The thermal management of power converters is not only crucial for their own optimal operation and reliability, but also for the overall system in which they are operating. Reliability is a very serious aspect because power electronics systems are being increasingly widely adopted in mission-critical applications in the e-mobility sector, in smart grids, and other applications where safety and operational continuity are essential. The current trend towards miniaturization of power conversion systems and, consequently, towards high power density solutions is speeding up the diffusion of Gallium Nitride (GaN) High Electron Mobility Transistor (HEMT). GaN HEMT-based high power density converters must be properly managed, making the estimation of the thermal characteristics of these devices essential. This paper proposes the use of some Thermo-Sensitive Electrical Parameters (TSEP) for a simple and effective thermal resistance evaluation. The primary advantages and limitations of these TSE... [more]

This study addresses heat and mass transfer of electrical magnetohydrodynamics (MHD) Williamson fluid flow over the moving sheet. The mathematical model for the considered flow phenomenon is expressed in a set of partial differential equations. Later, linear and nonlinear ordinary differential equations (ODEs) are obtained. The finite element method tackles a reduced system of ODEs with boundary conditions. Galerkin weighted residuals and constructs of weak formulations constitute the basis of this method. An iterative procedure is considered for handling nonlinear terms in a given system of ODEs. Some results acquired using the finite element method are compared with those reported in previous research via the Matlab solver bvp4c in order to validate the obtained solutions of ODEs. It is seen that the velocity profile is decayed by enhancing the Wiesenberg number. The finite element method also converges to an accurate solution by increasing the number of elements, whereas Matlab solv... [more]

Over the three-day gasification test of a large coal block with oxygen in atmospheric pressure conditions, the yield and composition of the tar collected was investigated. The tar was sampled approximately every 7 h into sorption tubes directly from the reactor outlet. Sand, with a moisture content of 11%, was used as an insulating material to simulate the environment of the gasified coal seam. Light aromatic hydrocarbons (BTEX), phenols, and polycyclic aromatic hydrocarbons (PAHs) were determined in the tar. The results that were obtained were recalculated into the concentrations of the individual components of the tar and its mass stream in the process gas. The residence time of the tar in the reactor, its molar mass, and the H/C ratio were also calculated. As the reaction progressed, the water that was contained in the wet sand started to react with the gasified coal, which significantly affected the composition and amount of the obtained process gas and the produced tar. Due to an... [more]

Safe drilling and effective fracturing are constant challenges for shale formations. One of the most important influencing factors is the accurate characterization of the deformation and damage caused by inherent lamination and natural fractures. Furthermore, shale formations exhibit fine-scale heterogeneity, which conventional laboratory methods (linear variable differential transformer (LVDT), strain gauges, etc.) cannot distinguish. To overcome these constraints, this research aims to investigate the damage and deformation characteristics of shale samples using three-dimensional digital image correlation (3D-DIC). Under uniaxial and diametrical compression, samples of Wolfcamp, Mancos, and Eagle Ford shale with distinct lamination and natural fractures are evaluated. The 3D-DIC system is utilized for image processing, visualization, and analysis of the shale damage process under varying loads. DIC made quantitative full-field strain maps with load (tension, compression, and shear),... [more]

Coiled tubing (CT) is used as a velocity string to transport high-velocity gas in drainage gas recovery technology. Sand particles flowing at high speed can cause serious erosion of the pipe wall. Long-term erosion wear leads to the degradation of the string strength and can even cause local perforation. In order to study the erosion wear problem of CT, a gas−solid erosion experimental device was established for a full-size pipe with different radii of curvature. A 3D laser confocal technique was used to examine and characterize the microscopic erosion morphology of the inner wall of the CT. The CFD erosion model was selected based on the erosion test data of the inner wall of the CT, and the erosion results of the Finnie model show minimal error and good agreement compared with other models. The average value of the error of the maximum erosion rate at different radii of curvature is 8.3%. The effect of the radius of curvature, gas velocity and solid particle size on the maximum erosi... [more]

This paper presents a review of the power and torque coefficients of various wind generation systems, which involve the real characteristics of the wind turbine as a function of the generated power. The coefficients are described by mathematical functions that depend on the trip speed ratio and blade pitch angle of the wind turbines. These mathematical functions are based on polynomial, sinusoidal, and exponential equations. Once the mathematical functions have been described, an analysis of the grouped coefficients according to their function is performed with the purpose of considering the variations in the trip speed ratio for all the coefficients based on sinusoidal and exponential functions, and with the variations in the blade pitch angle. This analysis allows us to determine the different coefficients of power and torque used in wind generation systems, with the objective of developing algorithms for searching for the point of maximum power generated and for the active control o... [more]

Studying a large number of scenarios is necessary to consider the uncertainty inherent to the energy transition. In addition, the integration of intermittent renewable energy sources requires complex energy system models. Typical days clustering is a commonly used technique to ensure the computational tractability of energy system optimisation models, while keeping an hourly time step. Its capability to accurately approximate the full-year time series with a reduced number of days has been demonstrated (i.e., a priori evaluation). However, its impact on the results of the energy system model (i.e., a posteriori evaluation) is rarely studied and was never studied on a multi-regional whole-energy system. To address this issue, the multi-regional whole-energy system optimisation model, EnergyScope Multi-Cells, is used to optimise the design and operation of multiple interconnected regions. It is applied to nine diverse cases with different numbers of typical days. A bottom-up a posteriori... [more]

Ammonia (NH3), as a derivative of hydrogen and energy carrier, is regarded as a low-carbon fuel provided that it is produced from a renewable source or a carbon abated process of fossil fuel. Co-firing ammonia with coal is a promising option for pulverized coal-fired power plants to reduce CO2 emission. Applying the co-firing in an existing pulverized coal-fired boiler can achieve satisfying combustion performance in the furnace but may affect the boiler performance. In the present work, a thermal calculation method was employed to evaluate the impact of ammonia co-firing on the boiler performance of an existing 600 MW supercritical utility boiler, covering the co-firing ratio range up to 40% (on heat basis). The calculations indicated that, as compared to sole coal combustion, co-firing ammonia changed the volume and composition and consequently the temperature and heat transfer characteristics of the flue gas. These resulted in increased variations in the heat transfer performance of... [more]

Sustained casing pressure (SCP) is a common problem during an entire life span of oil and gas wells. When conventional methods are deployed to resolve the issue, the methods seem to have some setbacks by being unable to seal microcracks in the wellbores. A new solid-free resin sealant was developed by increasing the amount of active hydrogen in the curing agent. This low-temperature cure results in low viscosity, excellent mechanical properties, and chemical stability. The experimental results show that the resin sealant can be used at temperatures ranging from 20 to 50 °C, and the curing time can be controlled within 0.25 to 20 h by increasing the curing agent content. The viscosity of the resin is reduced from 35.7 Pa·s to less than 0.065 Pa·s with the addition of the viscosity reducer, which can greatly promote resin penetration into the microcracks of the cement sheath. After 24 h of curing, the compressive strength can reach 55 Mpa, which is significantly higher than conventional... [more]

Environment control systems in broiler houses utilize non-renewable electricity and fuels as energy sources, contributing to the increase in greenhouse gases, while not providing optimal conditions. The heat pump (HP) is an energy-efficient technology that can continuously regulate the indoor temperature and relative humidity by combining different operation modes (heating, cooling, and dehumidifying). The current study presents an analytical numerical model developed in Simulink, capable of simulating the thermal loads of a broiler house and the dynamic operation of three heat pumps to cover its needs. Outdoor climatic conditions and broilers’ heat production are used as inputs, while all the heat exchange mechanisms with the external environment are considered. The study investigates the energy use and performance of each HP mode under different environmental conditions. A total of 7 different production periods (PPs) are simulated for a 10,000-broiler house in northern Greece, showi... [more]

Dramatic climate change has been well-observed for several years, mainly due to the effects of pollution caused by the burning of fossil fuels [...]

Piston engines fueled by kerosene have a strong application prospect in special vehicles and small aircrafts, but the low amount of octane in kerosene fuel causes its knock combustion phenomenon to be particularly serious. A knock will deteriorate the power and economy of the engine and will damage the engine in serious cases. Therefore, knocking is the key problem with kerosene engines. We propose a knock-prediction system for kerosene engines based on in-cylinder pressure signals. Firstly, the intrinsic mode function (IMF) caused by knock resonance is extracted from the in-cylinder pressure signal via empirical mode decomposition (EMD) and a time−frequency domain analysis. A time-domain statistical analysis (TDSA) combined with a principal component analysis (PCA) is used to extract features from the IMF. Finally, the data collected from the test bench are trained by a support vector machine to obtain the knock-prediction model. Compared with other technical combinations for training... [more]

The last decade’s studies show that the PoL (point-of-load) converter’s output capacitor is an important component for reliability, implying that its careful selection may determine the overall converter’s failure rate and lifetime. PoL converters are commonly found in many electronic systems, usually as part of the Intermediate Bus Architecture (IBA). Their important requirements are a stable output voltage at load current variation, good temperature stability, a low output ripple voltage, high efficiency, and reliability. If the electronic system is portable, a small footprint and low volume are also important considerations. These were recently well accomplished with eGaN (enhancement gallium nitride) transistor technology, whose VUFoM (vertical unipolar figure of merit) is 1.48 compared to 1.00 for silicon. This ensures a higher converter power density (watts/area). This paper reviews the most-used capacitor technologies, highlighting the reliability of these components as part of... [more]

Direct-drive permanent magnet machines are ideal candidates for remote renewable applications, due to their independence from gearboxes and minimization of maintenance needs. However, faults may still appear in the generator of such a machine and affect its operation and production. Not only can demagnetization cause a catastrophic breakdown if left unchecked, but it also directly impacts the output quality of generators. As such, demagnetization is a topic of great interest. This paper investigated the sensitivity of three diagnostic methods—current signature analysis (CSA), Park’s vector approach (PVA), and extended Park’s vector approach (EPVA)—for demagnetization fault detection on a coreless permanent magnet generator.

The European Union (EU) is a global leader in renewable energy, and it is working to maintain this position through setting high standards for itself as well as for its member states in this field. Among the goals set for 2030 in Directive (EU) 2018/2001 and changes published on 14 July 2021 is a 55% reduction in greenhouse gas (GHG) emissions (compared to 20% in 2020). The targets for individual countries vary and depend on the current level of development of renewable energy. This article focuses on evaluation of these targets in the Visegrad Group (V4) countries (Czech Republic, Hungary, Poland, and Slovakia). These are post-Communist countries that have undergone systemic transformations but still face challenges related to sustainable development in renewable energy. This article analyzes the 2030 goals and the prospects of their implementation. Evaluated criteria include greenhouse gas emissions, the share of renewable energy in energy consumption, energy consumption, energy effi... [more]

Health status assessment is the key link of transformer-condition-based maintenance. The health status assessment method of power transformers mostly adopts the method based on the health index, which has the problems of multiple parameters of each component and strong subjectivity in the selection of weight value, which is easily causes misjudgment. However, the existing online monitoring system for dissolved gas in transformer oil (DGA) can judge the normal or abnormal state of the transformer according to the gas concentration in a monitoring cycle. Still, there are problems, such as fuzzy evaluation results and inaccurate judgment. This paper proposes a dynamic state evaluation method for power transformers based on the Mahalanobis−Taguchi system. First, the oil chromatography online monitoring time series is used to screen key features using the Mahalanobis−Taguchi system to reduce the problem of excessive parameters of each component. Then, a Mahalanobis distance (MD) calculation... [more]

To ensure the applicability of accident-tolerant fuels, their behaviors under various accidental conditions must be assessed. While the dependences of the behavior of single physical parameters can be investigated in single- or separate-effect experiments, and more complex phenomena can be investigated using integral-effect tests, the behavior of an entire system as complex as a nuclear power plant core must be investigated using computer code modeling. One of the most commonly used computer codes for the assessment of severe accidents is MELCOR 2.2. In version 18019, the authors enabled the modeling of the behavior of the nuclear fuel with FeCrAl cladding (namely, alloy B136Y3) for the first time, using the GOX model. The ability of this model to reasonably accurately predict the behavior of FeCrAl cladding in accident conditions with quenching was verified in this work by modeling the QUENCH-19 experiment carried out in the Karlsruhe Institute of Technology on the QUENCH experimental... [more]

Offshore wind energy is a renewable energy source that is developing fast. It is considered to be the most promising energy source in the next decade. Besides, the expanding trend for this technology requires the consideration of diversified seabeds. In deep seabeds, floating offshore wind technology (FOWT) is needed. For this latter technology, such as for conventional WT, we need to consider aspects related to performance, aerodynamic force, and forces during operation. In this paper, a two-bladed downwind wind turbine model is utilized to conduct experiments. The collective pitch and cyclic pitch angle are adjusted using swashplated equipment. The fluid forces and moments acting on the rotor surface are measured by a six-component balancing system. By changing the pitch angle of the wind turbine blades, attempts are made to manage the fluid forces generated on the rotor surface. Under varied uniform wind velocities of 7, 8, 9, and 10 m/s, the effect of collective pitch control and c... [more]

Due to the uncontrollable generators, islanded microgrids powered only by renewable energy require costly energy storage systems. Energy storage needs are amplified when load and generation are misaligned on hourly, monthly, or seasonal timescales. Diversification of both loads and generation can smooth out such mismatches. However, the ideal type of battery to smooth out remaining generation deficits will depend on the duration(s) that energy is stored. This study presents a controls co-design approach to design an islanded microgrid, showing the benefit of hybridizing tidal and solar generation and hybridizing lithium-ion and flow battery energy storage. The optimization of the microgrid’s levelized cost of energy is initially studied in grid-search slices to understand convexity and smoothness. Then, a particle swarm optimization is proposed and used to study the sensitivity of the hybrid system configuration to variations in component costs. The study highlights the benefits of con... [more]

Microbial fuel cell (MFC) technology is anticipated to be a practical alternative to the activated sludge technique for treating domestic and industrial effluents. The relevant literature mainly focuses on developing the systems and materials for maximum power output, whereas understanding the fundamental electrochemical characteristics is inadequate. This experimental study uses a double-chamber MFC having graphite electrodes and an anion-exchange membrane to investigate the electrochemical process limitations and the potential of bioelectricity generation and dairy effluent treatment. The results revealed an 81% reduction in the chemical oxygen demand (COD) in 10 days of cell operation, with an initial COD loading of 4520 mg/L. The third day recorded the highest open circuit voltage of 396 mV, and the maximum power density of 36.39 mW/m2 was achieved at a current density of 0.30 A/m2. The electrochemical impedance spectroscopy analysis disclosed that the activation polarization of th... [more]

Numerous studies have been conducted on spent lithium-ion batteries (LIBs) recycled from electric vehicles. Research on pre-processing techniques to safely disassemble spent LIB packs has mainly focused on water-based discharge methods, such as salt-water discharge. However, salt-water discharge corrodes the electrodes and case, causing internal contamination. Therefore, we propose an electrical discharge process that is suitable for the direct recycling and safe disassembly of spent Li-ion batteries. Spent LIBs from electric vehicles (EV) that were scrapped after EV operation were recovered and electrochemically discharged to voltages of 0, 1, 2, and 2.5 V. These discharged spent LIBs were analyzed through X-ray diffraction, scanning electron microscopy, and electrochemical impedance spectroscopy. The spent LIB with a state-of-health (SoH) of 66.8% exhibited significantly increased swelling and bulging when over-discharged. Notably, the discharging of the spent battery to 0 V increase... [more]

Coal dust endangers the health and safety of workers in underground coal mines. Therefore, developing coal dust suppressants with dust prevention and explosion-proof properties is critical. The influence of molasses on the explosion and decomposition of the coal dust deposited in underground mines was investigated using 20 L explosion experiments and thermogravimetric and differential thermal analysis (TG-DTA). Findings reveal that, first, molasses can weakly promote the explosion of coal dust at low coal dust concentrations (<400 g/m3) but has no significant effect on the explosion at high coal dust concentrations (≥400 g/m3). Second, the decomposition process of the coal dust mixed with molasses has three stages: the moisture evaporation stage (0−150 °C), the molasses decomposition stage (150−300 °C), and the coal dust decomposition stage (300−500 °C). Molasses oxidation consumes oxygen and releases heat; at low coal dust concentrations, the released heat can promote coal dust dec... [more]

Recent research advances in sensors, wireless communications, network protocols, microelectronics, cloud computing, and machine learning, among others, are driving the growth of the Internet of Things (IoT) [...]

The concept of “oil to electricity” is crucial for expanding the share of electricity in final energy consumption as well as for encouraging energy efficiency and emission reduction. Initially, a multidimensional strategy analysis is conducted for the government, ports, and ships concerned. From an economics perspective, a mathematical model of electricity substitution benefit analysis based on multiagent cooperative game theory under cap and trade and carbon tax policies is constructed, and the effect of carbon emissions caused by ships on the environment and society is converted into economic value. How several variables, such as transformation costs, ship electricity consumption, subsidy rates, carbon tax prices, and the ratio of shore power usage time to berthing time, affect the functioning of shore power is analyzed. The best electricity price under various circumstances is determined while considering the benefits of the three parties to maximize social welfare. The reduction in... [more]

The increase in renewable energy sources (RESs) in distribution grids is a major driver for achieving green energy goals worldwide. However, RES power inverters affect power quality, increase power losses, and, in certain cases, may cause power interruptions due to harmonics, deterioration of the rate of change of frequency, and inability to rapidly react in grid faults. Today, phasor measurement units (PMUs) are the ultimate tools for real-time monitoring of distribution grids’ health, and they enable several data-driven added-value services such as fast and automated fault detection, isolation, and recovery; state estimation; power quality monitoring; dynamic events analysis, etc. The present paper proposes an open hardware and software PMU platform, which is low cost, high performance, expandable, and, in general, suitable for research and innovation activities. The system is based on two processor modules (a digital signal processor from Texas Instruments TMS320c5517, and a micropr... [more]