Next Issue
Volume 13, May-1
Previous Issue
Volume 13, April-1
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
6.2
3.0
Journals
Energies
Volume 13
Issue 8
energies-logo

Journal Menu

► Journal Menu

Journal Browser

► Journal Browser
share announcement

Energies, Volume 13, Issue 8 (April-2 2020) – 265 articles

Cover Story (view full-size image): In the European Union, renewable electricity generation by (non-combustible) sources involves a huge increase in wind power. Compared to hydro-based energy sources, wind energy has overtaken all renewable sources. However, the growing demand for green energy has forced investors in the power industry to look for resources further out at sea. View this paper.
  • Issues are regarded as officially published after their release is announced to the table of contents alert mailing list.
  • You may sign up for e-mail alerts to receive table of contents of newly released issues.
  • PDF is the official format for papers published in both, html and pdf forms. To view the papers in pdf format, click on the "PDF Full-text" link, and use the free Adobe Reader to open them.
Order results
Result details
Section
Show export options expand_more Show export options expand_less
Select all
Export citation of selected articles as:
15 pages, 5224 KiB  
Article
Performance Assessment of Axial-Flux Permanent Magnet Motors from a Manual Manufacturing Process
by Adrian Mlot and Juan González
Energies 2020, 13(8), 2122; https://doi.org/10.3390/en13082122 - 24 Apr 2020
Cited by 5 | Viewed by 5877
Abstract
Implementation of a new design for the process of assembling an axial-flux permanent magnet synchronous motor (AF PMSM) may lead to unstable motor parameters during operation at low and high speeds. In this paper, experimental data related to the AFPMSM used in an [...] Read more.
Implementation of a new design for the process of assembling an axial-flux permanent magnet synchronous motor (AF PMSM) may lead to unstable motor parameters during operation at low and high speeds. In this paper, experimental data related to the AFPMSM used in an electric traction motor was monitored. The paper presents tracing of machine performance in order to find quality-related issues and to evaluate the assembly process. To assess the manual manufacturing process (low-volume production) and electrical machine performance, several motors, characterized by the same size and topology, were extensively tested. Useful AF PMSM parameters such as continuous torque and continuous current were measured. The winding temperature of the stators was also monitored and carefully examined. An attempt to assess motor performance, based on measurements and aimed at the identification of the weakest parts of the electric motor design is presented. In this paper it can be seen how the subcomponents of the machine and its detailed assembly process and tolerances play key roles in achievement of the designed continuous performance with symmetrical temperature distribution in the stator winding. Selected conclusions drawn from the obtained measurements were explained by a rotor/stator misalignment study using 3-D finite element analysis. Full article
(This article belongs to the Section F: Electrical Engineering)
►▼ Show Figures

Figure 1

19 pages, 8056 KiB  
Article
Electrical Faults Signals Restoring Based on Compressed Sensing Techniques
by Milton Ruiz and Iván Montalvo
Energies 2020, 13(8), 2121; https://doi.org/10.3390/en13082121 - 24 Apr 2020
Cited by 8 | Viewed by 2965
Abstract
This research focuses on restoring signals caused by power failures in transmission lines using the basis pursuit, matching pursuit, and orthogonal matching pursuit sensing techniques. The original signal corresponds to the instantaneous current and voltage values of the electrical power system. The heuristic [...] Read more.
This research focuses on restoring signals caused by power failures in transmission lines using the basis pursuit, matching pursuit, and orthogonal matching pursuit sensing techniques. The original signal corresponds to the instantaneous current and voltage values of the electrical power system. The heuristic known as brute force is used to find the quasi-optimal number of atoms k in the original signal. Next, we search for the minimum number of samples known as m; this value is necessary to reconstruct the original signal from sparse and random samples. Once the values of k and m have been identified, the signal restoration is performed by sampling sparse and random data at other bus bars of the power electrical system. Basis pursuit allows recovering the original signal from 70% of the random samples of the same signal. The higher the number of samples, the longer the restoration times, approximately 12 s for recovering the entire signal. Matching pursuit allows recovering the same percentage, but with the lowest restoration time. Finally, orthogonal matching pursuit recovers a slightly lower percentage with a higher number of samples with a significant increase in its recovery time. Therefore, for real-time electrical fault signal restoration applications, the best selection will be matching pursuit due to the fact that it presents the lowest machine time, but requires more samples compared with orthogonal matching pursuit. Basis pursuit and orthogonal matching pursuit require fewer sparse and random samples despite the fact that these require a longer processing time for signal recovery. These two techniques can be used to reduce the volume of data that is stored by phasor measurement systems. Full article
(This article belongs to the Section F: Electrical Engineering)
►▼ Show Figures

Figure 1

12 pages, 1815 KiB  
Article
A New Analytical Model for Calculating Transient Temperature Response of Vertical Ground Heat Exchangers with a Single U-Shaped Tube
by Shichen Gao, Changfu Tang, Wanjing Luo, Jiaqiang Han and Bailu Teng
Energies 2020, 13(8), 2120; https://doi.org/10.3390/en13082120 - 24 Apr 2020
Cited by 4 | Viewed by 2577
Abstract
The transient temperature response is of great importance for evaluating the thermal capacity of ground heat exchangers (GHE). Based on the composition line source theory and superposition principle, we have developed a novel analytical model in Laplace space for calculating the temperature transient [...] Read more.
The transient temperature response is of great importance for evaluating the thermal capacity of ground heat exchangers (GHE). Based on the composition line source theory and superposition principle, we have developed a novel analytical model in Laplace space for calculating the temperature transient response. In comparison to the existing models, this proposed model can account for the fluid thermal storage effect and heat rate difference between the two legs of the single U-tube. With the aid of this proposed model, we conduct a thorough sensitivity analysis to investigate the effects of different influencing factors on the thermal transient response. The calculated results show that fluid thermal storage and the rate difference can significantly influence the thermal response during the early studied period. Therefore, the effect of fluid thermal storage should not be neglected when the early-time thermal response is investigated. The thermal interference between the two legs will reduce the heat capacity of GHEs. A large distance between these two legs can be favorable for practical use. Full article
►▼ Show Figures

Figure 1

23 pages, 1107 KiB  
Article
Explaining Factors Leading to Community Acceptance of Wind Energy. Results of an Expert Assessment
by Elena De Luca, Cecilia Nardi, Laura Gaetana Giuffrida, Michael Krug and Maria Rosaria Di Nucci
Energies 2020, 13(8), 2119; https://doi.org/10.3390/en13082119 - 24 Apr 2020
Cited by 20 | Viewed by 4688
Abstract
The present article deals with two key drivers of social acceptance of wind energy: procedural justice and distributional justice. It is based on a comparative expert assessment carried out in the frame of the Horizon 2020 project WinWind covering six European countries. The [...] Read more.
The present article deals with two key drivers of social acceptance of wind energy: procedural justice and distributional justice. It is based on a comparative expert assessment carried out in the frame of the Horizon 2020 project WinWind covering six European countries. The focus of the paper is on procedural and financial participation of citizens and local stakeholders in wind energy projects. The first part covers institutional arrangements for public engagement in two areas of the decision-making process—wind turbine zoning/siting in spatial plans and authorization procedures. Here, three levels of public involvement—information, consultation and participation—were analyzed. The second part examines active and financial participation of citizens and local stakeholders. Here, we distinguish between two different modes of governance: institutionalized forms of public governance and voluntary forms of corporate governance. The outcomes suggest that concrete paths to the social acceptance of wind energy are fostered via appropriate institutional spaces for public engagement. Furthermore, missing opportunities for active and passive financial participation can have strong negative consequences for community acceptance Full article
(This article belongs to the Section C: Energy Economics and Policy)
►▼ Show Figures

Graphical abstract

18 pages, 6860 KiB  
Article
Preliminary Design and Off-Design Analysis of a Radial Outflow Turbine for Organic Rankine Cycles
by Jun-Seong Kim and Do-Yeop Kim
Energies 2020, 13(8), 2118; https://doi.org/10.3390/en13082118 - 24 Apr 2020
Cited by 16 | Viewed by 4557
Abstract
Recently, the advantages of radial outflow turbines have been outstanding in various operating conditions of the organic Rankine cycle. However, there are only a few studies of such turbines, and information on the design procedure is insufficient. The main purpose of this study [...] Read more.
Recently, the advantages of radial outflow turbines have been outstanding in various operating conditions of the organic Rankine cycle. However, there are only a few studies of such turbines, and information on the design procedure is insufficient. The main purpose of this study is to provide more detailed information on the design methodology of the turbine. In this paper, a preliminary design program of a radial outflow turbine for organic Rankine cycles was developed. The program determines the main specifications of the turbine through iterative calculations using the enthalpy loss model and deviation angle model. For reliability evaluation of the developed algorithm, a 400.0 kW turbine for R143a was designed. The designed turbine was validated through computational fluid dynamics. As a result, the accuracy of the program was about 95% based on the turbine power, which shows that it is reliable. In addition, the turbine target performance could be achieved by fine-tuning the blade angle of the nozzle exit. In addition, performance evaluation of the turbine against off-design conditions was performed. Ranges of velocity ratio, loading coefficient, and flow coefficient that can expect high efficiency were proposed through the off-design analysis of the turbine. Full article
(This article belongs to the Section B: Energy and Environment)
►▼ Show Figures

Graphical abstract

21 pages, 6105 KiB  
Article
Energy Consumption and Lifecycle Cost Analysis of Electric City Buses with Multispeed Gearboxes
by Antti Ritari, Jari Vepsäläinen, Klaus Kivekäs, Kari Tammi and Heikki Laitinen
Energies 2020, 13(8), 2117; https://doi.org/10.3390/en13082117 - 24 Apr 2020
Cited by 33 | Viewed by 4892
Abstract
This study investigates the potential of improving the energy efficiency and reducing the lifecycle costs of electric city buses with multispeed gearboxes. A two-speed dual clutch gearbox and a continuously variable transmission were studied and compared to a reference fixed gear ratio powertrain. [...] Read more.
This study investigates the potential of improving the energy efficiency and reducing the lifecycle costs of electric city buses with multispeed gearboxes. A two-speed dual clutch gearbox and a continuously variable transmission were studied and compared to a reference fixed gear ratio powertrain. A novel two-level optimization model was introduced. The top level involves an exhaustive search algorithm and quasi-static vehicle dynamic model for optimizing the two-speed gearbox gear ratios, utilizing efficiency maps for the electric motor and the inverter. The second level is an integer programming model, which finds an optimal gear shifting policy subject to constraints on hysteresis and gear shifting induced losses. The model was applied with a standard driving cycle and additionally with three measured cycles acquired from a prototype battery electric city bus operating on a daily schedule on a suburban route in Espoo, Finland. The results showed that a two-speed gearbox reduced energy consumption by 2–3.2%, depending on the driving cycle characteristics. On the other hand, the continuously variable transmission was found to increase consumption by 1.9–4.0% due to large losses of the belt mechanism. It was concluded that the two-speed gearbox is a cost-effective investment for electric city buses characterized by operation profiles with frequent acceleration and braking events. Full article
(This article belongs to the Special Issue Electric Systems for Transportation)
►▼ Show Figures

Figure 1

24 pages, 3448 KiB  
Article
The Energy Saving Potential of Wide Windows in Hospital Patient Rooms, Optimizing the Type of Glazing and Lighting Control Strategy under Different Climatic Conditions
by Silvia Cesari, Paolo Valdiserri, Maddalena Coccagna and Sante Mazzacane
Energies 2020, 13(8), 2116; https://doi.org/10.3390/en13082116 - 24 Apr 2020
Cited by 18 | Viewed by 5123
Abstract
If not properly designed, the adoption of large windows can sometimes have a negative impact on building energy demand. For this reason, aggravated by the outdated building envelope of the healthcare building stock, large fenestration systems are usually avoided in hospitals, especially in [...] Read more.
If not properly designed, the adoption of large windows can sometimes have a negative impact on building energy demand. For this reason, aggravated by the outdated building envelope of the healthcare building stock, large fenestration systems are usually avoided in hospitals, especially in old structures. However, with appropriate glazing specifications, the adoption of wider openings can result into significant energy savings, lower costs and strong positive effects on patients and staff well-being. The present study investigates how different window sizes and types of glazing affect heating, cooling and lighting energy demand in a hospital patient room. The objective is to evaluate the energy savings that may be obtained when installing larger windows and to identify the glazing properties allowing one to reach the maximum energy reductions. Simulations were carried out using nine diverse glazing systems, already available on the market, and their energy performance was evaluated in relation to two different window areas: a common size opening, characterized by a 25% Window-to-Wall Ratio (WWR), and a floor to ceiling window, with 77% WWR. The analysis was conducted taking into consideration four different orientations in four Italian cities, supposing two artificial lighting control strategies. The results highlighted how the adoption of wider windows with appropriate glazings and a daylight-linked dimming lighting control strategy may lower the primary energy demand up to 17%. Full article
►▼ Show Figures

Figure 1

18 pages, 1225 KiB  
Review
Future Design Approaches for Energy Poverty: Users Profiling and Services for No-Vulnerable Condition
by Andrea Boeri, Valentina Gianfrate, Saveria Olga Murielle Boulanger and Martina Massari
Energies 2020, 13(8), 2115; https://doi.org/10.3390/en13082115 - 24 Apr 2020
Cited by 18 | Viewed by 4320
Abstract
Analyzing data from the Energy Poverty Observatory in Europe, it emerges that more than 50 million households in the EU live in energy poverty (people that cannot heat their homes during winter; cannot make their homes comfortable during the summer; pay their energy [...] Read more.
Analyzing data from the Energy Poverty Observatory in Europe, it emerges that more than 50 million households in the EU live in energy poverty (people that cannot heat their homes during winter; cannot make their homes comfortable during the summer; pay their energy bills late). Research studies realized in the last 20 years highlight that making energy demand efficient and effective is the more significant and socially important the more it is able to involve users who are unable to sustain energy demand. The evolution of the research sees a narrowing of the field of investigation by focusing on the user dimension of energy poverty, stressing the role of citizens not only as consumer but also as producers of solutions to tackle energy poverty, real energy communities of agents. The paper aims to provide a systematic literature review highlighting the major findings of the topic, investigating the relationship between spatial and social issues, and looking at the state of energy poverty by addressing the profiling of users and consequently of services useful to overcome their current vulnerable condition. The paper is structured in two core sections. The first one gives the results of a systematic literature review on the energy/fuel poverty topic, the second one deepens the role of communities and individuals need, crucial in defining new design approaches for supportive solutions to tackle energy poverty. Full article
(This article belongs to the Special Issue Energy Performance in Buildings and Quality of Life)
►▼ Show Figures

Graphical abstract

24 pages, 9029 KiB  
Article
Study of PTC System with Rectangular Cavity Receiver with Different Receiver Tube Shapes Using Oil, Water and Air
by Alireza Rafiei, Reyhaneh Loni, Gholamhassan Najafi and Talal Yusaf
Energies 2020, 13(8), 2114; https://doi.org/10.3390/en13082114 - 24 Apr 2020
Cited by 3 | Viewed by 2992
Abstract
Today, application of cavity receivers in solar concentrator systems is suggested as an interesting and novelty research subject for increasing thermal performance. In this research, a parabolic trough concentrator (PTC) with a rectangular cavity receiver was energetically investigated. The cavity receiver was studied [...] Read more.
Today, application of cavity receivers in solar concentrator systems is suggested as an interesting and novelty research subject for increasing thermal performance. In this research, a parabolic trough concentrator (PTC) with a rectangular cavity receiver was energetically investigated. The cavity receiver was studied with smooth and corrugated tubes. Different solar heat transfer fluids were considered, including water, air, and thermal oil. The effect of different operational parameters, as well as structural parameters, was investigated. The results showed that the linear rectangular cavity receiver with corrugated tube showed higher amounts of the absorbed heat and energy performance compared to the smooth tube as the cavity tube. Thermal performance of the rectangular cavity was improved using the application of water as the solar heat transfer fluid, which was followed by thermal oil and, finally, air, as the solar heat transfer fluid. Finally, it could be recommended that the rectangular cavity receiver with smooth tube using air as the solar heat transfer fluid is more appropriate for coupling this system with a Bryton cycle, whereas the rectangular cavity receiver with the corrugated tube using water or oil as the solar heat transfer fluid is recommended for achieving higher outlet temperature of the heat transfer fluid. Full article
(This article belongs to the Section A2: Solar Energy and Photovoltaic Systems)
►▼ Show Figures

Figure 1

19 pages, 6774 KiB  
Article
An Experimental Investigation of Wake Characteristics and Power Generation Efficiency of a Small Wind Turbine under Different Tip Speed Ratios
by Yu-Ting Wu, Chang-Yu Lin and Che-Ming Hsu
Energies 2020, 13(8), 2113; https://doi.org/10.3390/en13082113 - 24 Apr 2020
Cited by 4 | Viewed by 2910
Abstract
We carried out a wind tunnel experiment to examine the power generation efficiency of a stand-alone miniature wind turbine and its wake characteristics at different tip speed ratios (TSRs) under the same mean inflow velocity. Resistors in the electrical circuit were adjusted to [...] Read more.
We carried out a wind tunnel experiment to examine the power generation efficiency of a stand-alone miniature wind turbine and its wake characteristics at different tip speed ratios (TSRs) under the same mean inflow velocity. Resistors in the electrical circuit were adjusted to control the TSRs to 0.9, 1.5, 3.0, 4.1, 5.2, and 5.9. The currents were measured to estimate the turbine power outputs versus the TSRs and then establish the actual power generation coefficient Cp distribution. To calculate the mechanical power coefficient, a new estimation method of the mechanical torque constant is proposed. A reverse calibration on the blade rotation speed was performed with given electrical voltages and currents that are used to estimate the mechanical power coefficient Cp, mech. In the experiment, the maximum Cp,mech was approximately 0.358 (corresponding to the maximum Cp of 0.212) at the TSR of 4.1. Significant findings indicate that the turbine at the TSR of 5.2 produces a smaller torque but a larger power output compared with that at the TSR of 3.0. This comparison further displays that the turbine at the TSR of 5.2, even with larger power output, still produces a turbine wake that has smaller velocity deficits and smaller turbulence intensity than that at the TSR of 3.0. This behavior demonstrates the significance of the blade-rotation control (i.e., pitch regulation) system to the turbine operation in a large wind farm for raising the overall farm power productivity. Full article
►▼ Show Figures

Graphical abstract

19 pages, 1589 KiB  
Article
Analysis of Metal Oxide Varistor Arresters for Protection of Multiconductor Transmission Lines Using Unconditionally-Stable Crank–Nicolson FDTD
by Erika Stracqualursi, Rodolfo Araneo, Giampiero Lovat, Amedeo Andreotti, Paolo Burghignoli, Jose Brandão Faria and Salvatore Celozzi
Energies 2020, 13(8), 2112; https://doi.org/10.3390/en13082112 - 24 Apr 2020
Cited by 11 | Viewed by 3212
Abstract
Surge arresters may represent an efficient choice for limiting lightning surge effects, significantly reducing the outage rate of power lines. The present work firstly presents an efficient numerical approach suitable for insulation coordination studies based on an implicit Crank–Nicolson finite difference time domain [...] Read more.
Surge arresters may represent an efficient choice for limiting lightning surge effects, significantly reducing the outage rate of power lines. The present work firstly presents an efficient numerical approach suitable for insulation coordination studies based on an implicit Crank–Nicolson finite difference time domain method; then, the IEEE recommended surge arrester model is reviewed and implemented by means of a local implicit scheme, based on a set of non-linear equations, that are recast in a suitable form for efficient solution. The model is proven to ensure robustness and second-order accuracy. The implementation of the arrester model in the implicit Crank–Nicolson scheme represents the added value brought by the present study. Indeed, its preserved stability for larger time steps allows reducing running time by more than 60 % compared to the well-known finite difference time domain method based on the explicit leap-frog scheme. The reduced computation time allows faster repeated solutions, which need to be looked for on assessing the lightning performance (randomly changing, parameters such as peak current, rise time, tail time, location of the vertical leader channel, phase conductor voltages, footing resistance, insulator strength, etc. would need to be changed thousands of times). Full article
(This article belongs to the Special Issue Power and Signal Transmission Lines Modeling and Large Network Analysis)
►▼ Show Figures

Figure 1

25 pages, 7715 KiB  
Article
Boundary Identification for Traction Energy Conservation Capability of Urban Rail Timetables: A Case Study of the Beijing Batong Line
by Jiang Liu, Tian-tian Li, Bai-gen Cai and Jiao Zhang
Energies 2020, 13(8), 2111; https://doi.org/10.3390/en13082111 - 24 Apr 2020
Cited by 1 | Viewed by 2707
Abstract
Energy conservation is attracting more attention to achieve a reduced lifecycle system cost level while enabling environmentally friendly characteristics. Conventional research mainly concentrates on energy-saving speed profiles, where the energy level evaluation of the timetable is usually considered separately. This paper integrates the [...] Read more.
Energy conservation is attracting more attention to achieve a reduced lifecycle system cost level while enabling environmentally friendly characteristics. Conventional research mainly concentrates on energy-saving speed profiles, where the energy level evaluation of the timetable is usually considered separately. This paper integrates the train driving control optimization and the timetable characteristics by analyzing the achievable tractive energy conservation performance and the corresponding boundaries. A calculation method for energy efficient driving control solution is proposed based on the Bacterial Foraging Optimization (BFO) strategy, which is utilized to carry out batch processing with timetable. A boundary identification solution is proposed to detect the range of energy conservation capability by considering the relationships with average interstation speed and the passenger volume condition. A case study is presented using practical data of Beijing Metro Batong Line and two timetable schemes. The results illustrate that the proposed optimized energy efficient driving control approach is capable of saving tractive energy in comparison with the conventional traction calculation-based train operation solution. With the proposed boundary identification method, the capability space of the energy conservation profiles with respect to the energy reduction and energy saving rate is revealed. Moreover, analyses and discussions on effects from different passenger load conditions are given to both the weekday and weekend timetables. Results of this paper may assist the decision making of rail operators and engineers by enhancing the cost effectiveness and energy efficiency. Full article
(This article belongs to the Special Issue Optimal Design and Control of Transportation Energy Saving and Energy Management System)
►▼ Show Figures

Figure 1

11 pages, 5983 KiB  
Article
Development and Verification of Hybrid Power Controller Using Indoor HIL Test for the Solar UAV
by Sunghun Jung
Energies 2020, 13(8), 2110; https://doi.org/10.3390/en13082110 - 24 Apr 2020
Cited by 4 | Viewed by 2952
Abstract
A hybrid power system (HPS) is developed for the photovoltaic (PV) powered and tethered multirotor unmanned aerial vehicle (UAV) based on the robot operating system (ROS) and verified using an indoor hardware-in-the-loop (HIL) test. All the processes, including a UAV flight mode change [...] Read more.
A hybrid power system (HPS) is developed for the photovoltaic (PV) powered and tethered multirotor unmanned aerial vehicle (UAV) based on the robot operating system (ROS) and verified using an indoor hardware-in-the-loop (HIL) test. All the processes, including a UAV flight mode change (i.e., takeoff, hovering, and landing) and power flow control (consisting of PV modules, a LiPo battery pack, and a UAV) are completely automated using a combination of Pixhawk 2.1 and the Raspberry Pi 3 Model B (RPi 3B). Once the indoor HIL test starts, (1) the UAV takes off and hovers with a preassigned 10 m altitude at a fixed point and keeps hovering until the voltage drops below 13.4 V ; (2) the UAV lands when the voltage drops below 13.4 V, and the hybrid power controller (HPC) starts to charge the LiPo battery pack using the energy from PV modules; and (3) the UAV takes off when the voltage of the battery pack becomes more than 16.8 V, and the procedure repeats from (1). A PV-powered and tethered multirotor UAV using the proposed HPS can fly more safely for a longer time, particularly in an urban area, and so it is competitive to the traditional multirotor type UAV in the sense of both the flight time and the surveillance mission performance. Full article
(This article belongs to the Special Issue Smart Management of Distributed Energy Resources)
►▼ Show Figures

Figure 1

15 pages, 12056 KiB  
Article
Impedance-Based Stability Analysis of Paralleled Grid-Connected Rectifiers: Experimental Case Study in a Data Center
by Henrik Alenius and Tomi Roinila
Energies 2020, 13(8), 2109; https://doi.org/10.3390/en13082109 - 24 Apr 2020
Cited by 13 | Viewed by 4188
Abstract
Grid-connected systems often consist of several feedback-controlled power-electronics converters that are connected in parallel. Consequently, a number of stability issues arise due to interactions among multiple converter subsystems. Recent studies have presented impedance-based methods to assess the stability of such large systems. However, [...] Read more.
Grid-connected systems often consist of several feedback-controlled power-electronics converters that are connected in parallel. Consequently, a number of stability issues arise due to interactions among multiple converter subsystems. Recent studies have presented impedance-based methods to assess the stability of such large systems. However, only few real-life experiences have been previously presented, and practical implementations of impedance-based analysis are rare for large-scale systems that consist of multiple parallel-connected devices. This work presents a case study in which an unstable high-frequency operation, caused by multiple paralleled grid-connected rectifiers, of a 250 kW data center in southern Finland is reported and studied. In addition, the work presents an experimental approach for characterizing and assessing the system stability by using impedance measurements and an aggregated impedance-based analysis. Recently proposed wideband-identification techniques based on binary injection and Fourier methods are applied to obtain the experimental impedance measurements from the input terminals of a single data center rectifier unit. This work provides a practical approach to design and implement the impedance-based stability analysis for a system consisting of multiple paralleled grid-connected converters. It is shown that the applied methods effectively predict the overall system stability and the resonant modes of the system, even with very limited information on the system. The applied methods are versatile, and can be utilized in various grid-connected applications, for example, in adaptive control, system monitoring, and stability analysis. Full article
(This article belongs to the Special Issue Power Electronics in Renewable Energy Systems Ⅱ)
►▼ Show Figures

Graphical abstract

18 pages, 1288 KiB  
Article
Battery-Aware Electric Truck Delivery Route Exploration
by Donkyu Baek, Yukai Chen, Naehyuck Chang, Enrico Macii and Massimo Poncino
Energies 2020, 13(8), 2096; https://doi.org/10.3390/en13082096 - 24 Apr 2020
Cited by 8 | Viewed by 2870
Abstract
The energy-optimal routing of Electric Vehicles (EVs) in the context of parcel delivery is more complicated than for conventional Internal Combustion Engine (ICE) vehicles, in which the total travel distance is the most critical metric. The total energy consumption of EV delivery strongly [...] Read more.
The energy-optimal routing of Electric Vehicles (EVs) in the context of parcel delivery is more complicated than for conventional Internal Combustion Engine (ICE) vehicles, in which the total travel distance is the most critical metric. The total energy consumption of EV delivery strongly depends on the order of delivery because of transported parcel weight changing over time, which directly affects the battery efficiency. Therefore, it is not suitable to find an optimal routing solution with traditional routing algorithms such as the Traveling Salesman Problem (TSP), which use a static quantity (e.g., distance) as a metric. In this paper, we explore appropriate metrics considering the varying transported parcel total weight and achieve a solution for the least-energy delivery problem using EVs. We implement an electric truck simulator based on EV powertrain model and nonlinear battery model. We evaluate different metrics to assess their quality on small size instances for which the optimal solution can be computed exhaustively. A greedy algorithm using the empirically best metric (namely, distance × residual weight) provides significant reductions (up to 33%) with respect to a common-sense heaviest first package delivery route determined using a metric suggested by the battery properties. This algorithm also outperforms the state-of-the-art TSP heuristic algorithms, which consumes up to 12.46% more energy and 8.6 times more runtime. We also estimate how the proposed algorithms work well on real roads interconnecting cities located at different altitudes as a case study. Full article
(This article belongs to the Special Issue Energy Storage Systems for Electric Vehicles)
►▼ Show Figures

Figure 1

21 pages, 3471 KiB  
Article
Fatigue Reliability Analysis of Wind Turbine Drivetrain Considering Strength Degradation and Load Sharing Using Survival Signature and FTA
by Yao Li, Caichao Zhu, Xu Chen and Jianjun Tan
Energies 2020, 13(8), 2108; https://doi.org/10.3390/en13082108 - 23 Apr 2020
Cited by 14 | Viewed by 3617
Abstract
The wind turbine drivetrain suffers significant impact loads that severely affect the reliability and safety of wind turbines. Bearings and gears within the drivetrain are critical components with high repair costs and lengthy downtime. To realistically assess the system reliability, we propose to [...] Read more.
The wind turbine drivetrain suffers significant impact loads that severely affect the reliability and safety of wind turbines. Bearings and gears within the drivetrain are critical components with high repair costs and lengthy downtime. To realistically assess the system reliability, we propose to establish an electromechanical coupling dynamic model of the wind turbine considering the control strategy and environmental parameters and evaluate the system’s reliability of wind turbine drivetrain based on loads of gears and bearings. This paper focuses on the dynamic reliability analysis of the wind turbine under the control strategy and environmental conditions. SIMPACK (v9.7, Dassault Systèmes, Gilching, Germany) is used to develop the aero-hydro-servo-elastic coupling dynamic model with the full drivetrain that considers the flexibility of the tower and blade, the stochastic loads of wind and waves, gear meshing features, as well as the control strategy. The system reliability level of wind turbine drivetrain at different wind conditions is assessed using survival signature and fault tree analysis (FTA), and the influences of strength degradation of the transmission components on the system reliability are explored. Following this, the bending fatigue reliability and contact fatigue reliability concerning different wind conditions are compared in this paper. A case study is performed to demonstrate the effectiveness and feasibility of the proposed methodology. Full article
(This article belongs to the Section A3: Wind, Wave and Tidal Energy)
►▼ Show Figures

Graphical abstract

19 pages, 250 KiB  
Article
The Role of Low Temperature Waste Heat Recovery in Achieving 2050 Goals: A Policy Positioning Paper
by Edward Wheatcroft, Henry Wynn, Kristina Lygnerud, Giorgio Bonvicini and Daniela Leonte
Energies 2020, 13(8), 2107; https://doi.org/10.3390/en13082107 - 23 Apr 2020
Cited by 35 | Viewed by 6550
Abstract
Urban waste heat recovery, in which low temperature heat from urban sources is recovered for use in a district heat network, has a great deal of potential in helping to achieve 2050 climate goals. For example, heat from data centres, metro systems, public [...] Read more.
Urban waste heat recovery, in which low temperature heat from urban sources is recovered for use in a district heat network, has a great deal of potential in helping to achieve 2050 climate goals. For example, heat from data centres, metro systems, public sector buildings and waste water treatment plants could be used to supply 10% of Europe’s heat demand. Despite this, at present, urban waste heat recovery is not widespread and is an immature technology. Based on interviews with urban waste heat stakeholders, investors interested in green investments, and experience from demonstrator projects, a number of recommendations are made. It is suggested that policy raising awareness of waste heat recovery, encouraging investment and creating a legal framework should be implemented. It is also recommended that pilot projects should be promoted to help demonstrate technical and economic feasibility. A pilot credit facility is suggested aimed at bridging the gap between potential investors and heat recovery projects. Full article
(This article belongs to the Special Issue Economic Analysis on Energy and Environmental Issues and Policy)
15 pages, 8736 KiB  
Article
A Nearly Zero-Energy Microgrid Testbed Laboratory: Centralized Control Strategy Based on SCADA System
by Mostafa Kermani, Domenico Luca Carnì, Sara Rotondo, Aurelio Paolillo, Francesco Manzo and Luigi Martirano
Energies 2020, 13(8), 2106; https://doi.org/10.3390/en13082106 - 23 Apr 2020
Cited by 41 | Viewed by 4659
Abstract
Currently, despite the use of renewable energy sources (RESs), distribution networks are facing problems, such as complexity and low productivity. Emerging microgrids (MGs) with RESs based on supervisory control and data acquisition (SCADA) are an effective solution to control, manage, and finally deal [...] Read more.
Currently, despite the use of renewable energy sources (RESs), distribution networks are facing problems, such as complexity and low productivity. Emerging microgrids (MGs) with RESs based on supervisory control and data acquisition (SCADA) are an effective solution to control, manage, and finally deal with these challenges. The development and success of MGs is highly dependent on the use of power electronic interfaces. The use of these interfaces is directly related to the progress of SCADA systems and communication infrastructures. The use of SCADA systems for the control and operation of MGs and active distribution networks promotes productivity and efficiency. This paper presents a real MG case study called the LAMBDA MG testbed laboratory, which has been implemented in the electrical department of the Sapienza University of Rome with a centralized energy management system (CEMS). The real-time results of the SCADA system show that a CEMS can create proper energy balance in a LAMBDA MG testbed and, consequently, minimize the exchange power of the LAMBDA MG and main grid. Full article
(This article belongs to the Special Issue SCADA and Energy Management Applications in Electric Power Systems)
►▼ Show Figures

Figure 1

13 pages, 1787 KiB  
Article
Dynamic Mechanical Compression Impulse of Lithium-Ion Pouch Cells
by Alon Ratner, Richard Beaumont and Iain Masters
Energies 2020, 13(8), 2105; https://doi.org/10.3390/en13082105 - 23 Apr 2020
Cited by 10 | Viewed by 3753
Abstract
Strain rate sensitivity has been widely recognized as a significant feature of the dynamic mechanical properties of lithium-ion cells, which are important for their accurate representation in automotive crash simulations. This research sought to improve the precision with which dynamic mechanical properties can [...] Read more.
Strain rate sensitivity has been widely recognized as a significant feature of the dynamic mechanical properties of lithium-ion cells, which are important for their accurate representation in automotive crash simulations. This research sought to improve the precision with which dynamic mechanical properties can be determined from drop tower impact testing through the use of a diaphragm to minimize transient shock loads and to constrain off-axis motion of the indenter, specialized impact absorbers to reduce noise, and observation of displacement with a high speed camera. Inert pouch cells showed strain rate sensitivity in an increased stiffness during impact tests that was consistent with the poromechanical interaction of the porous structure of the jellyroll with the liquid electrolyte. The impact behaviour of the inert pouch cells was similar to that of an Expanded Polypropylene foam (EPP), with the exception that the inert pouch cells did not show hysteretic recovery under the weight of the indenter. This suggests that the dynamic mechanical behaviour of the inert pouch cells is analogous to a highly damped foam. Full article
(This article belongs to the Section D1: Advanced Energy Materials)
►▼ Show Figures

Graphical abstract

20 pages, 12419 KiB  
Article
System Designs and Experimental Assessment of a Seven-Mode Vehicle-Oriented Hybrid Powertrain Platform
by Chun-Hsin Chang, Hsuan-Yung Chang, Yi-Hsuan Hung, Chien-Hsun Wu and Ji-Jia Xu
Energies 2020, 13(8), 2104; https://doi.org/10.3390/en13082104 - 23 Apr 2020
Viewed by 2619
Abstract
This study developed a mechatronics platform for a seven-mode vehicle-oriented powertrain system. The innovative “all-in-one” concept was used for flexibly arranging various power or energy sources to be combined for various hybrid powertrains. Hence, it significantly reduces the cost and human resources for [...] Read more.
This study developed a mechatronics platform for a seven-mode vehicle-oriented powertrain system. The innovative “all-in-one” concept was used for flexibly arranging various power or energy sources to be combined for various hybrid powertrains. Hence, it significantly reduces the cost and human resources for evaluating new-type power systems or developed vehicle control strategies on the same experimental platform. In this study, three power sources were chosen for providing hybrid power. The first source is a 125 c.c. spark ignition (SI) engine, where a controllable throttle valve governs the output torque, while a fuel meter measures the consumed fuel. The second one is a 1.5kW hub motor, where a motor control unit (MCU) and a 48V lithium battery pack properly provide the required electric power. The third source is an air engine, where a 220V air compressor and other components provide the pneumatic power. For the experimental platform, a developed Matlab/Simulink package receives the measured signals and sends the control commands to actuators. Through the on/off state control of three controllable e-clutches, three single-source modes, three dual-source modes, and one three-source mode (3+3+1) can be conducted. A 1.1kW/24V magnetic powder brake emulates the road load. The results show that three dual-source modes and a three-source mode were successfully operated. The efficiencies, torques and speeds, mass flow rates, etc. have been measured and calculated. This platform is aimed for the research fields of green energies, advanced powertrains, and power flow management. Full article
(This article belongs to the Section E: Electric Vehicles)
►▼ Show Figures

Figure 1

19 pages, 3819 KiB  
Article
Influence of the Meteorological Record Length on the Generation of Representative Weather Files
by Michele Libralato, Giovanni Murano, Alessandra De Angelis, Onorio Saro and Vincenzo Corrado
Energies 2020, 13(8), 2103; https://doi.org/10.3390/en13082103 - 23 Apr 2020
Cited by 5 | Viewed by 3280
Abstract
Heat and moisture (HM) transfer simulations of building envelopes and whole building energy simulations require adequate weather files. The common approach is to use weather data of reference years constructed from meteorological records. The weather record affects the capability of representing the real [...] Read more.
Heat and moisture (HM) transfer simulations of building envelopes and whole building energy simulations require adequate weather files. The common approach is to use weather data of reference years constructed from meteorological records. The weather record affects the capability of representing the real weather of the resulting reference years. In this paper the problem of the influence of the length of the records on the representativeness of the reference years is addressed and its effects are evaluated also for the applicative case of the moisture accumulation risk analysis with the Glaser Method and with DELPHIN 6, confirming that records shorter than 10 years could lead to less representative reference years. On the other hand, it is shown that reference years obtained from longer periods are not representative of the most recent years, which present higher dry-bulb air temperatures due to a short-term climate change effect observed in all the considered weather records. An alternative representative year (Moisture Representative Year) to be used in building energy simulations with a strong dependence on moisture is presented. Full article
(This article belongs to the Special Issue Selected Papers from BS2019 – Building Simulation)
►▼ Show Figures

Graphical abstract

16 pages, 1243 KiB  
Article
Self-Attention Network for Partial-Discharge Diagnosis in Gas-Insulated Switchgear
by Vo-Nguyen Tuyet-Doan, Tien-Tung Nguyen, Minh-Tuan Nguyen, Jong-Ho Lee and Yong-Hwa Kim
Energies 2020, 13(8), 2102; https://doi.org/10.3390/en13082102 - 23 Apr 2020
Cited by 23 | Viewed by 4091
Abstract
Detecting, measuring, and classifying partial discharges (PDs) are important tasks for assessing the condition of insulation systems used in different electrical equipment. Owing to the implementation of the phase-resolved PD (PRPD) as a sequence input, an existing method that processes sequential data, e.g., [...] Read more.
Detecting, measuring, and classifying partial discharges (PDs) are important tasks for assessing the condition of insulation systems used in different electrical equipment. Owing to the implementation of the phase-resolved PD (PRPD) as a sequence input, an existing method that processes sequential data, e.g., the recurrent neural network, using a long short-term memory (LSTM) has been applied for fault classification. However, the model performance is not further improved because of the lack of supporting parallel computation and the inability to recognize the relevance of all inputs. To overcome these two drawbacks, we propose a novel deep-learning model in this study based on a self-attention mechanism to classify the PD patterns in a gas-insulated switchgear (GIS). The proposed model uses a self-attention block that offers the advantages of simultaneous computation and selective focusing on parts of the PRPD signals and a classification block to finally classify faults in the GIS. Moreover, the combination of LSTM and self-attention is considered for comparison purposes. The experimental results show that the proposed method achieves performance superiority compared with the previous neural networks, whereas the model complexity is significantly reduced. Full article
(This article belongs to the Special Issue Machine Learning and Artificial Intelligence for Power and Energy Networks)
►▼ Show Figures

Figure 1

14 pages, 909 KiB  
Article
An Improved Stability Criterion for Load Frequency Control of Power Systems with Time-Varying Delays
by Bi-Ying Chen, Xing-Chen Shangguan, Li Jin and Dan-Yun Li
Energies 2020, 13(8), 2101; https://doi.org/10.3390/en13082101 - 23 Apr 2020
Cited by 15 | Viewed by 2869
Abstract
This paper aims at developing a novel stability criterion to access the influence of the time-varying delay on the stability of power systems equipped with a proportional-integral (PI)-based load frequency control (LFC). The model of the LFC scheme considering time-varying communication delays is [...] Read more.
This paper aims at developing a novel stability criterion to access the influence of the time-varying delay on the stability of power systems equipped with a proportional-integral (PI)-based load frequency control (LFC). The model of the LFC scheme considering time-varying communication delays is established at first. Then, an improved stability condition related to the information of delay bounds is deduced by constructing an augmented Lyapunov–Krasovski functional and using a matrix inequality, and it is expressed as linear matrix inequalities (LMIs) for easily checking. Finally, case studies for one-area and two-area LFC systems are carried out to show the relationship between delay margins ensuring the stability and the PI gains of the LFC, and also verify the superiority of proposed stability criterion compared with the previous ones. Full article
(This article belongs to the Section F: Electrical Engineering)
►▼ Show Figures

Graphical abstract

29 pages, 3878 KiB  
Article
Baselines for Energy Use and Carbon Emission Intensities in Hellenic Nonresidential Buildings
by Kalliopi G. Droutsa, Constantinos A. Balaras, Spyridon Lykoudis, Simon Kontoyiannidis, Elena G. Dascalaki and Athanassios A. Argiriou
Energies 2020, 13(8), 2100; https://doi.org/10.3390/en13082100 - 23 Apr 2020
Cited by 14 | Viewed by 4117
Abstract
This work exploits data from 30,000 energy performance certificates of whole nonresidential (NR) buildings in Greece. The available information is analyzed for 30 different NR building uses (e.g., hotels, schools, sports facilities, hospitals, retails, offices) and four main services (space heating, space cooling, [...] Read more.
This work exploits data from 30,000 energy performance certificates of whole nonresidential (NR) buildings in Greece. The available information is analyzed for 30 different NR building uses (e.g., hotels, schools, sports facilities, hospitals, retails, offices) and four main services (space heating, space cooling, domestic hot water and lighting). Data are screened in order to exclude outliers and checked for consistency with the Hellenic NR building stock. The average energy use and CO2 emission intensities for all building uses are calculated, as well as the respective energy ratings in order to gain a better understanding of the NR sector. Finally, in an attempt to determine whether these values are representative for the various Hellenic NR building uses, their temporal evolution is investigated. The average primary energy use intensity is 448.0 kWh/m2 for all NR buildings, while the CO2 emissions reach 147.5 kgCO2/m2. The derived energy baselines reveal that indoor sports halls/swimming pools have the highest energy use, while private cram schools/conservatories have the lowest, due to their operational patterns. Generally, from the four services taken into account, lighting is the most energy consuming, followed by cooling, heating and finally domestic hot water. For a total of 11 building uses, more data from the certificates will be necessary for deriving representative baselines, but, when it comes to buildings categories, more data are required. Full article
(This article belongs to the Special Issue Building Energy Audits-Diagnosis and Retrofitting)
►▼ Show Figures

Figure 1

19 pages, 4751 KiB  
Article
Calibration of the Interaction Parameters between the Proppant and Fracture Wall and the Effects of These Parameters on Proppant Distribution
by Mingzhong Li, Chunting Liu and Guodong Zhang
Energies 2020, 13(8), 2099; https://doi.org/10.3390/en13082099 - 23 Apr 2020
Cited by 6 | Viewed by 2463
Abstract
Saltation and reputation (creep) dominate proppant transport rather than suspension during slickwater fracturing, due to the low sand-carrying capacity of the slickwater. Thus, the interaction parameters between proppants and fracture walls, which affect saltation and reputation, play a more critical role in proppant [...] Read more.
Saltation and reputation (creep) dominate proppant transport rather than suspension during slickwater fracturing, due to the low sand-carrying capacity of the slickwater. Thus, the interaction parameters between proppants and fracture walls, which affect saltation and reputation, play a more critical role in proppant transport. In this paper, a calibration method for the interaction parameters between proppants and walls is built. A three-dimensional coupled computational fluid dynamics–discrete element method (CFD–DEM) model is established to study the effects of the interaction parameters on proppant migration, considering the wall roughness and unevenly distributed diameters of proppants. The simulation results show that a lower static friction coefficient and rolling friction coefficient can result in a smaller equilibrium height of the sand bank and a smaller build angle and drawdown angle, which is beneficial for carrying the proppant to the distal end of the fracture. The wall roughness and the unevenly distributed diameter of the proppants increase the collision between proppant and proppant or the wall, whereas the interactions have little impact on the sandbank morphology, slightly increasing the equilibrium height of the sandbank. Full article
(This article belongs to the Special Issue Developments in Oil and Gas Engineering)
►▼ Show Figures

Graphical abstract

18 pages, 12235 KiB  
Article
AdViSED: Advanced Video SmokE Detection for Real-Time Measurements in Antifire Indoor and Outdoor Systems
by Alessio Gagliardi and Sergio Saponara
Energies 2020, 13(8), 2098; https://doi.org/10.3390/en13082098 - 23 Apr 2020
Cited by 23 | Viewed by 3832
Abstract
This paper proposes a video-based smoke detection technique for early warning in antifire surveillance systems. The algorithm is developed to detect the smoke behavior in a restricted video surveillance environment, both indoor (e.g., railway carriage, bus wagon, industrial plant, or home/office) or outdoor [...] Read more.
This paper proposes a video-based smoke detection technique for early warning in antifire surveillance systems. The algorithm is developed to detect the smoke behavior in a restricted video surveillance environment, both indoor (e.g., railway carriage, bus wagon, industrial plant, or home/office) or outdoor (e.g., storage area or parking area). The proposed technique exploits a Kalman estimator, color analysis, image segmentation, blob labeling, geometrical features analysis, and M of N decisor, in order to extract an alarm signal within a strict real-time deadline. This new technique requires just a few seconds to detect fire smoke, and it is 15 times faster compared to the requirements of fire-alarm standards for industrial or transport systems, e.g., the EN50155 standard for onboard train fire-alarm systems. Indeed, the EN50155 considers a response time of at least 60 s for onboard systems. The proposed technique has been tested and compared with state-of-art systems using the open access Firesense dataset developed as an output of a European FP7 project, including several fire/smoke indoor and outdoor scenes. There is an improvement of all the detection metrics (recall, accuracy, F1 score, precision, etc.) when comparing Advanced Video SmokE Detection (AdViSED) with other video-based antifire works recently proposed in literature. The proposed technique is flexible in terms of input camera type and frame size and rate and has been implemented on a low-cost embedded platform to develop a distributed antifire system accessible via web browser. Full article
(This article belongs to the Special Issue Applications in Electronics Pervading Industry, Environment and Society—Industrial Electronics and Cyber Physical Systems)
►▼ Show Figures

Figure 1

17 pages, 1160 KiB  
Article
An Online Grey-Box Model Based on Unscented Kalman Filter to Predict Temperature Profiles in Smart Buildings
by Marco Massano, Edoardo Patti, Enrico Macii, Andrea Acquaviva and Lorenzo Bottaccioli
Energies 2020, 13(8), 2097; https://doi.org/10.3390/en13082097 - 22 Apr 2020
Cited by 9 | Viewed by 3537
Abstract
Nearly 40% of primary energy consumption is related to the usage of energy in Buildings. Energy-related data such as indoor air temperature and power consumption of heating/cooling systems can be now collected due to the widespread diffusion of Internet-of-Things devices. Such energy data [...] Read more.
Nearly 40% of primary energy consumption is related to the usage of energy in Buildings. Energy-related data such as indoor air temperature and power consumption of heating/cooling systems can be now collected due to the widespread diffusion of Internet-of-Things devices. Such energy data can be used (i) to train data-driven models than learn the thermal properties of buildings and (ii) to predict indoor temperature evolution. In this paper, we present a Grey-box model to estimate thermal dynamics in buildings based on Unscented Kalman Filter and thermal network representation. The proposed methodology has been applied in two different buildings with two different thermal network discretizations to test its accuracy in indoor air temperature prediction. Due to a lack of a real-world data sampled by Internet of Things (IoT) devices, a realistic data-set has been generated using the software Energy+, by referring to real industrial building models. Results on synthetic and realistic data show the accuracy of the proposed methodology in predicting indoor temperature trends up to the next 24 h with a maximum error lower than 2 °C, considering one year of data with different weather conditions. Full article
(This article belongs to the Special Issue Selected Papers from the 19th IEEE International Conference on Environment and Electrical Engineering (19th IEEE EEEIC))
►▼ Show Figures

Figure 1

24 pages, 22831 KiB  
Article
Numerical and Experimental Analysis of the Thermal Performances of SiC/Water and Al2O3/Water Nanofluid Inside a Circular Tube with Constant-Increased-PR Twisted Tape
by Saadah Ahmad, Shahrir Abdullah and Kamaruzzaman Sopian
Energies 2020, 13(8), 2095; https://doi.org/10.3390/en13082095 - 22 Apr 2020
Cited by 13 | Viewed by 3238
Abstract
The simultaneous use of two passive methods (twisted tape and a nanofluid) in a heat transfer system will increase the average Nusselt number (Nu) of the system. However, the presence of inserts and nanoparticles inside the tube will create higher pressure [...] Read more.
The simultaneous use of two passive methods (twisted tape and a nanofluid) in a heat transfer system will increase the average Nusselt number (Nu) of the system. However, the presence of inserts and nanoparticles inside the tube will create higher pressure drop (ΔP) in the system, which can eventually affect the overall enhancement ratio (η), especially at higher Reynolds numbers (Re). Several modifications of twisted tapes have been made to reduce ΔP, but most showed a decreasing trend of η as Re increased. The objective of this study is to design a new geometry of twisted tape that yields a larger value of Nu and a smaller value of ΔP, which can result in a larger value of η especially at higher Re. A simulation and experimental analysis are conducted in which Re ranges from 4000–16,000 with two types of nanofluids (SiC/Water and Al2O3/Water) at various values of the volume fraction, (φ) (1–3%). ANSYS FLUENT software with the RNG k-ɛ turbulent model is adopted for the simulation analysis. Three types of twisted tape are used in the analysis: classic twisted tape with a pitch ratio of 2 (TT PR2), constant-increasing-pitch-ratio twisted tape (TT IPR) and constant-decreasing-pitch-ratio twisted tape (TT DPR). The use of TT IPR generates a stronger swirling flow at the inlet of the tube and smaller ∆P, especially near the outlet region. The highest value of η is obtained for 3% SiC/Water nanofluid that is flowing through a smooth circular tube with TT IPR inserts at Re of 10,000. Full article
►▼ Show Figures

Figure 1

15 pages, 1328 KiB  
Article
Chronological Transition of Relationship between Intracity Lifecycle Transport Energy Efficiency and Population Density
by Shoki Kosai, Muku Yuasa and Eiji Yamasue
Energies 2020, 13(8), 2094; https://doi.org/10.3390/en13082094 - 22 Apr 2020
Cited by 8 | Viewed by 3324
Abstract
Interests in evaluating lifecycle energy use in urban transport have been growing as a research topic. Various studies have evaluated the relationship between the intracity transport energy use and population density and commonly identified its negative correlation. However, a diachronic transition in an [...] Read more.
Interests in evaluating lifecycle energy use in urban transport have been growing as a research topic. Various studies have evaluated the relationship between the intracity transport energy use and population density and commonly identified its negative correlation. However, a diachronic transition in an individual city has yet to be fully analyzed. As such, this study employed transport energy intensity widely used for evaluating transport energy efficiency and obtained the transport energy intensity for each transportation means including walk, bicycle, automobile (conventional vehicles, electric vehicles, hybrid vehicles, and fuel cell vehicles), bus and electric train by considering the lifecycle energy consumption. Then, the intracity lifecycle transport energy intensity of 38 cities in Japan in 1987–2015 was computed, assuming that the cause of diachronic transition of intracity transport energy efficiency is the modal shifting and electricity mix change. As a result, the greater level of population density was associated with the lower intracity transport energy intensity in Japanese cities. The negative slope of its regression line increased over time since the intracity lifecycle transport energy intensity in cities with low population density continuously increased without any significant change of population density. Finally, this study discussed the strategic implications particularly in regional areas to improve the intracity lifecycle transport energy efficiency. Full article
(This article belongs to the Special Issue Life Cycle Assessment (LCA) of Environmental and Energy Systems)
►▼ Show Figures

Figure 1

29 pages, 6612 KiB  
Article
Implementation of Particle Swarm Optimization (PSO) Algorithm for Tuning of Power System Stabilizers in Multimachine Electric Power Systems
by Humberto Verdejo, Victor Pino, Wolfgang Kliemann, Cristhian Becker and José Delpiano
Energies 2020, 13(8), 2093; https://doi.org/10.3390/en13082093 - 22 Apr 2020
Cited by 46 | Viewed by 4500
Abstract
The application of artificial intelligence-based techniques has covered a wide range of applications related to electric power systems (EPS). Particularly, a metaheuristic technique known as Particle Swarm Optimization (PSO) has been chosen for the tuning of parameters for Power System Stabilizers (PSS) with [...] Read more.
The application of artificial intelligence-based techniques has covered a wide range of applications related to electric power systems (EPS). Particularly, a metaheuristic technique known as Particle Swarm Optimization (PSO) has been chosen for the tuning of parameters for Power System Stabilizers (PSS) with success for relatively small systems. This article proposes a tuning methodology for PSSs based on the use of PSO that works for systems with ten or even more machines. Our new methodology was implemented using the source language of the commercial simulation software DigSilent PowerFactory. Therefore, it can be translated into current practice directly. Our methodology was applied to different test systems showing the effectiveness and potential of the proposed technique. Full article
(This article belongs to the Section F: Electrical Engineering)
►▼ Show Figures

Figure 1

Show export options expand_more Show export options expand_less
Select all
Export citation of selected articles as:
 
Displaying articles 1-265
Previous Issue
Next Issue
Back to TopTop