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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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A highly efficient Q-switched Ho:YLF laser pumped by a Tm:fiber laser has been designed and demonstrated. When the pump power is 30 W, the pulse energy is 30mJ at the repetition rate of 100Hz.
NASA Glenn Research Center is developing a 1.4~MW high-efficiency electric machine for future electrified aircraft to reduce energy consumption, emissions, and noise. This wound-field, synchronous machine employs a self-cooled, superconducting rotor to achieve excellent specific power and efficiency. The design of the superconducting rotor and the optimization of its electromagnetic and structural responses are analyzed in this paper. Candidate designs are evaluated in terms of absolute performance, specific performance, and performance per cost. It is found that optimizing the electromagnetic response for absolute or specific performance yields designs that are similar to each other, but opposite of the cost-optimized design. A method to define the thermal requirements of the superconducting coils and integrated cryocooler is also presented.
NASA Glenn Research Center is developing a 1.4 MW high-efficiency electric machine for future electrified aircraft to reduce energy consumption, emissions, and noise. This wound-field, synchronous machine employs a self-cooled, superconducting rotor to achieve excellent specific power and efficiency. The design of the superconducting rotor and the optimization of its electromagnetic and structural responses are analyzed in this paper. Candidate designs are evaluated in terms of absolute performance, specific performance, and performance per cost. It is found that optimizing the electromagnetic response for absolute or specific performance yields designs that are similar to each other, but opposite of the cost-optimized design. A method to define the thermal requirements of the superconducting coils and integrated cryocooler is also presented.
Future manned and unmanned space missions will require reliable, high efficiency energy conversion systems. For a manned Mars mission, power levels in the range of 10 to 100 kWe will be needed. The Alkali Metal Thermoelectric Converter (AMTEC) is a direct energy conversion technology with the potential to meet these needs. The AMTEC is a thermally regenerative electrochemical device that derives its operation from the sodium ion conducting properties of beta-alumina solid electrolyte (BASE). To date, an efficiency of 19%, area power density of 1 W/sq cm, and a lifetime of 10,000 hours at high temperature were demonstrated in laboratory devices. Systems studies show that projected AMTEC systems equal or surpass the performance of other static or dynamic systems in applications of 1 kWe-1 MWe. Thus, the laboratory experiments and applications studies conducted to date have shown that the AMTEC posseses great potential. In order to bring this technology to the stage where prototype units can be built and operated, several technical issues must be addressed. These include the need for long life, high power electrodes, minimization of radiative parasitic losses, and high temperature seals. In summary, the evidence shows that if AMTEC is developed, it can play a significant role in future space power applications.
Single aisle class electric aircraft require high power density and efficiency megawatt electric machines to be competitive with their tradition turbofan counterparts. Superconducting machines are seen as a key enabling technology for achieving the electric motor power density and efficiency needed by single aisle class electric aircraft. NASA’s High Efficiency Megawatt Motor (HEMM) is a partially superconducting machine being developed at NASA Glenn Research Center as a technology demonstration of a practical near-term superconducting machine. HEMM is being developed to meet the requirements of the generators on NASA’s STARC-ABL reference aircraft. HEMM is expected to achieve greater than 16 kW/kg electromagnetic specific power and greater than 98% efficiency at a nominal operating condition of 1.4 MW and 6800 RPM. In this paper, a design optimization algorithm for partially superconducting machines based on HEMM’s technologies is used to explore the possible performance of HEMM technology at other machine power levels and operating conditions. The design optimization algorithm is detailed in full and results for achievable geared and direct drive machine performance are presented.
The feasibility of fabricating space-resistant, high efficiency, light-weight, low-cost GaAs shallow-homojunction solar cells for space application is demonstrated. This program addressed the optimal preparation of ultrathin GaAs single-crystal layers by AsCl3-GaAs-H2 and OMCVD process. Considerable progress has been made in both areas. Detailed studies on the AsCl3 process showed high-quality GaAs thin layers can be routinely grown. Later overgrowth of GaAs by OMCVD has been also observed and thin FaAs films were obtained from this process.
The self-cooled, superconducting rotor included in the design of the High Efficiency Megawatt Motor (HEMM) can produce magnetic field strengths far higher than those produced using conventional approaches. However, the superconductivity properties of high-temperature superconducting coils can degrade as the coil is repeatedly thermally cycled, significantly impacting the HEMM’s performance. To explore ways to reduce this risk, NASA researchers fabricated and tested several coils of increasing complexity. The results of the testing campaign indicate that NASA can fabricate and test full-scale superconducting coils for the rotor of the HEMM that can reliably survive repeated thermal cycling with no or acceptably slow degradation.
With advancements in additive manufacturing (AM) techniques, high-quality triply periodic minimal surface (TPMS) structures can now be produced. TPMS walled heat exchangers (HX) hold significant potential for industrial applications and are receiving increasing attention. This paper explores the impact of various TPMS design variables on flow and thermal performance to optimize TPMS heat exchangers for compactness, high efficiency, and low pressure drop. The design variables examined include the type of TPMS lattice, unit cell size, wall thickness, aspect ratio, TPMS orientation, and equivalent thickness. The study reveals that the flow and heat transfer performance of TPMS structures are significantly affected by these design variables. For the Gyroid, Diamond, and SplitP lattices, performance is nearly identical when the surface-to-volume ratio is kept constant. The average velocity of the fluid in the TPMS HX should be 0.3 m/s. The corresponding Re is between 300~800. Thin wall thickness, small equivalent thickness, and flat lattice configurations can significantly reduce pressure drop while maintaining the overall heat transfer coefficient. Additionally, the angle between the flow direction and TPMS orientation can increase pressure drop. Three aluminum heat exchangers were successfully printed using an AM machine, and testing results are comparable with theoretical prediction.
Design of wideband high efficiency optical modulation system tested over 100-MHz band
A technology for fabricating high efficiency, thin film GaAs solar cells on substrates appropriate for space and/or terrestrial applications was developed. The approach adopted utilizes organometallic chemical vapor deposition (OM-CVD) to form a GaAs layer epitaxially on a suitably prepared Ge epi-interlayer deposited on a substrate, especially a light weight silicon substrate which can lead to a 300 watt per kilogram array technology for space. The proposed cell structure is described. The GaAs epilayer growth on single crystal GaAs and Ge wafer substrates were investigated.
Performance data are presented for a flight-like, lightweight, high efficiency pulse tube cryogenic cooler. The cooler has a mass of less than 4.0 kg, and an efficiency of 12 W/W, which is 18% of Carnot at 95 K, nearly double the efficiency of previous cooler designs, The mass of the cooler has been reduced by approximately a factor of three. The design point cooling power is 10 watts at 95 K at a heat rejection temperature of 300 K. The no-load temperature is 45 K. The compressor is built by Hymatic Engineering, UK, and is of a horizontally opposed piston design using flexure bearings. The vertical pulse tube is built by TRW with the heat exchanger or cold block located approximately mid-way along the tube. The final assembly and integration is also performed by TRW. The inertance tube and dead volume are contained within one of the compressor end caps. The cooler was developed by TRW under a joint NASA-DOD program, and has a goal of 10 yr operating lifetime. Potential NASA applications will focus on using coolers of this type in Zero boil off (ZBO) cryogen storage topologies for next generation launch vehicles. Zero boil off systems will feature significant reductions in tank size and Initial Mass to Low Earth Orbit (IMLEO), thereby significantly reducing the cost of access to space, and enabling future missions. The coolers can be used directly in liquid oxygen (LOx) or liquid methane ZBO systems, as shield coolers in liquid hydrogen tanks, or as first stage coolers in two-stage liquid hydrogen (LH2) ZBO cooler systems. Finally, the coolers could find applications in exploration missions where either propellants or breathable oxygen are extracted from the planetary atmosphere using a Sabatier or similar process. The gases could then be liquefied for storage either directly in return vehicle propellant tanks or on the planetary surface. Data presented were taken with the cooler operating in a vacuum of 10 (exp -5) torr, at controlled rejection temperatures from 300 K down to 275 K using a cold water heat exchanger bolted to the cooler. Heat loads were varied between 0.5 W and 15 W by supplying current to a 50 omega resistor mounted on a copper cold plate which was bolted to the cooler cold block. Silicon diodes mounted on both the cold plate and the heat exchanger provided accurate temperature measurement to within plus or minus 0.25 K and plus or minus 0.5 K respectively, up to 100 K with plus or minus 1% accuracy above 100 K. Input power to the compressor was limited to 180 W, corresponding to a maximum stroke of 80%.
This study delineates a meticulous exploration of technologies to enhance the energy efficiency of rooftop air conditioning units, employing the DOE/ORNL heat pump design model for comprehensive engineering design and optimization. A baseline rooftop air conditioning unit, featuring a 13 ton (45.7 kW) cooling capacity and a 17.9 integrated energy efficiency ratio, served as the point of departure for substantive efficiency enhancements. Key modifications included the consolidation of two refrigerant circuits into one, integrating three parallel 2-stage (dual-speed) compressors, fan replacements with high-efficiency substitutes. Notably, a lower global warming potential refrigerant, R452B, was evaluated as a substitute for R-410A, demonstrating better performance in the lab prototype. Further, the achieved measured integrated energy efficiency ratio of 21.4 in the lab prototype surpassed the baseline integrated energy efficiency ratio. Comparative evaluations between R410A and R452B indicated heightened efficiency with the latter, showcasing a lab-demonstrated integrated energy efficiency ratio of 22.4 at the rated capacity of 13.8 ton (48.5 kW) and 23.9 integrated energy efficiency ratio at the rated capacity of 10 ton (35.2 kW). This research underscores the successful development of a rigorous, energy efficient rooftop air conditioning unit prototype with noteworthy environmental and economic implications.
The specific activity was to improve the tandem junction Cell (TJC) as a high efficiency solar cell. The TJC development was to be consistent with module assembly and should contribute to the overall goals of the Low-Cost Solar Array Project. During 1978, TJC efficiency improved from approximately 11 percent to approximately 16 percent (AMI). Photogenerated current densities in excess of 42 mA/sq cm were observed at AMO. Open circuit voltages as high as 0.615 V were measured at AMO. Fill factor was only 0.68 - 0.75 due to a nonoptimum metal contact design. A device model was conceived in which the solar cell is modelled as a transitor. There are virtually no interconnect or packaging factor systems and the TJC is compatible with all conventional module fabrication systems. A modification of the TJC, the Front Surface Field (FSF) cell, was also explored.
We report on a newly solid state laser transmitter, designed and packaged for Earth and planetary space-based remote sensing applications for high efficiency, low part count, high pulse energy scalability/stability, and long life. Finally, we have completed a long term operational test which surpassed 2 Billion pulses with no measured decay in pulse energy.
Brushless dc motor operates as a commutator in a vacuum environment with high efficiency and long life. Because of its excellent response time, it can be used in the servomechanism field.
Oxygen and carbon related defects in silicon, particularly as related to high-efficiency silicon solar cells were studied. A summary of oxygen processes in silicon versus process temperature was shown along with experimental results. The anamolous diffusion of oxygen was explained by the dissociation of the center allowing O sub i to move through the lattices.
The original vaned configuration of the High Efficiency Centrifugal Compressor (HECC) was developed with aggressive design targets to facilitate advancement of state-of-the-art technology in gas turbine compressors. This work documents modifications to the Small Engine Components Compressor Test Facility to support testing of the HECC vaneless diffuser and transition duct configurations, both of which are open geometries. These configurations were developed as follow-up studies to improve understanding of the differences between the predicted and actual performance of the original HECC vaned diffuser stage. Specifically, the vaneless diffuser was designed to provide the impeller with ideal exit conditions such that the impeller performance could be isolated from downstream stationary components, and the additively manufactured transition duct inlet configuration enables investigation into the effects of the inlet flow path on the stage performance. Features of note in the facility are active clearance control, bleed flow regulation, modular inlet configurations, and steady-state and fast-response instrumentation throughout the flow path. Details of the facility and instrumentation are presented as well as the baseline performance of the compressor stage. The geometry, performance, and detailed aerodynamic data have been made available to the public at https://storage.googleapis.com/heccdata/NASA-HECC-Data-Archive.zip.
The original vaned configuration of the High Efficiency Centrifugal Compressor (HECC) was developed with aggressive design targets to facilitate advancement of state-of-the-art technology in gas turbine compressors. This work documents modifications to the Small Engine Components Compressor Test Facility to support testing of the HECC vaneless diffuser and transition duct configurations, both of which are open geometries. These configurations were developed as follow-up studies to improve understanding of the differences between the predicted and actual performance of the original HECC vaned diffuser stage. Specifically, the vaneless diffuser was designed to provide the impeller with ideal exit conditions such that the impeller performance could be isolated from downstream stationary components, and the additively manufactured transition duct inlet configuration enables investigation into the effects of the inlet flow path on the stage performance. Features of note in the facility are active clearance control, bleed flow regulation, modular inlet configurations, and steady-state and fast-response instrumentation throughout the flow path. Details of the facility and instrumentation are presented as well as the baseline performance of the compressor stage. The geometry, performance, and detailed aerodynamic data have been made available to the public at https://storage.googleapis.com/hecc-data/NASA-HECC-Data-Archive.zip.