Partial discharge (PD) has caused considerable challenges to the safety and stability of high voltage equipment. Therefore, highly accurate and effective PD detection has become the focus of research. Hilbert−Huang Transform (HHT) features have been proven to have great potential in the PD analysis of transformer, gas insulated switchgear and power cable. However, due to the insufficient research available on the PD features of power lines, its application in the PD recognition of power lines has not yet been systematically studied. In the present study, an enhanced light gradient boosting machine methodology for PD recognition is proposed; the HHT features are extracted from the signal and added to the feature pool to improve the performance of the classifier. A public power-line PD recognition contest dataset is introduced to evaluate the effectiveness of the proposed feature. Numerical studies along with comparison results demonstrate that the proposed method can achieve promising p... [more]

Lignin is the second most abundant biopolymer in the world. Due to its complex structure, lignin can be considered a valuable source of energy and different chemicals. In addition, using different reactive sites on lignin, it is possible to prepare different value-added products, such as resins, polyurethanes, and many more. Different functional groups are presented on the lignin macromolecule and can be modified via different pathways. Hydroxyl groups are the most promising reactive sites for lignin modifications. Both modified and unmodified lignins could be used for preparing different biomaterials. This paper shows several possible applications of lignin. The main goal of this publication is to show the possible valorization of lignin in different value-added products throughout the actual market prices of non-biobased materials. This review proves that lignin has unquestionable advantages in material technology and can replace different substances which will lead to a higher poten... [more]

This paper presents the design of a Superconducting Fault Current Limiter (SFCL) and calculation results of forces and stresses in the windings of a resistive fault current limiter. The design of the fault current limiter consists of two parallelly connected and magnetically coupled windings, cooled by a single stage cryocooler. Magnetically compensated windings made of HTS tape give a very low voltage on the limiter at a nominal current. Limitation of the short-circuit time and the value of the maximum initial fault current reduces the thermal and dynamic effects of the passage of a fault current. Using devices which limit the value of a fault current can lower the level of required short-circuit capacity of the elements in a system. However, selected means of fault currents limitation must maintain the power quality standards. A perfect fault current limiter is required to have substantial impedance in fault conditions and zero impedance at work currents. Such requirements are met by... [more]

In this study, the effects of the maldistribution coefficient on the thermo-hydraulic performance of discontinuous fin printed circuit heat exchanger (DF-PCHE) entrance head and channels are numerically investigated. To improve the flow uniformity at the entrance head, the flow in the exchanger with three types of spoiler perforated boards (SPBs) having 3 × 3, 4 × 4, and 5 × 5 holes and three kinds of hole diameters (Φd = 30, 25, and 20 mm), respectively, are compared to the flow in an exchanger with no SPB. The results show that a small maldistribution coefficient for the inlet velocity field is beneficial for the thermo-hydraulic performance of the DF-PCHE channels, and a maldistribution coefficient of 0.7 is an acceptable velocity distribution for the PCHE channel inlet. Using the 3 × 3 SPB with Φd = 30 mm, the maldistribution coefficient becomes 0.7, the fastest among all the SPB application cases at ΔL = 150 mm. Moreover, its heat transfer coefficient and pressure drop increase by... [more]

Underground mining is one of the riskiest industries. It is well established that the investigation of geomechanical parameters at the design stage of an underground mine provides the approximate rock mass characteristics, which are associated with some risks in the design. From a realistic risk assessment point of view, it is essential to classify risky design parameters as relevant to risk groups and determine a suitable weighting strategy for risk-prone elements aiming at risk assessment. Therefore, a realistic weighting procedure is an essential step in making realistic design decisions to increase the safety of mining operations and economic vitality. This study aimed to develop a realistic weighting procedure to assess and compare various geomechanical parameters that pose a risk to opening stability. In this research, sub-level stoping mining methods, which are commonly used in the Kazakhstan mining industry, were selected to test the developed weighting algorithm. In this study... [more]

The increasing number of security breaches in centralized systems provides the necessity to introduce decentralization in more fields. The Blockchain is a widely utilized decentralization technology that is implemented in various industries. Therefore, this technology can be used to protect sensitive services, such as those associated with the configuration changing of information systems. This article proposes a new protocol operating as a decentralization layer over any configuration scheme. It uses smart contracts—programs existing on the Blockchain—to keep track of configuration proposals and authorize new configurations. The configuration change can be proposed at any time. However, only once it is authorized by appropriate parties can it be introduced to the system. The new protocol provides an additional security layer, ensuring that every action is accounted for and authenticated. Furthermore, it enforces that administrators authorize every change. The protocol was designed to... [more]

The current legal and policy system of renewable energy in China has set up a framework of policy instruments, which provides an important foundation for dealing with climate change and promoting the healthy development of the renewable energy industry with the goal of “carbon neutrality” and “emission peak”. However, the current policy instruments cannot meet the needs for rapid development of the renewable energy industry. This paper investigates, analyzes, and concludes the status of renewable energy development along with related policy instruments in different renewable energy sources by literature and points out the problems of current policy instruments, and puts forward corresponding countermeasures. Moreover, from the perspective of energy consumption market transformation, the authors carried out an analysis of China’s challenges of policy instruments, pointing out that China’s renewable energy policy instruments have the potential to take one step further in the areas of the... [more]

Ammonia/water absorption chillers are driven by low-grade heat and cover wide refrigeration temperatures. This paper analyses single-stage ammonia/water absorption chillers. A numerical model was developed based on the heat exchanger performance. The model captures variational heat exchanger performances and describes the actual cycle with varying boundary conditions. The detrimental effects of refrigerant impurity were analysed quantitatively under different operating conditions. The model was validated with experimental data. A basic cycle and three advanced cycles were analysed for sub-zero refrigeration by comparing the thermodynamic performances. A compression-assisted cycle extended the activation temperature from 80 to 60 °C. At the heat source of 120 °C, when a counter-current desorber or bypassed rich solution was used, the COP increased from 0.51 to 0.58 or 0.57, respectively. The operating parameters included the heat source temperatures, heat sink temperatures, the mass flo... [more]

Oil mist adversely affects the health of workplace workers, and for this reason, regulations on the limitation of the oil-mist exposure of workers are becoming stricter. In order to reduce the amount of the exposure of workers to oil mist, it is important to effectively remove oil mist from machine tools. In this study, the collection efficiency according to the geometry of the oil-mist-collection cyclone consisting of several disks and the output power and rotation speed of the motor were evaluated. Most of the generated oil mists were less than 10 μm, and the mist removal was assessed using an optical particle counter. The cyclone airflow rate increased linearly with the rotational speed, and the rate was affected more by the cyclone geometry than by the power consumption. The mist-removal performance was significantly enhanced when plate- and cone-type disks were added to the rotating blades. The removal efficiencies of PM10 and PM2.5 under the maximum operational conditions of 5000... [more]

APV systems producing both crops and electricity are becoming popular as an alternative way of producing renewable energy in many countries with land shortage issues (e.g., South Korea). This study aims at developing a hybrid performance model of an Agrophotovoltaic (APV) system that produces crops underneath the PV modules. In this study, the physical model used to estimate solar radiation is integrated with a polynomial regression approach to forecast the amount of electricity generation and crop production in the APV system. The model takes into account not only the environmental factors (i.e., daily temperature, precipitation, humidity, and wind speed) but also physical factors (i.e., shading ratio of the APV system) related to the performance of the APV system. For more accurate modelling, the proposed approach is validated based on field experiment data collected from the APV system at Jeollanam-do Agricultural Research and Extension Services in South Korea. As a result, the prop... [more]

Fossil fuels are the most widely used resource for energy production. Carbon dioxide (CO2) emissions are correlated with climate change, and therefore these emissions must be reduced in the future. It is possible by means of many different technologies, and one of the most promising seems to be oxyfuel combustion. This process, with oxygen and recirculating gas, produces a concentrated stream of CO2 and water. In recent years, many scientists carried out research and studies on the oxyfuel process, but a sufficient level of knowledge was not yet reached to exploit the great potential of this new technology. Although such areas of research are still highly active, this work provides an overview and summary of the research undertaken, the state of development of the technology, and a comparison of different plants so far.

Dynamic inductive charging is a contact-free technology to provide electric vehicles with energy while they are in motion, thus eliminating the need to conductively charge the batteries of those vehicles and, hence, the required vehicle downtimes. Airport aprons of commercial airports are potential systems to employ this charging technology to reduce aviation-induced CO2 emissions. To date, many vehicles operating on airport aprons are equipped with internal combustion engines burning diesel fuel, hence contributing to CO2 emissions and the global warming problem. However, airport aprons exhibit specific features that might make dynamic inductive charging technologies particularly interesting. It turns out that using this technology leads to some strategic infrastructure design questions for airport aprons about the spatial allocation of the required system components. In this paper, we experimentally analyze these design questions to explore under which conditions we can expect the re... [more]

This paper demonstrates the applicability of machine learning algorithms in sand production problems with natural gas hydrate (NGH)-bearing sands, which have been regarded as a grave concern for commercialization. The sanding problem hinders the commercial exploration of NGH reservoirs. The common sand production prediction methods need assumptions for complicated mathematical derivations. The main contribution of this paper was to introduce machine learning into the prediction sand production by using data from laboratory experiments. Four main machine learning algorithms were selected, namely, K-Nearest Neighbor, Support Vector Regression, Boosting Tree, and Multi-Layer Perceptron. Training datasets for machine learning were collected from a sand production experiment. The experiment considered both the geological parameters and the sand control effect. The machine learning algorithms were mainly evaluated according to their mean absolute error and coefficient of determination. The e... [more]

The present study numerically investigated a cylinder under oscillating motions at a low Reynolds number. The effects of two oscillation frequencies and amplitudes on the lift drag coefficient, near-field surface pressure fluctuation, and far-field noise were studied. The models were examined at a Mach number of 0.05, corresponding to a Reynolds number of 1.0 × 105. In this paper, the incompressible Navier−Stokes equations (INSE) and linearized perturbed compressible equations (LPCE) were coupled to form a hybrid noise prediction method, which was used to solve the flow field and acoustic radiation field. Based on the simulation results of the acoustic radiation field, the frequency characteristics of the acoustic waves were analyzed by the dynamic modal decomposition (DMD) method. It was observed that when the oscillation amplitude was the same, the variation amplitude and mean value of the lift-drag coefficient increased with the increase in the oscillation frequency. Under the same... [more]

Battery participation in the service of power system frequency regulation is universally recognized as a viable means for counteracting the dramatic impact of the increasing utilization of renewable energy sources. One of the most complex aspects, in both the planning and operation stage, is the adequate characterization of the dynamic variation of the state of charge of the battery in view of lifetime preservation as well as the adequate participation in the regulation task. Since the power system frequency, which is the input of the battery regulation service, is inherently of a stochastic nature, it is easy to argue that the most proper methodology for addressing this complex issue is that of the theory of stochastic processes. In the first part of the paper, a preliminary characterization of the power system frequency is presented by showing that with an optimal degree of approximation it can be regarded as an Ornstein−Uhlenbeck process. Some considerations for guaranteeing desirab... [more]

This article deals with the numerical simulation of unsteady cavitating flow around hydrofoils, supported by experimental research realized in a cavitation tunnel situated in the Centre of Hydraulic Research. Two straight NACA hydrofoils (NACA0020 and NACA2412) were employed. The comprehensive unsteady CFD analysis was based on scale-resolving simulations (hereinafter SRS) with the aim of capturing correctly the interactions between the cavitation structures and re-entrant flow as well as the compressibility and thermal effects of cavitation. The static pressure fluctuations during the cavity oscillation cycles and the evaporation and condensation processes are discussed in detail. To predict correctly the high-pressure peaks during the bubble cloud collapses and the pressure pulse propagation speed, the real properties of water and the mixture total energy conservation equation were considered. In addition, the estimated content of undissolved air was taken into account. The numerical... [more]

Noticeable climate change in recent years is reducing the comfort of public spaces in the urban environment, and is becoming an element of urban policies. The adaptation to climate change requires the development of new design guidelines for the development of public spaces. The appropriate definition of development density, choice of building materials, technologies, planting species, and the used directions is a challenge that depends on local conditions. A representative public space located in the area of a multi-family housing estate built in the second half of the 20th century in Lublin (Poland) was selected for the study. The space has undergone redevelopment twice in the last 10 years. The aim of the study was to determine to what extent the executed and designed changes actually improve the thermal comfort of users. Quantitative and qualitative indicators of the successive phases of the investment were analyzed in the context of projected climate change. The simulation was dev... [more]

Energy system models have become crucial to assess the effectiveness of possible energy policies in pursuing the declared environmental objectives. Among bottom-up models, the tools most widely used by researchers and institutions to perform scenario analyses and policy evaluations rely on commercial software and closed databases, limiting the transparency of the studies. The purpose of this work is to demonstrate that open-source tools, relying on open databases, can be used as a valid alternative to commercial tools, getting equivalent results not only for simple case studies as done so far, but also for complex (national, regional, or multi-regional) reference energy systems. Working on the already available open TEMOA optimization framework, a bottom-up technology-rich model is developed here for the Italian reference energy system on an extended TEMOA version, comparable in detail and complexity to the equivalent TIMES framework. The accuracy of the novel TEMOA-Italy model in a bu... [more]

As wearable electronic devices are becoming an integral part of modern life, there is a vast demand for safe and efficient energy storage devices to power them. While the research and development of microbatteries and supercapacitors (SCs) have significantly progressed, the latter has attracted much attention due to their excellent power density, longevity, and safety. Furthermore, SCs with a 1D fiber shape are preferred because of their ease of integration into today’s smart garments and other wearable devices. Fiber supercapacitors based on carbon nanotubes (CNT) are promising candidates with a unique 1D structure, high electrical and thermal conductivity, outstanding flexibility, excellent mechanical strength, and low gravimetric density. This review aims to serve as a comprehensive publication presenting the fundamentals and recent developments on CNT-fiber-based SCs. The first section gives a general overview of the supercapacitor types based on the charge storage mechanisms and e... [more]

In order to explore the influences of effective stress change on gas adsorption−desorption behaviors, primary undeformed coal (PUC) and tectonically deformed coal (TDC) from the same coal seam were used for adsorption−desorption experiments under different effective stress conditions. Experimental results showed that gas adsorption and desorption behaviors were controlled by the coal core structure and the pore-fissure connectivity under effective stress. The coal matrixes and fissures were compressed together under effective stress to reduce connectivity, and it was difficult for gas to absorb and desorb as the stress increased in primary undeformed coal. The loose structure of tectonically deformed coal cores can help gas to fully contact with the coal matrix, resulting in higher adsorption gas volumes. The support of coal particles in tectonically deformed coal cores weakens the compression of intergranular pores when effective stress increases, which in this study manifested in the... [more]

SF6, which is currently widely used in gas-insulated power transmission equipment, is a greenhouse gas with a very strong greenhouse effect. Therefore, developing environmentally friendly gas insulation equipment to gradually reduce the use of SF6 has become a hot research topic. As the most potential alternative gas, C4F7N is of great significance to study the electrical characteristics of the medium-voltage switching field to promote the green development of the power industry. Based on multi-physical field coupling to construct the 40.5 kV circuit breaker mode, this paper uses C4F7N/CO2 mixed gas to compare and study the dynamic characteristics of a C4F7N/CO2 mixed gas circuit breaker when breaking the short-circuit current and the dielectric recovery strength with no-load breaking, as well as to evaluate the electrical performance of C4F7N mixed gas in a 40.5 kV breaker with the gas breakdown criterion. The results show that mixing O2 in a high current can improve the breaking perf... [more]

Hydrochars (HTCD) derived from digestates, namely D1 and D2 (from two plants) of sewage sludge, were examined with respect to their fuel properties. The hydrothermal carbonization (HTC) tests were performed at temperatures of 200 and 220 °C, for 2 and 4 h of residence times, and with 1:10 and 1:8 digestate to water ratios (D/W), causing an increase of ash content (max. 55.8%), and a decrease c.a. 20% of the higher heating value except for a slight increase to 15 kJ/kg at 200 °C and 4 h in hydrochars. Conversely, the combustion profiles of hydrochars moved towards higher temperatures (225−257 °C) and finished earlier at lower temperatures (423−438 °C). The HTCD from D1 and D2 showed very similar properties under the same conditions (200 °C, 4 h, 1:8 D/W) for combustion characteristic temperatures, indices and profiles. The best efficiency was found for HTCD2. In addition, the polluted post-processing liquid phase was treated by a distillation process providing 30% higher pH, 50% lower B... [more]

The heat transfer between a porous ceramic radiant burner (PCRB) and a target environment was studied. The black aluminum pot (BAP) and white aluminum pot (WAP) with an emissivity of 0.72 and 0.22 were experimentally used to obtain the temperature distribution and thermal efficiency of a burner. Under the same heat load, the porous ceramic plate (PCP) of WAP is 79~90 °C higher than BAP, but the measured thermal efficiency of BAP is 15~20% higher than WAP. A heat transfer model for PCRB and pots was established based on the radiant and convection heat transfer theories. This model is applicable to common infrared radiant burners. The heat gain type of the pot was analyzed quantitively, with a relative error of less than 7%. The influence of the pot surface emissivity on the burner and heat transfer change of the pot was discussed, and the solid radiation heat gain of BAP is approximately double that of BAP under the same heat load. For PCRBs whose main heat is from radiation, the pot wi... [more]

This paper investigates the model development of the state-of-power (SoP) estimation for a 43 Ah large-capacity prismatic nickel-manganese-cobalt oxide (NMC) based lithium-ion cell with a thorough aging investigation of the cells’ internal resistance increase. For a safe operation of the vehicle system, a battery management system (BMS) integrated with SoP estimation functions is crucial. In this study, the developed SoP model used for the estimation of power throughout the lifetime of the cell is coupled with a dual-polarization equivalent-circuit model (DP_ECM) for achieving the precise estimation of desired parameters. The SoP model is developed based on the pulse-trained internal resistance evolution approach, and hence the power is estimated by determining the rate of internal resistance increase. Hybrid pulse power characterization (HPPC) test results are used for extraction of the impedance parameters. In the DP_ECM, Coulomb counting and extended Kalman filter (EKF) state estima... [more]

Distillation has relatively low thermodynamic efficiency, so it is a prime target for process intensification studies. The current research aims to study exergy losses in various heat-integrated distillation columns. A conventional industrial-scale i-butane/n-butane fractionator has been selected as a case study for the comparison of the performances of various heat-integrated designs. The Aspen Plus® process simulator is used to perform steady-state simulations and exergy analyses of the conventional distillation column (CDC), internally heat-integrated distillation column (iHIDiC), externally heat-integrated double distillation columns (EHIDDiC), and vapor recompression (VRC) systems. The results of these exergy analyses show that a modified VRC system (ηE = 10.69%) is the most efficient design for this separation. The exergy efficiency of the conventional VRC system is the same as that of the CDC (ηE = 9.27%). The EHIDDiC system (ηE = 9.77%) is somewhat better than the CDC, whereas... [more]