Journal Description
Energies
Energies
is a peer-reviewed, open access journal of related scientific research, technology development, engineering policy, and management studies related to the general field of energy, from technologies of energy supply, conversion, dispatch, and final use to the physical and chemical processes behind such technologies. Energies is published semimonthly online by MDPI. The European Biomass Industry Association (EUBIA), Association of European Renewable Energy Research Centres (EUREC), Institute of Energy and Fuel Processing Technology (ITPE), International Society for Porous Media (InterPore), CYTED and others are affiliated with Energies and their members receive a discount on the article processing charges.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within Scopus, SCIE (Web of Science), Ei Compendex, RePEc, Inspec, CAPlus / SciFinder, and other databases.
- Journal Rank: CiteScore - Q1 (Engineering (miscellaneous))
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 16.1 days after submission; acceptance to publication is undertaken in 3.3 days (median values for papers published in this journal in the second half of 2023).
- Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
- Sections: published in 41 topical sections.
- Testimonials: See what our editors and authors say about Energies.
- Companion journals for Energies include: Fuels, Gases, Nanoenergy Advances and Solar.
Impact Factor:
3.2 (2022);
5-Year Impact Factor:
3.3 (2022)
Latest Articles
Elevational Earth-Sheltered Buildings with Horizontal Overhang Photovoltaic-Integrated Panels—New Energy-Plus Building Concept in the Territory of Serbia
Energies 2024, 17(9), 2100; https://doi.org/10.3390/en17092100 (registering DOI) - 27 Apr 2024
Abstract
The global scientific community is intensively promoting energy-plus buildings. Following the leading world trends, this paper presents a new energy-plus building concept—elevational earth-sheltered buildings with three different types of horizontal overhang photovoltaic-integrated panels: wooden support columns covered with clay tiles, steel pipes as
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The global scientific community is intensively promoting energy-plus buildings. Following the leading world trends, this paper presents a new energy-plus building concept—elevational earth-sheltered buildings with three different types of horizontal overhang photovoltaic-integrated panels: wooden support columns covered with clay tiles, steel pipes as support columns covered with sheet steel, and concrete support columns with concrete coverage. In this instance, the specific multi-numerical case study building model for the city of Kragujevac (located in central Serbia with favorable climatic conditions) was performed over 7 months (from 1 October to 30 April), taking into account the soil temperature, the effects of solar shading, the performance of the heating system—a ground source heat pump—and the characteristics of the artificial and automatic lighting control system. The simulation results show that the optimal depth of a horizontal overhang (energy-plus status) depends on the occupant’s habits, in addition to meteorological conditions. The presented methodology can be used for any other location, both in Europe and the world.
Full article
(This article belongs to the Special Issue Energy Efficiency of the Buildings III)
Open AccessReview
Agricultural Wastes and Their By-Products for the Energy Market
by
Magdalena Zielińska and Katarzyna Bułkowska
Energies 2024, 17(9), 2099; https://doi.org/10.3390/en17092099 (registering DOI) - 27 Apr 2024
Abstract
The conversion of lignocellulosic agricultural waste into biofuels and other economically valuable compounds can reduce dependence on fossil fuels, reduce harmful gas emissions, support the sustainability of natural resources, including water, and minimize the amount of waste in landfills, thus reducing environmental degradation.
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The conversion of lignocellulosic agricultural waste into biofuels and other economically valuable compounds can reduce dependence on fossil fuels, reduce harmful gas emissions, support the sustainability of natural resources, including water, and minimize the amount of waste in landfills, thus reducing environmental degradation. In this paper, the conversion of agricultural wastes into biomethane, biohydrogen, biodiesel, bioethanol, biobutanol, and bio-oil is reviewed, with special emphasis on primary and secondary agricultural residues as substrates. Some novel approaches are mentioned that offer opportunities to increase the efficiency of waste valorization, e.g., hybrid systems. In addition to physical, chemical, and biological pretreatment of waste, some combined methods to mitigate the negative effects of various recalcitrant compounds on waste processing (alkali-assisted thermal pretreatment, thermal hydrolysis pretreatment, and alkali pretreatment combined with bioaugmentation) are evaluated. In addition, the production of volatile fatty acids, polyhydroxyalkanoates, biochar, hydrochar, cellulosic nanomaterials, and selected platform chemicals from lignocellulosic waste is described. Finally, the potential uses of biofuels and other recovered products are discussed.
Full article
(This article belongs to the Special Issue Transformation of Energy Markets: Description, Modeling of Functioning Mechanisms and Determining Development Trends – Second Edition)
Open AccessArticle
Hydrothermal Co-Liquefaction of Food and Plastic Waste for Biocrude Production
by
Silvan Feuerbach, Saqib Sohail Toor, Paula A. Costa, Filipe Paradela, Paula A.A.S. Marques and Daniele Castello
Energies 2024, 17(9), 2098; https://doi.org/10.3390/en17092098 (registering DOI) - 27 Apr 2024
Abstract
In this study, hydrothermal co-liquefaction of restaurant waste for biocrude production was conducted. The feedstock was resembled using the organic fraction of restaurant waste and low-density polyethylene, polypropylene, polystyrene, and polyethylene terephthalate, four plastic types commonly present in municipal solid waste. Using design
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In this study, hydrothermal co-liquefaction of restaurant waste for biocrude production was conducted. The feedstock was resembled using the organic fraction of restaurant waste and low-density polyethylene, polypropylene, polystyrene, and polyethylene terephthalate, four plastic types commonly present in municipal solid waste. Using design of experiment and a face-centered central composite design, three factors (feedstock plastic fraction, temperature, time) were varied at three levels each: feedstock plastic fraction (0, 0.25, 0.5), temperature (290 °C, 330 °C, 370 °C), and reaction time (0 min, 30 min, 60 min). The literature reports positive synergistic interactions in hydrothermal co-liquefaction of biomass and plastics; however, in this work, only negative synergistic interactions could be observed. A reason could be the high thermal stability of produced fatty acids that give little room for interactions with plastics. At the same time, mass might transfer to other product phases.
Full article
(This article belongs to the Special Issue New Trends in Biofuels and Bioenergy for Sustainable Development II)
Open AccessArticle
Structural Investigation of Orthoborate-Based Electrolytic Materials for Fuel Cell Applications
by
Jarosław Milewski, Piotr Ryś, Anna Krztoń-Maziopa, Grażyna Żukowska, Karolina Majewska, Magdalena Zybert, Jacek Kowalczyk and Maciej Siekierski
Energies 2024, 17(9), 2097; https://doi.org/10.3390/en17092097 (registering DOI) - 27 Apr 2024
Abstract
The paper presented delivers the proof for one of the possible solutions to the so-called medium-temperature gap—the lack of electrolytic systems able to efficiently work in a temperature range spanning from 200 to 450 °C. Regardless of the progress made in this field,
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The paper presented delivers the proof for one of the possible solutions to the so-called medium-temperature gap—the lack of electrolytic systems able to efficiently work in a temperature range spanning from 200 to 450 °C. Regardless of the progress made in this field, the commercially available systems are still operating either at close to ambient temperatures, where hydrogen purity requirements are a significant limit, or above ca. 600 °C, where they suffer from increased corrosion and excessive thermal stresses occurring during startup and shutdown. Alkali metal orthoborates (M3BO3 M = Li, Na, K, or the mixture of these), in contrast to commercially used tetra-(M2B4O7) and meta-(MBO2) borates of these metals, are compounds with relatively poorly understood structure and physicochemical properties. The possibility of their application as an electrolyte in a fuel cell is a relatively new idea and has been preliminary reported. Therefore, an extended phase-focused analysis of the materials applied was needed to re-optimize both the synthetic strategy and the application route. Results of PXRD and FT-IR investigations showed, on the one hand, a complicated multi-phase structure, including the main orthoborate phase, as well as the presence of additional borate-based phases, including boric oxoacid. On the other hand, DTA tests proved not only that their melting temperatures are lower than these characteristics for the tetra- and meta-counterparts, but also that cation mixing leads to a subsequent decrease in this important functional parameter of the materials studied.
Full article
(This article belongs to the Collection Batteries, Fuel Cells and Supercapacitors Technologies)
Open AccessArticle
Grid Quality Services from Smart Boilers: Experimental Verification on Realistic Scenarios for Micro-Grids with Demand-Side Management Oriented to Self-Consumption
by
Georgios S. Dimitrakakis, Konstantinos G. Georgakas, Evangelos S. Topalis and Panagis N. Vovos
Energies 2024, 17(9), 2096; https://doi.org/10.3390/en17092096 (registering DOI) - 27 Apr 2024
Abstract
The deeper penetration of renewables in the energy mix is an intense requirement in order to reduce global carbon dioxide emissions. In addition, new technologies are being developed, such as electric mobility and Distributed Generation (DG) in urban areas. However, the unpredictable fluctuations
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The deeper penetration of renewables in the energy mix is an intense requirement in order to reduce global carbon dioxide emissions. In addition, new technologies are being developed, such as electric mobility and Distributed Generation (DG) in urban areas. However, the unpredictable fluctuations in energy generation from roof-installed PVs and the switching operation of their inverters greatly aggravate the already-present grid quality problems. In this paper, the Smart Boiler (SB) concept for grid quality improvement is presented. Furthermore, its experimental verification is implemented on a flexible testbed that accurately emulates several realistic scenarios for the low voltage distribution grid, under complex operating conditions. The proposed low-cost electronic kit, which contains a converter of fairly simple topology and requires connection to the internet, is used to upgrade conventional domestic boilers to smart devices. The SB automatically regulate the local reactive power flow, helping to stabilize the voltage level and suppress the grid current harmonic content, with both services provided in a matter of seconds. The higher the active power consumed and the denser the SB cluster, the wider the beneficial impact on the affected network area. While this service is provided, excess energy generated by PVs is temporarily stored as heat in the boiler tanks, given the users’ hot water consumption habits. The whole application, as a powerful demand-side management tool, proves beneficial for both the network operator and the end-user, especially when self-consumption is desirable in order to achieve a Nearly Zero Energy Building.
Full article
(This article belongs to the Special Issue Applications of High-Efficiency Converters)
Open AccessArticle
Assessment of CH4 Emissions in a Compressed Natural Gas-Adapted Engine in the Context of Changes in the Equivalence Ratio
by
Artur Jaworski, Hubert Kuszewski, Krzysztof Balawender, Paweł Woś, Krzysztof Lew and Mirosław Jaremcio
Energies 2024, 17(9), 2095; https://doi.org/10.3390/en17092095 (registering DOI) - 27 Apr 2024
Abstract
The results of diagnostic tests under steady-state speed conditions of an unloaded engine do not fully reflect the emissivity of vehicles adapted to run on natural gas. Therefore, it is reasonable to pay attention to the emissions performance of these vehicles under dynamic
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The results of diagnostic tests under steady-state speed conditions of an unloaded engine do not fully reflect the emissivity of vehicles adapted to run on natural gas. Therefore, it is reasonable to pay attention to the emissions performance of these vehicles under dynamic conditions. In this regard, the tests were carried out on a chassis dynamometer with the engine fueled by gasoline and natural gas. Due to the area of operation of natural gas vehicles being usually limited to urban areas, the urban phases of the NEDC (New European Driving Cycle) and WLTC (Worldwide harmonized Light-duty vehicles Test Cycle) were adapted. While CO2 emissions are lower when fueled by natural gas, CH4 emissions can be high, which is related to momentary changes in the composition of the combustible mixture. Although CH4 emissions are higher when the engine runs on natural gas, the CO2eq value is, depending on the driving cycle, about 15–25% lower than when running on petrol. Additionally, studies have shown that in engines adapted to run on CNG (compressed natural gas), it is advisable to consider the use of catalytic converters optimized to run on natural gas, as is the case with vehicles which are factory–adapted to run on CNG.
Full article
(This article belongs to the Special Issue Internal Combustion Engine: Research and Application—2nd Edition)
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Open AccessArticle
Geometrical Optimization of Segmented Thermoelectric Generators (TEGs) Based on Neural Network and Multi-Objective Genetic Algorithm
by
Wei Sun, Pengfei Wen, Sijie Zhu and Pengcheng Zhai
Energies 2024, 17(9), 2094; https://doi.org/10.3390/en17092094 (registering DOI) - 27 Apr 2024
Abstract
In this study, a neural network and a multi-objective genetic algorithm were used to optimize the geometric parameters of segmented thermoelectric generators (TEGs) with trapezoidal legs, including the cold end width of thermoelectric (TE) legs (Wc), the ratios of cold-segmented
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In this study, a neural network and a multi-objective genetic algorithm were used to optimize the geometric parameters of segmented thermoelectric generators (TEGs) with trapezoidal legs, including the cold end width of thermoelectric (TE) legs (Wc), the ratios of cold-segmented length to the total lengths of the n- and p-legs (Sn,c and Sp,c), and the width ratios of the TE legs between the hot end and the cold end of the n- and p-legs (Kn and Kp). First, a neural network with high prediction accuracy was trained based on 5000 sets of parameters and the corresponding output power values of the TEGs obtained from finite element simulations. Then, based on the trained neural network, the multi-objective genetic algorithm was applied to optimize the geometric parameters of the segmented TEGs with the objectives of maximizing the output power (P) and minimizing the semiconductor volume (V). The optimal geometric parameters for different semiconductor volumes were obtained, and their variations were analyzed. The results indicated that the optimal Sn,c, Sp,c, Kn, and Kp remained almost unchanged when V increased from 52.8 to 216.2 mm3 for different semiconductor volumes. This work provides practical guidance for the design of segmented TEGs with trapezoidal legs.
Full article
Open AccessArticle
The Formation–Structure–Functionality Relationship of Catalyst Layers in Proton Exchange Membrane Fuel Cells
by
Donglei Yang, Nitul Kakati, Mrittunjoy Sarker, Felipe Mojica and Po-Ya Abel Chuang
Energies 2024, 17(9), 2093; https://doi.org/10.3390/en17092093 (registering DOI) - 27 Apr 2024
Abstract
Understanding the relationship between the formation, structure, and functionality of catalyst layers is crucial for designing catalyst layers with specific high-current-density operations. In this study, we investigated the impact of the ionomer-to-carbon (I/C) ratio and solid content on transport properties. We conducted fuel
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Understanding the relationship between the formation, structure, and functionality of catalyst layers is crucial for designing catalyst layers with specific high-current-density operations. In this study, we investigated the impact of the ionomer-to-carbon (I/C) ratio and solid content on transport properties. We conducted fuel cell performance and diagnostic measurements to demonstrate the combined effects of the I/C ratio and solid content on the mass transport, particularly oxygen transport. To elucidate the roles of the I/C ratio and solid content in catalyst layer formation, we utilized dynamic light scattering and rheological measurements. By analyzing the local and global structure of ionomer-Pt/C assemblages in the catalyst inks, we observed that the I/C ratio and solid content influence the competition between homo-aggregation and hetero-aggregation, the strengths of inter- and intra-cluster bonds, and the rigidity and connectivity of the particulate structure. Additionally, high-shear-application simulations tend to reduce the connectivity of the particulate network and induce cluster densification, unless the global structure is mechanically stable and resilient. Based on this understanding, we established the formation–structure–functionality relationship for catalyst layers, thereby providing fundamental insights for designing catalyst layers tailored to specific functionalities.
Full article
(This article belongs to the Special Issue Advances in Hydrogen Energy III)
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Open AccessArticle
A Comparison of Different Biomass Combustion Mechanisms in the Transient State
by
Filipe Neves, Armando A. Soares and Abel Rouboa
Energies 2024, 17(9), 2092; https://doi.org/10.3390/en17092092 (registering DOI) - 27 Apr 2024
Abstract
Different combustion reaction process models were used to numerically study the behavior of the temperature, velocity, and turbulence fields, as well as to gain a better understanding of the differences between the reaction products obtained with each model. Transient-state simulations were conducted for
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Different combustion reaction process models were used to numerically study the behavior of the temperature, velocity, and turbulence fields, as well as to gain a better understanding of the differences between the reaction products obtained with each model. Transient-state simulations were conducted for a gasifier under specific operating conditions. The standard K-epsilon (2eq) turbulence model was utilized, along with the incorporation of species transport, volumetric responses, and eddy dissipation. In this study, the impacts of one-, two-, and four-step reaction mechanisms on the mass fraction of the products of the reactions, as well as the maximum values of velocity, turbulence, and temperature, were examined. The findings demonstrated that for all mechanisms, the greater maximum values of velocity and turbulence are attained at early time steps and decrease with subsequent time steps. The temperature rises as much in the early time steps and nearly stays the same in the late time steps. In all situations examined, the species’ fraction mass varies slightly in the early time steps but becomes nearly constant in the latter time stages. Similar species mass fraction values were found for both one-step and four-step methods. The results also suggest that the lower half of the gasifier is where the highest mass fraction values are found.
Full article
(This article belongs to the Section A4: Bio-Energy)
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Open AccessArticle
Optimizing Solar Heating for Thangka Exhibition Halls: A Case Study in Malkang Cultural Village
by
Wenyang Han, Yan Bai, Miao Du, Yujie Tao, Yin Zhang and Qianru Yang
Energies 2024, 17(9), 2091; https://doi.org/10.3390/en17092091 (registering DOI) - 27 Apr 2024
Abstract
With the continuous development of rural revitalization and urbanization in China, the sustainable transformation of traditional rural architecture has become increasingly important. This study takes the Thangka exhibition hall in rural Malkang, Sichuan Province, as the research object and proposes a Thangka exhibition
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With the continuous development of rural revitalization and urbanization in China, the sustainable transformation of traditional rural architecture has become increasingly important. This study takes the Thangka exhibition hall in rural Malkang, Sichuan Province, as the research object and proposes a Thangka exhibition hall architectural design centered around solar heating and aiming for near-zero energy consumption. The research method involves establishing a solar energy system model on the roof of the exhibition hall and utilizing solar angle and area calculation formulas along with simulation software to calculate the optimal installation angle and area of solar panels, with the aim of achieving indoor temperatures that meet Thangka protection requirements while achieving zero-energy heating. Preliminary results indicate that this solar-centric near-zero energy architectural design can effectively promote the increase in indoor temperature through solar thermal conversion. Additionally, through calculation and simulation, the optimal installation angle for the solar panels achieving zero-energy heating is determined to be 24.25 with an azimuth angle of −1.2. The optimum installation area for solar panels is 8.2 square meters in the showroom and 2.7 square meters in the storeroom. Among these, the solar panel area for the Thangka exhibition hall constitutes 4.12% of the total area and is required for maintaining Thangka protection temperature requirements throughout the year, while the solar panel area for the storage room constitutes 1.88% and is also needed for the same purpose. Studying the optimal installation angle and area of solar panels can transform the exhibition hall into a near-zero-energy building, meeting the temperature requirements for Thangka preservation and human thermal comfort, while also achieving optimal economic benefits. This provides guidance and a reference for promoting near-zero-energy buildings in rural areas.
Full article
(This article belongs to the Special Issue Development of Energy-Efficient Solutions for Smart Buildings)
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Open AccessArticle
Experimental Analysis of the Light Wavelength’s Impact on the Performance of a Silicon Solar Cell
by
Catarina Pinho Correia Valério Bernardo, Ricardo A. Marques Lameirinhas, João Paulo N. Torres, António Baptista and Maria João Marques Martins
Energies 2024, 17(9), 2090; https://doi.org/10.3390/en17092090 (registering DOI) - 26 Apr 2024
Abstract
The main aim of this article is to analyse the Si solar cell’s behaviour when it is exposed to light of different colours. An experimental work, with 100 experimental tests, was carried out, using an RGB LED. In order to obtain better fitting
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The main aim of this article is to analyse the Si solar cell’s behaviour when it is exposed to light of different colours. An experimental work, with 100 experimental tests, was carried out, using an RGB LED. In order to obtain better fitting of the characteristic curves’ results, we used a novel discrete model, d1MxP. The obtained results showed that all experimental points of the tests were inside the two triangles that connected the three theoretical primary colours and the three experimental primary colours in the chromaticity diagram. With this diagram, the colour purity could be determined, which presented values between 20% and 60%. The primary colours of the three different LEDs of the light source presented a dominant wavelength that corresponded to the peak wavelengths of the light source spectrum, which showed high purity. However, the obtained results show that mixing colours may not lead to an increase in the cell’s output power. Additionally, an increase in the cell’s temperature was observed, due to the surplus absorbed energy, which was converted into heat, being one of the causes of the cell’s efficiency reduction.
Full article
(This article belongs to the Section A2: Solar Energy and Photovoltaic Systems)
Open AccessReview
Research Progress and Prospect of Condition Assessment Techniques for Oil–Paper Insulation Used in Power Systems: A Review
by
Zaijun Jiang, Xin Li, Heng Zhang, Enze Zhang, Chuying Liu, Xianhao Fan and Jiefeng Liu
Energies 2024, 17(9), 2089; https://doi.org/10.3390/en17092089 (registering DOI) - 26 Apr 2024
Abstract
Oil–paper insulation is the critical insulation element in the modern power system. Under a harsh operating environment, oil–paper insulation will deteriorate gradually, resulting in electrical accidents. Thus, it is important to evaluate and monitor the insulation state of oil–paper insulation. Firstly, this paper
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Oil–paper insulation is the critical insulation element in the modern power system. Under a harsh operating environment, oil–paper insulation will deteriorate gradually, resulting in electrical accidents. Thus, it is important to evaluate and monitor the insulation state of oil–paper insulation. Firstly, this paper introduces the geometric structure and physical components of oil–paper insulation and shows the main reasons and forms of oil–paper insulation’s degradation. Then, this paper reviews the existing condition assessment techniques for oil–paper insulation, such as the dissolved gas ratio analysis, aging kinetic model, cellulose–water adsorption isotherm, oil–paper moisture balance curve, and dielectric response technique. Additionally, the advantages and limitations of the above condition assessment techniques are discussed. In particular, this paper highlights the dielectric response technique and introduces its evaluation principle in detail: (1) collecting the dielectric response data, (2) extracting the feature parameters from the collected dielectric response data, and (3) establishing the condition assessment models based on the extracted feature parameters and the machine learning techniques. Finally, two full potential studies are proposed, which research hotspots’ oil–paper insulation and the electrical–chemical joint evaluation technique. In summary, this paper concludes the principles, advantages and limitation of the existing condition assessment techniques for oil–paper insulation, and we put forward two potential research avenues.
Full article
(This article belongs to the Special Issue Power Electronic Converter Topologies and Control for Integration of Renewable Energy and Multi-Energy Sources)
Open AccessArticle
Improved Switchable Heat Pipe Based on Adsorption: Against-Gravity Operation and Enhanced Dynamics
by
Simon Boda, Markus Winkler, Robert Schießl, Christian Teicht, Daniel Schwarz, Jan Schipper, Kilian Bartholomé, Olaf Schäfer-Welsen and Sandra Pappert
Energies 2024, 17(9), 2088; https://doi.org/10.3390/en17092088 (registering DOI) - 26 Apr 2024
Abstract
Controlling heat transfer through components with adjustable thermal resistance can be of great benefit in a wide range of applications such as the thermal management of spacecraft or electric vehicles. A novel concept for both thermal switching and thermal regulation is the use
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Controlling heat transfer through components with adjustable thermal resistance can be of great benefit in a wide range of applications such as the thermal management of spacecraft or electric vehicles. A novel concept for both thermal switching and thermal regulation is the use of a water-loaded adsorbent within a reservoir that a regular heat pipe is expanded with. By reversibly desorbing or adsorbing water, states of low and high thermal resistance can be achieved. This concept has been studied so far only in thermosiphons that rely on gravity support. To expand potential application fields, we successfully investigated the utilization of heat pipes with a capillary structure, achieving against-gravity operation. Adsorption-based heat pipe demonstrators were experimentally examined regarding their characteristic properties. Thermal resistances during the on and off state of 0.25 KW−1 and 6.5 KW−1, respectively, were measured, yielding switching ratios of up to 26. Furthermore, the role of the adsorbent reservoir heat exchanger was examined and found to have a significant potential to yield an improvement with regards to dynamic performance. With an improved demonstrator design, the dynamic performance was enhanced as the hysteresis behavior was reduced and a minimum switching time of 5 min was recorded.
Full article
(This article belongs to the Section J: Thermal Management)
Open AccessArticle
Process Optimization of Pellet Manufacturing from Mixed Materials in Ultrasonic Vibration-Assisted Pelleting
by
Wentao Li, Rongwei Yu, Lina Luo and Hongying Shi
Energies 2024, 17(9), 2087; https://doi.org/10.3390/en17092087 (registering DOI) - 26 Apr 2024
Abstract
Achieving carbon neutrality and alleviating the rural energy predicament are crucial aspects in rural areas, particularly in the severe cold regions of northeast China. Pellets serve as clean, renewable energy sources and are ideal alternative fuels. This study investigated the influencing factors and
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Achieving carbon neutrality and alleviating the rural energy predicament are crucial aspects in rural areas, particularly in the severe cold regions of northeast China. Pellets serve as clean, renewable energy sources and are ideal alternative fuels. This study investigated the influencing factors and effects of mixed raw materials in ultrasonic vibration-assisted pelleting (UV-A pelleting). Rice straw and corn stover were mixed to produce pellets, and a central composite rotatable design (CCRD) was conducted to analyze the variables and their interactions on pellet density and durability. Mathematical regression models for pellet density and durability were established and then validated through ANOVA analysis. The results showed that all variables significantly affected the density and durability of pellets. The mixing ratio had a greater impact on pellet durability compared to density due to differences in ingredients. The optimal combination of process parameters included a mixing ratio of 25%, molding pressure of 4 MPa, pelleting time of 37 s, and ultrasonic power output at 200 W, resulting in a pellet density of 1301.18 kg/m3 with a durability reaching 94.26%. The desirability value (0.997) under these optimal conditions confirmed the validity of the models; further experiments also verified their effectiveness. The combustion of the optimized pellet was analyzed using thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis in an air atmosphere. Four combustion stages and ignition temperature were provided.
Full article
(This article belongs to the Section B: Energy and Environment)
Open AccessArticle
Systematic Development of Application-Oriented Operating Strategies for the Example of an Industrial Heating Supply System
by
Lukas Theisinger, Michael Frank and Matthias Weigold
Energies 2024, 17(9), 2086; https://doi.org/10.3390/en17092086 (registering DOI) - 26 Apr 2024
Abstract
The ongoing challenge to ensure a sustainable and affordable energy supply forces industrial companies to transform their energy system. This transformation usually leads to an increase in topological complexity, which in turn results in increased operational complexity. Existing approaches from the field of
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The ongoing challenge to ensure a sustainable and affordable energy supply forces industrial companies to transform their energy system. This transformation usually leads to an increase in topological complexity, which in turn results in increased operational complexity. Existing approaches from the field of supervisory and optimal control are capable of mastering complex operational problems. However, due to the complex and non-transparent implementation, there is still no industrial penetration, which hinders the necessary transformation of energy systems. This work aims at establishing trust in these control approaches and presents a procedure model for the systematic development of application-oriented operating strategies for industrial energy heating systems. It combines research approaches from the fields of sequencing control and approximate MPC to extract rule-based operating strategies, which are inherently easy to understand and implementable. By splitting the procedure model into five phases, expert knowledge can be integrated in a targeted manner. The procedure model is validated by the exemplary application to an industrial heating supply system. As part of an optimization study, the operating strategy developed is compared with both an MPC strategy and a baseline strategy. While the conventional MPC approach represents the upper limit of optimality, the operating strategy developed is able to achieve comparable results. Compared to the baseline strategy, a relative reduction in operating costs of 5.4% to 37.0% is achieved.
Full article
(This article belongs to the Section G: Energy and Buildings)
Open AccessArticle
Assessing the Costs of Commercialising Tidal Energy in the UK
by
Donald R. Noble, Kristofer Grattan and Henry Jeffrey
Energies 2024, 17(9), 2085; https://doi.org/10.3390/en17092085 (registering DOI) - 26 Apr 2024
Abstract
There is a need for increased renewable energy to meet net-zero targets and decarbonise the economy. Harnessing the predictable power of the tides with tidal stream turbines can contribute to this. Tidal energy is a nascent technology with higher costs at present. However,
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There is a need for increased renewable energy to meet net-zero targets and decarbonise the economy. Harnessing the predictable power of the tides with tidal stream turbines can contribute to this. Tidal energy is a nascent technology with higher costs at present. However, cost reductions have been observed with an increased deployment in other renewable energy technologies that have received financial support, and it is postulated that similar will happen with tidal energy. The first tidal stream projects have been awarded market support in the UK through the Contracts for Difference (CfD) scheme, with almost 100 MW expected to be commissioned by 2028. This work uses learning rates to investigate how much investment in ongoing market support might be needed to achieve cost reductions through subsidised deployment alongside research and innovation. Using a range of informed `what if?’ scenarios, it shows sensitivity to key inputs. The results show that the support needed is most sensitive to the learning rate, reducing it from 15% to 12.5% or 10% doubles or more than quadruples the investment required, respectively. The support is also highly dependent on the starting cost from which learning occurs, taken as the CfD Strike Price in 2025. Varying this between 156 and 220 GBP/MWh results in total investment of GBP 6.7 and 22.3 bn, respectively. Most importantly, a balance is needed between subsidising deployment to drive down costs through learning and funding innovation to maintain a high learning rate.
Full article
(This article belongs to the Section C: Energy Economics and Policy)
Open AccessReview
Industrial Waste Heat Utilization in the European Union—An Engineering-Centric Review
by
Vojtěch Turek, Bohuslav Kilkovský, Ján Daxner, Dominika Babička Fialová and Zdeněk Jegla
Energies 2024, 17(9), 2084; https://doi.org/10.3390/en17092084 (registering DOI) - 26 Apr 2024
Abstract
The efficient utilization of waste heat from industrial processes can provide a significant source of energy savings for production plants, as well as be a driver of sustainable operations and the abatement of emissions. Industrial waste heat usually is contained in liquid or
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The efficient utilization of waste heat from industrial processes can provide a significant source of energy savings for production plants, as well as be a driver of sustainable operations and the abatement of emissions. Industrial waste heat usually is contained in liquid or gaseous outlet streams. Although the possible ways to utilize waste heat are discussed in a wide variety of papers, these either provide only a general overview of utilization options and opportunities or focus on a narrow range of industrial processes. The aim of the present paper is to discuss the practical aspects of waste heat utilization in the European Union so that the reader can gain perspective on (i) the thermal classification of waste heat, (ii) liquid and gaseous waste streams and their typical temperatures for industrial use cases, (iii) the technical, economic, physical, and environmental aspects barring full utilization of the available waste heat, (iv) waste heat sources in various industries, and (v) standardized equipment and technologies applicable to industrial waste heat utilization, including their advantages, disadvantages, and weak points.
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(This article belongs to the Collection Advances in Heat Transfer Enhancement)
Open AccessArticle
Numerical Simulation of Fracturing Fluid Storage in Shale Reservoirs Based on Experimental Measurements of Stress Sensitivity of Hydraulic Fracture Network Conductivity
by
Tianhao Wang and Fujian Zhou
Energies 2024, 17(9), 2083; https://doi.org/10.3390/en17092083 (registering DOI) - 26 Apr 2024
Abstract
Hydraulic fracturing is used in shale reservoir production, with low flowback rates and a large amount of fracturing fluid retained inside the reservoir. In this study, a stress sensitivity analysis experiment on the fracture inflow capacity was implemented to investigate the relationship between
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Hydraulic fracturing is used in shale reservoir production, with low flowback rates and a large amount of fracturing fluid retained inside the reservoir. In this study, a stress sensitivity analysis experiment on the fracture inflow capacity was implemented to investigate the relationship between the hydraulic fracture (HF) and natural fracture (NF) inflow capacities and effective stress. A three-dimensional shale reservoir model was also constructed to couple the experimentally obtained laws with the numerical model to investigate the effects of the connection and closure of the fracture network on the retention of the fracturing fluid. The results show that the stress sensitivity of natural fractures is two orders of magnitude higher than that of hydraulic fractures. The seepage-absorption effect of capillary forces is not the whole reason for the large amount of fracturing fluid retention. The closure of the fracture network formed by natural and hydraulic fractures during the production process led to the storage of a large amount of fracturing fluid, and this process maintained the stability of the water production rate during the steady water production period.
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(This article belongs to the Section H: Geo-Energy)
Open AccessArticle
Research on Multi-Objective Optimization Design of University Student Center in China Based on Low Energy Consumption and Thermal Comfort
by
Ming Liu, Yufei Que, Nanxin Yang, Chongyi Yan and Qibo Liu
Energies 2024, 17(9), 2082; https://doi.org/10.3390/en17092082 (registering DOI) - 26 Apr 2024
Abstract
Ensuring optimal building performance is vital for enhancing student activity comfort and fostering energy-saving initiatives toward low-carbon objectives. This paper focuses on university student centers in China, aiming to diminish building energy consumption while enhancing indoor thermal comfort. Parametric modeling of typical cases
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Ensuring optimal building performance is vital for enhancing student activity comfort and fostering energy-saving initiatives toward low-carbon objectives. This paper focuses on university student centers in China, aiming to diminish building energy consumption while enhancing indoor thermal comfort. Parametric modeling of typical cases is executed using the Grasshopper 1.0.0007 software package, and the simulation of building energy consumption and indoor thermal comfort relies on the Ladybug and Honeybee plug-in. Employing a multi-objective optimization design method and the Octopus multi-objective optimization algorithm, this study integrates numerical simulations and on-site surveys to analyze how factors like building form, orientation, envelope structure, and others impact the indoor and outdoor environment. A comprehensive optimization design approach is implemented for the building’s exterior components, including the walls, windows, roof, and shading system. After conducting a comparative analysis of the annual comprehensive energy consumption and indoor thermal comfort before and after the optimization plan, it is determined that implementing these measures reduces the annual comprehensive energy consumption of the building under study by 58.8% and extends the duration of indoor thermal comfort by 53.0%. This study presents a practical optimization design methodology for university student center architecture in China, aiding architects in decision making and advocating for energy-efficient building designs.
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(This article belongs to the Special Issue Optimizing Energy Efficiency and Thermal Comfort in Building)
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Open AccessArticle
Experimental Study on Two-Phase Countercurrent Flow Limitation in Horizontal Circular Pipes
by
Xixi Zhu, Chende Xu, Mingzhou Gu and Naihua Wang
Energies 2024, 17(9), 2081; https://doi.org/10.3390/en17092081 - 26 Apr 2024
Abstract
The two-phase countercurrent flow limitation (CCFL) in horizontal channels is important in relation to nuclear reactor safety. In this study, we aim to investigate the CCFL characteristics and the flow behaviors in horizontal circular pipes with small diameters. The effects of pipe diameter
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The two-phase countercurrent flow limitation (CCFL) in horizontal channels is important in relation to nuclear reactor safety. In this study, we aim to investigate the CCFL characteristics and the flow behaviors in horizontal circular pipes with small diameters. The effects of pipe diameter and the water head in the upper plenum on CCFL characteristics are experimentally studied. An image-processing technique and statistical treatments are implemented to analyze the horizontal countercurrent flow. The results show that the CCFL characteristics for the horizontal circular pipes with small diameters can be well correlated using the dimensionless parameters, which are based on adding fluid viscosity to the Wallis parameters. The CCFL characteristics are significantly affected by the pipe diameter and are slightly affected by the water head above the horizontal pipe. The gas–liquid interface fluctuates with certain periods, and flow pattern transitions happen in the horizontal air–water countercurrent flow. As the air flow rate increases, the occurrence location of the liquid slug appears to shift towards the water entrance. In addition, the further away from the water entrance, the lower the average of liquid holdup.
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