This study applies the Physical Optimum (PhO) as a reference value to rate the efficiency of two technical options for the oxygen supply of a hospital. The systematic comparison of the alternative processes using the PhO as a benchmark for the minimum input (exergy in this case) required to run a process with a certain benefit allows to determine the potential for optimization of each technology. Differences are analyzed by visualizing the losses of each individual production step in a process as well as by the resulting overall energy demand, including the primary energy. Possible alternatives are purchasing liquid oxygen from a cryogenic process or the production by means of Pressure Swing Adsorption (PSA) on site. The cryogenic production shows a lower exergy demand even though it also has a higher potential for optimization. Yet, the total losses, significantly impacted by the unavoidable transportation, sum up, resulting in the conclusion that the PSA is the preferable option over... [more]

To meet the increased demand of hydroelectric power generation, a novel drag-based Savonius turbine with the characteristics of a simpler fabrication process and good starting characteristics is designed, fabricated, and analyzed. The newly designed turbine is suitable to be installed in rivers, irrigation channels, ocean currents, etc., for small-scale hydroelectric power generation. In the present study, experiments are carried out to investigate the influence of the design parameters of this turbine on its power performance in order to improve its efficiency, including blade arc angles (180°, 135°), blade placement angles (0°, ±22.5°), and the number of blades (2, 3, 6, and 8). Further, three-dimensional CFD simulations are performed with Re = 6.72×105, matching the experimental conditions, in order to study the changes in the flow field and the rotation characteristics of the turbine. The research results indicate that a six-bladed turbine with a blade arc angle of 135° and a blade... [more]

Multistage hydraulic fracturing is one of the most prevalent approaches for shale reservoir development. Due to the complexity of constructing reservoir environments for experiments, numerical simulation is a vital method to study flow behavior under reservoir conditions. In this paper, we propose a numerical model that considers a multistage fractured horizontal well with a hilly-terrain trajectory in a shale reservoir with the presence of natural fractures. The model was constructed based on the MATLAB Reservoir Simulation Toolbox and used the Embedded Discrete Fractured Model (EDFM) to describe the interrelationship between the matrix, fractures, and wellbore. The model was then applied to an actual condensate gas well producing from a shale reservoir, and the effects of reservoir parameters on the simulation data were studied based on this well case. The simulation results were highly consistent with the actual production data, which validates the accuracy of this model and proves... [more]

With the development of smart grids, the application of localized relay protection devices has greatly reduced the distance between the secondary equipment and the primary equipment. The secondary equipment will be in a more complex electromagnetic environment during the operation of the GIS disconnector. The present study takes the multi-path electromagnetic disturbance on the secondary cable caused by the disconnector switching operation of the domestic 1000 kV ultra-high voltage GIS test circuit as the research background, solves the field-line coupling problem based on the finite integral technique, and combines the multi-conductor transmission line theory to solve the radiation disturbance and obtains its influencing factors. The results demonstrate that the radiated disturbance accounted for 16% of the overall electromagnetic disturbance when both ends of the shielding layer are grounded. The use of grounding at both ends of the shielding layer, reducing the height of the seconda... [more]

The article aimed to present the balance of outlays and the effects of restructuring Polish hard coal mining companies in the face of directions of the Energy Policy of Poland PEP 2040. The research problem is defined by the following question: have the goals of restructuring coal mining companies been achieved (and to what extent), and has the restructuring-related expenditure been economically rational? An answer to this question is based on the verification of five research hypotheses, in particular, have the incurred costs of restructuring contributed to changes to the energy mix (its desired time and degree), reducing related expenditure? The scope of research comprises all companies engaged in the extraction of solid mineral energy resources (the entire industry). An assessment of the restructuring process was conducted from two perspectives related to its time and scope. The first perspective was the restructuring programme as a sub-process of the economic transformation (1990−2... [more]

There is a lot of research on the neural models used for short-term load forecasting (STLF), which is crucial for improving the sustainable operation of energy systems with increasing technical, economic, and environmental requirements. Neural networks are computationally powerful; however, the lack of clear, readable and trustworthy justification of STLF obtained using such models is a serious problem that needs to be tackled. The article proposes an approach based on the local interpretable model-agnostic explanations (LIME) method that supports reliable premises justifying and explaining the forecasts. The use of the proposed approach makes it possible to improve the reliability of heuristic and experimental neural modeling processes, the results of which are difficult to interpret. Explaining the forecasting may facilitate the justification of the selection and the improvement of neural models for STLF, while contributing to a better understanding of the obtained results and broade... [more]

Accurate identification of the lithofacies and sedimentary facies of coal-bearing series is significant in the study of peat accumulation, coal thickness variation and coal-measured unconventional gas. This research integrated core, logging and 3D seismic data to conduct a comprehensive seismic−geological study on the sedimentary evolution characteristics and peat accumulation regularity of the Shanxi Formation in the Xinjing mining area of the Qinshui Basin. Firstly, the high-resolution sequence interface was identified, and the isochronous stratigraphic framework of the coal-bearing series was constructed. Then, the temporal and spatial evolution of sedimentary filling and sedimentary facies was dynamically analyzed using waveform clustering, phase rotation, stratal slice and frequency−division amplitude fusion methods. The results show that the Shanxi Formation in the study area can be divided into one third-order sequence and two fourth-order sequences. It developed a river-dominat... [more]

As a form of energy storage with high power and efficiency, a flywheel energy storage system performs well in the primary frequency modulation of a power grid. In this study, a three-phase permanent magnet synchronous motor was used as the drive motor of the system, and a simulation study on the control strategy of a flywheel energy storage system was conducted based on the primary frequency modulation of wind power. The speed and current double closed-loop control strategy was used in the system start-up phase, and the power and current double-closed-loop control strategy were used in the power compensation phase. The model reference adaptive control was used to accurately estimate the speed and position of the rotor. The system compensates for the wind power output by using a wind turbine in real-time and conducting simulation experiments to verify the feasibility of the charge and discharge control strategy. At the same time, it can be verified that the flywheel energy storage syste... [more]

Power capacitors are widely used in power transmission systems. During their operation, an electric force acting on the electrodes of the power capacitors actuates mechanical vibrations and radiates an audible noise. Considering a power capacitor as a general system, the frequency response with the electric force as the input and mechanical vibration as the output have been measured by engineers in recent years and used to evaluate the acoustic and mechanical features of products. Accidentally, it was found that the frequency of the capacitor vibration was not consistent with its excitation due to electro-mechanical coupling. This electro-mechanical coupling had not been considered in previous vibration models of power capacitors. Therefore, a new vibration model of power capacitors was built up in this paper and a so-called multi-frequency vibration characteristic was revealed. A theoretical analysis showed that the electric force and mechanical vibration of the power capacitors were... [more]

In this paper, an experimental study investigating the effect of the geometrical shape of the circular and rectangular pin fins on the heat transfer performance and the boiling phenomenon is presented. A pool boiling experiment in the HFE-7100 dielectric working fluid under atmospheric pressure was conducted. Boiling curves and boiling heat transfer coefficients of different test cases were plotted to evaluate the heat transfer performance as well as the captured images of the boiling phenomenon on the test samples. Two quantities, flow resistance and wetted perimeter, were calculated to understand the behaviour of the boiling physics due to variation of fin geometrical shape and, hence, their effect on the heat transfer performance. It was found that the cooling performance of the rectangular pin fins was higher than that of the circular pin fins, despite having a slightly higher flow resistance of 4% and 7%, respectively. This is believed to be the result of the longer wetted perimet... [more]

Nuclear energy is presently the single major low-carbon electricity source in Europe and is overall expected to maintain (perhaps eventually even increase) its current installed power from now to 2045. Long-term operation (LTO) is a reality in essentially all nuclear European countries, even when planning to phase out. New builds are planned. Moreover, several European countries, including non-nuclear or phasing out ones, have interests in next generation nuclear systems. In this framework, materials and material science play a crucial role towards safer, more efficient, more economical and overall more sustainable nuclear energy. This paper proposes a research agenda that combines modern digital technologies with materials science practices to pursue a change of paradigm that promotes innovation, equally serving the different nuclear energy interests and positions throughout Europe. This paper chooses to overview structural and fuel materials used in current generation reactors, as we... [more]

Submarine power cables are expected to last 20 years without maintenance to be considered technologically reliable enough and economically beneficial. One of the main issues facing this target is the development of what is called commonly water-trees (nanometer-sized flaws filled with residual humidity), that form within XLPE (cross-linked Polyethylene) insulators and then migrate towards copper, thus leading to its corrosion and further to possible shut-down. Water trees are resulting from the coalescence of nanovoids filled with residual humidity that migrate towards copper under the combined effects of electrical forces and plastic deformation. The nanovoids are originated during manufacturing, shipping, handling and embedding in deep seas. The formation of these nanovoids leads to the degradation of the service lifetime of submarine power cables. Current research is intended to come up with a way to go a little further towards the generalization of coalescence of n nanovoids. In th... [more]

The rapid development of renewable energy sources and electricity storage technologies is further driving the change and evolution of traditional energy systems. The aim is to interconnect the different electricity systems between and within countries to ensure greater reliability and flexibility. However, challenges are faced in reaching it, such as the power grid complexity, the system control, voltage fluctuations due to the reverse power flow, equipment overloads, resonance, incorrect island setting, and the diversity of user needs. The electricity grid digitalization in the market also requires the installation of smart devices to enable real-time information exchange between the generator and the user. Inverter-based distributed generation (DG) may be used to control the grid voltage. Smart PV inverters have the capability to supply both inductive and capacitive reactive power to control the voltage at the point of interconnection with the grid, and only technical parameters of s... [more]

A comprehensive uncertainty analysis in the event of a severe accident in a two-loop pressurized water reactor is conducted using an uncertainty package integrated in the ASYST code. The plant model is based on the nuclear power plant (NPP) Krško, a Westinghouse-type power plant. The station blackout scenario with a small break loss of coolant accident is analyzed, and all processes of the in-vessel phase are covered. A best estimate plus uncertainty (BEPU) methodology with probabilistic propagation of input uncertainty is used. The uncertain parameters are selected based on their impact on the safety criteria, the operation of the NPP safety systems and to describe uncertainties in the initial and boundary conditions. The number of required calculations is determined by the Wilks formula from the desired percentile and confidence level, and the values of the uncertain parameters are randomly sampled according to appropriate distribution functions. Results showing the thermal hydraulic... [more]

This paper compares multiple techniques to detect suboptimal conditions in the PV system. Detection of suboptimal conditions in the PV system is required to achieve optimal photovoltaic (PV) systems. Therefore, maintenance managers need to choose the most suitable techniques objectively. However, there is a lack of objective information comparing the effectiveness of the methods. This article calculates and compares the effectiveness of Infrared thermography (IRT), visual inspection (VI), and electrical analysis (EA) in detecting soiling, partial shadows, and electrical faults experimentally. The results showed that the VI was the best at detecting soiling and partial shading with 100% of effectiveness. IRT and EA had an effectiveness of 78% and 73%, respectively, detecting the three types of conditions under study. It was not possible to achieve maximum detection using only one of the techniques, but that VI must be combined with IR or EA. This research represents a significant contri... [more]

The emission of mercury from coal combustion has caused consequential hazards to the ecosystem. The key challenge to abating the mercury emission is to explore highly efficient adsorbents. Herein, sulfur-functionalized carbon (S-C) was synthesized by using a molten-salt pyrolysis strategy and employed for the removal of elemental mercury from coal-combustion flue gas. An ideal pore structure, which was favorable for the internal diffusion of the Hg0 molecule in carbon, was obtained by using a SiO2 hard template and adjusting the HF etching time. The as-prepared S-C with an HF etching time of 10 h possessed a saturation Hg0 adsorption capacity of 89.90 mg·g−1, far exceeding that of the commercial sulfur-loaded activated carbons (S/C). The S-C can be applied at a wide temperature range of 25−125 °C, far exceeding that of commercial S/C. The influence of flue gas components, such as SO2, NO, and H2O, on the Hg0 adsorption performance of S-C was insignificant, indicating a good applicabili... [more]

In northern China, a large volume of coal is consumed for heating in winter, resulting in frequent smog and air pollution, which has a serious effect on people’s health and quality of life. Clean heating is a national important livelihood strategy related to residents’ warmth. Whether haze weather can be effectively reduced and whether the heating energy structure can really be improved needs to be verified. This study takes 115 heating cities in the northern area as the research objects, takes 12 pilot cities implementing clean heating policy as the treatment group, employs the Propensity Score Matching method to match the non-pilot cities to get the reasonable control group city, uses the double-difference method to carry out the quantitative test on the implementation effect of the clean heating policy. The results show that clean heating in northern China reduces the air pollution in winter, and the air pollution level in winter decreases 46.6% after the implementation of the polic... [more]

A novel Artificial Neural Network (ANN) Based Optimal Feedforward Torque Control (OFTC) strategy is proposed which, after proper ANN design, training and validation, allows to analytically compute the optimal reference currents (minimizing copper and iron losses) for Interior Permanent Magnet Synchronous Machines (IPMSMs) with highly operating point dependent nonlinear electric and magnetic characteristics. In contrast to conventional OFTC, which either utilizes large look-up tables (LUTs; with more than three input parameters) or computes the optimal reference currents numerically or analytically but iteratively (due to the necessary online linearization), the proposed ANN-based OFTC strategy does not require iterations nor a decision tree to find the optimal operation strategy such as e.g., Maximum Torque per Losses (MTPL), Maximum Current (MC) or Field Weakening (FW). Therefore, it is (much) faster and easier to implement while (i) still machine nonlinearities and nonidealities such... [more]

Energy efficiency is one of the most important current challenges, and its impact at a global level is considerable. To solve current challenges, it is critical that consumers are able to control their energy consumption. In this paper, we propose using a time series of window-based entropy to detect anomalies in the electricity consumption of a household when the pattern of consumption behavior exhibits a change. We compare the accuracy of this approach with two machine learning approaches, random forest and neural networks, and with a statistical approach, the ARIMA model. We study whether these approaches detect the same anomalous periods. These different techniques have been evaluated using a real dataset obtained from different households with different consumption profiles from the Madrid Region. The entropy-based algorithm detects more days classified as anomalous according to context information compared to the other algorithms. This approach has the advantages that it does not... [more]

Nowadays, pump-turbine units have to experience multiple start-stops every day to balance the power production and consumption on the grid. During the transient process of turbine start-up, the hydraulic forces applied to the head-cover would change dramatically and induce high-level stresses on the head-cover bolts. As key components of large hydraulic turbine units, the head-cover bolts are subjected to tens of thousands of tonnes of hydraulic excitation force during operation. Special attention should be paid to the design of the head-cover bolts of large hydraulic pump-turbine units because these units have high water heads and high hydraulic excitation forces. Therefore, the safe design of the head-cover bolts is extremely important to maintain the operational safety of the whole unit. This paper investigates the flow-induced stress characteristics of the head-cover bolts during turbine start-up in a large prototype pump-turbine unit. A complete 3D fluid model and a corresponding... [more]

Exergy and energy analyses of two biodiesel production processes that integrate solar energy as the main energy source were developed to determine the process with the higher efficiency from an energy and exergy approach. The biodiesel production processes were simulated in ASPEN PLUS®, and the solar energy supply was studied in TRNSYS®, using EXCEL® simultaneously for the exergetic analysis. The solar thermal energy collection system can supply 81% of the energy required by the alkali process in the Flash separation equipment. For the supercritical process, solar thermal energy can supply 74.5% of the energy in the preheating and separation stages. The energy efficiency of the supercritical process is higher; nevertheless, the exergetic efficiency of the alkaline process is higher than the supercritical one. Solar collection systems contribute from 85% to 93% of the exergy destroyed by the global process for both cases. The alkaline biodiesel production process has the highest advanta... [more]

The accumulation of waste and toxic compounds has become increasingly harmful to the environment and human health. In this context, the use of laccases has become a focus of interest, due to the properties of these versatile enzymes: low substrate specificity, and water formation as a non-toxic end product. Thus, we begin our study with a general overview of the importance of laccase for the environment and industry, starting with the sources of laccases (plant, bacterial and fungal laccases), the structure and mechanism of laccases, microbial biosynthesis, and the immobilization of laccases. Then, we continue with an overview of agro-waste treatment by laccases wherein we observe the importance of laccases for the biodisponibilization of substrates and the biodegradation of agro-industrial byproducts; we then show some aspects regarding the degradation of xenobiotic compounds, dyes, and pharmaceutical products. The objective of this research is to emphasize and fully investigate the e... [more]

The cooling of PV models is an important process that enhances the generated electricity from these models, especially in hot areas. In this work, a new, active cooling algorithm is proposed based on active fan cooling and an artificial neural network, which is named the artificial dynamic neural network Fan cooling algorithm (DNNFC). The proposed system attaches five fans to the back of a PV model. Subsequently, only two fans work at any given time to circulate the air under the PV model in order to cool it down. Five different patterns of working fans have been experimented with in this work. To select the optimal pattern for any given time, a back propagation neural network model was trained. The algorithm is a dynamic algorithm since it re-trains the model with new recorded surface temperatures over time. In this way, the model automatically adapts to any weather and environmental conditions. The model was trained with an indoor dataset and tested with an outdoor dataset. An accura... [more]

This work aims to develop a novel system, including software and hardware, to perform independent control tasks in a genuine parallel manner. Currently, to control processes with various sampling periods, distributed control systems are most commonly utilized. The main goal of this system is to propose an alternative solution, which allows simultaneous control of both fast and slow processes. The presented approach utilizes FPGA (Field Programmable Gate Array) with Nios II processor (Intel Soft Processor Series) to implement and maintain instances of independent controllers. Instances can implement FDMC (Fast Dynamic Matrix Control) and PID (Proportional-Integral-Derivative) control algorithms with various sampling times. The FPGA-based design allows for true independence of controllers’ execution both from one another and the managing processor. Also, pure parallel execution allows for implementing slow and fast controllers in the same device. The complete flexible system with a matri... [more]

This study aims to effectively solve the problem of the destruction of the coal roof and floor overlying rock after mining the protective layer, and determines whether the gas in the protected layer can be effectively released. We do this based on the engineering background of the Weng’an Coal Mine; research and analysis of the movement of the roof and floor overlying rocks; the evolution of cracks and the pressure relief characteristics of the protected layer after mining the protective layer; and through theoretical analysis and similar simulation experiments. Through numerical simulation, it was found that the protected layer was depressurized due to the mining of the protective layer, and the decompression rate of the protected layer was 0.2−0.8. In addition, the overall expansion rate of the protected layer was greater than the requirements of the “Detailed Rules for Prevention and Control of Coal and Gas Outbursts” for coal mines, and the investigation of the residual gas pressur... [more]