battery is a component of concern because although it is not over its operational temperature limit, efficiency greatly decreases if it operates at the currently predicted temperatures. In the second Design and Analysis Cycle (DAC2), many steps were taken to mitigate the overheating of components, including isolating several high temperature components, removal of components, and rearrangement of systems. These changes have greatly increased the thermal margin available.

Mauro, Stephanie↗

DOE OSTI2023

Plasma production and ion heating systems for the Material Plasma Exposure eXperiment

Plasma production and ion heating in the Material Plasma Exposure eXperiment (MPEX), whose design is nearing completion, is accomplished using continuous wave RF power with average power density up to 1.6 MW/m2 at the plasma interface. Plasma is produced using helicon waves coupled through a single helical antenna at 13.56 MHz with power supplied by three 100 kW fixed-frequency RF generators feeding a power combiner network followed by the matching network and launcher. The helicon source can utilize various gasses including hydrogen, deuterium, and helium, with a magnetic field strength in the source region up to 0.2 T, and maximum device |B| of 2.5 T. Power is coupled to ions via ion cyclotron heating at the fundamental resonance using a pair of phased helical antennas operating in the frequency range 4-9 MHz, that launch waves towards the resonance from the antenna region where ω > ωci. ICH power is supplied by a single 500 kW tunable RF transmitter through a 90° power splitter and matching/decoupling network. In the case of both the helicon and ICH systems the antennas are located external to the vacuum, with power transferred through novel water-cooled coaxial vacuum windows consisting of fused quartz outer cylinders and silicon nitride inner cylinders with forced convection water cooling between them. The antenna enclosures are pressurized with dry air to 3 bar absolute for voltage standoff.Several 3-D COMSOL models have been created to simulate the two systems. A model of the helicon region utilizing a cold plasma dielectric tensor with accurate magnetic field and realistic plasma density profiles has been used to calculate the plasma loading/complex antenna input impedance at the launcher feed for various ne and |B| values, for the purpose of estimating power handling. It also incorporates the geometry of all launcher structures relevant to this determination. A still more detailed model of the launcher together with a lossy dielectric plasma surrogate has been used to determine RF electric field values and power losses in the device components.Similar models have been produced to predict the performance and power handling of the ICH launcher. For this device the impedance matrix of the two-element antenna array is calculated using a warm plasma model, necessary to properly determine the wave propagation and absorption.

Goulding, Richard↗

DOE OSTI2024

Elucidating the degradation mechanisms of Pt-free anode anion-exchange membrane fuel cells after durability testing

The development of anion-exchange membrane fuel cells (AEMFCs) has recently accelerated due to synergistic improvements yielding highly conductive membranes, stable ionomers, and enhanced alkaline electrocatalysts. However, cell durability, especially under realistic conditions, still poses a major challenge. Herein, we employ low-loadings of Pt-free Pd-based catalysts in the anode of AEMFCs and elucidate potential degradation mechanisms impacting long-term performance under conditions analogous to the real-world (high current density, H 2 –air (albeit CO 2 -free), and intermittent operation). Our high-performing AEMFCs achieve impressive performance with power densities approaching 1 W cm —2 and current densities up to 3.5 A cm —2 . Over a 200 h period of continuous operation in H 2 –air at a current density of 600 mA cm —2 , our model Pd/C–CeO 2 anode cell exhibits record stability (~30 μV h —1 degradation) compared to the literature and up to 6× better stability than our Pd/C and commercial Pt/C anode cells. Following an 8 h shutdown, the Pd/C–CeO 2 anode cell was restarted and continued for an additional 300 h with a higher degradation rate of ~600 μV h —1 . Thorough in situ evaluations and post-stability analyses provide insights into potential degradation mechanisms to be expected during extended operation under more realistic conditions and provide mitigation strategies to enable the widespread development of highly durable AEMFCs.

08 HYDROGEN↗

NASA NTRS1991

Shot model parameters for Cygnus X-1 through phase portrait fitting

Shot models for systems having about 1/f power density spectrum are developed by utilizing a distribution of shot durations. Parameters of the distribution are determined by fitting the power spectrum either with analytic forms for the spectrum of a shot model with a given shot profile, or with the spectrum derived from numerical realizations of trial shot models. The shot fraction is specified by fitting the phase portrait, which is a plot of intensity at a given time versus intensity at a delayed time and in principle is sensitive to different shot profiles. These techniques have been extensively applied to the X-ray variability of Cygnus X-1, using HEAO 1 A-2 and an Exosat ME observation. The power spectra suggest models having characteristic shot durations lasting from milliseconds to a few seconds, while the phase portrait fits give shot fractions of about 50 percent. Best fits to the portraits are obtained if the amplitude of the shot is a power-law function of the duration of the shot. These fits prefer shots having a symmetric exponential rise and decay. Results are interpreted in terms of a distribution of magnetic flares in the accretion disk.

Lochner, James C.↗

NASA NTRS2003

Fuel Cells for Space Science Applications

Fuel cell technology has been receiving more attention recently as a possible alternative to the internal combustion engine for our automobile. Improvements in fuel cell designs as well as improvements in lightweight high-pressure gas storage tank technology make fuel cell technology worth a look to see if fuel cells can play a more expanded role in space missions. This study looks at the specific weight density and specific volume density of potential fuel cell systems as an alternative to primary and secondary batteries that have traditionally been used for space missions. This preliminary study indicates that fuel cell systems have the potential for energy densities of greater than 500 W-hr/kg, greater than 500W/kg and greater than 400 W-hr/liter, greater than 200 W/liter. This level of performance makes fuel cells attractive as high-power density, high-energy density sources for space science probes, planetary rovers and other payloads. The power requirements for these space missions are, in general, much lower than the power levels where fuel cells have been used in the past. Adaptation of fuel cells for space science missions will require down-sizing the fuel cell stack and making the fuel cell operate without significant amounts of ancillary equipment.

Burke, Kenneth A.↗

DOE OSTI2024

Thermal and hydraulic performance of volumetrically heated triply periodic minimal surface heaters

Advanced heat transfer surfaces, mainly Triply Periodic Minimal Surfaces (TPMSs) have great potential to increase heat transfer performance over traditional heat transfer surfaces due to their tortuous flow path and higher surface area-volume ratio. The emergence of additive manufacturing of nuclear fuel motivates experimental investigation of such advanced geometries in the context of a nuclear reactor core. Here, this study employed a novel method to explore the performance of gyroid and diamond TPMS geometries. Volumetrically heated heaters were additively manufactured from conductive polymer filament, and airflow was used to simulate the convective heat transfer from the core within a nuclear reactor. The mass flow and volumetric generation rates were varied, local Nusselt number correlations were obtained using embedded thermocouples to measure the solid and fluid temperature, and friction factor correlations were developed using differential pressure measurements. The gyroid TPMS presented a friction factor 1.5 times higher than the diamond TPMS and 90 times that of the rod bundle. TPMS geometries showed Nusselt numbers 8–10 times higher than that of the rod bundle, also maintaining colder internal temperatures, which suggested that they could sustain 250–275 % higher power density than the rod bundle for a given centerline temperature. Hence, having the potential to greatly increase the safety margins and power output of a nuclear reactor core with similar volume.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗

DOE OSTI2026

Large-scale white noise and cosmology

The generation of white noise on large scales is a generic property of the dynamics of physical systems described by local nonlinear partial differential equations. Nonlinearities prevent the small-scale dynamics from being erased by smoothing. Unresolved small-scale dynamics act as an uncorrelated (white or Poissonian) noise (seemingly stochastic but actually deterministic) contribution to large-scale dynamics. This white noise exists even when the dynamics is very nearly linear. In cases where the power spectrum is sub-Poissonian on large scales, this noise will dominate on the largest scale power no matter the amplitude of the inhomogeneities. Such is the case in the standard model of cosmology, where the primordial density power spectrum is expected to have an almost Harrison-Zel’dovich, P [ k ] ∼ k , spectrum on a much broader range of scales than can be observed. Even though linear gravitational evolution dominates nonlinear corrections by a factor of ∼ 10 5 , the nonobservation of white noise on the Hubble scale precludes the extrapolation of this power law below the comoving 1 pc scale. More generally, observation or nonobservation of large-scale white noise provides a powerful probe of the Universe on very small scales in the early Universe. Gravitational radiation, phase transitions, vorticity, and running of the spectral index are all phenomena that can be probed with large-scale white noise. Large-scale white noise is a nonoptional feature of all cosmological models but one which has not heretofore been appreciated.

Barenboim, Gabriela [Valencia U., IFIC; Valencia U↗

NASA NTRS1993

Laser diode ignition activities at Sandia National Laboratories

The topics are presented in viewgraph form and include the following: ignition subsystems, enhanced safety, optical ordnance power densities, optical ignition factors, low energy optical ordnance program, absorptance of 2-(5-cyanotetrazolato) pentaaminecobalt(III) perchlorate (CP) near 800 nm, power dependence of doped CP, system operational electrical requirements, dopant concentration effects for different CP particle sizes, ZR/KCLO4 optical ignition thresholds, and electrostatic discharge testing.

Merson, John A.↗