bluuebunny/crossref_metadata_2025 huggingface dataset:
Impact of vesicular glutamate leakage on synaptic transmission at the calyx of Held
Authors: Takami Chihiro , Eguchi Kohgaku , Hori Tetsuya , Takahashi Tomoyuki
Published: November 2016

Key points

It is controversial whether glutamate can leak out of vesicles in the nerve terminal.

To address this issue, we abolished vesicular glutamate uptake by washing out presynaptic cytosolic glutamate or by blocking vacuolar ATPase activity using bafilomycin A1.

In the absence of vesicular glutamate uptake, both spontaneous and nerve‐evoked EPSCs underwent a rundown, suggesting that vesicular glutamate can leak out of vesicles.

However, the rundown of evoked EPSCs was caused mainly by accumulation of unfilled vesicles after exocytic release of glutamate, suggesting a minor influence of glutamate leakage on synaptic transmission.

Glutamate leaks out of synaptic vesicles when the transvesicular proton gradient is dissipated in isolated vesicle preparations. In the nerve terminal, however, it is controversial whether glutamate can leak out of vesicles. To address this issue, we abolished vesicular glutamate uptake by washing out presynaptic cytosolic glutamate in whole‐cell dialysis or by blocking vacuolar ATPase using bafilomycin A1 (Baf) at the calyx of Held in mouse brainstem slices. Presynaptic glutamate washout or Baf application reduced the mean amplitude and frequency of spontaneous miniature (m)EPSCs and the mean amplitude of EPSCs evoked every 10 min. The percentage reduction of mEPSC amplitude was much less than that of EPSC amplitude or mEPSC frequency, and tended to reach a plateau. The mean amplitude of mEPSCs after glutamate washout or Baf application remained high above the detection limit, deduced from the reduction of mEPSC amplitude by the AMPA receptor blocker 6‐cyano‐7‐nitroquinoxaline‐2,3‐dione. Membrane capacitance measurements from presynaptic terminals indicated no effect of glutamate washout on exocytosis or endocytosis of synaptic vesicles. We conclude that glutamate can leak out of vesicles unless it is continuously taken up from presynaptic cytosol. However, the magnitude of glutamate leakage was small and had only a minor effect on synaptic responses. In contrast, prominent rundowns of EPSC amplitude and mEPSC frequency observed after glutamate washout or Baf application are likely to be caused by accumulation of unfilled vesicles in presynaptic terminals retrieved after spontaneous and evoked glutamate release.
Simultaneous Schlieren–PLIF Studies for Ignition and Soot Luminosity Visualization With Close-Coupled High-Pressure Double Injections of n-Dodecane
Authors: Moiz Ahmed Abdul , Cung Khanh D. , Lee Seong-Young
Published: November 2016

Studies are performed in a constant volume preburn type combustion vessel over a range of ambient temperatures (750 K, 800 K, and 900 K) at constant density (22.8 kg/m3) with 15% O2 by volume in the ambient at 1200 bar (n-dodecane) fuel injection pressure. The influence of the pilot (first) spray flame on the ignition and combustion characteristics of the main (second) injection is investigated while varying injection pressure, dwell time, and injection strategy. Simultaneous schlieren (with soot luminosity imaging) and 355 nm planar laser-induced fluorescence (PLIF) imaging for formaldehyde (CH2O) and polycyclic aromatic hydrocarbons (PAH) visualization was performed. At both 900 K and 800 K ambient, main injection exhibits a reduction in ignition delay (ID) by a factor of 2 over their respective pilots. For the ambient temperature condition of 750 K, reducing injection pressure from 1500 bar to 1200 bar causes a significant increase in ignition delay (by ∼0.8 ms), which was attributed to the influence of injection pressure on spray-mixing and early development of cool flame. Also, at 750 K ambient condition, multiple injection schedule having two 0.5 ms injections separated by a 0.5 ms dwell was found to have a shorter ignition delay than a single 0.5 ms injection. Studies carried at an 800 K ambient show that by increasing the dwell time, main interaction with pilot reactive intermediates can be controlled to avoid an early rich ignition of the main spray and to reduce soot precursors.
Laboratory Infrared Thermal Assessment of Laser-Sintered High-Pressure Nozzle Guide Vanes to Derisk Engine Design Programs
Authors: Kirollos Benjamin , Povey Thomas
Published: November 2016

The continuing maturation of metal laser-sintering technology (direct metal laser sintering (DMLS)) presents the opportunity to derisk the engine design process by experimentally down-selecting high-pressure nozzle guide vane (HPNGV) cooling designs using laboratory tests of laser-sintered—instead of cast—parts to assess thermal performance. Such tests could be seen as supplementary to thermal-paint test engines, which are used during certification to validate cooling system designs. In this paper, we compare conventionally cast and laser-sintered titanium alloy parts in back-to-back experimental tests at engine-representative conditions over a range of coolant mass flow rates. Tests were performed in the University of Oxford Annular Sector Heat Transfer Facility. The thermal performance of the cast and laser-sintered parts—measured using new infrared processing techniques—is shown to be very similar, demonstrating the utility of laser-sintered parts for preliminary engine thermal assessments. We conclude that the methods reported in this paper are sufficiently mature to make assessments which could influence engine development programs.
Visualizations of Flow Structures in the Rotor Passage of an Axial Compressor at the Onset of Stall
Authors: Chen Huang , Li Yuanchao , Tan David , Katz Joseph
Published: November 2016

Experiments preformed in the JHU refractive index matched facility examine flow phenomena developing in the rotor passage of an axial compressor at the onset of stall. High-speed imaging of cavitation performed at low pressures qualitatively visualizes vortical structures. Stereoscopic particle image velocimetry (SPIV) measurements provide detailed snapshots and ensemble statistics of the flow in a series of meridional planes. At prestall condition, the tip leakage vortex (TLV) breaks up into widely distributed intermittent vortical structures shortly after rollup. The most prominent instability involves periodic formation of large-scale backflow vortices (BFVs) that extend diagonally upstream, from the suction side (SS) of one blade at midchord to the pressure side (PS) near the leading edge of the next blade. The 3D vorticity distributions obtained from data recorded in closely spaced planes show that the BFVs originate form at the transition between the high circumferential velocity region below the TLV center and the main passage flow radially inward from it. When the BFVs penetrate to the next passage across the tip gap or by circumventing the leading edge, they trigger a similar phenomenon there, sustaining the process. Further reduction in flow rate into the stall range increases the number and size of the backflow vortices, and they regularly propagate upstream of the leading edge of the next blade, where they increase the incidence angle in the tip corner. As this process proliferates circumferentially, the BFVs rotate with the blades, indicating that there is very little through flow across the tip region.
On the Effectiveness of Composites for Repair of Pipelines Under Various Combined Loading Conditions: A Computational Approach Using the Cohesive Zone Method
Authors: Shadlou Shahin , Taheri Farid
Published: November 2016

ASTM PCC-2 standard provides a series of equations for establishing the composite repair's thickness required for bringing the capacity of dented/damaged pipes, to their original design state. However, the accuracy of the equations' predictions for pipes subjected to various combined loadings has not been fully explored. Moreover, the influence of the state of a pipe/composite wrap (CW) interface (i.e., whether perfectly intact or not intact), in reference to the predictions of the ASTM equations, has not been studied either. In consideration of the above-mentioned issues, a comprehensive finite-element (FE) study is conducted, using the cohesive zone methodology (CZM) to simulate the response of pipes repaired with composite wraps, under single and various combined loading conditions. Moreover, the influence of perfect (or tied) and imperfect (unintact) pipe/CW interface on the load-bearing capacity of repaired pipes is systematically investigated. Finally, the effects of composite repairs' thickness and length on their efficacy are also investigated. The results show that, although the pipe/CW interface state does not have any noticeable effect when the pipe is subjected to a combined loading state of bending moment and internal pressure, it plays a crucial role when the pipe is under a combined internal pressure and uniaxial loading condition. Furthermore, the predicted values calculated according to the ASME standard are compared with the finite-element results, demonstrating that ASTM-based predictions do not provide accurate results when a repaired pipe is subjected to an axial loading condition.
Engineering Approach Based on Reference Stress Concept for Calculating J and Crack Opening Displacement of Complex-Cracked Pipes
Authors: Jeong Jae-Uk , Choi Jae-Boong , Huh Nam-Su , Shim Do-Jun , Kim Yun-Jae
Published: November 2016

In this study, an engineering approach for estimations of fracture mechanics parameters, i.e., J-integral and crack opening displacement (COD), for complex-cracked pipes was suggested based on reference stress concept, where stress-strain data of the material was used to assess structural integrity of complex-cracked pipes. In the present study, new reference loads that can reduce the dependency on strain hardening of the material have been suggested for complex-cracked pipes under each loading mode. By using the proposed optimized reference load for complex-cracked pipes, J-integral and COD estimation procedures have been proposed based on the reference stress concept together with the elastic solutions for complex-cracked pipes. The predicted J-integrals and CODs based on the proposed method have been validated against published experimental data and FE results using actual stress–strain data. Moreover, the predictions using the proposed methods are also compared with those using the existing solutions for simple through-wall cracks (TWCs) based on reduced thickness analogy concept.
Bi-BCM: A Closed-Form Solution for Fixed-Guided Beams in Compliant Mechanisms
Authors: Ma Fulei , Chen Guimin
Published: November 2016

A fixed-guided beam, with one end is fixed while the other is guided in that the angle of that end does not change, is one of the most commonly used flexible segments in compliant mechanisms such as bistable mechanisms, compliant parallelogram mechanisms, compound compliant parallelogram mechanisms, and thermomechanical in-plane microactuators. In this paper, we split a fixed-guided beam into two elements, formulate each element using the beam constraint model (BCM) equations, and then assemble the two elements' equations to obtain the final solution for the load–deflection relations. Interestingly, the resulting load–deflection solution (referred to as Bi-BCM) is closed-form, in which the tip loads are expressed as functions of the tip deflections. The maximum allowable axial force of Bi-BCM is the quadruple of that of BCM. Bi-BCM also extends the capability of BCM for predicting the second mode bending of fixed-guided beams. Besides, the boundary line between the first and the second modes bending of fixed-guided beams can be easily obtained using a closed-form equation. Bi-BCM can be immediately used for quick design calculations of compliant mechanisms utilizing fixed-guided beams as their flexible segments (generally no iteration is required). Different examples are analyzed to illustrate the usage of Bi-BCM, and the results show the effectiveness of the closed-form solution.
Modeling and Robust Low Level Control of an Omnidirectional Mobile Robot
Authors: Comasolivas Ramon , Quevedo Joseba , Escobet Teresa , Escobet Antoni , Romera Juli
Published: November 2016

This paper presents the modeling and robust low-level control design of a redundant mobile robot with four omnidirectional wheels, the iSense Robotic (iSRob) platform, that was designed to test safe control algorithms. iSRob is a multivariable nonlinear system subject to parameter uncertainties mainly due to friction forces. A multilinear model is proposed to approximate the behavior of the system, and the parameters of these models are estimated from closed-loop experimental data applying Gauss–Newton techniques. A robust control technique, quantitative feedback theory (QFT), is applied to design a proportional–integral (PI) controller for robust low-level control of the iSRob system, being this the main contribution of the paper. The designed controller is implemented, tested, and compared with a gain-scheduling PI-controller based on pole assignment. The experimental results show that robust stability and control effort margins against system uncertainties are satisfied and demonstrate better performance than the other controllers used for comparison.
Adaptive Self-Learning Fuzzy Autopilot Design for Uncertain Bank-to-Turn Missiles
Authors: Rong Hai-Jun , Yang Zhao-Xu , Wong Pak Kin , Vong Chi Man
Published: November 2016

This paper proposes an adaptive self-learning fuzzy autopilot design for uncertain bank-to-turn (BTT) missiles due to external disturbances and system errors from the variations of the aerodynamic coefficients and control surface loss. The self-learning fuzzy systems called extended sequential adaptive fuzzy inference systems (ESAFISs) are utilized to compensate for these uncertainties in an adaptive backstepping architecture. ESAFIS is a real‐time self-learning fuzzy system with simultaneous structure identification and parameter learning. The fuzzy rules of the ESAFIS can be added or deleted based on the input data. Based on the Lyapunov stability theory, adaptation laws are derived to update the consequent parameters of fuzzy rules, which guarantees both tracking performance and stability. The robust control terms with the adaptive bound-estimation schemes are also designed to compensate for modeling errors of the ESAFISs by augmenting the self-learning fuzzy autopilot control laws. The proposed autopilot is validated under the control surface loss, aerodynamic parameter perturbations, and external disturbances. Simulation study is also compared with a conventional backstepping autopilot and a neural autopilot in terms of the tracking ability. The results illustrate that the designed fuzzy autopilot can obtain better steady‐state and transient performance with the dynamically self-learning ability.
Mitigating the Effects of Sensor Uncertainties in Networked Multi-Agent Systems
Authors: Arabi Ehsan , Yucelen Tansel , Haddad Wassim M.
Published: November 2016

Networked multi-agent systems consist of interacting agents that locally exchange information, energy, or matter. Since these systems do not in general have a centralized architecture to monitor the activity of each agent, resilient distributed control system design for networked multi-agent systems is essential in providing high system performance, reliability, and operation in the presence of system uncertainties. An important class of such system uncertainties that can significantly deteriorate the achievable closed-loop system performance is sensor uncertainties, which can arise due to low sensor quality, sensor failure, sensor bias, or detrimental environmental conditions. This paper presents a novel distributed adaptive control architecture for networked multi-agent systems with undirected communication graph topologies to mitigate the effect of sensor uncertainties. Specifically, we consider agents having identical high-order, linear dynamics with agent interactions corrupted by unknown exogenous disturbances. We show that the proposed adaptive control architecture guarantees asymptotic stability of the closed-loop dynamical system when the exogenous disturbances are time-invariant and uniform ultimate boundedness when the exogenous disturbances are time-varying. Two numerical examples are provided to illustrate the efficacy of the proposed distributed adaptive control architecture.
Model-Based Control for Mode Transition Between Spark Ignition and HCCI Combustion
Authors: Zhang Shupeng , Song Ruitao , Zhu Guoming G. , Schock Harold
Published: November 2016

While the homogeneous charge compression ignition (HCCI) combustion has its advantages of high thermal efficiency with low emissions, its operational range is limited in both engine speed and load. To utilize the advantage of the HCCI combustion, an HCCI capable spark ignition (SI) engine is required. One of the key challenges of developing such an engine is to achieve smooth mode transition between SI and HCCI combustion, where the in-cylinder thermal and charge mixture properties are quite different due to the distinct combustion characteristics. In this paper, a control strategy for smooth mode transition between SI and HCCI combustion is developed and experimentally validated for an HCCI capable SI engine equipped with electrical variable valve timing (EVVT) systems, dual-lift valves, and electronic throttle control (ETC) system. During the mode transition, the intake manifold air pressure is controlled by tracking the desired throttle position updated cycle-by-cycle; and an iterative learning fuel mass controller, combined with sensitivity-based compensation, is used to manage the engine torque in terms of net mean effective pressure (NMEP) at the desired level for smooth mode transition. Note that the NMEP is directly correlated to the engine output torque. Experiment results show that the developed controller is able to achieve smooth combustion mode transition, where the NMEP fluctuation is kept below 3.8% during the mode transition.
An Analytical Model for Contact Pressure Prediction Considering Dimensional Error of Stamped Bipolar Plate and Gas Diffusion Layer in Proton Exchange Membrane Fuel Cell Stack Assembly
Authors: Peng Linfa , Qiu Diankai , Yi Peiyun , Lai Xinmin
Published: November 2016

Contact pressure distribution between bipolar plate (BPP) and gas diffusion layer (GDL) has significant impact on performance and life time of proton exchange membrane (PEM) fuel cell. Most current studies for contact pressure prediction are based on finite-element analysis (FEA), requiring huge computation for the whole fuel cell assembly. Comparatively speaking, the more generalized and well-developed analytical methods are deficient in this field. The objective of this study is to propose a full-scale continuous equivalent model to predict GDL contact pressure effectively in the PEM fuel cell. Using the model, the nonuniform pressure distribution resulted from dimensional errors of metallic BPP and GDL could be obtained. First, a parameterized theoretical model of BPP/GDL assembly is established based on equivalent stiffness analysis of components, and definition methods of dimensional errors are proposed according to actual measurements and Monte Carlo simulation (MCS). Then, experiments are carried out to obtain the actual GDL contact pressure and the model results show good agreement with experimental results. At last, effects of dimensional errors are investigated. Acceptable assembly pressure for a given fuel cell is suggested based on the model. This model is helpful to understand the effect of the dimensional errors, and it also could be adopted to guide the manufacturing of BPP, GDL, and the assembling of PEM fuel cell.
Apparent Emissivity of Combustion Soot Aggregate Coating at High Temperature
Authors: Ran Fu Tai , Bin Tian Ji , Sheng Wang Hua
Published: November 2016

Soot aggregates frequently occur during combustion or pyrolysis of fuels. The radiative properties of soot aggregates at high temperature are important for understanding soot characteristics and evaluating heat transfer in combustion systems. However, few data for soot radiative properties at high temperature were available. This work experimentally investigated the apparent emissivity of the soot aggregate coating at high temperature using spectral and total hemispherical measurements. The soot aggregate coatings were formed on nickel substrates by a paraffin flame. The surface and inner morphology of the coatings were characterized by scanning electron microscope (SEM). The thickness of the coating was 30.16 μm so the contribution of the smooth nickel substrate to the apparent radiation from the coating could be neglected. The total hemispherical emissivity of the coating on the nickel substrate was measured using the steady-state calorimetric method at different temperatures. The spectral directional emissivity of the coating was measured for the wavelength of 0.38–16.0 μm at the room temperature. The measurements show that the total hemispherical emissivity decreases from 0.895 to 0.746 as the temperature increases from 438 K to 1052 K. The total hemispherical emissivity of the coating deposited on the nickel substrate is much larger than those of the nickel substrate and a nickel oxidization film. The measured spectral emissivity of the coating at the room temperature was used to theoretically calculate the total hemispherical emissivity at different temperatures by integration with respect to wavelength. The measured and calculated total hemispherical emissivities were similar, but their changes relative to temperature were completely opposite. This difference is due to the fact that the spectral emissivity of the coating is a function of temperature. The present results provide useful reference data for analyzing radiative heat transfer at high temperature of soot aggregates in combustion processes.
Effects of Rotation and Buoyancy Forces on the Flow Field Behavior Inside a Triangular Rib Roughened Channel
Authors: Furlani Luca , Armellini Alessandro , Casarsa Luca
Published: November 2016

The flow field inside a triangular cooling channel for the leading edge of a gas turbine blade has been investigated. The efforts were focused on the investigation of the interaction between effects of rotation, of buoyancy forces, and those induced by turbulence promoters, i.e., perpendicular square ribs placed on both leading and trailing sides of the duct. Particle image velocimetry (PIV) and stereo-PIV measurements have been performed for ReDh = 104, rotation number of 0, 0.2, and 0.6, and buoyancy parameter equal to 0, 0.08, and 0.7. Coriolis secondary flows are detected in the duct cross section, but contrary to the smooth case, they are characterized by a single main vortex and are less affected by an increase of the rotation parameter. Moreover, their main topology is only marginally sensitive to the buoyancy forces. Conversely, the features of the recirculation structure downstream the ribs turned out to be more sensitive to both the buoyancy forces and to the stabilizing/destabilizing effect on the separated shear layer induced by rotation.
Thermodynamic Analysis of an Advanced Solar-Assisted Compressed Air Energy Storage System
Authors: Udell Kent , Beeman Michael
Published: November 2016

The performance of CAES is evaluated for various configurations, with and without thermal energy storage. First, a conventional compressed air energy storage process is modeled using a time series iterative forward differencing method to simulate the round trip efficiency, exergy storage, cavern temperatures and pressures, and the gas expander exit temperature of a CAES plant. The computational model was validated experimentally by comparing trended data of the compression cycle of a 280 HP Gardener-Denver tandem horizontal two-stage compressor to computational results. It was found that the process of cooling the compressors resulted in a large exergy loss and the inefficiencies of the expanders lead to higher temperature gas being exhausted back to ambient pressures. Second, Advanced Adiabatic Compressed Air Energy Storage (AACAES) was simulated to study the effectiveness of storing the thermal energy removed from the compressors to be added to the compressed air as it enters the expanders at a later time. Third, the concept of increasing the capacity of the thermal energy storage systems to allow recharge with concentrated solar heat was explored. It was found that the thermal efficiency of converting the solar thermal energy to power would be high (> 60%). Further, the expander exhaust temperature and exergy are high (> 500 K), implying that additional waste heat energy recovery will be possible. Taken together, the results of this study show that an integrated, high efficiency, on-demand, water-free, solar energy delivery system is possible if combined with an AACAES system.
On the Recent Climatological and Energy Trends in Mexico City
Authors: Lentz Alvaro E. , Angeles Moises , Glenn Equisha , Ramírez Nazario , González Jorge E.
Published: November 2016

This is a first report of a comprehensive effort to determine the nexus between energy demands, population growth, and a changing climate for Mexico region. We first report here Mexico City climatology, trends in temperatures, heat index and heat waves registered in the Valley of Mexico and its potential relation to electricity consumption. The work is motivated by the environmental impacts that densely populated cities such as Mexico City produces manifested by energy consumption and emissions to the environment and direct consequences in the quality of its inhabitants and on the local environment. We used eight weather stations spread over the valley of Mexico to analyze temporal trends of maximum and minimum daily temperatures and relative humidity. The heat index and the human discomfort index are derived as tools to determine trends in environmental variables that may be linked to energy demands in the Valley. The actual power consumption in the valley of Mexico are further analyzed for formulating relationship between power consumption and maximum temperatures during long-term scenarios and during specific extreme heat events. The relationship between power consumption with changes in the population in the valley of Mexico is also investigated.
Numerical Analysis of a Large-Scale Hydraulic Wind Farm With Integrated Hydraulic Energy Storage
Authors: Buhagiar Daniel , Sant Tonio
Published: November 2016

Offshore wind farms are presently facing numerous technical challenges that are affecting their viability. High failure rates of expensive nacelle-based electronics and gearboxes are particularly problematic. On-going research is investigating the possibility of shifting to a seawater-based hydraulic power transmission, whereby wind turbines pressurise seawater that is transmitted across a high-pressure pipeline network. A 9-turbine hydraulic wind farm with three different configurations is simulated in the present work and a previously developed method for open-loop pressure control of a single turbine has been adapted for this multiple-turbine scenario. A conceptual quasi-constant-pressure accumulator is also included in the model. This system is directly integrated within each hydraulic wind turbine and it allows the output power from the wind farm to be scheduled on an hourly basis. The shift in control methodology when integrating storage is illustrated in the present work. Simulation results indicate a strong relationship between hydraulic performance attributes and the specific wind turbine array layout. The beneficial effects of storage can also be observed, particularly in smoothing the output power and rendering it more useable. Finally, the energy yields from 24-hour simulations of the 9-turbine wind farms are calculated. Integrated storage leads to a slight increase in yield since it eliminates bursts of high flow, which induce higher frictional losses in the pipeline network.
Fuel Cell Temperature Control With a Pre-Combustor in SOFC Gas Turbine Hybrids During Load Changes
Authors: Zaccaria Valentina , Branum Zachary , Tucker David
Published: November 2016

The use of high temperature fuel cells, such as Solid Oxide Fuel Cells (SOFCs), for power generation, is considered a very efficient and clean solution to conservation of energy resources. Especially when the SOFC is coupled with a gas turbine, the global system efficiency can go beyond 70% on natural gas LHV. However, the durability of the ceramic material and the system operability can be significantly penalized by thermal stresses due to temperature fluctuations and non-even temperature distributions. Thermal management of the cell during load following is therefore very critical.

The purpose of this work was to develop and test a pre-combustor model for real-time applications in hardware-based simulations, and to implement a control strategy in order to keep cathode inlet temperature as constant as possible during different operative conditions of the system. The real-time model of the pre-combustor was incorporated into the existing SOFC model and tested in a hybrid system facility, where a physical gas turbine and hardware components were coupled with a cyber-physical fuel cell for flexible, accurate, and cost-reduced simulations.

The control of the fuel flow to the pre-combustor was proven to be very effective in maintaining a constant cathode inlet temperature during a step change in fuel cell load. After imposing a 20 A load variation to the fuel cell, the controller managed to keep the temperature deviation from the nominal value below 0.3% (2 K). Temperature gradients along the cell were maintained below 10 K/cm. An efficiency analysis was performed in order to evaluate the impact of the pre-combustor on the overall system efficiency.
On-Line Performance Monitoring and Diagnostics for Large Combined Cycle Power Plant
Authors: Chudnovsky B. , Levin L. , Talanker A. , Mankovsky V. , Kunin A.
Published: November 2016

Diagnostics of large size combined-cycle power plant components (such as: Gas Turbine, HRSG, Steam Turbine and Condenser) plays a significant role in improving power plant performance, availability, reliability and maintenance scheduling. In order to prevent various faults in cycle operation and as a result a reliability reduction, special monitoring and diagnostic techniques is required, for engineering analysis and utility production management.

In this sense an on-line supervision system has developed and implemented for 370 MW combined-cycle. The advanced diagnostic methodology is based on a comparison between actual and target conditions. The actual conditions are calculated using data set acquired continuously from the power plant acquisition system. The target conditions are calculated either as a defined actual best operation (Manufacturer heat balances) or by means of a physical model that reproduces boiler and plant performance at off-design. Both sets of data are then compared to find the reason of performance deviation and then used to monitor plant degradation, to support plant maintenance and to assist on-line troubleshooting. The performance calculation module provides a complete Gas Turbine, HRSG and Steam Turbine island heat balance and operating parameters. This paper describes a study where an on-line performance monitoring tool was employed for continuously evaluating power plant performance. The methodology developed and summarized herein has been successfully applied to large size 360–370 MW combined cycles based on GE and Siemens Gas Turbines, showing good capabilities in estimating the degradation of the main equipment during plant lifetime. Consequently, it is a useful tool for power plant operation and maintenance.
Damage Mechanisms Found in Generator Rotor 18Mn18Cr Retaining Rings
Authors: Moore William
Published: November 2016

Generator rotor retaining rings are one of the most highly stressed components in the generator rotor. Additionally, some retaining ring materials such as 18Mn5Cr, have been susceptible to Stress Corrosion Cracking (SCC). 18Mn18Cr retaining ring material has been used to replace older 18Mn5Cr material rings with great success. The 18Mn18Cr material has been found to be resistant to SCC in the presence of moisture. Recently, one OEM (Original Equipment Manufacturer) called for inspections of 18Mn18Cr rings, despite its reliable performance in the industry. Although resistant to SCC, some 18Mn18Cr rings have been found with cracks and other damage. The author’s company felt that it would be of value to go back through past job records with rotors that were identified to have 18Mn18Cr retaining rings, and review those records and report on the results of ring inspections due to damage. The author’s company typically rewinds dozens of rotors per year, with many of the rings manufactured from 18Mn18Cr. As part of a rewind, rings are disassembled and inspected. Of course, many rewinds are done because of failures, mostly related to the field winding. An XRF (X-Ray Fluorescence) analyzer is used to determine a ring’s composition. It has excellent accuracy, and can easily distinguish between 18Mn18Cr material and other non-magnetic steels, such as the once common 18Mn5Cr. Magnetic rings are easily distinguishable by a magnet, by manufacturer and rating, and / or by ventilation method.

A total of seventeen (17) 18Mn18Cr ring metallurgical investigation reports were reviewed. These metallurgical investigations were conducted between 2008 and 2014. Reports reviewed included only those retaining ring inspections that were done to diagnose some visible damage to one or two retaining rings. In other words, if an 18Mn18Cr retaining had some indication of damage, the detailed inspection report and analysis was included and reviewed as part of this paper. Rings that were inspected and had no issues are not included. Rings that had damage due to some obvious man-made issues were not included. For example, one generator rotor had an 18Mn18Cr ring that had an obvious grinding wheel cut. The owner was aware that this damage had occurred during a prior repair. This metallurgical investigation was not included in this study. Another finding not included in this study was an 18Mn18Cr retaining ring with a high hardness variation, well beyond the tolerance standards and acceptance criteria used by NEC. Since there was no physical damage to the ring surface and no cracking, pitting or other abnormality present, this ring’s inspection report was also excluded. Only rings with some type of visual evidence of pitting, corrosion, fretting or material upset were included and make up the 17 generator rotors.
A Study on Superheat Utilization of Extraction Steam in a 1000MW Double Reheat Ultra-Supercritical Unit
Authors: Wang Weiliang , Zhang Hai , Lv Junfu , Ni Weidou , Li Yongsheng , Liu Jianmin
Published: November 2016

The world’s first 1000MW double reheat ultrasupercritical unit has been in operation since September 25th, 2015 in Taizhou, China. The thermal efficiency at turbine heat-rate acceptance (THA) condition is around 51%, which is the highest among all condensing units in coal-fired power plants around the world. However, the resultant superheat degree of the extraction steam is relatively high, leading to a large temperature difference in heat transfer process in the regenerative system, thereby a great exergy loss.

In order to utilize the superheat of turbine bleeds more effectively, we present a scheme by employing an outer steam cooler (OSC) after the last high pressure heater in series to use the superheat to heat the feed water. Based on the newly installed unit in Taizhou, we examine the energy saving effect of the superheat utilization of different bleeds and their possible combinations respectively. The influencing factors of the mass flow rate, superheat, and effective superheat of the extraction steam are studied.

Thermodynamic analyses revealed that the second extraction steam has not only high effective superheat, but also large mass flow rate, so in the overall efficiency improvement it ranks first and the third extraction steam ranks second. Although the fourth extraction steam has the largest superheat, it ranks third as the result of relatively lower mass flow rate. It was found that at nominal load, by adopting OSC’s to utilize the superheat of the second to sixth extraction steam, temperature of the feed water can increase by 8.1 °C, 3.5 °C, 2.6 °C, 1.1 °C, and 1 °C respectively, and the net coal consumption reduces by 0.73g/kWh, 0.47g/kWh, 0.40g/kWh, 0.21g/kWh and 0.22g/kWh accordingly.

Consequently, three possible schemes are recommended for future design: one is to adopt one OSC to utilize the superheat of the second extraction steam, in return of 8.1°C increment in feed water temperature and 0.73g/kWh reduction of the net coal consumption; the second is to adopt two OSC’s to utilize the superheat of the second and third extraction steam at the same time, in return of 11.4 °C increment in feed water temperature and 1.21g/kWh reduction of the net coal consumption; and the last is to apply three OSC’s to utilize the superheat of the second to the fourth extraction steam simultaneously, to achieve 13.9°C increment in feed water temperature, and 1.62g/kWh reduction of the net coal consumption.
Efficiency Optimization of Four Gas Turbine Power Plant Configurations
Authors: Almodarra Sultan , Alabdulkarem Abdullah
Published: November 2016

Gas turbine power plants fueled by natural gas are common due to their quick start-up operation and low emissions compared with steam power plants that are directly fired. However, the efficiency of basic gas turbine power plant is considered low. Any improvement in the efficiency would result in fuel savings as well as reduction in CO2 emissions. One way to improve the efficiency is to utilize exhaust gas waste heat. Two waste heat utilization options were considered. The first option was to run a steam power plant (i.e. combined cycle power plant) while the other option was to use a regenerator which reduces the size of the combustion chamber. The regenerator utilizes the waste heat to preheat the compressed air before the combustion chamber. In addition, the efficiency can be improved with compressor intercooling and turbine reheating. In this paper, four gas turbine power plant configurations were investigated and optimized to find the maximum possible efficiency for each configuration. The configurations are (1) basic gas turbine, (2) combined cycle, (3) advanced combined cycle and (4) gas turbine with regenerator, intercooler and reheater. The power plants were modeled in EES software and the basic model was validated against vendor’s data (GE E-class gas turbine Model 7E) with good agreement. Maximum discrepancy was only 3%. The optimization was carried out using conjugate directions method and improvements in the baseline design were as high as 25%. The paper presents the modeling work, baseline designs, optimization and analysis of the optimization results using T-s diagrams. The efficiency of the optimized configurations varied from 49% up 65%.
Generalized Regeneration Theory and its Energy Saving and Emission Reduction Effects on Coal-Fired Power Generation
Authors: Feng Weizhong
Published: November 2016

Concerns related to global warming and environmental pollution concerns have pressured coal-fired power plants to improve efficiency and reduce emissions. However, the conventional efficiency improvement methods — increasing steam pressure and temperature and reducing condenser pressure are limited by material technology and the temperature of the available cooling medium. The next step for increasing efficiency would be to add additional reheat or regenerative cycles, but this is not feasible for existing plants.

In addition, as the share of renewable energy and the grid’s demands on the coal-fired power plants increases, China’s coal-fired units are faced with more and tougher challenges, including large peak-valley gaps, frequent startups and shutdowns and cost pressures. As a result, the boiler combustion efficiency decreases and incidents such as furnace explosions, aggravation and collapsing of slag and burning of facilities located downstream of the economizer become more frequent.

To address these problems, the generalized regeneration theory has been proposed and a series of related technologies have been developed, providing a new approach for not only improving the efficiency of coal-fired power plants, but also resulted in boiler operation that is cleaner and safer. These technologies which include anew boiler startup technology, the high efficiency combustion and low emission technology under low load and the low oxygen, and a low NOx and high efficiency combustion technology under high load have been implemented successfully in the Shanghai Waigaoqiao No. 3 power plant.

By improving the utilization of turbine extraction and reducing the exhaust loss, these innovative technologies greatly improve the environmental performance, efficiency and safety of the units in various operating conditions. In addition, improvements have been made in the boilers ability to adapt to changing coal supplies, particularly for coal with high slagging tendencies and high moisture content.
Numerical Modeling of Liquid-to-Vapor Phase Change in Porous Medium Under Solar Heat Localization
Authors: Bahraseman Hamidreza Ghasemi , Languri Ehsan Mohseni
Published: November 2016

Evaporation process is a crucial part of many fundamental industrials and medicals process. This paper numerically model a novel method of steam generation and enhanced evaporation using solar thermal energy. In this model, a capillary-raised fluid flows through a porous medium under localized heating condition, and the phase change from liquid to vapor at the liquid-vapor interface occurs. The hydrophilic porous material facilitates the capillary forces for better transportation of the bulk water through the porous media to the surface of porous media where the absorbed solar energy deliver to the amount of water inside the pores. The high capillary force due to the micro size inter connected pores inside the medium will rise the fluid from the cold bulk reservoir and the highly concentrated solar radiation focused inside the medium will evaporates the liquid very effectively. Based on this approach, the absorbed solar energy is delivered into the specific small pores of porous media that initiate the localized evaporation process. The steam generated from this economical technique could be used greatly for thermal solar desalinations process, sterilization process, etc. A CAD model of such porous media was developed using SolidWorks package. The mesh will be generated on the CAD file and the model was imported into the ANSYS Fluent for solving the governing equations. The mass transfer along with the fluid flow and heat transfer then solved. The simulations were done under different conditions including the hour distribution of irradiation in an average summer day and winter day to estimate steam generation rate. Produced vapor were from 13.96 kg/m2 to 18.95 kg/m2 in typical summer and winter days, respectively. The results show a temperature changes between 26.9°C and 54.4 °C. Development of the 3D numerical model and its implementation in existing data facilitates better understanding of the transport phenomena through the porous media.
Site Characterization and the Aerodynamics of an Offshore Wind Power Plant: Statistical, Numerical and Analytical Approaches
Authors: Agbormbai J. , Yu M. , Zhu W. D.
Published: November 2016

Prior to choosing a site for a wind farm, its wind resources must be known. On-site measurement of wind speed, using an anemometer or any other appropriate measuring device or the use of historical meteorological data for the site (if they exist) enhance the knowledge of the site’s wind resources. Typically, the use of 50-year historical data is recommended by Wind Energy Engineering Standards. For the offshore site in study, only the 24-year historical data from the National Oceanic and Atmospheric Administration (NOAA) data base is available. Wind speed determined from NOAA’s error bars is used to plot Rayleigh probability distribution curves for each month of the year, based on the operational limit of the 5MW NREL reference wind turbine. The site’s average wind speed and gust are determined based on average wind energy capture. A Gumbel probability distribution curve is plotted based on the operational range of the wind turbine in study, using NOAA’s error bars for the 24year historical hourly wind gust for the site. This study uses the estimated mean wind speed and mean gust, to implement BEMT simulations to investigate the aerodynamic forces caused by the wind or gust on the blades of the HAWT rotor. The wind power captured and the power coefficient are estimated for each scenario. Empirical formulae are developed for the estimation of the rotor blade airfoil’s chord length in terms of blade element radius and the axial induction factor for each scenario, in terms of blade element radius.
Effect of Blade Deflection Angles, Pressure Drop, Flow and Work Co-Efficients on Stage Performance of a Gas Turbine Shrouded HP Compressor Blade
Authors: Nagarajaiah Vinayaka , Banerjee Nilotpal , Ajay Kumar B. S. , Gowda Kumar K.
Published: November 2016

In this paper a methodology for stage performance analysis of an axial flow compressor is carried out. A 1D/2D simulation based on Aero-thermodynamics is used to study the on and off-design performance of the HP compressor. Performance curves are obtained by changing the performance parameters in terms of design parameters like blade deflection angles, pressure drop, flow and work co-efficient’s, diffusion factor, solidity and Mach number. Results show the effect of diffusion factor on increasing efficiency than that of solidity and also the effect of both diffusion factor and solidity in increasing the amount of compression and compressor efficiency. Highest efficiency was found at the mean line between the root and tip of the blade. Best compressor efficiency is found at outlet metal angle in the range 51° to 55°. It was found that at hot section, HP compressor blades typically fail because of creep. Creep occurred as components are operated under high stresses and temperature over a time period. As per thumb rule (>15°C), i.e 20°C to 25°C increase in blade temperature if observed cuts creep life by 50%. Creep strain is of prime importance, because it leads to progressive reduction of rotor tip clearances causing axial and radial blade tip rubs, calling for fixity of shrouds at the rotor HP blade tip. Creep behavior in rotor HP blades are analyzed effectively by use of Industrial best practice like Larson Miller Parameter diagram.
Development of a Ceramic Heat Exchanger for Application as Solid Oxide Fuel Cell Cathode Air Preheater
Authors: Córdova José Luis , Heshmat Hooshang
Published: November 2016

A ceramic heat exchanger with high effectiveness and low-pressure drop is being developed for application as a cathode air preheater for a Solid Oxide Fuel Cell (SOFC). At the operating conditions of SOFCs, typical metallic alloys as those used in commercial heat exchangers may undergo chromium volatilization, which is a known cathode degradation mechanism that reduces SOFC performance and life. Use of ceramics such as alumina or alumina-silicate instead of chromium-containing metal is one approach to eliminate the effects of chromium on the SOFC cathode. This project leverages the geometric design of a heat exchanger previously prototyped and tested, and demonstrated to have a nearly constant heat transfer effectiveness of 92% with low pressure drop [1], to fabricate a novel heat exchanger made from a ceramic material. This paper calculates heat exchanger performance requirements based on state of the art SOFC operating conditions, presents a thermal-based tradeoff analysis for ceramic material selection, and presents a modular heat exchanger and its heat exchange elements. The modular concept presented allows for incremental aggregation of modules to target a broad range of operating conditions typical of present and upcoming SOFC applications (e.g., 25 to 400 kWe). A fabricated sample ceramic heat exchange element is shown to demonstrate the viability of the concept for a real SOFC application.