SEARCH · Engineering Papers

Results for “power conversion efficiency”

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.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,333 records · Page 74

All sources NASA NTRS DOE OSTI

NASA NTRS2004

Review of Computational Stirling Analysis Methods

Nuclear thermal to electric power conversion carries the promise of longer duration missions and higher scientific data transmission rates back to Earth for both Mars rovers and deep space missions. A free-piston Stirling convertor is a candidate technology that is considered an efficient and reliable power conversion device for such purposes. While already very efficient, it is believed that better Stirling engines can be developed if the losses inherent its current designs could be better understood. However, they are difficult to instrument and so efforts are underway to simulate a complete Stirling engine numerically. This has only recently been attempted and a review of the methods leading up to and including such computational analysis is presented. And finally it is proposed that the quality and depth of Stirling loss understanding may be improved by utilizing the higher fidelity and efficiency of recently developed numerical methods. One such method, the Ultra HI-Fl technique is presented in detail.

Dyson, Rodger W.↗

DOE OSTI2018

Ultrahigh Power Factor in Thermoelectric System Nb 0.95 M 0.05 FeSb (M = Hf, Zr, and Ti)

Abstract Conversion efficiency and output power are crucial parameters for thermoelectric power generation that highly rely on figure of merit ZT and power factor (PF), respectively. Therefore, the synergistic optimization of electrical and thermal properties is imperative instead of optimizing just ZT by thermal conductivity reduction or just PF by electron transport enhancement. Here, it is demonstrated that Nb 0.95 Hf 0.05 FeSb has not only ultrahigh PF over ≈100 µW cm −1 K −2 at room temperature but also the highest ZT in a material system Nb 0.95 M 0.05 FeSb (M = Hf, Zr, Ti). It is found that Hf dopant is capable to simultaneously supply carriers for mobility optimization and introduce atomic disorder for reducing lattice thermal conductivity. As a result, Nb 0.95 Hf 0.05 FeSb distinguishes itself from other outstanding NbFeSb‐based materials in both the PF and ZT . Additionally, a large output power density of ≈21.6 W cm −2 is achieved based on a single‐leg device under a temperature difference of ≈560 K, showing the realistic prospect of the ultrahigh PF for power generation.

24 POWER TRANSMISSION AND DISTRIBUTION↗

NASA NTRS2004

How to Overcome Numerical Challenges to Modeling Stirling Engines

Nuclear thermal to electric power conversion carries the promise of longer duration missions and higher scientific data transmission rates back to Earth for a range of missions, including both Mars rovers and deep space missions. A free-piston Stirling convertor is a candidate technology that is considered an efficient and reliable power conversion device for such purposes. While already very efficient, it is believed that better Stirling engines can be developed if the losses inherent in current designs could be better understood. However, they are difficult to instrument and so efforts are underway to simulate a complete Stirling engine numerically. This has only recently been attempted and a review of the methods leading up to and including such computational analysis is presented. And finally it is proposed that the quality and depth of Stirling loss understanding may be improved by utilizing the higher fidelity and efficiency of recently developed numerical methods. One such method, the Ultra HI-FI technique is presented in detail.

Dyson, Rodger W.↗

NASA NTRS2006

Performance and Mass Modeling Subtleties in Closed-Brayton-Cycle Space Power Systems

A number of potential NASA missions could benefit from closed-Brayton-cycle (CBC) power conversion systems. The human and robotic mission power applications include spacecraft, surface base, and rover scenarios. Modeling of CBC subsystems allows system engineers, mission planners and project managers to make informed decisions regarding power conversion system characteristics and capabilities. To promote thorough modeling efforts, a critical review of CBC modeling techniques is presented. Analysis of critical modeling elements, component influences and cycle sensitivities is conducted. The analysis leads to quantitative results addressing projections on converter efficiency and overall power conversion system mass. Even moderate modeling errors are shown to easily over-predict converter efficiencies by 30% and underestimate mass estimates by 20%. Both static and dynamic modeling regimes are evaluated. Key considerations in determining model fidelity requirements are discussed. Conclusions and recommendations are presented that directly address ongoing modeling efforts in solar and nuclear space power systems.

Barrett, Michael J.↗

NASA NTRS2005

Performance and Mass Modeling Subtleties in Closed-Brayton-Cycle Space Power Systems

A number of potential NASA missions could benefit from closed-Brayton-cycle (CBC) power conversion systems. The human and robotic mission power applications include spacecraft, surface base, and rover scenarios. Modeling of CBC subsystems allows system engineers, mission planners and project managers to make informed decisions regarding power conversion system characteristics and capabilities. To promote thorough modeling efforts, a critical review of CBC modeling techniques is presented. Analysis of critical modeling elements, component influences and cycle sensitivities is conducted. The analysis leads to quantitative results addressing projections on converter efficiency and overall power conversion system mass. Even moderate modeling errors are shown to easily over-predict converter efficiencies by 30 percent and underestimate mass estimates by 20 percent. Both static and dynamic modeling regimes are evaluated. Key considerations in determining model fidelity requirements are discussed. Conclusions and recommendations are presented that directly address ongoing modeling efforts in solar and nuclear space power systems.

Barrett, Michael J.↗

NASA NTRS1980

Rectenna session: Micro aspects

Two micro aspects of rectenna design are discussed: evaluation of the degradation in net rectenna RF to DC conversion efficiency due to power density variations across the rectenna (power combining analysis) and design of Yagi-Uda receiving elements to reduce rectenna cost by decreasing the number of conversion circuits (directional receiving elements). The first of these involves resolving a fundamental question of efficiency potential with a rectenna, while the second involves a design modification with a large potential cost saving.

Gutmann, R. J.↗

NASA NTRS1980

Rectenna session: Micro aspects

Two micro aspects of the rectenna design are addressed: evaluation of the degradation in net rectenna RF to DC conversion efficiency due to power density variations across the rectenna (power combining analysis) and design of Yagi-Uda receiving elements to reduce rectenna cost by decreasing the number of conversion circuits (directional receiving elements). The first of these micro aspects involves resolving a fundamental question of efficiency potential with a rectenna, while the second involves a design modification with a large potential cost saving.

Gutmann, R. J.↗

NASA NTRS2007

Advanced Stirling Technology Development at NASA Glenn Research Center

The NASA Glenn Research Center has been developing advanced energy-conversion technologies for use with both radioisotope power systems and fission surface power systems for many decades. Under NASA's Science Mission Directorate, Planetary Science Theme, Technology Program, Glenn is developing the next generation of advanced Stirling convertors (ASCs) for use in the Department of Energy/Lockheed Martin Advanced Stirling Radioisotope Generator (ASRG). The next-generation power-conversion technologies require high efficiency and high specific power (watts electric per kilogram) to meet future mission requirements to use less of the Department of Energy's plutonium-fueled general-purpose heat source modules and reduce system mass. Important goals include long-life (greater than 14-yr) reliability and scalability so that these systems can be considered for a variety of future applications and missions including outer-planet missions and continual operation on the surface of Mars. This paper provides an update of the history and status of the ASC being developed for Glenn by Sunpower Inc. of Athens, Ohio.

Shaltens, Richard K.↗

DOE OSTI2018

Continuous electrochemical heat engines

Given the large magnitude of energy in waste heat, its efficient conversion to electrical power offers a significant opportunity to lower greenhouse gas emissions. Furthermore, it has been difficult to optimize the performance of new direct energy conversion approaches because of the coupling between entropy change and thermal and electrical transport in continuously operating devices. With electrochemical cells driving flowing electrolytes in symmetric redox reactions at different temperatures, we demonstrate two continuous electrochemical heat engines that operate at 10–50 °C and at 500–900 °C, respectively. Simulations of kilowatt-scale systems using electrochemical cells stacked in series suggest efficiencies over 30% of the Carnot limit and areal power densities competitive with solid-state thermoelectrics at maximum power. Although entropy change, thermal transport and electrical transport are inherently coupled in solid-state thermoelectrics, they can be somewhat circumvented in electrochemical systems, thus offering new opportunities to engineer efficient energy conversion systems.

30 DIRECT ENERGY CONVERSION↗

NASA NTRSDate not supplied

Dynamic Radioisotope Power Systems Development Status and Path to Flight

Dynamic power conversion offers the potential to produce Radioisotope Power Systems (RPS) that generate higher power outputs and utilize the Pu-238 radioisotope more efficiently. Additionally, dynamic power conversion offers the potential of producing generators with minimal degradation resulting in more power at the end of the mission, when the power is needed. Dynamic power conversion technologies being developed for space applications include the Stirling and Brayton thermodynamic cycle machines. Machines can be built based on these cycles while eliminating wear mechanisms of the moving components, enabling long design life necessary for space missions. The Dynamic Radioisotope Power Systems (DRPS) project at NASA Glenn Research Center (Glenn Research Center) is pursuing the realization of this type of power source on a flight mission. The project currently has three convertor development contracts that will deliver prototype hardware in 2020. This hardware will undergo a gamut of experimental performance verification efforts at NASA GRC. In parallel, the project has also initiated generator design efforts based on these underlying convertor options, and is also on track to build an in-house version of a generator for laboratory system-level testing. The project is also funding control electronics technology, which are necessary to convert alternating current from the dynamic devices to direct current for use by a spacecraft. A lunar mission is being targeted as the first use of this new technology, as DRPS enables a wide range of high-return scientific missions on the moon, while the mission being short in duration (2 years rather than 10 years for an outer planets mission).

Salvatore M Oriti↗

NASA NTRSDate not supplied

Dynamic Radioisotope Power Systems Status and Path to Flight

Salvatore Oriti↗

DOE OSTI2014

An electrostatic nanogenerator based on ZnO/ZnS core/shell electrets with stabilized quasi-permanent charge

ZnO-based nanogenerators with excellent performance and convenient functionalization are particularly desirable for self-powered technology, which is however difficult to achieve simultaneously in traditional piezoelectric ZnO nanogenerators. Here, we report a design of electrostatic ZnO nanogenerator by virtue of a type-II ZnO/ZnS core/shell nanostructure electrets, which can turn acoustic waves into electric power with an energy conversion efficiency of 2.2%. The ZnO/ZnS core/shell electrets are charged by ultraviolet irradiation with a long-term stability of the electrostatic charges under ambient condition. The electronic and atomic structure evolution in the charged ZnO/ZnS core/shell electrets are also discussed by detailed experimental and theoretical investigations. This design opens up an alternative path for fabricating robust ZnO-based nanogenerator for future nanotechnology application.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2025

Cross-cutting strategies to lower electricity use of miscellaneous electric loads in the domestic sector

Miscellaneous Electric Loads (MELs) account for roughly one quarter of building electricity use in most developed countries. A product-specific approach to lowering MELs electricity use in this category takes too long and costs too much because there are so many MELs, each providing unique services. An alternative approach focusing on key functionalities was therefore explored. These functionalities include: (1) power management, (2) power scaling, and (3) power conversion. Cross-cutting efficiency improvements to these functionalities can be incorporated into broad categories of MELs, thus saving electricity and lowering costs. Even though the population of MELs is diverse and rapidly evolving, major technical opportunities exist to improve their efficiency in these functionalities. Research into energy-saving solutions within the cross-cutting technologies will probably have larger savings than focusing on single products.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

NASA NTRS1990

A high-efficiency ferruleless coupled-cavity traveling-wave tube with phase-adjusted taper

The design and performance of the first traveling-wave tube (TWT) to be built with a phase-adjusted taper (PAT) is discussed. By adjusting the phase of the electron bunch with respect to the RF wave for strong electron bunch formation at the beginning of the taper and strong power conversion at the end, the PAT achieves a high efficiency of power conversion from the electron beam to the RF wave. A PAT incorporated into the output section of a baseline 29-30 GHz ferruleless coupled-cavity TWT experimentally increased the peak RF power from 420 to 1000 W and the peak RF interaction efficiency from 9.6 to 22.6 percent.

Wilson, Jeffrey D.↗

NASA NTRSDate not supplied

Dynamic Radioisotope Power Systems (DPRS) Status and Path to Flight

NASA and DOE are pursuing a novel Dynamic Radioisotope Power System (DRPS) that has mission-enabling potential. Improvements over currently available power systems include: higher conversion efficiency, less waste heat, low degradation, and higher end-of-mission power. Degradation-free life of dynamic heat-engine-based conversion has been demonstrated in the laboratory on the time scales required by even the longest Planetary Science missions.

S. Oriti↗

NASA NTRSDate not supplied

Selection of Alternator Voltage for Dynamic Radioisotope Power Systems

In this paper, we present a study to select an appropriate alternator voltage of the free-piston Stirling convertors (FPSC) for efficient and light Dynamic Radioisotope Power Systems (DRPS). With a system thermal-to-electrical efficiency 3-4 times greater than radioisotope thermoelectric generator (RTG) systems and a higher power density than Brayton systems in the power range of interest for radioisotope-powered systems, Stirling-based DRPS is uniquely suited to benefit upcoming NASA missions. Much effort has been invested in the design and optimization of the thermal, mechanical, and materials aspects of FPSCs, but the electrical aspect has been more nebulous. Therefore, in this paper, a preliminary study will be presented to select the appropriate Stirling alternator voltage to develop a light and efficient system using available flight components. Power conversion systems face a trade between efficiency and system volume/mass with the optimal trade being determined by the application. Neglecting non-idealities related to insulation thickness and winding packing factor and assuming a constant winding area, alternator efficiency is independent of alternator voltage. Because wire size and alternator current can be traded against turn count and alternator voltage without impacting efficiency, the guidance on the optimal design comes from analysis of the controller power electronics and the remainder of the system. Properties of available flight-qualified electrical components, such as rated voltage/current and on-resistance, typically come in discrete values instead of a continuous range of values. With multiple components being required to form the power conversion stage of the controller, each limited to incremental values, a continuous optimization is of little benefit. Instead of a continuous optimization, a random process using properties of the available components can be used to develop a Pareto design front indicating the optimized trade space. The most advantageous trade between system efficiency and mass for the system at hand can then be selected from the range of feasible designs. In the final paper, the design process, assumptions, and preliminary results will be presented.

Free-Piston Stirling Convertor Controller, Dynamic↗

NASA NTRS1980

Power processing and control requirements of dispersed solar thermal electric generation systems

Power Processing and Control requirements of Dispersed Receiver Solar Thermal Electric Generation Systems are presented. Kinematic Stirling Engines, Brayton Engines and Rankine Engines are considered as prime movers. Various types of generators are considered for ac and dc link generations. It is found that ac-ac Power Conversion is not suitable for implementation at this time. It is also found that ac-dc-ac Power Conversion with a large central inverter is more efficient than ac-dc-ac Power Conversion using small dispersed inverters. Ac-link solar thermal electric plants face potential stability and synchronization problems. Research and development efforts are needed in improving component performance characteristics and generation efficiency to make Solar Thermal Electric Generation economically attractive.

Das, R. L.↗

NASA NTRS1987

Refractory semiconductors for high temperature thermoelectric energy conversion

Thermoelectric energy conversion utilizing nuclear heat sources has been employed for several decades to generate power for deep space probes. In the past, lead telluride and, more recently, silicon-germanium alloys have been the prime choices as thermoelectric materials for this application. Currently, a number of refractory semiconductors are under investigation at the Jet Propulsion Laboratory in order to produce power sources of higher conversion efficiency and, thus, lower mass per unit of power output. Included among these materials are improved Si-Ge alloys, rare earth compounds and boron-rich borides. The criteria used to select thermoelectric materials, in general, and the above materials, in particular, will be discussed. The current state of the art and the accomplishments to date in thermoelectric materials research will be reviewed.

Wood, Charles↗