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Energies, Volume 15, Issue 9 (May-1 2022) – 505 articles

Cover Story (view full-size image): The current European regulations thrust original equipment manufacturers toward the design of new components for the life-time extension of gas turbines, characterized by increased thermodynamic performance and by reduced pollutant emissions to match the 2050 single-digit goal. The present work exploits a conjugate heat transfer approach to investigate into different feeding geometries for the internal cooling channels of a turbine blade using computational fluid dynamics. The impact of each configuration on coolant distribution, blade metal temperature, and tip leakage flows is jointly studied by Politecnico di Torino and EthosEnergy Group S.p.A. to detect a design solution for the secondary air systems for improved overall blade performance. View this paper.
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33 pages, 6618 KiB  
Article
Metal–Organic Frameworks (MOFs) Containing Adsorbents for Carbon Capture
by Linda Ansone-Bertina, Viesturs Ozols, Lauris Arbidans, Linda Dobkevica, Kristaps Sarsuns, Edgars Vanags and Maris Klavins
Energies 2022, 15(9), 3473; https://doi.org/10.3390/en15093473 - 9 May 2022
Cited by 11 | Viewed by 3389
Abstract
In this study, new composite materials of montmorillonite, biochar, or aerosil, containing metal–organic frameworks (MOF) were synthesized in situ. Overall, three different MOFs—CuBTC, UTSA-16, and UiO-66-BTEC—were used. Obtained adsorbents were characterized using powder X-ray diffraction, thermogravimetric analysis, nitrogen adsorption porosimetry, scanning electron microscopy, [...] Read more.
In this study, new composite materials of montmorillonite, biochar, or aerosil, containing metal–organic frameworks (MOF) were synthesized in situ. Overall, three different MOFs—CuBTC, UTSA-16, and UiO-66-BTEC—were used. Obtained adsorbents were characterized using powder X-ray diffraction, thermogravimetric analysis, nitrogen adsorption porosimetry, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and Fourier transform infrared spectrophotometry. Additionally, the content of metallic and nonmetallic elements was determined to investigate the crystalline structure, surface morphology, thermal stability of the obtained MOF-composites, etc. Cyclic CO2 adsorption analysis was performed using the thermogravimetric approach, modeling adsorption from flue gasses. In our study, the addition of aerosil to CuBTC (CuBTC-A-15) enhanced the sorbed CO2 amount by 90.2% and the addition of biochar (CuBTC-BC-5) increased adsorbed the CO2 amount by 75.5% in comparison to pristine CuBTC obtained in this study. Moreover, the addition of montmorillonite (CuBTC-Mt-15) increased the adsorbed amount of CO2 by 27%. CuBTC-A-15 and CuBTC-BC-5 are considered to be the most perspective adsorbents, capturing 3.7 mmol/g CO2 and showing good stability after 20 adsorption-desorption cycles. Full article
(This article belongs to the Special Issue Carbon Capture, Utilisation and Storage)
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15 pages, 6249 KiB  
Article
Optimization of Oil Productivity from the Ultra−Depth Strike−Slip Fault−Controlled Carbonate Reservoirs in Northwestern China
by Xinxing He, Rujun Wang, Jianping Yang, Shiyin Li, Chao Yao and Guanghui Wu
Energies 2022, 15(9), 3472; https://doi.org/10.3390/en15093472 - 9 May 2022
Cited by 9 | Viewed by 2075
Abstract
The largest ultra−deep (>7000 m) strike−slip fault−controlled oilfield was found in the tight Ordovician carbonates in the Tarim Basin. Because oil production wells in the Fuman Oilfield generally have bottom water, a reasonable production design is of significant importance for extending the water−free [...] Read more.
The largest ultra−deep (>7000 m) strike−slip fault−controlled oilfield was found in the tight Ordovician carbonates in the Tarim Basin. Because oil production wells in the Fuman Oilfield generally have bottom water, a reasonable production design is of significant importance for extending the water−free oil recovery period and improving oil recovery. However, there is no economical and effective quantitative method to determine a reasonable production capacity and a corresponding reasonable work system for stable−production wells in fault−controlled fractured carbonate reservoirs. In this contribution, we integrated the dynamic and static data of different types of wells in the Fuman Oilfield. It was found that there is a positive relationship between well−controlled dynamic reserves and reasonable productivity, and the productivity corresponding to the upper limit of the reserve can be defined as reasonable productivity. Further, we proposed a correlation equation between well−controlled dynamic reserves and reasonable productivity that shows the reasonable productivity of a stable well from the well−controlled dynamic reserve, which was obtained by combining the well productivity test and analogous well productivity test methods. The relationship between the reasonable productivity per unit nozzle and the rational productivity was obtained according to the determined matching relationship between the reasonable productivity of the stable−production well and the nozzle. The application results show that it can not only quickly determine the reasonable production capacity of stable−production wells but also deepen the understanding of the quantitative characteristics of the production capacity of the Fuman Oilfield. It also provides insight in the rational production allocation of new wells and optimize the development design, which supports the 1500 × 104 bbl/year oil production from the ultra−deep fractured carbonate reservoirs along the strike−slip fault zones in the Tarim Basin. Full article
(This article belongs to the Special Issue The Optimization of Well Testing Operations for Oil and Gas Field)
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9 pages, 1458 KiB  
Article
Substrate Characteristics Fluctuations in Full-Scale Anaerobic Digesters Treating Food Waste at Marginal Organic Loading Rates: A Case Study
by Seung Gu Shin, Sang Hyeok Park and Seokhwan Hwang
Energies 2022, 15(9), 3471; https://doi.org/10.3390/en15093471 - 9 May 2022
Cited by 3 | Viewed by 1692
Abstract
The design of a full-scale bioprocess is typically based on parameters derived from smaller-scale experiments from a previous study. However, disagreements often occur at up-scaling of waste-to-energy processes due to the fluctuations of the substrate characteristics, etc. Therefore, once a commercial-scale waste digester [...] Read more.
The design of a full-scale bioprocess is typically based on parameters derived from smaller-scale experiments from a previous study. However, disagreements often occur at up-scaling of waste-to-energy processes due to the fluctuations of the substrate characteristics, etc. Therefore, once a commercial-scale waste digester has been built and operated, it is essential to test if the performance of the process agrees with its design value; during this process, fluctuations might occur in digesters operated at marginal organic loading rates. In this study, triplicate full-scale anaerobic digesters treating food waste were monitored for five months. The digesters, operated at the design feeding ratio, showed increasing volatile fatty acid (VFA) trends (per total alkalinity) due to a 30% higher chemical oxygen demand of the influent, than the design. The organic loading rate was adjusted on a daily basis until a stable performance was observed. Significant shifts of methanogen populations from Methanobacteriales to Methanomicrobiales and Methanosarcinales were observed during the stable operation period. Full article
(This article belongs to the Topic Anaerobic Digestion Processes)
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34 pages, 53240 KiB  
Article
Application of IIA Method and Virtual Bus Theory for Backup Protection of a Zone Using PMU Data in a WAMPAC System
by Aníbal Antonio Prada Hurtado, Eduardo Martinez Carrasco, Maria Teresa Villén Martínez and Jose Saldana
Energies 2022, 15(9), 3470; https://doi.org/10.3390/en15093470 - 9 May 2022
Cited by 6 | Viewed by 2195
Abstract
Many wide area monitoring, protection, and control (WAMPAC) systems are being deployed by grid operators to deal with critical operational conditions that may occur in power systems. Thanks to the real-time measurements provided by a set of distributed phasor measurement units (PMUs), different [...] Read more.
Many wide area monitoring, protection, and control (WAMPAC) systems are being deployed by grid operators to deal with critical operational conditions that may occur in power systems. Thanks to the real-time measurements provided by a set of distributed phasor measurement units (PMUs), different protection algorithms can be run in a central location. In this context, this article presents and validates a novel method that can be used as a backup protection for a selected area in a power system. It merges the integrated impedance angle (IIA) protection method with the theory of virtual buses in wide area electrical power systems. The backup protection works this way: once a fault is detected (pickup time), another delay (added to the pickup time) is defined in order to wait for the primary protection to act. If this does not happen, the algorithm generates its backup trip. The proposed method has been called the zone integrated impedance angle (Zone IIA). A real-time PMU laboratory has been used to test the proposed algorithm using a real-time digital simulator (RTDS). The algorithm has been programmed in a real-time automation controller (RTAC). It has been tested in two different simulated setups: first, a 400 kV transmission system, with and without the use of renewable energy sources (RES); second, a 150 kV submarine line between the Greece mainland and an island, which is currently the longest submarine alternating current connection in the world. The results obtained during the tests have yielded tripping times for area protection in the order of 48 ms, if no time delay is used between the fault detection and the trip order. According to the test results, the proposed method is stable, reliable, obedient, and secure, also with RES installed in the power system. Additionally, the method is selective, i.e., during the tests no trip was executed for external faults, no trip was executed in no-fault condition, and all the applied internal faults were detected and tripped correctly. Finally, the protection method is easy to implement. The method is also applicable to protection against short circuits in distribution systems. According to the trip times observed during the tests, it is clear that these algorithms are well suited to implement backup protections in transmission grids, even in scenarios with high penetration of renewable energies. Considering that backup trip times in transmission grids are usually set between 400 and 1000 ms, and that the actuation times obtained by the proposed algorithm are under 100 ms, the method is suitable for its use as a backup protection. Full article
(This article belongs to the Special Issue Wide Area Monitoring, Protection and Control of Modern Power Systems)
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15 pages, 5765 KiB  
Article
A Flying Restart Strategy for Position Sensorless PMSM Driven by Quasi-Z-Source Inverter
by Yanfei Cao, Shuxin Xiao and Zhichen Lin
Energies 2022, 15(9), 3469; https://doi.org/10.3390/en15093469 - 9 May 2022
Viewed by 1788
Abstract
The accurate estimation of rotor position and speed before flying restart is of great significance to improve the operation reliability of permanent magnet synchronous motor systems. The traditional multizero vector short-circuit method can improve the estimation accuracy of speed and rotor position, but [...] Read more.
The accurate estimation of rotor position and speed before flying restart is of great significance to improve the operation reliability of permanent magnet synchronous motor systems. The traditional multizero vector short-circuit method can improve the estimation accuracy of speed and rotor position, but the increased number of short-circuits reduces the electromagnetic torque response speed after the power supply recovers. In order to accurately estimate the initial speed and rotor position before the flying restart and effectively improve the electromagnetic torque response speed, a shoot-through zero vector short-circuit method based on quasi-Z-source inverter (qZSI) is proposed. This method breaks the limitation of regulating DC link voltage under the normal operation of the motor in the conventional methods, and puts forward a new idea of advancing the regulation of the DC link voltage to the stage of abnormal operation before the motor restarts. By designing the insertion mode of the mixed vectors and analyzing the action time of each vector before the flying restart, the accurate estimation of position and speed is realized and, meanwhile, the boost of the qZSI’s DC link voltage is achieved, thus giving the sensorless flying restart method a faster torque response speed for the PMSM system driven by qZSIs. Full article
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25 pages, 22596 KiB  
Project Report
Design Considerations for Reducing Battery Storage in Off-Grid, Stand-Alone, Photovoltaic-Powered Cold Storage in Rural Applications
by Johan Meyer and Sune von Solms
Energies 2022, 15(9), 3468; https://doi.org/10.3390/en15093468 - 9 May 2022
Cited by 2 | Viewed by 2851
Abstract
This paper presents design considerations for the design and implementation of stand-alone photovoltaic-powered containerized cold storage solutions for rural off-grid applications. The work presented is based on a case study of an off-grid photovoltaic-powered cold storage unit located in rural South Africa. Although [...] Read more.
This paper presents design considerations for the design and implementation of stand-alone photovoltaic-powered containerized cold storage solutions for rural off-grid applications. The work presented is based on a case study of an off-grid photovoltaic-powered cold storage unit located in rural South Africa. Although solar-powered solutions for off-grid rural applications are very attractive and offer many benefits, including increased food security, skills development, income generation, and productivity due to the presence of solar power, the application of cold storage requires careful consideration of the design aspects to ensure that the solution is feasible and sustainable. The challenge of maintaining low temperatures inside a cold storage system in an excessively warm environment, such as that frequently encountered in most African rural settings, has stimulated discussions of design considerations for optimal efficiency. Not only are the design aspects of the PV panel mounting and tilt associated with the geographic location of the application, but the heating implications are also derived from the physical orientation of the storage unit. Results from mathematical models are substantiated with field data collected from a case deployment. The design considerations for the sizing of the electrical components in the system are presented. The paper concludes by answering the research question as to what design aspects should be considered for an off-grid, PV-powered containerized cold storage system to reduce the size of the battery storage unit. Full article
(This article belongs to the Special Issue Optimal Design of Off-Grid Power Systems)
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15 pages, 4777 KiB  
Article
A Fault-Line Selection Method for Small-Current Grounded System Based on Deep Transfer Learning
by Xianxin Su and Hua Wei
Energies 2022, 15(9), 3467; https://doi.org/10.3390/en15093467 - 9 May 2022
Cited by 5 | Viewed by 1349
Abstract
Usually, data-driven methods require many samples and need to train a specific model for each substation instance. As different substation instances have similar fault features, the number of samples required for model training can be significantly reduced if these features are transferred to [...] Read more.
Usually, data-driven methods require many samples and need to train a specific model for each substation instance. As different substation instances have similar fault features, the number of samples required for model training can be significantly reduced if these features are transferred to the substation instances that lack samples. This paper proposes a fault-line selection (FLS) method based on deep transfer learning for small-current grounded systems to solve the problems of unstable training and low FLS accuracy of data-driven methods in small-sample cases. For this purpose, fine-turning and historical averaging techniques are proposed for use in transfer learning to extract similar fault features from other substation instances and transfer these features to target substation instances that lack samples to improve the accuracy and stability of the model. The results show that the proposed method obtains a much higher FLS accuracy than other methods in small-sample cases; it has a strong generalization ability, low misclassification rate, and excellent application value. Full article
(This article belongs to the Collection Electrical Power and Energy System: From Professors to Students)
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28 pages, 11307 KiB  
Article
Systematic Method for Developing Reference Driving Cycles Appropriate to Electric L-Category Vehicles
by David Watling, Patrícia Baptista, Gonçalo Duarte, Jianbing Gao and Haibo Chen
Energies 2022, 15(9), 3466; https://doi.org/10.3390/en15093466 - 9 May 2022
Viewed by 1901
Abstract
Increasingly, demanding environmental standards reflect the need for improved energy efficiency and reduced externalities in the transportation sector. Reference driving cycles provide standard speed profiles against which future developments and innovations may be tested. In the paper, we develop such profiles for a [...] Read more.
Increasingly, demanding environmental standards reflect the need for improved energy efficiency and reduced externalities in the transportation sector. Reference driving cycles provide standard speed profiles against which future developments and innovations may be tested. In the paper, we develop such profiles for a class of electric L-category vehicles, which are anticipated to play an increasing future role in urban areas. While such driving cycles exist for regular L-category vehicles, these may not be suitable in the case of electric vehicles, due to their power output limitations. We present a methodology for deriving these new driving cycles, developed from empirically deduced power relationships, before demonstrating their application under different assumptions on the terrain and vehicle characteristics. The applications demonstrate the feasibility of the method in developing appropriate driving patterns for alternative real-world contexts. On flat terrain, the adjustments made to cope with the power limitations of L-EV do not introduce significant differences in energy consumption, suggesting that the certification does not require extensive modification. However, when considering road slope, differences of up to 5% in energy use and up to 10% in regenerated energy were observed, showing the importance of the developed method for assessing vehicle performance in real-world driving. Full article
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14 pages, 2295 KiB  
Article
Modeling of Multi-Layer Phase Change Material in a Triplex Tube under Various Thermal Boundary Conditions
by Ali M. Sefidan, Mehdi E. Sangari, Mathieu Sellier, Md. Imran Hossen Khan and Suvash C. Saha
Energies 2022, 15(9), 3465; https://doi.org/10.3390/en15093465 - 9 May 2022
Cited by 2 | Viewed by 1465
Abstract
Nowadays, limited energy resources face ever-growing demands of the modern world. One engineering approach to mitigate this problem which has received considerable attention in recent years is using latent heat thermal storage (LHTS) systems, a significant opportunity which is provided by phase change [...] Read more.
Nowadays, limited energy resources face ever-growing demands of the modern world. One engineering approach to mitigate this problem which has received considerable attention in recent years is using latent heat thermal storage (LHTS) systems, a significant opportunity which is provided by phase change materials (PCMs). In the present study, a numerical investigation was devoted to estimate the simultaneous freezing and melting processes of a double-layer PCM in terms of heat transfer and fluid flow phenomena. A double-pipe cylindrical channel with two compartments, A and B, was considered for locating two PCMs of RT28 and RT35 in various arrangements. The inner and outer walls were exposed to both hot and cold heat transfer fluids (HHTFs and CHTFs, respectively) beginning with solid or liquid initial state, which led to solid–liquid phase change process through PCMs. The numerical simulation was handled by a two-dimensional finite volume method (FVM) with a fixed Rayleigh number of 106 in which conduction and convection heat transfer mechanisms are taken into account. The effects of employing double-layer PCM and their arrangements, inner and outer walls’ boundary conditions, and initial statuses of PCMs are discussed, and the details of the compared results are shown in the form of temperature and liquid fraction variations over time. Full article
(This article belongs to the Section G2: Phase Change Materials for Energy Storage)
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14 pages, 9895 KiB  
Article
A Study on the Improvement of Torque Density of an Axial Slot-Less Flux Permanent Magnet Synchronous Motor for Collaborative Robot
by Dong-Youn Shin, Min-Jae Jung, Kang-Been Lee, Ki-Doek Lee and Won-Ho Kim
Energies 2022, 15(9), 3464; https://doi.org/10.3390/en15093464 - 9 May 2022
Cited by 7 | Viewed by 2822
Abstract
In this paper, an axial slot-less permanent magnet synchronous motor (ASFPMSM) was designed to increase the power density. The iron core of the stator was replaced with block coils, and the stator back yoke was removed because 3D printing can provide a wide [...] Read more.
In this paper, an axial slot-less permanent magnet synchronous motor (ASFPMSM) was designed to increase the power density. The iron core of the stator was replaced with block coils, and the stator back yoke was removed because 3D printing can provide a wide range of structures of the stator. The proposed model also significantly impacts efficiency because it can reduce iron loss. To meet size and performance requirements, coil thickness and number of winding layers in the block, the total amount of magnet, and pole/slot combinations were considered. The validity of the proposed model was proved via finite elements analysis (FEA). Full article
(This article belongs to the Special Issue Advanced Permanent Magnet Machines and Drives)
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23 pages, 5268 KiB  
Article
Evaluation of Various Tree-Based Ensemble Models for Estimating Solar Energy Resource Potential in Different Climatic Zones of China
by Zhigao Zhou, Aiwen Lin, Lijie He and Lunche Wang
Energies 2022, 15(9), 3463; https://doi.org/10.3390/en15093463 - 9 May 2022
Cited by 4 | Viewed by 1716
Abstract
Solar photovoltaic (PV) electricity generation is growing rapidly in China. Accurate estimation of solar energy resource potential (Rs) is crucial for siting, designing, evaluating and optimizing PV systems. Seven types of tree-based ensemble models, including classification and regression trees (CART), [...] Read more.
Solar photovoltaic (PV) electricity generation is growing rapidly in China. Accurate estimation of solar energy resource potential (Rs) is crucial for siting, designing, evaluating and optimizing PV systems. Seven types of tree-based ensemble models, including classification and regression trees (CART), extremely randomized trees (ET), random forest (RF), gradient boosting decision tree (GBDT), extreme gradient boosting (XGBoost), gradient boosting with categorical features support (CatBoost) and light gradient boosting method (LightGBM), as well as the multi-layer perceotron (MLP) and support vector machine (SVM), were applied to estimate Rs using a k-fold cross-validation method. The three newly developed models (CatBoost, LighGBM, XGBoost) and GBDT model generally outperformed the other five models with satisfactory accuracy (R2 ranging from 0.893–0.916, RMSE ranging from 1.943–2.195 MJm−2d−1, and MAE ranging from 1.457–1.646 MJm−2d−1 on average) and provided acceptable model stability (increasing the percentage in testing RMSE over training RMSE from 8.3% to 31.9%) under seven input combinations. In addition, the CatBoost (12.3 s), LightGBM (13.9 s), XGBoost (20.5 s) and GBDT (16.8 s) exhibited satisfactory computational efficiency compared with the MLP (132.1 s) and SVM (256.8 s). Comprehensively considering the model accuracy, stability and computational time, the newly developed tree-based models (CatBoost, LighGBM, XGBoost) and commonly used GBDT model were recommended for modeling Rs in contrasting climates of China and possibly similar climatic zones elsewhere around the world. This study evaluated three newly developed tree-based ensemble models of estimating Rs in various climates of China, from model accuracy, model stability and computational efficiency, which provides a new look at indicators of evaluating machine learning methods. Full article
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28 pages, 1999 KiB  
Review
The State of the Art of Smart Energy Communities: A Systematic Review of Strengths and Limits
by Francesca Ceglia, Elisa Marrasso, Giovanna Pallotta, Carlo Roselli and Maurizio Sasso
Energies 2022, 15(9), 3462; https://doi.org/10.3390/en15093462 - 9 May 2022
Cited by 34 | Viewed by 3835
Abstract
The Smart Energy Community topic has attracted a lot of interest from policy, research centres, companies and private citizens since 2018, when in Europe the recast of the Renewable Energy Directive, and later in 2019 the Internal Electricity Market Directive, came into force [...] Read more.
The Smart Energy Community topic has attracted a lot of interest from policy, research centres, companies and private citizens since 2018, when in Europe the recast of the Renewable Energy Directive, and later in 2019 the Internal Electricity Market Directive, came into force to support the new role of users in energy systems. Following these directives, energy community experimentations, real projects and/or simulations and case studies have been developed and investigated in the literature. In this review paper, an investigation of recent literature about Smart Energy Communities in terms of common characteristics, fundamental scopes, and principal indexes used for their evaluation, has been realized by considering 111 scientific references, 78 of which have been published since 2018. The reference papers have been selected through the “Preferred Reporting Items for Systematic reviews and Meta-Analysis” methodology. In developing the review, significant barriers to Smart Energy Communities’ diffusion emerged. The main shortcomings concern citizens’ uncertainty about these new projects, due to their poor information and technical skills. These issues often hide energy, economic, environmental, and social benefits of Smart Energy Communities. Therefore, this study wants to be an opportunity for bringing to the attention of citizens Smart Energy Communities’ positive outcomes, especially from the social point of view, thus boosting their spreading and overcoming still existing criticalities. Full article
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19 pages, 4456 KiB  
Article
Geological Characteristics and Development Techniques for Carbonate Gas Reservoir with Weathering Crust Formation in Ordos Basin, China
by Haijun Yan, Ailin Jia, Jianlin Guo, Fankun Meng, Bo Ning and Qinyu Xia
Energies 2022, 15(9), 3461; https://doi.org/10.3390/en15093461 - 9 May 2022
Cited by 2 | Viewed by 1444
Abstract
The carbonate gas reservoir is one of the most important gas formation types; it comprises a large proportion of the global gas reserves and the annual gas production rate. However, a carbonate reservoir with weathering crust formation is rare, and it is of [...] Read more.
The carbonate gas reservoir is one of the most important gas formation types; it comprises a large proportion of the global gas reserves and the annual gas production rate. However, a carbonate reservoir with weathering crust formation is rare, and it is of significant interest to illustrate the geological characteristics of this kind of formation and present the emerging problems and solution measures that have arisen during its exploitation. Therefore, in this research, a typical carbonate gas reservoir with weathering crust formation that is located in Ordos Basin, China, was comprehensively studied. In terms of formation geology, for this reservoir, the distribution area is broad and there are multiple gas-bearing layers with low abundance and strong heterogeneity, which have led to large differences in gas well production performance. Some areas in this reservoir are rich in water, which seriously affects gas well production. Regarding production dynamics, the main production areas in this gas reservoir have been stable on a scale of 5.5 billion cubic meters for more than a decade, and the peripheral area has been continually evaluated to improve production capacity. Nevertheless, after decades of exploration and development, the main areas of this reservoir are faced with several problems, including an unclear groove distribution, an unbalanced exploitation degree, low formation pressure, and increases in intermittent gas wells. To deal with these problems and maintain the stability of gas reservoir production, a series of technologies have been presented. In addition, several strategies have been proposed to solve issues that have emerged during the exploration and exploitation of peripheral reservoir areas, such as low-quality formation, unclear ancient land and complex formation-water distribution. These development measures employed in the carbonate gas reservoir with weathering crust formation in the Ordos Basin will surely provide some guidance for the efficient exploitation of similar reservoirs in other basins all over the world. Full article
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16 pages, 3342 KiB  
Article
Three-Phase Unbalance Improvement for Distribution Systems Based on the Particle Swarm Current Injection Algorithm
by Chien-Kuo Chang, Shih-Tang Cheng and Bharath-Kumar Boyanapalli
Energies 2022, 15(9), 3460; https://doi.org/10.3390/en15093460 - 9 May 2022
Cited by 6 | Viewed by 2114
Abstract
The aim of this study is to improve the three-phase unbalanced voltage at the secondary side of a distribution transformer. The proposed method involves compensation sources injecting three different single-phase currents into the connected point of a grid. The computations of optimal single-phase [...] Read more.
The aim of this study is to improve the three-phase unbalanced voltage at the secondary side of a distribution transformer. The proposed method involves compensation sources injecting three different single-phase currents into the connected point of a grid. The computations of optimal single-phase currents are performed using the circuit analysis method and particle swarm optimization algorithm. An unbalanced three-phase power distribution system model is constructed, including a transformer Δ–Δ connection, V–V connection, load balance, load unbalance combination, and three single-phase compensation current sources. The results show that the voltage unbalance rate of the electricity user side is improved to less than 1%, and the three-phase total compensation apparent power is approximately 0 VA. In the future, the application of the model as an auxiliary service could be achieved by adding an energy storage system. Full article
(This article belongs to the Special Issue Frontiers in Smart Grids: Systems and Devices)
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16 pages, 3839 KiB  
Article
Internal Film Cooling with Discrete-Slot Injection Orifices in Hydrogen/Oxygen Engine Thrust Chambers
by Xingyu Ma, Bing Sun, Di Liu and Taiping Wang
Energies 2022, 15(9), 3459; https://doi.org/10.3390/en15093459 - 9 May 2022
Viewed by 1691
Abstract
In the present study, a hydrogen and oxygen heat-sink engine thrust chamber and the corresponding injection faceplate with discrete slot orifices are devised to study the cooling performance near the faceplate region. Moreover, a set of experiments and numerical simulations are conducted to [...] Read more.
In the present study, a hydrogen and oxygen heat-sink engine thrust chamber and the corresponding injection faceplate with discrete slot orifices are devised to study the cooling performance near the faceplate region. Moreover, a set of experiments and numerical simulations are conducted to evaluate the effects of various factors on combustion performance and film cooling efficiency. According to the obtained result, the circumferential cooling efficiency has an M-shaped distribution in the near-injector region. Furthermore, it has been discovered that when the film flow ratio increases, so does the cooling efficiency. This is especially more pronounced in the range of 30–80 mm from the faceplate. The cooling efficiency is found to be proportional to the film flow rate ratio’s 0.4 power. Compared with the slot thickness, the reduction in the slot width is more beneficial in improving the cooling efficiency, and the advantage is more prominent for small film flow ratios. In addition, when the amount of coolant is not enough, the cooling effect of the discrete slot film orifice is better than that of the common cylindrical orifice. The present article demonstrates that setting the area ratio of the adjacent film orifices is an effective way to reduce the uneven circumferential distribution of the wall surface temperature. Full article
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30 pages, 13394 KiB  
Article
Dynamic Performance Analysis by Laboratory Tests of a Sustainable Prefabricated Composite Structural Wall System
by Evangelia Georgantzia, Themistoklis Nikolaidis, Konstantinos Katakalos, Katerina Tsikaloudaki and Theodoros Iliadis
Energies 2022, 15(9), 3458; https://doi.org/10.3390/en15093458 - 9 May 2022
Cited by 2 | Viewed by 1987
Abstract
In recent decades, steel frames infilled with precast load-bearing walls have been successfully employed as lateral load-resisting structural systems in high-rise buildings. This is due to their structural efficiency as outer and major inner facades and to the higher construction speed of the [...] Read more.
In recent decades, steel frames infilled with precast load-bearing walls have been successfully employed as lateral load-resisting structural systems in high-rise buildings. This is due to their structural efficiency as outer and major inner facades and to the higher construction speed of the building. This paper presents a detailed experimental investigation of a sustainable, prefabricated, composite structural wall system, using a representative test model named the Precast Concrete Steel Panel-Infilled Steel Frame (PCSP-ISF) in full-scale dimensions and subjected to in-plane cyclic loading. A series of experiments was conducted on critical structural specimens, including three-point bending, concentric axial compression, and diagonal compression, together with additional cycling loading tests on steel connection joint specimens, with the aim of validating the reliability and the structural response of the connections. The resulting test data and the observed failure mechanisms are discussed carefully to optimise the sustainable structural performance of the system. A theoretical approach for the evaluation of the shear capacity of the total frame system is also discussed to expand the experimental results for several numerical and experimental research cases. The failure mechanism of this module was formed by a combination of developed plastic hinges on the steel joints and diagonal cracks on the concrete panel. The obtained hysteretic behavior of the system at a parameter with major impact is mainly analysed and discussed. The outcomes indicate a satisfactory and sustainable seismic performance of the PCSP-ISF model, indicating that it can be a very promising lateral load-resisting system for earthquake-prone regions. Full article
(This article belongs to the Special Issue Innovative Building Envelope Materials and Sustainable Constructions)
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18 pages, 11406 KiB  
Article
Indonesia’s Vast Off-River Pumped Hydro Energy Storage Potential
by David Firnando Silalahi, Andrew Blakers, Bin Lu and Cheng Cheng
Energies 2022, 15(9), 3457; https://doi.org/10.3390/en15093457 - 9 May 2022
Cited by 4 | Viewed by 6714
Abstract
Indonesia has vast solar energy potential, far more than needed to meet all its energy requirements without the use of fossil fuels. This remains true after per capita energy consumption rises to match developed countries, and most energy functions are electrified to minimize [...] Read more.
Indonesia has vast solar energy potential, far more than needed to meet all its energy requirements without the use of fossil fuels. This remains true after per capita energy consumption rises to match developed countries, and most energy functions are electrified to minimize the use of fossil fuels. Because Indonesia has relatively small energy potential from hydro, wind, biomass, geothermal and ocean energy, it will rely mostly on solar for its sustainable energy needs. Thus, Indonesia will require large amounts of storage for overnight and longer periods. Pumped hydro comprises 99% of global energy storage for the electricity industry. In this paper, we demonstrate that Indonesia has vast practical potential for low-cost off-river pumped hydro energy storage with low environmental and social impact; far more than it needs to balance a solar-dominated energy system. Full article
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43 pages, 7204 KiB  
Review
Harvesting Energy from Ocean: Technologies and Perspectives
by Muhammed Zafar Ali Khan, Haider Ali Khan and Muhammad Aziz
Energies 2022, 15(9), 3456; https://doi.org/10.3390/en15093456 - 9 May 2022
Cited by 30 | Viewed by 8788
Abstract
The optimal utilization of renewable energies is a crucial factor toward the realization of sustainability and zero carbon in a future energy system. Tidal currents, waves, and thermal and salinity gradients in the ocean are excellent renewable energy sources. Ocean tidal, osmotic, wave, [...] Read more.
The optimal utilization of renewable energies is a crucial factor toward the realization of sustainability and zero carbon in a future energy system. Tidal currents, waves, and thermal and salinity gradients in the ocean are excellent renewable energy sources. Ocean tidal, osmotic, wave, and thermal energy sources have yearly potentials that exceed the global power demand of 22,848 TWh/y. This paper extensively reviews the technologies related to energy harvesting from waves, tidal, ocean thermals, and the salinity gradient. Moreover, the socio-economic, social, and environmental aspects of the above technologies are also discussed. This paper provides a better picture of where to invest in the future energy market and highlights research gaps and recommendations for future research initiatives. It is expected that a better insight into ocean energy and a deep understanding of various potential devices can lead to a broader adoption of ocean energy. It is also clear that further research into control strategies is needed. Policy makers should provide financial support for technologies in the demonstration stage and employ road mapping to accelerate the cost and risk reductions to overcome economic hurdles. To identify traditional and online sources on the topic, the authors used electronic databases and keyword searching approaches. Among them, the International Renewable Energy Agency data were the primary database utilized to locate sources. Full article
(This article belongs to the Topic Wave and Tidal Energy)
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16 pages, 4999 KiB  
Article
Combined Network Intrusion and Phasor Data Anomaly Detection for Secure Dynamic Control Centers
by André Kummerow, Kevin Schäfer, Parul Gupta, Steffen Nicolai and Peter Bretschneider
Energies 2022, 15(9), 3455; https://doi.org/10.3390/en15093455 - 9 May 2022
Cited by 4 | Viewed by 1783
Abstract
The dynamic operation of power transmission systems requires the acquisition of reliable and accurate measurement and state information. The use of TCP/IP-based communication protocols such as IEEE C37.118 or IEC 61850 introduces different gateways to launch cyber-attacks and to compromise major system operation [...] Read more.
The dynamic operation of power transmission systems requires the acquisition of reliable and accurate measurement and state information. The use of TCP/IP-based communication protocols such as IEEE C37.118 or IEC 61850 introduces different gateways to launch cyber-attacks and to compromise major system operation functionalities. Within this study, a combined network intrusion and phasor data anomaly detection system is proposed to enable a secure system operation in the presence of cyber-attacks for dynamic control centers. This includes the utilization of expert-rules, one-class classifiers, as well as recurrent neural networks to monitor different network packet and measurement information. The effectiveness of the proposed network intrusion and phasor data anomaly detection system is shown within a real-time simulation testbed considering multiple operation and cyber-attack conditions. Full article
(This article belongs to the Special Issue Energy and Artificial Intelligence)
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22 pages, 11055 KiB  
Article
Computational Fluid Dynamic Study with Comfort Analysis in Large Atrium of the Angelo Hospital in Venice
by Margherita Ferrucci, Piercarlo Romagnoni, Fabio Peron and Mauro Strada
Energies 2022, 15(9), 3454; https://doi.org/10.3390/en15093454 - 9 May 2022
Cited by 1 | Viewed by 1569
Abstract
To improve the thermal comfort in the hall of the Angelo Hospital (Venezia) an analysis was developed by using Computation Fluid Dynamics and considering some configurations for the air-conditioning system and for the solar shading devices. The reference configuration consists of the installation [...] Read more.
To improve the thermal comfort in the hall of the Angelo Hospital (Venezia) an analysis was developed by using Computation Fluid Dynamics and considering some configurations for the air-conditioning system and for the solar shading devices. The reference configuration consists of the installation of four fan coils in the area coupled with a 3 m high metal casing used for solar shading. Then, three other solutions are proposed: by increasing the number of fan coils and changing their position, by adding some radiant panels arranged on the walls, and by inserting a physical confinement as a lateral confinement. The study consists of three sections. Firstly, a section in which the study area is modelled through a strong simplification that allows to represent only a slice of the domain but to immediately evaluate the role of the casing. A second section in which the area is completely modelled, and a third section in which a comfort evaluation is carried out. The analysis shows that the metal casing brings a substantial benefit due to the solar shielding it causes. The radiant panels cool the area only near the wall. The increasing of the number of the fans leads to an excessively high air speed and localized discomfort due to drafts. The lateral confinement on the north and south side is the one that guarantees better cooling of the study area. Full article
(This article belongs to the Special Issue Thermal Comfort and Energy Use in Buildings)
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28 pages, 14259 KiB  
Article
Design and Control of Brushless DC Motor Drives for Refrigerated Cabinets
by Kuei-Hsiang Chao, Long-Yi Chang and Chih-Yao Hung
Energies 2022, 15(9), 3453; https://doi.org/10.3390/en15093453 - 9 May 2022
Cited by 2 | Viewed by 2425
Abstract
The purpose of this study is to develop a variable frequency brushless DC motor drive for the compressors of refrigerated cabinets. It is based on the microcontroller unit (MCU) produced by Renesas Co., Ltd. using the space vector pulse width modulation (SVPWM) for [...] Read more.
The purpose of this study is to develop a variable frequency brushless DC motor drive for the compressors of refrigerated cabinets. It is based on the microcontroller unit (MCU) produced by Renesas Co., Ltd. using the space vector pulse width modulation (SVPWM) for the modulation of the inverter. In addition, at the AC power supply side of the inverter developed, a circuit for suppressing electromagnetic interference (EMI) and a power factor corrector (PFC) are integrated to control the power factor (PF) at the AC power supply side to be above 0.95, which is far better than the commercially available inverters with a power factor of only 0.5. Finally, an intelligent variable frequency control approach based on the extension theory is designed to classify the rotational speed difference and the rate of change in rotational speed difference between the rotational speed commands and the actual rotational speed of the compressor into 20 zones. Then, for the rotational speed difference and the rate of change in rotational speed difference actually measured, their correlations to the 20 zone categories are calculated to determine an appropriate rotational speed command. The temperature of the refrigerated cabinets can quickly be determined to reach the set target value. The proposed extension speed control is simple in computation and does not require much learning data, making it easy to implement. Furthermore, the drive developed is verified by actual testing and its performance is compared to the compressor drives of the refrigerated cabinets commercially available. It is proved that the performance of the drives developed is indeed far better than that of the drives commercially available. Full article
(This article belongs to the Special Issue Design and Control of Electrical Motor Drives II)
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20 pages, 3296 KiB  
Review
A Comprehensive Survey of Alkaline Electrolyzer Modeling: Electrical Domain and Specific Electrolyte Conductivity
by Frank Gambou, Damien Guilbert, Michel Zasadzinski and Hugues Rafaralahy
Energies 2022, 15(9), 3452; https://doi.org/10.3390/en15093452 - 9 May 2022
Cited by 42 | Viewed by 9532
Abstract
Alkaline electrolyzers are the most widespread technology due to their maturity, low cost, and large capacity in generating hydrogen. However, compared to proton exchange membrane (PEM) electrolyzers, they request the use of potassium hydroxide (KOH) or sodium hydroxide (NaOH) since the electrolyte relies [...] Read more.
Alkaline electrolyzers are the most widespread technology due to their maturity, low cost, and large capacity in generating hydrogen. However, compared to proton exchange membrane (PEM) electrolyzers, they request the use of potassium hydroxide (KOH) or sodium hydroxide (NaOH) since the electrolyte relies on a liquid solution. For this reason, the performances of alkaline electrolyzers are governed by the electrolyte concentration and operating temperature. Due to the growing development of the water electrolysis process based on alkaline electrolyzers to generate green hydrogen from renewable energy sources, the main purpose of this paper is to carry out a comprehensive survey on alkaline electrolyzers, and more specifically about their electrical domain and specific electrolytic conductivity. Besides, this survey will allow emphasizing the remaining key issues from the modeling point of view. Full article
(This article belongs to the Special Issue Fuel Cell Renewable Hybrid Power Systems 2021)
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29 pages, 9534 KiB  
Article
New Method to Determine the Dynamic Fluid Flow Rate at the Gear Pump Outlet
by Valeriy Sanchugov and Pavel Rekadze
Energies 2022, 15(9), 3451; https://doi.org/10.3390/en15093451 - 9 May 2022
Cited by 3 | Viewed by 2912
Abstract
External gear pumps are among the most popular fluid power positive displacement pumps; however, they often suffer from excessive flow pulsation transmitted to the downstream circuit. To meet the increasing demand of quiet operation for modern fluid power systems, it is necessary to [...] Read more.
External gear pumps are among the most popular fluid power positive displacement pumps; however, they often suffer from excessive flow pulsation transmitted to the downstream circuit. To meet the increasing demand of quiet operation for modern fluid power systems, it is necessary to give a physically sound method of analyzing the operation of a volumetric pump. The analysis of the basic approach used by the majority of researchers for calculating the flow rate of a gear pump by E.M. Yudin is presented. The article presents a new method for analyzing the operation of volumetric pumps. The method is suitable for the pumps whose dynamic characteristics should be considered according to the model of an equivalent source of flow fluctuations by V.P. Shorin. The method is based on wave theory, the method of hydrodynamic analogies and the impedance method, where the pump is considered according to the model in lumped parameters. The method consists in determining the pressure pulsations at the pump output in bench systems with known dynamic characteristics and recalculating the pump flow rate in pulsations. Computational dynamic models of bench systems in lumped parameters are proposed for subsequent use in dynamic tests of pumps in the form of equivalent sources of fluid flow fluctuations. We give recommendations for the formation of test bench systems with a throttle, a cavity and a pipeline at the pump output. Using the example of an external gear pump with a working volume of 14 cm3/rev, the implementation of the proposed method is considered. The pump’s own pulsation characteristic of the flow rate in a bench system with an “infinitely long” pipeline along two harmonic components of the spectrum is determined, and a test of the method based on the method of determining the instantaneous flow rate by R.N. Starobinskiy is proposed. It is shown that, according to the proposed method and the method of R.N. Starobinskiy, the divergence of the amplitudes of flow pulsations does not exceed (5–10)%. The high degree of coincidence of the results confirms that the external gear pump in question should be considered according to the equivalent source of flow fluctuations model. Full article
(This article belongs to the Topic Power System Modeling and Control, 2nd Volume)
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16 pages, 30389 KiB  
Article
Charging Mobile Devices in Indoor Environments
by Diogo Matos, Ricardo A. M. Pereira, Helena Ribeiro, Bernardo Mendes, Daniel Belo, Arnaldo Oliveira and Nuno Borges Carvalho
Energies 2022, 15(9), 3450; https://doi.org/10.3390/en15093450 - 9 May 2022
Cited by 4 | Viewed by 1939
Abstract
Wireless power transfer promises to revolutionize the way in which we use and power mobile devices. However, low transfer efficiencies prevent this technology from seeing wide scale real-world adoption. The aim of this work is to use quasioptics to develop a system composed [...] Read more.
Wireless power transfer promises to revolutionize the way in which we use and power mobile devices. However, low transfer efficiencies prevent this technology from seeing wide scale real-world adoption. The aim of this work is to use quasioptics to develop a system composed of a dielectric lens fed by a phased array to reduce spillover losses, increasing the beam efficiency, while working on the antenna system’s Fresnel zone. The DC-RF electronics, digital beamforming and beam-steering by an FPGA, and radiating 4 × 4 microstrip patch phased array have been developed and experimented upon, while the lens has been designed and simulated. This paper details these preliminary results, where the phased array radiation pattern was measured, showing that the beam is being generated and steered as expected, prompting the lens construction for the complete system experimentation. Full article
(This article belongs to the Special Issue Next Generation Wireless Charging System for Mobile Devices)
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19 pages, 7983 KiB  
Article
A Three-Dimensional Finite-Element Model in ABAQUS to Analyze Wellbore Instability and Determine Mud Weight Window
by Mohammad Javad Bozorgi, Masoud Parham, Omeid Rahmani, Ali Piroozian, Haylay Tsegab Gebretsadik and Syed Muhammad Ibad
Energies 2022, 15(9), 3449; https://doi.org/10.3390/en15093449 - 9 May 2022
Cited by 1 | Viewed by 3068
Abstract
Wellbore instability is one of the main problems of the oil industry, causing high costs in the drilling operation. Knowing about the mechanical properties of involved formations and in-situ stresses is a privilege gained by determining an appropriate mud weight window (MWW). To [...] Read more.
Wellbore instability is one of the main problems of the oil industry, causing high costs in the drilling operation. Knowing about the mechanical properties of involved formations and in-situ stresses is a privilege gained by determining an appropriate mud weight window (MWW). To this aim, a three-dimensional (3D) finite-element model was simulated in ABAQUS to analyze in-situ stresses and determine the MWW in the drilling operation of wellbore-D in the Azar oilfield. The results from the 3D finite model revealed that the Azar oilfield is structurally under the impact of a complex tectonic system dominated by two reverse faults with a configuration of σH > σh > σv across the Sarvak Formation. The amount of vertical, minimum, and maximum horizontal stresses was 90.15, 90.15, and 94.66 MPa, respectively, at a depth of 4 km. Besides, the amount of pore pressure and its gradient was 46 MPa and 11.5 MPa/km, respectively. From drilling wellbore-D in the direction of the maximum horizontal stress, the lower limit of the MWW was obtained at 89 pcf. In this case, the results showed that the wellbore with a deviation angle of 10° is critical with a mud weight lower than 89 pcf. It caused the fall of the wellbore wall within the plastic zone sooner than other deviation angles. Also, in the case of drilling wellbore in the direction of minimum horizontal stress, the lower limit of the MWW was 90.3 pcf. Moreover, in the deviation angle of approximately 90°, the wellbore wall remained critical while the mud weight was below 90.3 pcf. Comparison of the results of numerical and analytical modeling showed that the modeling error falls within an acceptable value of < 4%. As a result, the wellbore with the azimuth of the maximum horizontal stress needed less mud weight and decreased the drilling costs. This particular research finding also provides insights for obtaining the lower limit of the mud weight window and determining the optimal path of the well-bore when using directional drilling technology. Full article
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24 pages, 2256 KiB  
Article
Do Nuclear Energy, Renewable Energy, and Environmental-Related Technologies Asymmetrically Reduce Ecological Footprint? Evidence from Pakistan
by Muhammad Usman, Atif Jahanger, Magdalena Radulescu and Daniel Balsalobre-Lorente
Energies 2022, 15(9), 3448; https://doi.org/10.3390/en15093448 - 9 May 2022
Cited by 54 | Viewed by 3810
Abstract
Can Pakistan’s environmental-related technologies (ERT) and nuclear and renewable energy mitigate environmental pollution? As global warming and climate change rise dramatically, economies shift to friendly energy substitutions and eco-friendly technologies, contributing to the mitigation of environmental contamination. In this scenario, policy and academic [...] Read more.
Can Pakistan’s environmental-related technologies (ERT) and nuclear and renewable energy mitigate environmental pollution? As global warming and climate change rise dramatically, economies shift to friendly energy substitutions and eco-friendly technologies, contributing to the mitigation of environmental contamination. In this scenario, policy and academic analysts have paid more concentration to renewable and nuclear energy deployment with ERT installation. To achieve this goal, the present study scrutinizes the asymmetric effects of nuclear energy, renewable energy, and ERT on the ecological footprint of Pakistan. The current research applies a novel non-linear autoregressive distributive lag method from 1991 to 2020. The results of the current analysis show that negative changes in nuclear energy increase emissions levels in the long run, while positive and negative changes in renewable energy deployment significantly overcome the burden on the environment. Similarly, positive and negative changes in ERT reduce pollution levels in the long run. Moreover, these long-run outcomes are analogous to short-run findings for Pakistan. Therefore, there is a dire requirement to increase the consumption of renewable and nuclear energy sources and take advantage of the noteworthy impact of an uncontaminated atmosphere through clean ERT potentials. Full article
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26 pages, 15769 KiB  
Review
Multi-Skin Adaptive Ventilated Facade: A Review
by Darya Andreeva, Darya Nemova and Evgeny Kotov
Energies 2022, 15(9), 3447; https://doi.org/10.3390/en15093447 - 9 May 2022
Cited by 6 | Viewed by 3191
Abstract
Multi-skin ventilated facades with integrated building elements that respond to climatic conditions (mechanized openings and automatic shading with intelligent control) present the potential of improving overall annual energy savings by adapting the thermal properties of buildings. This paper presents a literature review on [...] Read more.
Multi-skin ventilated facades with integrated building elements that respond to climatic conditions (mechanized openings and automatic shading with intelligent control) present the potential of improving overall annual energy savings by adapting the thermal properties of buildings. This paper presents a literature review on multi-skin adaptive ventilated facades. Additionally, this article presents a literature review on building envelopes that contain inner-air layers. The operation modes of the air layer used in building enclosure structures are classified and summarized and the thermal performance and benefits of climate-adaptive facades are discussed and reviewed. The existing operation modes of the air layer used in building envelopes are summarized, outlined and roughly classified into the following types: the enclosed type, the naturally ventilated type and the mechanically ventilated type. One of the sustainable development trends is the investigation and application of energy-efficient climate-adaptive facades. In this study, the energy modeling of a high-rise office building was calculated using the Green Building Studio. The annual energy, the annual CO2 emissions, and life cycle energy for the following three types of facade were estimated: a single-layer facade made of three-layer glass with argon, a double ventilated facade, and a triple ventilated facade with a double chamber. The calculation results show that the annual energy of the building with an adaptive triple-skin facade could be reduced by 15% compared with buildings with a single skin facade. Full article
(This article belongs to the Section G: Energy and Buildings)
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18 pages, 5735 KiB  
Article
Numerical Study on Characteristics of Bedrock and Surface Failure in Mining of Shallow-Buried MCS
by Guangchun Liu, Wenzhi Zhang, Youfeng Zou, Huabin Chai and Yongan Xue
Energies 2022, 15(9), 3446; https://doi.org/10.3390/en15093446 - 9 May 2022
Viewed by 1428
Abstract
Coal is one of the important energy sources for industry. When it is mined, it will cause the destruction of bedrock and surface. However, it is more severe in mining shallow-buried multi coal seams (SBMCS). To better reveal the characteristics of the bedrock [...] Read more.
Coal is one of the important energy sources for industry. When it is mined, it will cause the destruction of bedrock and surface. However, it is more severe in mining shallow-buried multi coal seams (SBMCS). To better reveal the characteristics of the bedrock and surface damage, we have carried out a theoretical analysis, as well as used numerical simulations and field monitoring methods to study the surface and bedrock damage caused by the mining of SBMCS. The characteristics of bedrock and surface failure structure, settlement, and stress distribution were studied and analyzed. The findings show that the collapsed block, formed by the rupture of the overlying stratum, interacts with the surrounding rock to form large cavities and gaps, and the stress concentration occurs between them. The maximum downward vertical concentration stress is about 9.79 MPa. The mining of the lower coal seam can lead to repeated failure of the upper bedrock and goaf. The settlement of bedrock presents gradient change, and the settlement of upper bedrock is large, about 8.0 m, and the maximum settlement is 8.183 m, while that of lower bedrock is small and about 3.5–4.0 m. The weak rock stratum in the bedrock is crushed by the change stress of repeated mining, and formed a broken rock stratum. The cracks in the bedrock develop directly to the ground. On the ground, tensile cracks, compression uplift, stepped cracks, and even collapse pits are easy to cause in mining SBMCS. Affected by repeated mining, the variation of surface vertical stress is complex and disorderly in the middle of the basin, and the variation of horizontal stress is mainly concentrated on the edge of the basin. The maximum stress reaches 100 KPa, and the minimum stress is about 78 KPa. Through theoretical analysis and discussion, the size of the key blocks is directly related to the thickness and strength of the rock stratum. Full article
(This article belongs to the Topic Mining Safety and Sustainability)
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23 pages, 2488 KiB  
Article
Calorific Value of Festuca rubra Biomass in the Phytostabilization of Soil Contaminated with Nickel, Cobalt and Cadmium Which Disrupt the Microbiological and Biochemical Properties of Soil
by Jadwiga Wyszkowska, Edyta Boros-Lajszner and Jan Kucharski
Energies 2022, 15(9), 3445; https://doi.org/10.3390/en15093445 - 9 May 2022
Cited by 9 | Viewed by 1894
Abstract
The choice of optimal plant species for phytoremediation and organic fertilization plays an important role in stabilizing the functions of soils contaminated with heavy metals. The influence of nickel, cobalt and cadmium on the biomass yield and calorific value of Festuca rubra, [...] Read more.
The choice of optimal plant species for phytoremediation and organic fertilization plays an important role in stabilizing the functions of soils contaminated with heavy metals. The influence of nickel, cobalt and cadmium on the biomass yield and calorific value of Festuca rubra, heavy metal concentrations in soil and plants and the microbiological, biochemical and physicochemical proprieties of soil were analyzed in a pot experiment. The tolerance index (TI) describing Festuca rubra’s ability to tolerate heavy metals, as well as the translocation (TF), accumulation (AF) and bioaccumulation (BF) factors of heavy metals in Festuca rubra were calculated. The experiment was conducted in two series: In soil fertilized and not fertilized with compost. Nickel and cobalt significantly inhibited the growth and development of Festuca rubra. The experiment demonstrated that this plant species can be grown on soil contaminated with heavy metals. Festuca rubra contained on average 46.05% C, 34.59% O, 5.91% H, 3.49% N, 0.19% S and 9.76% ash. Festuca rubra has a stable calorific value which is not affected by heavy metals; therefore, biomass harvested from heavy metal-polluted soil can be used for energy generation. The calorific value of Festuca rubra ranged from 15.924 to 16.790 MJ kg−1 plant d.m., and the heat of combustion from 17.696 to 18.576 MJ kg1. It has a stable calorific value which is not affected by heavy metals, therefore biomass harvested from heavy metal-polluted soil can be used for energy generation. Festuca rubra is particularly useful for the phytostabilization of soil contaminated with cadmium and cobalt. Compost minimizes the adverse effects of heavy metal pollution on the microbiological, biochemical and physicochemical properties of soil. Full article
(This article belongs to the Special Issue Biomass Energy for Environmental Sustainability)
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19 pages, 948 KiB  
Article
Numerical Study on the Long-Term Performance and Load Imbalance Ratio for Medium-Shallow Borehole Heat Exchanger System
by Ruifeng Wang, Fenghao Wang, Yuze Xue, Jinghua Jiang, Yuping Zhang, Wanlong Cai and Chaofan Chen
Energies 2022, 15(9), 3444; https://doi.org/10.3390/en15093444 - 9 May 2022
Cited by 8 | Viewed by 1671
Abstract
To contribute to the goal of carbon neutralization, the closed-loop borehole heat exchanger system is widely applied to use geothermal energy for building cooling and heating. In this work, a new type of medium-shallow borehole heat exchanger (MSBHE) is proposed, which is coaxial [...] Read more.
To contribute to the goal of carbon neutralization, the closed-loop borehole heat exchanger system is widely applied to use geothermal energy for building cooling and heating. In this work, a new type of medium-shallow borehole heat exchanger (MSBHE) is proposed, which is coaxial type and has a depth range between 200 m to 500 m. To investigate the long-term performance of MSBHE in the area with unbalanced cooling and heating load of buildings and the sustainable load imbalance ratio under different design parameters, a comprehensive numerical model is established. The results show that the drilling depth significantly influences the sustainable load imbalance ratio of MSBHE. As the drilling depth is increased from 200 m to 500 m, the load imbalance ratio of the MSBHE increases from 20.76% to 60.29%. In contrast, the load imbalance ratio is always kept at the same level with different inlet velocities and operation modes. Furthermore, in a 9-MSBHE array system, the heat exchanger located in the middle of the array has the lowest load imbalance ratio of 48.97%, which is 15.98% lower than the borehole in the edge location. This is caused by the significant influence of the shifted-load phenomenon among MSBHEs in an array system. The findings of the work imply that this newly proposed MSBHE can sustain a notable load imbalance ratio, which is particularly applicable to the areas with a strong imbalance of annual building load. Full article
(This article belongs to the Special Issue Energy Conservation in Buildings: Renewable Energy Utilization Method)
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