| 1. |
- Baldi, Francesco, 1986, et al.
(författare)
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Energy and exergy analysis of ship energy systems - The case study of a chemical tanker
- 2015
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Ingår i: International Journal of Applied Thermodynamics. - : International Centre for Applied Thermodynamics (ICAT). - 1301-9724 .- 2146-1511. ; 18:2, s. 82-93
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Tidskriftsartikel (refereegranskat)abstract
- Shipping contributes today to 2.1% of global anthropogenic greenhouse gas emissions and its share is expected to grow together with global trade in the coming years. At the same time, bunker prices are increasing and companies start to feel the pressure of growing fuel bills in their balance sheet. In order to address both challenges, it is important to improve the understanding of the energy consumption trends on ships through a detailed analysis of their energy systems. In this paper, energy and exergy analysis are applied to the energy system of a chemical tanker, for which both measurements and technic knowledge of ship systems were available. The application of energy analysis to the case-study vessel allowed for the comparison of different energy flows and therefore identifying system components and interactions critical for ship energy consumption. Exergy analysis allowed instead identifying main inefficiencies and evaluating waste flows. Results showed that propulsion is the main contributor to ship energy consumption (70%), but that also auxiliary heat (16.5%) and power (13.5%) needs are relevant sources of energy consumption. The potential for recovering waste heat is relevant, especially from the exhaust gases, as their exergetic value represents 18% of the engine power output.
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| 2. |
- Castro Flores, José Fiacro, et al.
(författare)
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Energetic and exergetic analysis of alternative low-temperature based district heating substation arrangements
- 2016
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Ingår i: International Journal of Thermodynamics. - : International Centre for Applied Thermodynamics (ICAT). - 1301-9724 .- 2146-1511. ; 19:2, s. 71-80
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Tidskriftsartikel (refereegranskat)abstract
- District Heating (DH) technology is an efficient and cost-effective solution to provide heating services to the built environment. However, the existing DH technology may not be technically and economically effective to service buildings with low energy demands. Here, low-temperature based district heating (LTDH) can provide a better match between supply and demand in terms of energy quality and quantity. This paper deals with the energy and exergy analyses of a LTDH substation supplying a secondary LTDH network as a subnet of the existing DH system. In order to improve the temperature match, a mix of supply and return streams from the main DH network are used to supply the substation. Based on modelling and simulation, an energy and exergy analysis is employed to compare the performance of two proposed substation configurations to that of a conventional DH substation operating at low temperatures. The results of this analysis show that the proposed LTDH substation reduced the share of energy demand covered by the main DH supply by 20% to 25%. Likewise, by using the flow from the main DH return pipe, the final exergy efficiency of the overall system increased by 5% on average. The exergy destruction occurring at the system components was also identified and compared: during high heat demands the substation heat exchanger is responsible for the largest share of exergy destruction, whereas for low heat demands, it is due to the pumping effort. Based on these results, the proposed system is seen as an effective approach to increase the quality and quantity match between the low-temperature network and the conventional supply.
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| 3. |
- Heyne, Stefan, 1979, et al.
(författare)
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Numerical simulations of a prechamber autoignition engine operating on natural gas
- 2011
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Ingår i: International Journal of Applied Thermodynamics. - : International Centre for Applied Thermodynamics (ICAT). - 1301-9724 .- 2146-1511. ; 14:2, s. 43-50
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Tidskriftsartikel (refereegranskat)abstract
- At our laboratory extensive research has been conducted on the conversion of conventional Diesel cogeneration engines to operation on natural gas and biogas. In the framework of this research, a numerical simulation of a prechamber autoignition gas engine has been performed based on an experimental test case. With a simplified finiterate/ eddy-dissipation model for the combustion of natural gas, it was possible to properly reproduce the experiment considering the combustion duration, ignition timing and overall energy balance. A modification of the original cylindrical-conical prechamber geometry to a simpler cylindrical one was tested with the simulation model. The influence of burnt gases inside the prechamber was assessed simulating the mixture formation inside the prechamber. The simulations showed little effect of taking into account the non-homogeneities in the gas phase on the combustion duration. The new cylindrical geometry envisaged did not show any improvement in the combustion homogeneity inside the prechamber and its volume (limited by the real engine geometry) is in fact not sufficient to properly ignite the main chamber according to the simulations. The model can be used to further guide design modifications of the prechamber engine to improve performance.
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| 4. |
- Kjelstrup, S., et al.
(författare)
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A thermodynamic metric for assessing sustainable use of natural resources
- 2015
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Ingår i: International Journal of Applied Thermodynamics. - : International Centre for Applied Thermodynamics (ICAT). - 1301-9724 .- 2146-1511. ; 18:1, s. 66-72
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Tidskriftsartikel (refereegranskat)abstract
- A thermodynamic metric is proposed to supplement existing scales in the assessment of the way we use our natural resources. This metric has the advantage of being absolute and independent of economy, suitable for comparison of technologies, and can be used at molecular level as well as process-units and systems levels. It measures loss of useful work (exergy) in cradle-to-grave or complete recycling systems in terms of generalized friction or entropy production and may deliver realistic targets for process operations. This absolute scale can be useful also for international legislation and to foster a development in direction of more sustainable technologies. In an extended perspective, the presented approach may form a universal basis for analysis and development of national economies and policies regarding industry, engineering and environment. This may give new opportunities to put political resource discussions on a solid objective footing.
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| 5. |
- Firat, Coskun, et al.
(författare)
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Effects of Particle-Wall Interactions on the Thermodynamic Behavior of Gases at the Nano Scale
- 2011
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Ingår i: International Journal of Thermodynamics. - 1301-9724. ; 14:4, s. 155-161
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Tidskriftsartikel (refereegranskat)abstract
- The thermodynamic behavior of gases confined in nano structures is considerably different than those in macro onesdue to the effects of both particle-wall interactions and the wave character of particles. The homogeneous density distribution of a gas at thermodynamic equilibrium is disturbed by these effects. Because of particle-wallinteractions, the local density of a gas changes drastically near the domain boundaries. Also, the wave character ofthe particles causes an inhomogeneous density distribution, especially near the boundaries. Consequently, the apparent density (number of particles over the domain volume) is different than the real one. All the density dependent thermodynamic properties are affected by the inhomogeneity in the density distribution. Therefore, it is important to consider these effects on local density to analyze the thermodynamic behaviors of gases confined innano structures. The detailed analysis of these effects on local density also gives a base of knowledge for the experimental verification of quantum size effects on local density due to the wave character of particles. In thisstudy, the density distributions of classical (Maxwellian) and quantum (both Fermi and Bose) gases are calculated and investigated by considering both particle-wall interactions and quantum size effects. The results can be used for experimental verification of quantum size effects on gas density as well as the modeling of nano heat engines.
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| 6. |
- Lazzaretto, Andrea, et al.
(författare)
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Analytical and neural network models for gas turbine design and off-design simulation
- 2001
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Ingår i: International Journal of Thermodynamics. - 1301-9724. ; 4:4, s. 173-182
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a gas turbine design and off-design model in which the difficulties due to lack of knowledge about stage-by-stage performance are overcome by constructing artificial machine maps through appropriate scaling techniques applied to generalized maps taken from the literature and validating them with test measurement data from real plants. In particular, off-design performance is obtained through compressor map modifications according to variable inlet guide vane closure. The set of equations of the developed analytical model is solved by a commercial package, which provides great flexibility in the choice of independent variables of the overall system. The results obtained from this simulator are used for neural network training: problems associated with the construction and use of neural networks are discussed and their capability as a tool for predicting machine performance is analyzed.
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| 7. |
- Ozturk, Z Fatih, et al.
(författare)
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Quantum Effects on Gas Diffusion at the Nano Scale
- 2011
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Ingår i: International Journal of Thermodynamics. - 1301-9724. ; 14:4, s. 163-166
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Tidskriftsartikel (refereegranskat)abstract
- The thermodynamic and transport properties of gases confined at the nano scale are considerably different than those at the macro scale. At the nano scale, quantum size effects (QSE) become important and changes the behavior of gases. In this study, the diffusion coefficients of monatomic Fermi and Bose gases are analytically derived by considering QSE. The influences of QSE and quantum degeneracy on the diffusion coefficients are examined separately to analyze these effects individually. The variations of the ratio of diffusion coefficients of He3 and He4 gases with the concentration of He3 are analyzed for both low and high density conditions.
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| 8. |
- Sciubba, Enrico, et al.
(författare)
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A brief commented history of exergy from the beginnings to 2004
- 2007
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Ingår i: International Journal of Thermodynamics. - Istanbul, Turkey : International Centre for Applied Thermodynamics. - 1301-9724. ; 10:1, s. 1-26
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents a brief critical and analytical account of the development of the conceptof exergy and of its applications. It is based on a careful and extended (in time)consultation of a very large body of published references taken from archival journals,textbooks and other monographic works, conference proceedings, technical reports andlecture series. We have tried to identify the common thread that runs through all of thereferences, to put different issues into perspective, to clarify dubious points, to suggestlogical and scientific connections and priorities. It was impossible to eliminate ourrespective biases that still affect the “style” of the present paper: luckily, some of ourindividual biases “cancelled out” at the time of writing, and some were corrected by ourReviewers (to whom we owe sincere thanks for the numerous and very relevant correctionsand suggestions).The article is organized chronologically and epistemologically: it turns out that the twocriteria allow for a quite clear systematization of the subject matter, because thedevelopment of the exergy concept was rather “linear”.This work is addressed to our Colleagues who are involved in theoretical research,industrial development, and societal applications of exergy concepts: if they extract fromthis article the idea of an extraordinary epistemological uniformity in the development ofthe concept of exergy, our goal will be achieved. The other addressees of this paper areGraduate Students taking their first steps in this field: in their case, we hope thatconsultation of our paper will prompt them to adopt and maintain throughout their career ascholarly valid method of research, which implies studying and respecting our scientificroots (the sources) but venturing freely and creatively into unknown territory.In the Conclusions we try to forecast future developments: this is the only part of the paperthat is an intentional expression of our own views: the previous historical-scientificexposition is instead based on verifiable facts and accepted opinions.
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| 9. |
- Toffolo, Andrea, et al.
(författare)
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A practical tool to generate complex energy system configurations based on the synthsep methodology
- 2019
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Ingår i: International Journal of Thermodynamics. - : Yaşar DEMİREL. - 1301-9724. ; 22:1, s. 45-53
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Tidskriftsartikel (refereegranskat)abstract
- Traditional fossil fueled power plants are commonly based on steam Rankine cycle or Brayton Joule cycle. Using water or air as working fluid is obviously the most obvious choice for the wide availability of these substances in nature. However, the scarcity of natural energy sources and the strong need of reducing environmental impact have necessarily drawn the research to new energy systems configurations operating with other working fluids, which are able to recover lower temperature sources, such as Sun or industrial wasted heat. The variety of new working fluids (refrigerants or organic fluids) widens the choice to a variety of configurations that can be tailored to the specific source characteristics and boundary constraints. It is not always easy or even possible to conceive the best configuration for given specifications with the mere experience of a common designer. To design a new system configuration, the designer normally uses some “non-codified rules” deriving from his knowledge of basic thermodynamics and energy engineering. This paper aims instead at showing a practical tool that is based on a new methodology, named SYNTHSEP, to generate new energy system configurations. This methodology starts from the simple thermodynamic cycles operated by a given fluid made up of the four fundamental processes (compression, heating, expansion and cooling) and uses a rigorous set of codified rules to build the final system configuration. The paper presents the basics of the new methodology and how it has been implemented in a practical tool that simply requires the information about the elementary cycles and their shared processes as input data.
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| 10. |
- Toffolo, Andrea, et al.
(författare)
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Energy system diagnosis by a fuzzy expert system with genetically evolved rules
- 2008
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Ingår i: International Journal of Thermodynamics. - 1301-9724. ; 11:3, s. 115-121
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Tidskriftsartikel (refereegranskat)abstract
- The problem of malfunction diagnosis in energy systems can be approached using an expert system which compares the experimental data measured by the plant acquisition system and the calculated data evaluated by a plant simulator under the same operating conditions. In this paper the rules that form the "knowledge base" of the expert system are not assigned heuristically by trying to code the expertise of plant personnel, as it is usually done, but they are artificially and randomly generated by the recombination and selection operators of an evolutionary algorithm. A two-objective optimization problem is set up, in order to search for the optimal sets of rules having the minimum complexity but simultaneously maximizing the number of correct fault identifications for a given set of malfunctioning operating conditions. A global and a local approach are applied to a real test case, a two-shaft gas turbine used as the gas section of a combined-cycle cogeneration plant, in order to evaluate the potentialities and the limits of this methodology.
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