SEARCH · Engineering Papers

Results for “Cycle Performance”

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 955 records · Page 53

All sources NASA NTRS DOE OSTI

DOE OSTI2017

CYCLE MODELING AND OPTIMIZATION OF AN INTEGRALLY GEARED sCO2 COMPANDER

This paper presents the selection of a system configuration and off-design control method for an integrally geared compander based on cycle modeling and optimization. The goal of the cycle modeling was to determine a cycle configuration that would reach an efficiency of 50% at design conditions and to optimize off-design control to maintain high efficiencies. The compander is being developed for use in a concentrated solar power supercritical carbon dioxide power plant with expected turbine inlet temperatures of 705°C and utilizing dry cooling leading to compressor inlet temperature varying between 35°C and 55°C. The compander is unique as it consists of eight turbomachinery stages on four pinions all being driven by a single bull gear. The separate stages offer the opportunity to consider a variety of flow splits and cycle configurations including intercooling and multiple stages of reheat. Cycle modeling was conducted in two stages: on-design and off-design. On-design modeling was simulated with all components operating at their design point. This was used to compare the performance of different cycle configurations and design temperatures. Off-design modeling was then performed to investigate the temperature dependence of the cycle efficiency and power output and to develop a control strategy. Strategies considered and discussed include: turbine bypass, compressor recycle, inlet guide vanes, and inventory control. To determine the best operating conditions for each configuration and control strategy, a genetic algorithm was implemented to optimize the cycle performance across the range of operating temperatures being considered. The final selection of cycle configuration, design temperature and control strategy is also presented.

bennett, jeffrey↗

DOE OSTI2025

Technologies for Enhanced Condensation in sCO 2 Power Cycles

The direct fired supercritical carbon dioxide power cycle has higher efficiency, compact machinery footprint, and is resilient under transient operation. It has been shown that improving the cycle main cooler significantly improves performance, including increased cycle efficiency, decreased cost of electricity and decreased cooler outlet temperatures. One way to improve this process is through enhanced condensation techniques and management of condensation fluid. This manuscript provides an overview of active and passive enhanced condensation technologies, with a focus on the passive approaches. compared to passive approaches, active approaches can have higher heat transfer enhancement, but the additional power and infrastructure can be problematic. The passive approaches identified include microfins (helical and herringbone), corrugated tubing, dimpled tubing and pin fins. After comparison it is found that the microfin geometry has the best performance characteristics followed by the additively manufactured pin fins. It is noted that current literature around additively manufactured enhancements is lacking, and investigation of conventional as well as novel geometries fabricated in this manner may be worth further investigation. Benchmark correlations for these geometries are identified and their limitations outlined. For further investigation, a matrix of test articles is presented for possible experimentation.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗

NASA NTRS2016

Practical Techniques for Modeling Gas Turbine Engine Performance

The cost and risk associated with the design and operation of gas turbine engine systems has led to an increasing dependence on mathematical models. In this paper, the fundamentals of engine simulation will be reviewed, an example performance analysis will be performed, and relationships useful for engine control system development will be highlighted. The focus will be on thermodynamic modeling utilizing techniques common in industry, such as: the Brayton cycle, component performance maps, map scaling, and design point criteria generation. In general, these topics will be viewed from the standpoint of an example turbojet engine model; however, demonstrated concepts may be adapted to other gas turbine systems, such as gas generators, marine engines, or high bypass aircraft engines. The purpose of this paper is to provide an example of gas turbine model generation and system performance analysis for educational uses, such as curriculum creation or student reference.

aerothermodynamics↗

NASA NTRS2016

Practical Techniques for Modeling Gas Turbine Engine Performance

aerothermodynamics↗

NASA NTRS2007

Wetlife Study of Nickel Hydrogen Cells

A study was undertaken to determine the residual Nickel Precharge, and to understand the Performance and Cycle Life of Aged Nickel Hydrogen cells that were in cold storage up to thirteen (13) years. Comsat Technical Services, Aerospace Corporation, and NSWC/Crane test data to date indicate a nominal electrical performance with a small second plateau and the presence of Nickel Precharge in the cells: Cell Teardown, Plate (active Nickel Precharge determination), and Electrolyte Analyses are in progress. Preliminary Thermal Imaging data indicates that older the cell greater the heat generation, but cell over charge (capacity) could dominate heat generation. U.S. Govt. cells has completed 1150 nominal 60% LEO cycles. The completion date for this study is January 31, 2008.

Source record↗

DOE OSTI2018

Performance-Based Incentive Mechanisms in Life-Cycle Contracts

Within the framework of lean production, Russian industry needs to develop and introduce more effective mechanisms ensuring the fulfillment of state orders for capital- and technology-intensive systems, on the basis of performance-based logistics (PBL). In the present work, the introduction of PBL on the basis of a life-cycle contract for a specific program (product) is analyzed. One mechanism recommended in order to overcome the risks of indeterminacy is stepwise correction of incentive systems in the fulfillment of life-cycle contracts (with targeted increase in incentives for the attainment of specified results).

29 ENERGY PLANNING, POLICY, AND ECONOMY↗

DOE OSTI2022

Highly Loaded Sulfur Cathode, Coated Separator and Gel Electrolyte for High Rate Li-Sulfur Batteries

As one of DOE Battery 500 Seedling projects, Cornell University and EIC Labs investigated and developed i) highly loaded sulfur cathodes (> 3 mg/cm 2 ), ii) hybrid separators, and iii) gel ceramic electrolytes (GCE) to mitigate the low rate capability, shuttling effect and limited cycle life in high performance Li-Sulfur batteries. Scalable nanomanufacturing processes such as air-controlled electrospray (ACES) and gas-assisted electrospinning (GAES) have been utilized to develop directly deposited electrodes and polymer/ceramic hybrid separators. First, in the development of highly loaded cathodes, alternating layers of sulfur impregnated mesoporous carbon and graphene were fabricated via ACES and the resulting layered cathodes and coated separators exhibit higher capacity and capacity retention (about 1,000 mAh/g capacity with less than 0.02% fade/cycles) than single layer cathode or cathode prepared by conventional slurry cast. Alternating layer approach via ACES has been applied to high loading systems (3 - 5 mg S/cm 2 ), demonstrating the potential to increase sulfur utilization and capacity retention. We have also incorporated iron oxides (Fe 3 O 4 ) into S/mesoporous carbon/graphene cathodes to enhance sulfur utilization and mitigation of polysulfide shuttling. and the effect of Fe 3 O 4 in mesoporous carbon and Gr is highly pronounced at high C rates of 1C and 2C cycling performance. To further improve the cathodes at high rates, graphene nanoribbons (GNR) which can promote ion transport were incorporated in the cathode, resulting in 550 mAh/g at 5C/5C rates. Hybrid Li-ion/Li-S cathodes has also been explored to better engage unreacted polysulfides during charge/discharge. S/LFP hybrid cathodes offer higher sulfur utilization and enhanced rate capability, as well as higher areal loading. This study suggests inclusion of iron phosphide (Fe2P) which can chemically interact with polysulfides can further enhance sulfur utilization and mitigation of soluble polysulfides at high rates. Secondly, in the development of hybrid separators, we first employed graphene coating on the commercial polyolefin separators, which exhibits higher capability, better capacity retention and enhanced rate capability. To improve the rate capability with enhanced safety features such as thermal stability and nonflammability, we developed polymer/ceramic hybrids based on thermally stable polyimide (PI) and room temperature curable ceramic precursors such as organopolysilazane (OPSZ) or polysilsesquioxanes (PSSQ), which exhibit no shrinkages up to 300 ºC and non-flammability. To improve mechanical properties and electrochemical stability, polybenzimidazole (PBI) and alumina have been incorporated in polymer/ceramic hybrid separator, replacing PI and OPSZ/PSSQ, respectively. Finally, the gel ceramic electrolyte (GCE) based on ceramic cross linkers have been applied to make Li-S cells even safer and also to mitigate the polysulfide shuttling further. The resulting gel ceramic electrolyte offers improved capacity retention and rate capability, and also effectively mitigates polysulfide shuttling which was also confirmed by modeling. Inclusion of high ion conducting additives into GCE together with polymer/ceramic hybrid separators exhibit the higher ionic conductivity than liquid electrolyte with commercial polyolefin separator. We demonstrated that the developed highly loaded sulfur cathodes, polymer/ceramic hybrid separators and gel ceramic electrolyte can effectively mitigate the low rate capability, shuttling effect and limited cycle life in high performance Li-Sulfur batteries with improved safety.

25 ENERGY STORAGE↗

DOE OSTI2016

Electron/Ion Transport Enhancer in High Capacity Li-Ion Battery Anodes

In this paper, magnetite (Fe 3 O 4 ) was used as a model high capacity metal oxide active material to demonstrate advantages derived from consideration of both electron and ion transport in the design of composite battery electrodes. The conjugated polymer, poly[3-(potassium-4-butanoate) thiophene] (PPBT), was introduced as a binder component, while polyethylene glycol (PEG) was coated onto the surface of Fe 3 O 4 nanoparticles. The introduction of PEG reduced aggregate size, enabled effective dispersion of the active materials and facilitated ionic conduction. As a binder for the composite electrode, PPBT underwent electrochemical doping which enabled the formation of effective electrical bridges between the carbon and Fe 3 O 4 components, allowing for more efficient electron transport. Additionally, the PPBT carboxylic moieties effect a porous structure, and stable electrode performance. Finally, the methodical consideration of both enhanced electron and ion transport by introducing a carboxylated PPBT binder and PEG surface treatment leads to effectively reduced electrode resistance, which improved cycle life performance and rate capabilities.

25 ENERGY STORAGE↗

NASA NTRS2002

Impact of Charge Methodology Upon the Performance of Lithium Ion Cells

This viewgraph gives an overview on the impact of charge methodology upon the performance of lithium ion cells. Charge characteristics are given on the following: (1) lithium ion prototype cells, including charge rate characteristics at different temperatures, the effect of charge methodology upon cycle life performance, the effect of charge voltage upon cell performance; (2) three-electrode cells; and (3) lithium-ion eight-cell batteries.

Smart, M. C.↗

NASA NTRS2008

High-Pressure Oxygen Generation for Outpost EVA

Low Lunar Orbit (LLO) poses unique thermal challenges for the orbiting space craft, particularly regarding the performance of the radiators. The emitted infrared (IR) heat flux from the lunar surface varies drastically from the light side to the dark side of the moon. Due to the extremely high incident IR flux, especially at low beta angles, a radiator is oftentimes unable to reject the vehicle heat load throughout the entire lunar orbit. One solution to this problem is to implement Phase Change Material (PCM) Heat Exchangers. PCM Heat Exchangers act as a "thermal capacitor, storing thermal energy when the radiator is unable to reject the required heat load. The stored energy is then removed from the PCM heat exchanger when the environment is more benign. Because they do not use an expendable resource, such as the feed water used by sublimators and evaporators, PCM Heat Exchangers are ideal for long duration Low Lunar Orbit missions. The Advanced Thermal Control project at JSC is completing a PCM heat exchanger life test to determine whether further technology development is warranted. The life test is being conducted on four nPentadecane, carbon filament heat exchangers. Fluid loop performance, repeatability, and measurement of performance degradation over 2500 meltfreeze cycles will be performed and reported in the current document.

Jeng, Frank↗

NASA NTRS2001

Impact of Charge Methodology upon the Performance of Lithium Ion Cells

lithium ion cells↗

DOE OSTI2018

Imaging of 3D morphological evolution of nanoporous silicon anode in lithium ion battery by X-ray nano-tomography

Nanostructured silicon with its high theoretical capacity and ability to accommodate volume expansion has attracted great attention as a promising anode material for Lithium ion (Li-ion) batteries. Liquid metal dealloying method, is a novel method to create nanoporous silicon (np-Si). The assembled Li-ion batteries based on such np- Si anode can be cycled beyond 1500 cycles, in 1000 mA h/g constant capacity cycling mode with consistent performance; however, it suffers from degradation after ~ 460 cycles, while being cycled under 2000 mA h/g. To reveal the failure mechanism and differences in the morphological evolution in different capacity cycling modes in the np-Si anode, we conducted synchrotron X-ray nano-tomography studies. The three dimensional (3D) morphological evolution was visualized and quantified as a function of the number of cycles and cycling capacities. By comparing the 3D morphology under each cycling condition and correlating these 3D morphological changes with cycling-life performance, we elucidate the failure mechanism of the np-Si electrodes resulting from a mesoscopic to macroscopic deformation, involving volume expansion and gradual delamination. In particular, the shorter cycling life in higher-capacity cycling mode stems from particle agglomeration. Overall, while the nanoporous structure can accommodate the volume expansion locally, these mesoscopic and macroscopic deformations ultimately result in heterogeneous stress distribution with faster delamination. As a result, the work thus sheds the light on the importance to consider the structural evolution at the mesoscopic and macroscopic scales, while designing nano-structured energy storage materials for enhanced performances, particularly for long cycling-life durability.

25 ENERGY STORAGE↗

NASA NTRS1990

Capacity decline of ambient temperature secondary Li-TiS2 cells

The main objective of the study described was to identify the causes responsible for the capacity losses observed during cycling of secondary Li-TiS2 cells. Experimental Li-TiS2 cells were fabricated and tested for their cycle life performance. The open circuit voltage of the cells was monitored during the rest period between the charging and discharging. The polarization at the Li and TiS2 electrodes was also monitored during cycling. Cycled cells were disassembled and the cathodes were analyzed by various analytical techniques. The results of the study indicate that the observed capacity loss is almost entirely due to the increased polarization of the TiS2 electrode with cycling. The electrolyte was found to degrade during cycling and the degradation products were found to deposit at the TiS2 electrode, which probably lead to the higher polarization.

Subbarao, S.↗

NASA NTRS1992

Performance measurement for information systems: Industry perspectives

Performance measurement has become a focal topic for information systems (IS) organizations. Historically, IS performance measures have dealt with the efficiency of the data processing function. Today, the function of most IS organizations goes beyond simple data processing. To understand how IS organizations have developed meaningful performance measures that reflect their objectives and activities, industry perspectives on IS performance measurement was studied. The objectives of the study were to understand the state of the practice in IS performance techniques for IS performance measurement; to gather approaches and measures of actual performance measures used in industry; and to report patterns, trends, and lessons learned about performance measurement to NASA/JSC. Examples of how some of the most forward looking companies are shaping their IS processes through measurement is provided. Thoughts on the presence of a life-cycle to performance measures development and a suggested taxonomy for performance measurements are included in the appendices.

Bishop, Peter C.↗

DOE OSTI2015

EDF's used fuel management french policy - 15199

Regarding back-end fuel cycle, EDF's strategy, implemented from the very beginning of French nuclear production, consists in reprocessing of used fuel; decision to recycle plutonium in French PWR was taken from 1984. This reprocessing and recycling strategy, relying on existing industrial facilities (AREVA La Hague and Melox plants), has proven to be reliable and efficient. Treatment leads to a stabilization of used fuel total inventory in interim storage. Vitrification process ensures a safe packaging for high level and long-lived waste under a reduced volume. Recycling of fissile materials saves natural uranium requirements. Concentration of Pu in MOX used fuel leaves open the option to reuse it for starting next Generation IV systems beyond 2040. In 2008, EDF and AREVA, supported by French Government, agreed on commercial terms covering long term fuel reprocessing and recycling (up to 2040). Currently, EDF fuel management strategy relies on flow equilibrium in order to respect fuel cycle consistency and sustainability. The underlying principle is to strictly adjust separated plutonium production to recycling possibilities (i.e. licensed reactors and MOX fuel fabrication facilities). Given that fuel cycle policy, any trend in NPP core management that may impact the fuel cycle should be anticipated within times in order to avoid technical or administrative incompatibilities, and guarantee a high level of safety and robustness. In collaboration with industrial operators, EDF have to perform periodic 'Cycle Impact' analyses and report to the French Nuclear Safety Authority (ASN); next exercise is scheduled by the end of 2016. (authors)

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2021

Thermomechanical and sequential stress performance of photovoltaic backsheets

Photovoltaic backsheet technology is utilized to protect the interior components of solar modules from environmental stress as well as provide electrical insulation to the module. The growing demand for solar energy and longer module service life requirements have brought backsheet performance into focus. Despite being a protective packaging material, many backsheets have exhibited failure in the field, limiting the performance and service life of entire modules. Most backsheets consist of multiple polymeric layers laminated together using adhesives. A new backsheet, with a high performance polyamide structure, has been developed as the solution to module failure. Primarily, it contains a unique polyamide-ionomer alloy targeted at improved weather resistance. In this study, several photovoltaic industry standard backsheets, and the novel polyamide compositions of multilayered backsheets fabricated from the coextrusion process, were examined using thermomechanical analysis (TMA). The coefficient of thermal expansion (CTE) for entire backsheets and their constituent layers was used to model the thermomechanical behavior of various backsheet constructions. Subsequently, thermal cycling was performed in the TMA to examine the intrinsic thermal behavior of the backsheets. Thermal cycling in the TMA indicates the resilience and dimensional stability in the coextruded structures as opposed to the laminated structures. Lastly, results from a Module Accelerated Sequential Testing (MAST), are included to show the mechanical integrity of these backsheets after sequential exposure to stressors including damp heat, ultra-violet (UV) light radiation, and thermal cycling. The laminate backsheets deteriorated extensively after sequential exposure to these stressors, while the novel coextruded structures retained their physical properties.

14 SOLAR ENERGY↗

DOE OSTI2020

Addition of Chloroform in a Solvent-in-Salt Electrolyte: Outcomes in the Microscopic Dynamics in Bulk and Confinement

Solvent-in-salt electrolytes (SISEs) are a promising alternative to the electrolytes currently used in commercial devices. Despite the SISEs’ advantages, their utilization is not yet realized due to the poor mobility of their chemical species. Here, we explore this problem by adding chloroform to a SISE formed by acetonitrile and a Li-salt. First, we performed illustrative cycling experiments to highlight the potential of this approach. Then, we focused on the description of the microscopic dynamics of the electrolytes and exposed the relevant aspects to be considered for their optimal performance. While the conductivity at low temperatures may be enhanced by the addition of chloroform, only subtle changes occur at room temperature. As revealed by molecular dynamics simulations and quasielastic neutron scattering (QENS) experiments, this effect is related to the preservation of the structure expected for a highly concentrated solution and promotion of the formation of ionic aggregates. These outcomes occur despite the increase in the overall mobility of the chemical species. The dynamics of the electrolytes in porous carbon was also investigated using QENS. In these circumstances, low concentrations of chloroform lead to diffusivities of the molecular species higher than those observed for the bulk electrolytes. As chloroform’s concentration increases, no further changes in the diffusivities are observed. Nonetheless, chloroform is mostly immobilized on the carbon surfaces and this behavior may be intensified at compositions closer to the eutectic mixture.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2021

Development of electronically passivating surfaces to enhance battery performance

For many decades, lithium metal batteries (LMBs) have been studied for their high energy density, though they suffer from high reactivity, which safety concerns such as explosions and fires. These events can occur as a result of degradation due to redox reactions and lithium morphology that evolve during cycling. Mostly, the failure is caused by the electrolyte degradation leading to the creation of a solid electrolyte interphase (SEI), which tends to induce electron leakage, lithium dendrite growth, and capacity decay. SEI formation is practically inevitable. This work investigated the minimization of degradation events by modifying different battery configurations. Modifications were made by exchanging electrolytes, electrode surfaces, and even annexing innovative components. Our goal is to achieve a configuration where Li-ion transfer is facilitated, and electron transfer is limited which would enable a longer lithium metal battery life cycle. When performing these modifications and testing their electrochemical performance, a current reduction was observed when the electrodes were spontaneously coated with preformed SEI. Herein several classes of artificial SEI layers are explored for their ability to form passivating layers through use of a redox active molecule.

25 ENERGY STORAGE↗