General Electric (Germany)

The stator end-windings are critical focus area in large electrical rotating machines, particularly in medium and high voltage motors and generators. These components face numerous challenges due to the elevated voltage gradients, exposure to cooling media, vibration, and the manual, handcrafted nature of their construction. The intricacies involved in forming and connecting the end-windings make them susceptible to more variation than other parts of the winding, potentially introducing imperfections that can impact the reliability and performance of the machines over time. The importance of maintaining and monitoring end-windings cannot be overstated, as they are vital for the overall health and reliability of electrical rotating machines. Continuous improvement and focus on potential interventions are essential for owners, operators, and service engineers. This paper aims to share practical experiences in assessing end-windings, identifying early indications of potential issues, and presenting case studies where corrective actions were successfully implemented to avert catastrophic failures and to improve the service life. The discussion will emphasize also on challenges associated with on-site repairs. Often, there is a pressing need to design specialized tools and engineer processes that can be executed in-situ, ensuring the quality of repairs matches that expected from a dedicated service shop facility. The paper will cover various assessment techniques, both visual and measurable, to highlight areas where existing literature is sparse. This information aims to support engineering and technical consultants in determining the ideal timing for interventions and improving the overall maintenance strategy for stator. By focusing on real-world problems and solutions, this paper intends to provide valuable insights into the end-winding maintenance and repair process. It will offer practical guidance to those involved in the operation/servicing of rotating machines.

Pyrite (FeS2) is the end-product of microbial sulfur cycling in reduced environments and is the main burial pathway of sulfur in marine sediments. Pyrite forms by a series of reactions between sulfide and Fe(II)/Fe(III), and sulfur-metabolizing microorganisms play an important role in mediating their formation. Here we tested microbial pyrite formation by the iron(III)- and sulfur-reducing bacterium Geobacter sulfurreducens in the presence of the Fe(III) (oxyhydr)oxide mineral ferrihydrite and elemental sulfur (S0). Over 6 months of incubation, two main stages were observed for the geochemical evolution of the system. In the initial ferruginous stage, rapid release of aqueous Fe(II) into the solution is accompanied by mackinawite (FeS) formation through the reaction between sulfide and ferrihydrite. In the second sulfidic stage, sulfide and polysulfides accumulate in solution, catalyzing mackinawite’s transformation to greigite (Fe3S4) and eventually to pyrite. Scanning electron microscopy demonstrated that individual spherulitic pyrites formed on the surfaces of elemental sulfur, eventually replacing it completely while still preserving the original shape of the sulfur particles. Hence, elemental sulfur is a significant reactant with key functions in polysulfide formation and templating effect on microbial pyrite formation. Therefore, our results suggest a mechanism for microbial pyrite formation in microenvironments in modern sediments and sulfate-poor ecosystems throughout time (e.g., Archean Earth). Future research will be focused on the bioavailability of microbial pyrite to have a complete picture of the role of pyrite in microbial sulfur cycle.

A cooperative group instructional strategy is being used to teach a unit on neutron transport and diffusion theory in a first-year-graduate level, Reactor Theory course that was formerly presented in the traditional lecture/discussion style.Students are divided into groups of two or three for the duration of the unit.Class meetings are divided into traditional lecture/discussion segments punctuated by cooperative group exercises.The group exercises were designed to require the students to elaborate, summarize, or practice the material presented in the lecture/discussion segments.Both positive interdependence and individual accountability are fostered by adjusting individual grades on the unit exam by a factor dependent upon group achievement.Group collaboration was also encouraged on homework assignments by assigning each group a single grade on each assignment.The results of the unit exam have been above average in the two classes in which the cooperative group method was employed.In particular, the problem solving ability of the students has shown particular improvement.Further, the students felt that the cooperative group format was both more educationally effective and more enjoyable than the lecture/discussion format.

Abstract Funding Acknowledgements Type of funding sources: None. Background Phase-sensitive inversion recovery improves tissue contrast by correcting for imperfect choice of inversion recovery time, however it is challenging to combine with a free-breathing acquisition. Deep learning (DL) algorithms have growing applications in cardiac MRI to improve image quality during image reconstruction. Purpose Here, we introduce a single-shot phase-sensitive myocardial delayed enhancement sequence with respiratory triggering (SShPSMDE-RT) (Figure 1). This novel sequence allows faster free-breathing acquisition of late gadolinium enhancement (LGE) images with reduced motion artifact (Figure 2.a). We combined this with a DL noise reduction algorithm to further improve image quality as compared to a standard segmented breath-hold (BH) PSMDE sequence. Methods 61 subjects (29 male, age 51±15) underwent cardiac MRI with the SShPSMDE-RT sequence and a standard BH sequence. The DL algorithm was applied at increasing levels (DL25, DL50, DL75, DL100) (Figure 2.b). Qualitative metrics were image quality, artifact severity, and diagnostic confidence, graded on a 5-point Likert scale. Quantitative metrics were sharpness of the left ventricle septum border and the LGE region (distance in mm for signal intensity to drop from 80% to 20%), blood-myocardium contrast-to-noise ratio (CNR), LGE-myocardium CNR, LGE signal-to-noise ratio (SNR), and LGE burden. 324 slices were included in the analysis. The sequences were compared via paired T-test. Results 27 subjects had positive LGE as determined by CMR experts. The average time to acquire a slice for SShPSMDE-RT is 4–7 seconds versus ∼30–40 seconds for the BH scan. The single-shot sequence had significantly better image quality (SShPSMDE-RT 2.1±0.8 vs. BH 1.5±0.6, p<0.001), less artifact (1.2±0.5 vs. 2.6±1.1, p<0.001), and better diagnostic confidence (3.4±0.7 vs. 2.6±0.8, p<0.001). Septum sharpness was slightly worse in SShPSMDE-RT images (4.1±1.7 mm vs. 3.8±1.6 mm, p = 0.008), but the DL algorithm improved sharpness of SShPSMDE-RT images such that there was no significant difference compared to BH images (p>0.5). There was no significant difference in LGE sharpness between the sequences. The SShPSMDE-RT images had superior blood-myocardium CNR (17.2±6.9 vs. 16.4±6.0, p = 0.040), LGE-myocardium CNR (12.1±7.2 vs. 10.4±6.6, p = 0.054), and LGE SNR (59.8±26.8 vs. 31.2±24.1, p<0.001); these metrics all improved with application of the DL algorithm. There was no significant difference in measured LGE burden (p = 0.12). Conclusions Our novel SShPSMDE-RT sequence significantly reduces scan time and motion artifact. This free-breathing sequence combined with a DL noise reduction algorithm provides better or similar image quality on both qualitative and quantitative metrics as compared to a standard BH PSMDE sequence. This technique can be used to obtain LGE imaging in patients who are unable to breath-hold or tolerate longer scan times.

Abstract The changing energy landscape leads to a rising demand of more flexible power generation. A system for steam turbine (ST) warm-keeping provides the ability to shutdown conventional power plants during periods with a high share of renewable power. Simultaneously, these power plants are ready for grid stabilization on demand without an excessive consumption of lifetime during the start-up. One technical solution to keep a ST warm is the use of hot air, which is passed through the turbine. In addition, the air supply prevents corrosion during standstill and also enables the prewarming after maintenance or long outages. This paper investigates the warm-keeping process of an intermediate pressure (IP) ST (double-shell configuration) through the use of dynamic numerical finite element (FE) simulations. As a representative test case, warm-keeping calculations during a weekend shutdown (60 h) are conducted to investigate the temperatures, their distribution, and gradients within the rotor and the casing. For this purpose, an improved numerical calculation model is developed. This detailed three-dimensional FE model (including blades and vanes) uses heat transfer correlations conceived for warm-keeping with low air mass flows in gear mode operation. These analytical correlations take heat radiation, convection, and contact heat transfer at the blade roots into account. The thermal boundary conditions (BCs) at the outer walls of the rotor and casing are determined by use of experimental natural cool-down data. The calculation model is finally compared and verified with this dataset. The results offer valuable information about the thermal condition of the ST for a subsequent start-up procedure. The warm-keeping operation with air is able to preserve hot start conditions for any time period. Most of the heat is transferred close to the steam inlet of the turbine, which is caused by similar flow directions of air and steam. Thus, temperatures in the last stages and in the casing remain well below material limits. This allows higher temperatures at the first blade groove of the turbine, which is highly loaded during a turbine startup and thus crucial to the lifetime.

Level of Evidence: 5Technical Efficacy Stage: 1

\nThe neutron scattering properties of water ice are of interest to the nuclear criticality safety community for the transport and storage of nuclear materials in cold environments. The common hexagonal phase ice Ih has locally ordered, but globally disordered, H2O molecular orientations. A 96-molecule supercell is modeled using the VASP ab initio density functional theory code and PHONON lattice dynamics code to calculate the phonon vibrational spectra of H and O in ice Ih. These spectra are supplied to the LEAPR module of the NJOY2012 nuclear data processing code to generate thermal neutron scattering laws for H and O in ice Ih in the incoherent approximation. The predicted vibrational spectra are optimized to be representative of the globally averaged ice Ih structure by comparing theoretically calculated and experimentally measured total cross sections and inelastic neutron scattering spectra. The resulting scattering kernel is then supplied to the MC21 Monte Carlo transport code to calculate time eigenvalues for the fundamental mode decay in ice cylinders at various temperatures. Results are compared to experimental flux decay measurements for a pulsed-neutron die-away diffusion benchmark.\n

Aircraft engines emit particulate matter (PM) that affects the air quality in the vicinity of airports and contributes to climate change. Nonvolatile PM (nvPM) emissions from aircraft turbine engines depend on fuel aromatic content, which varies globally by several percent. It is uncertain how this variability will affect future nvPM emission regulations and emission inventories. Here, we present black carbon (BC) mass and nvPM number emission indices (EIs) as a function of fuel aromatic content and thrust for an in-production aircraft gas turbine engine. The aromatics content was varied from 17.8% (v/v) in the neat fuel (Jet A-1) to up to 23.6% (v/v) by injecting two aromatic solvents into the engine fuel supply line. Fuel normalized BC mass and nvPM number EIs increased by up to 60% with increasing fuel aromatics content and decreasing engine thrust. The EIs also increased when fuel naphthalenes were changed from 0.78% (v/v) to 1.18% (v/v) while keeping the total aromatics constant. The EIs correlated best with fuel hydrogen mass content, leading to a simple model that could be used for correcting fuel effects in emission inventories and in future aircraft engine nvPM emission standards.