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Challenges, technology drivers and the role of power boilers in rapidly decarbonizing energy systems
No full textThis vision article accompanies a Special Issue of Applied Thermal Engineering dedicated to the 14th International Conference on Boiler Technology (ICBT 2022) on 'Transition technologies towards carbon neutrality and reduced environmental impacts'. The aim of the conference was to discuss recent progress, achievements and new solutions in the field of thermal power production, covering scientific research from a wide range of universities and research centres on topics relating to the design and operation of boilers and auxiliary devices for thermal power generation. This article discusses a selection of papers presented at this conference and selected for publication in Applied Thermal Engineering
Overview and outlook of research and innovation in energy systems with carbon dioxide as the working fluid
No full textCarbon dioxide (CO2, R744) is a natural working fluid with interesting thermophysical properties that have stimulated strong attention by the academic and industrial communities for a broad range of energy applications. The technology readiness level of CO2-based energy systems is very diverse due to the increasing consideration that the fluid has been receiving since the 1990s. Hence, the state of the art in CO2 energy research spans from fundamental thermofluid and chemistry science to commercial system innovations. After a brief compendium on ongoing activities, this paper proposes a roadmap for CO2 energy research with reference to the cooling, heating and power sectors. The key knowledge gaps and the main challenges at system and component levels are critically discussed. Pathways to advance the understanding and the technological maturity of CO2 energy systems are also outlined
Editorial/ preface of VSI:ATE_AESMT'22
No full textThe special issue “VSI:AESMT′ 22“ aims to provide novel research papers in the field of the Renewable Energy as a part of the conference “Alternative energy sources, materials and technologies (AESMT′ 22)”. The conference was foreseen to be held in Veliko Tarnovo, Bulgaria. However due to the pandemic the conference was held on-line on 27–28 June 2022. The following distinguished scientists gave plenary reports during the conference: - Prof. Soteris Kalogirou (Editor-in-Chief of “Renewable Energy”, Cyprus); - Prof. André Thess (Director, German Aerospace Center, Institute of Engineering Thermodynamics, Germany). Some more important points about the AESMT'22 conference are as follows: - Representatives of 23 countries sent papers to the conference, namely from Belarus, Brazil, Bulgaria, China, Chile, France, Germany, India, Iran, Israel, Italy, Kazakhstan, Kuwait, Latvia, Poland, Portugal, Romania, Russia, Serbia, Spain, Tajikistan, Turkey, and United Kingdom; - The total number of the presented articles was 67 (25 of them orally, the others were posters); - After the preliminary review, 15 articles have been selected for submission in “Applied Thermal Engineering” journal
Multiphase flows with thermal engineering applications: A special issue for MTCUE-2022
No full textMultiphase flow is a basic science to study multiphase fluid flow, heat and mass transfer, combustion, chemical reaction, etc., in which two or more substances with different phases, states and components coexist and have a clear interface. Multiphase flow and its phenomena have been encountered in various application fields, such as fossil energy, renewable energy, hydrogen energy, nuclear energy, power engineering, petrochemical industry, environment and so on. It builds a bridge between basic theoretical research and industrial applications, which plays a supporting and irreplaceable role in the breakthrough of energy science theories and technologies, and the revolution of industry and human society systems. This special issue aims to provide a platform for publishing high-quality papers on multiphase flow in the design, development and demonstration of components, devices, equipment, technologies, systems and, in general, solutions involving thermal processes for the production, storage, utilization and conservation of energy, with a focus on engineering application
Preface of VSI: ATE_AESMT’23
No full textThe special issue “VSI:ATE_AESMT‘23“ aims to provide novel research papers in the field of the Renewable Energy as a part of the conference “Alternative energy sources, materials and technologies (AESMT’23)”. The conference was held in Sofia, Bulgaria in the time period 16–17 May 2023. Some more important points about the AESMT’23 conference are as follows: - Representatives of 24 countries (Bulgaria, Canada, China, Cuba, Germany, Greece, India, Iraq, Israel, Italy, Kazakhstan, Kosovo, Latvia, Macedonia, Poland, Portugal, Romania, Russia, Serbia, Singapore, Spain, Turkey, Ukraine, United Kingdom) sent their works to the conference; - The total number of the presented articles was 76 (46 of them orally, the others were posters); - After the preliminary review, 16 articles have been selected for submission in “Applied Thermal Engineering” journal
Decarbonizing power and fuels production by chemical looping processes: Systematic review and future perspectives
No full textThe decarbonization of power and fuels production is a crucial element of the energy transition. Among several available technologies, chemical looping processes promise to be a feasible solution to support the decarbonization of large-scale industrial sectors. They involve a solid material, commonly called an oxygen carrier, that circulates between two or more reactors according to a redox process. In the reduction step, the oxygen carrier loses some its oxygen atoms by reaction with a fuel. In the oxidation step, it is oxidized back to the initial phase by an oxidizing agent such as air, steam and/or CO2. The flexibility of this process enables it to be used in diverse applications, such as: (1) fuel combustion; (2) hydrocarbon reforming; (3) solid fuels gasification, with limited energy penalties for CO2 separation and possibility of autothermal operation within the cycle. Therefore, this technology has a significant potential to contribute to the sustainable transition. This review paper aims at shedding light on a range of chemical looping progresses and to explore open questions in this field. The discussion is divided into three main chemical looping variants: combustion, reforming, and gasification. For each of these, recent progresses and challenges are highlighted by considering two scales of analysis: lab-scale and system scale. At the lab-scale, advances in materials development and process performance are discussed, while at the system scale, technical, environmental and economic analyses are presented in comparison with benchmark alternative technologies. Materials development and testing represents a crucial element hampering chemical looping development. Combination of costly and often toxic synthetic materials with natural ores is considered a promising solution that can reduce cost, increase stability and environmental compatibility. Iron oxides have several decontaminating properties and due to their low cost, large availability and high stability and appear as promising oxygen carriers. The synergistic mixing of metal oxides is also a solution to optimizing oxygen carrier properties. Different reactor configurations have been proposed with circulating fluidized beds being the most mature in terms of operational hours. Nevertheless, pressurized operation has been mainly conducted with fixed bed reactors. Techno-economic analyses indicate that chemical looping reforming can approach competitiveness with the unabated benchmark, while in power production the limit in the maximum reactor temperature is a significant drawback. An interesting application with still limited experimental and modelling research is the application of chemical looping for energy storage applications
Technoeconomic assessments of hybrid photovoltaic-thermal vs. conventional solar-energy systems: Case studies in heat and power provision to sports centres
Full text linkThis paper presents a comprehensive analysis of the energetic, economic and environmental potentials of hybrid photovoltaic-thermal (PVT) and conventional solar energy systems for combined heat and power provision. A solar combined heat and power (S-CHP) system based on PVT collectors, a solar-power system based on PV panels, a solar-thermal system based on evacuated tube collectors (ETCs), and a S-CHP system based on a combination of side-by-side PV panels and ETCs (PV-ETC) are assessed and compared. A conventional CHP system based on a natural-gas-fired internal combustion engine (ICE) prime mover is also analysed as a competing fossil-fuel based solution. Annual simulations are conducted for the provision of electricity, along with space heating, swimming pool heating and hot water to the University Sports Centre of Bari, Italy. The results show that, based on a total installation area of 4000 m2 in all cases, the PVT S-CHP system outperforms the other systems in terms of total energy output, with annual electrical and thermal energy yields reaching 82.3% and 51.3% of the centre's demands, respectively. The PV system is the most profitable solar solution, with the shortest payback time (9.4 years) and lowest levelised cost of energy (0.089 €/kWh). Conversely, the ETC solar-thermal system is not economically viable for the sports centre application, and increasing the ETC area share in the combined PV-ETC S-CHP system is unfavourable due to the low natural gas price. Although the PVT S-CHP system has the highest investment cost, the high annual revenue from the avoided energy bills elevates its economic performance to a level between those of the conventional PV and ETC-based S-CHP systems, with a payback time of 13.7 years and a levelised cost of energy of 0.109 €/kWh. However, at 445 tCO2/year, the CO2 emission reduction potential of the PVT S-CHP system is considerably higher (by 40–75%) than those of the all other solar systems (254–317 tCO2/year). Compared to the solar energy systems, the ICE-CHP system has the shortest payback time (6.2 years), but its CO2 emission reduction (25 tCO2/year) is significantly lower. A high carbon price is beneficial for improving the cost-competitiveness of the solar energy systems, boosting its market penetration and helping to meet any carbon emission targets
Computational fluid dynamics modelling of the regular wave flow regime in air-water downwards annular flows
Full text linkAlthough the global flow characteristics of annular gas-liquid flows have been studied experimentally for more than 50 years, the spatiotemporally-resolved details of these flows have remained relatively unexplored until recently, with data provided via advanced experimental methods based, e.g., on optical techniques. Similarly, the numerical modelling of annular flows is still an immature process. The present work aims to provide a computational fluid dynamics (CFD) model based on the volume of fluid (VOF) method for simulating annular gas-liquid flows, setting the stage for a deeper investigation of these flows at global and local scales. The work focuses on the most common downwards annular flow (DAF) flow pattern: the regular wave regime. 3-D and 2-D axisymmetric transient simulations have been performed using a commercial code (ANSYS Fluent 2021 R1). The code is validated through available experimental data regarding topological flow properties, mainly film thickness and wave statistics. The validation results suggest that 3-D simulations are needed to provide predictions that agree with the experimental data, highlighting strong 3-D features in the flow
Multi-energy islands: Advances in local district heating, cooling and power systems
No full textThe trend of the global energy matrix change is toward a smart energy system with an optimized interaction between the demand-side and the supply-side. In this perspective, a smart energy system has many features such as a high share of renewable energy systems, concrete integration of energy systems, active interactions of different energy sectors, utilization of the most advanced clean energy technologies, the lowest rate of losses using local energy systems (i.e., the so-called energy islands) and the highest possible rate of utilization of waste or freely available energy flows. On the other hand, fast-growing of energy production from renewable energy sources offers more attractive, cost-effective opportunities to design and employ the local energy systems. Although integrating more renewable energy sources is a technological and economic challenge for the electricity network, it can be accounted as an opportunity to optimize the electricity system operation in synergy with other energy vectors such as district heating/cooling or gas networks to increase the hosting capacity for renewable sources
Innovations in pulsating heat pipes: From origins to future perspectives
Full text linkSince the early 1990s, the pulsating heat pipe (PHP) has emerged as one of the most innovative, effective and potentially more convenient passive two-phase heat transfer systems, thanks to its good performance, versatility, and construction simplicity. On the other hand, the PHP is characterized by complex thermohydraulic behaviour that still presents a true challenge to designers, which has led to significant interest by a growing number of researchers. The technological readiness level (TLR) of this technology is quite broad depending on the application: for instance, the industrial community is starting to consider the PHP as a reliable solution for electronic cooling in ground conditions, while implementations in the cryogenic temperature range and in space environments is also being extensively explored. This vision paper aims at shedding light on the current knowledge and prediction capability of PHP numerical models, on unsolved phenomenological issues, on the current technological challenges and the future perspectives of this fascinating heat transfer device. Specifically, after a general introduction and a brief overview of the current knowledge and the open issues of PHPs, special focus is devoted to the following topics: flat-plate PHP assessments; advancements in PHP modelling and simulation; flow stabilization techniques; non-conventional fluids subdivided into fluid mixtures, self-rewetting fluids, nanofluids; cryogenic applications, space applications, and finally the newest frontiers of flexible PHPs. Each section is accompanied by a brief roadmap providing directions for future research based on key challenges, which are also gathered and summarized in the final outlook section
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