This paper describes the analysis and characterization of NayWOx bronze nanowires bundles and evaluation of their effective adsorption of methylene blue dye (MB). The Na-doped WOx bronze nanowires bundles were first synthesized via a simple solvothermal method, which were then fully characterized by using different techniques including TEM, XRD, XPS and UV-Vis, to validate the successful Na+ insertion into the WOx framework. The adsorption activities of the resulting NayWOx bronze nanowires bundles, compared with the undoped WOx form, were investigated by evaluating the adsorption effect on methylene blue under both UV and visible light irradiations. An enhanced adsorption performance of the Na-doped WOx bronze samples was recorded, which demonstrated a 90% of removal efficiency of the MB under different conditions (dark, visible and UV light). Moreover, the NayWOx bronze samples also offered a 4 times better kinetic rate of MB removal than the plain WOx nanowires.

The objective of this research is to establish an appropriate operating strategy for a radiant floor heating system that additionally has an air source heat pump for providing convective air heating separately, leading to heating energy saving and thermal comfort in residential buildings. To determine the appropriate optimal operating ratio of each system taking charge of combined heating systems, the energy consumption of the entire system was drawn, and the adaptive floor surface temperature was reviewed based on international standards and literature on thermal comfort. For processing heating loads with radiant floor heating and air source heating systems, the heating capacity of radiant floor heating by 1 °C variation in floor temperature was calculated, and the remaining heating load was handled by the heating capacity of the convective air heating heat pump. Consequently, when the floor temperature was 25 °C, all heating loads were removed by radiant floor heating only. When hand... [more]

Electrochemical water splitting is considered a promising way of producing hydrogen and oxygen for various electrochemical energy devices. An efficient single, bi-functional electrocatalyst that can perform hydrogen evolution reactions (HERs) and oxygen evolution reactions (OERs) is highly essential. In this work, Co@NC core-shell nanoparticles were synthesized via a simple, eco-friendly, solid-state synthesis process, using cobalt nitrate and with pyrazole as the N and C source. The morphological analysis of the resulting Co@NC nanoparticles was performed with a scanning and transmission electron microscope, which showed Co nanoparticles as the core and the pyrolysis of pyrazole organic ligand N-doped carbon derived shell structure. The unique Co@NC nanostructures had excellent redox sites for electrocatalysis, wherein the N-doped carbon shell exhibited superior electronic conductivity in the Co@NC catalyst. The resulting Co@NC nanocatalyst showed considerable HER and OER activity in... [more]

Various industrial fields use motors as key power sources, and their importance is increasing. In motor manufacturing, various tests are conducted for each motor before shipping. The no-load test is one such test, in which, for instance, the current flowing into the motor and temperature of the bearing is measured to confirm whether they are within specific values. Reducing labor, cost, and time in identifying an initially defective product requires a simple and reliable method. This study proposes a new diagnosis to identify the motor conditions based on the rotating sound of the motor in the no-load test. First, the rotating sounds of motors were measured using several healthy motors and motors with faults. Second, their sound characteristics were analyzed, and it was found that the characteristic signals appeared in a specific frequency range periodically. Then, considering these phenomena, a diagnostic method based on deep learning was proposed to judge the faults using long short-... [more]

Although this is a fact that is not very explored in the literature, there are two possible forms to connect the stator winding of an induction motor in the delta. The choice for one of these forms defines the amplitude of the stator transient current during the switching from star to delta connection when the motor is driven by a star-delta starting system, which is the most widely used and diffused method for starting an induction motor. One of the possible forms of the delta connection gives rise to a switching current with a relatively small amplitude, which gives it the denomination of preferential. The other form has a relatively higher amplitude of switching current, but it is the most recommended and indicated in diagrams of catalogues and motor plates. Therefore, it is here called “common”. With the aim of evidencing how the differences between these two forms of delta connection are manifested, this paper approaches the issue experimentally, through a methodology with statist... [more]

The need for regulating the operation of unhealthy motor drives has motivated the researchers to modify the control techniques in order to be valid for the new drive state. The use of a fault-tolerant facility is an attractive feature of multiphase machines; therefore, the applicability of different controllers has been established for the operation under open-phase fault conditions. The considered control algorithms were utilized to analyze the operation of the unhealthy system and evaluating the capability of the control to regulate the speed and torque under the fault condition. However, the majority of these studies considered only one control algorithm to be tested with the faulty system without comparing its performance with other techniques. The performance comparison is a vital way to visualize the features and characteristics of each algorithm. For this purpose, this paper deals with the performance comparison of the hysteresis controller, RFOC based on resonant controller and... [more]

To improve the energy efficiency of an industrial process thermochemical energy storage (TCES) can be used to store excess or typically wasted thermal energy for utilisation later. Magnesium carbonate (MgCO3) has a turning temperature of 396 °C, a theoretical potential to store 1387 J/g and is low cost (~GBP 400/1000 kg). Research studies that assess MgCO3 for use as a medium temperature TCES material are lacking, and, given its theoretical potential, research to address this is required. Decomposition (charging) tests and carbonation (discharging) tests at a range of different temperatures and pressures, with selected different gases used during the decomposition tests, were conducted to gain a better understanding of the real potential of MgCO3 for medium temperature TCES. The thermal decomposition (charging) of MgCO3 has been investigated using thermal analysis techniques including simultaneous thermogravimetric analysis and differential scanning calorimetry (TGA/DSC), TGA with atta... [more]

Confined phase behavior plays a critical role in predicting production from shale reservoirs. In this work, a pseudo-potential lattice Boltzmann method is applied to directly model the phase equilibrium of fluids in nanopores. First, vapor-liquid equilibrium is simulated by capturing the sudden jump on simulated adsorption isotherms in a capillary tube. In addition, effect of pore size distribution on phase equilibrium is evaluated by using a bundle of capillary tubes of various sizes. Simulated coexistence curves indicate that an effective pore size can be used to account for the effects of pore size distribution on confined phase behavior. With simulated coexistence curves from pore-scale simulation, a modified equation of state is built and applied to model the thermodynamic phase diagram of shale oil. Shifted critical properties and suppressed bubble points are observed when effects of confinement is considered. The compositional simulation shows that both predicted oil and gas pro... [more]

Equilibrium phase formations below 600 K in the parts Ag2Te−FeTe2−F1.12Te−Ag2Te and Ag8GeTe6−GeTe−FeTe2−AgFeTe2−Ag8GeTe6 of the Fe−Ag−Ge−Te system were established by the electromotive force (EMF) method. The positions of 3- and 4-phase regions relative to the composition of silver were applied to express the potential reactions involving the AgFeTe2, Ag2FeTe2, and Ag2FeGeTe4 compounds. The equilibrium synthesis of the set of phases was performed inside positive electrodes (PE) of the electrochemical cells: (−)Graphite ‖LE‖ Fast Ag+ conducting solid-electrolyte ‖R[Ag+]‖PE‖ Graphite(+), where LE is the left (negative) electrode, and R[Ag+] is the buffer region for the diffusion of Ag+ ions into the PE. From the observed results, thermodynamic quantities of AgFeTe2, Ag2FeTe2, and Ag2FeGeTe4 were experimentally determined for the first time. The reliability of the division of the Ag2Te−FeTe2−F1.12Te−Ag2Te and Ag8GeTe6−GeTe−FeTe2−AgFeTe2−Ag8GeTe6 phase regions was confirmed by the calculat... [more]

Space charge behavior has a strong impact on the long-term operation reliability of high voltage−direct current (HVDC) cables. This study intended to reveal the effect of trap density and depth on the space charge and electric field evolution behavior in HVDC cable insulation under different load currents and voltages by combined numerical bipolar charge transport (BCT) and thermal field simulation. The results show that when the load current is 1800 A (normal value), the temperature difference between the inside and the outside of the insulation is 20 °C, space charge accumulation and electric field distortion become more serious with the increase in the trap depth (Et) from 0.80 to 1.20 eV for the trap densities (Nt) of 10 × 1019 and 80 × 1019 m−3, and become more serious with the increase in Nt from 10 × 1019 to 1000 × 1019 m−3 for Et = 0.94 eV. Simultaneously decreasing trap depth and trap density (such as Et = 0.80 eV, Nt = 10 × 1019 m−3) or increasing trap depth and trap density... [more]

Semi-natural grassland habitats are most often limited to animal grazing and low intensity farming. Their potential in bioenergy production is complicated due to the heterogeneity, variation, accessibility, and need for complex pre-treatment/hydrolysis techniques to convert into valuable products. In this research, fermentable sugar production efficiency from various habitats at various vegetation periods was evaluated. The highest fermentable sugar yields (above 0.2 g/g volatile solids) over a period of 3 years were observed from habitats “xeric and calcareous grasslands” (Natura 2000 code: 6120) and “semi-natural dry grasslands and scrubland facies on calcareous substrates” (Natura 2000 code: 6210). Both had a higher proportion of dicotyledonous plants. At the same time, the highest productivity (above 0.7 t sugar/ha) was observed from lowland hay meadows in the initial stage of the vegetation. Thus, despite variable yield-affecting factors, grasslands can be a potential resource for... [more]

This paper presents an advanced adaptive single-pole auto-reclosing (ASPAR) scheme based on harmonic characteristics of the secondary arc voltage. For analysis of the harmonics, short-time Fourier transform (STFT), which is a universal signal processing tool for transforming a signal from the time domain to the frequency domain, is utilized. STFT is applied to extract the abnormal harmonic signature from the voltage waveform of a faulted phase when a transient or permanent fault occurs on a power transmission line. The proposed scheme uses the total harmonic distortion (THD) factor to determine the fault type based on the variation and distortion characteristics of the harmonics. Harmonic components in the order of odd/even are also utilized to detect the secondary arc extinction time and guide the reclosing operation. Based on these factors, two coordinated algorithms are proposed to reduce the unnecessary dead time in conventional auto-reclosing methods and enable an optimal reclosin... [more]

Understanding the flow in urban environments is an increasingly relevant problem due to its significant impact on air quality and thermal effects in cities worldwide. In this review we provide an overview of efforts based on experiments and simulations to gain insight into this complex physical phenomenon. We highlight the relevance of coherent structures in urban flows, which are responsible for the pollutant-dispersion and thermal fields in the city. We also suggest a more widespread use of data-driven methods to characterize flow structures as a way to further understand the dynamics of urban flows, with the aim of tackling the important sustainability challenges associated with them. Artificial intelligence and urban flows should be combined into a new research line, where classical data-driven tools and machine-learning algorithms can shed light on the physical mechanisms associated with urban pollution.

Wind turbines have become a significant part of the global power production and are still increasing in capacity. Pitch systems are an important part of modern wind turbines where they are used to apply aerodynamic braking for power regulation and emergency shutdowns. Studies have shown that the pitch system is responsible for up to 20% of the total down time of a wind turbine. Reducing the down time is an important factor for decreasing the total cost of energy of wind energy in order to make wind energy more competitive. Due to this, attention has come to condition monitoring and fault detection of such systems as an attempt to increase the reliability and availability, hereby the reducing the turbine downtime. Some methods for fault detection and condition monitoring of fluid power systems do exists, though not many are used in today’s pitch systems. This paper gives an overview of fault detection and condition monitoring methods of fluid power systems similar to fluid power pitch s... [more]

Oxygenated fuels, in this case short carbon-chain alcohols, have been investigated as alternative fuels to power compression ignition engines. A major advantage of short-chain alcohols is that they can be produced from renewable resources, i.e., cultivated commodities or biomass-based biorefineries. However, before entering the market, the effects of short-chain alcohols on engine performance, exhaust emissions, noise and sound quality need to be understood. This work sheds light on the relationship between the physicochemical properties of the alcohol/diesel fuel blends (ethanol and 1-propanol) on engine performance, exhaust emissions and, for the first time, on noise and sound quality. It has been demonstrated that when the content of alcohol in blends increased, soot and soluble organic material emissions drastically decreased, mainly due to the increase of oxygen content in the fuel. Reduction in soot emissions combined with higher thermodynamic efficiency of alcohol fuels, with re... [more]

In recent years, natural draft dry cooling systems with only one tower have been adopted in some 2 × 660 MW power-generating units owing to the advantage of lower construction costs. The operating cases of two power-generating units and one power-generating unit will both appear based on the power load requirement, which may lead to very different flow and heat transfer performances of this typical cooling system. Therefore, this research explores the local thermo-flow characteristics of air-cooled heat exchangers and sectors, and then analyzes the overall cooling performance of the above two operating cases under various wind conditions. Using the numerical modeling method, the results indicate that the flow and heat transfer performance of this cooling system decreases significantly in the case of one unit with half sectors dismissed. At wind speeds lower than 8 m/s, the difference in turbine back pressure between two units and one unit appears obviously higher than in other wind con... [more]

The article deals with the problem of detecting moisture in the walls of historical buildings. As part of the presented research, the following four methods based on mathematical modeling and machine learning were compared: total variation, least-angle regression, elastic net, and artificial neural networks. Based on the simulation data, the systems for the reconstruction of “pixel by pixel” tomographic images were trained. In order to test the reconstructive algorithms obtained during the research, images were generated based on real measurements and simulation cases. The method comparison was performed on the basis of three indicators: mean square error, relative image error, and image correlation coefficient. The above indicators were applied to four selected variants that corresponded to various parts of the walls. The variants differed in the dimensions of the tested wall sections, the number of electrodes used, and the resolution of the 3D image meshes. In all analyzed variants,... [more]

High-Voltage Direct Current (HVDC) systems are a feasible solution that allows the transmission of energy between several power networks. As a consequence of the use of HVDC systems, renewable energy sources can be integrated more easily into distribution grids and smart grids. Furthermore, HVDC systems can contribute to improving the power quality (PQ) of the grids to which they are connected. This paper presents a multiterminal HVDC system that not only controls the flows of active power between four different networks, but also compensates imbalances and harmonics in the grid currents to maintain balanced and sinusoidal voltages at the point of common coupling of the various grids. The compensation is carried out by the voltage-source converters (VSCs) connected to their respective AC grids. A control scheme based on the use of resonant regulators and proportional−integral (PI) controllers is responsible for of achieving the necessary power flow control with the amelioration of the... [more]

This paper investigates optimal power management of a fuel cell hybrid small unmanned aerial vehicle (sUAV) from the perspective of endurance (time of flight) maximization in a stochastic environment. Stochastic drift counteraction optimal control is exploited to obtain an optimal policy for power management that coordinates the operation of the fuel cell and battery to maximize the expected flight time while accounting for the limits on the rate of change of fuel cell power output and the orientation dependence of fuel cell efficiency. The proposed power management strategy accounts for known statistics in transitions of propeller power and climb angle during the mission, but does not require the exact preview of their time histories. The optimal control policy is generated offline using value iterations implemented in Cython, demonstrating an order of magnitude speedup as compared to MATLAB. It is also shown that the value iterations can be further sped up using a discount factor, bu... [more]

State-of-the-art ultra-fast battery chargers for electric vehicles simultaneously require high efficiency and high power density, leading to a challenging power converter design. In particular, the grid-side filter, which ensures sinusoidal current absorption with low pulse-width modulation (PWM) harmonic content, can be a major contributor to the overall converter size and losses. Therefore, this paper proposes a complete analysis, design and optimization procedure of a three-phase LCL filter for a modular DC fast charger. First, an overview of the basic LCL filter modeling is provided and the most significant system transfer functions are identified. Then, the optimal ratio between grid-side and converter-side inductance is discussed, aiming for the maximum filtering performance. A novel design methodology, based on a graphical representation of the filter design space, is thus proposed. Specifically, several constraints on the LCL filtering elements are enforced, such that all feasi... [more]

This paper covers the active voltage balancing method of secondary batteries. The number of applications using secondary batteries is increasing, and the batteries are normally connected in series/parallel to increase discharge cycle and power. The problem is that when there is a voltage imbalance between the cells or modules of a battery, there is a risk of an accident in the near-sighted way, shortening the life of the battery cells. Although this risk was prevented through passive balancing, this approach has limitations, including heat generation, long balancing time, and in the case of a battery that needs to be balanced between modules (or between stacks), its effectiveness decreases. Therefore, in this paper, an active cell balancing method that can overcome the limitations mentioned before is proposed. The proposed method uses a multi-winding transformer, and to increase the power density, the magnetizing inductance is decreased, and an auxiliary circuit is added. The validity... [more]

We integrate life cycle indicators for various technologies of an energy system model with high spatiotemporal detail and a focus on Europe and North Africa. Using multi-objective optimization, we calculate a pareto front that allows us to assess the trade-offs between system costs and life cycle greenhouse gas (GHG) emissions of future power systems. Furthermore, we perform environmental ex-post assessments of selected solutions using a broad set of life cycle impact categories. In a system with the least life cycle GHG emissions, the costs would increase by ~63%, thereby reducing life cycle GHG emissions by ~82% compared to the cost-optimal solution. Power systems mitigating a substantial part of life cycle GHG emissions with small increases in system costs show a trend towards a deployment of wind onshore, electricity grid and a decline in photovoltaic plants and Li-ion storage. Further reductions are achieved by the deployment of concentrated solar power, wind offshore and nuclear... [more]

In preparation for the electric mobility technological transition in Colombia, an impact assessment of the electric power system is required, considering the increasing loading that must be able to be managed in the future. In this paper, a plug-in electric vehicle (PEV) charging simulation methodology is developed in order to dimension the impact of this type of load on power grids. PEV electric properties, user charging behaviors, geographic location, trip distances, and other variables of interest are modeled from empirical or known probability distributions and later evaluated in different scenarios using Monte Carlo simulation and load flow analysis. This methodology is later applied to the transmission network of Antioquia (a department of Colombia) resulting in load increases of up to 40% on transmission lines and 20% on transformers in a high PEV penetration scenario in 2030, increases that are well within the expected grid capacity for that year, avoiding the need for addition... [more]

A mesoporous MnO network (MMN) structure and MMN/C composites were prepared and evaluated as anodes for high-energy and high-rate lithium-ion batteries (LIB) in comparison to typical manganese oxide nanoparticle (MnNP) and graphite anodes, not only in a half-cell but also in a full-cell configuration (assembled with an NCM523, LiNi0.5Co0.2Mn0.3O2, cathode). With the mesoporous features of the MMN, the MMN/C exhibited a high capacity (approximately 720 mAh g−1 at 100 mA g−1) and an excellent cycling stability at low electrode resistance compared to the MnNP/C composite. The MMN/C composite also showed much greater rate responses than the graphite anode. Owing to the inherent high discharge (de-lithiation) voltage of the MMN/C than graphite as anodes, however, the MMN‖NCM523 full cell showed approximately 87.4% of the specific energy density of the Gr‖NCM523 at 0.2 C. At high current density above 0.2 C, the MMN‖NCM523 cell delivered much higher energy than the Gr‖NCM523 mainly due to th... [more]

Drilling more efficiently and with less non-productive time (NPT) is one of the key enablers to reduce field development costs. In this work, we investigate the application of a data-driven optimization method called extremum seeking (ES) to achieve more efficient and safe drilling through automatic real-time minimization of the mechanical specific energy (MSE). The ES algorithm gathers information about the current downhole conditions by performing small tests with the applied weight on bit (WOB) and drill string rotational rate (RPM) while drilling and automatically implements optimization actions based on the test results. The ES method does not require an a priori model of the drilling process and can thus be applied even in instances when sufficiently accurate drilling models are not available. The proposed algorithm can handle various drilling constraints related to drilling dysfunctions and hardware limitations. The algorithm’s performance is demonstrated by simulations, where t... [more]