An examination of exergy destruction in organic Rankine cycles
TL;DR: In this paper, an exergy topological method is used to present a quantitative estimation of the exergy destroyed in an organic Rankine cycle (ORC) operating on R113.
Abstract: The exergy topological method is used to present a quantitative estimation of the exergy destroyed in an organic Rankine cycle (ORC) operating on R113. A detailed roadmap of exergy flow is presented using an exergy wheel, and this visual representation clearly depicts the exergy accounting associated with each thermodynamic process. The analysis indicates that the evaporator accounts for maximum exergy destroyed in the ORC and the process responsible for this is the heat transfer across a finite temperature difference. In addition, the results confirm the thermodynamic superiority of the regenerative ORC over the basic ORC since regenerative heating helps offset a significant amount of exergy destroyed in the evaporator, thereby resulting in a thermodynamically more efficient process. Parameters such as thermodynamic influence coefficient and degree of thermodynamic perfection are identified as useful design metrics to assist exergy-based design of devices. This paper also examines the impact of operating parameters such as evaporator pressure and inlet temperature of the hot gases entering the evaporator on ORC performance. It is shown that exergy destruction decreases with increasing evaporator pressure and decreasing turbine inlet temperatures. Finally, the analysis reveals the potential of the exergy topological methodology as a robust technique to identify the magnitude of irreversibilities associated with real thermodynamic processes in practical thermal systems. Copyright © 2008 John Wiley & Sons, Ltd.
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TL;DR: An overview of ORC architectures can be found in this paper, where the performance evaluation criteria and boundary conditions are clearly stated, as well as an overview of the available experimental data is given.
Abstract: The organic Rankine cycle (ORC) is commonly accepted as a viable technology to convert low temperature heat into electricity. Furthermore, ORCs are designed for unmanned operation with little maintenance. Because of these excellent characteristics, several ORC waste heat recovery plants are already in operation. Although the basic ORC is gradually adopted into industry, the need of increased cost-effectiveness persists. Therefore, a next logical step is the development of new ORC architectures. Even though there has been a strong renaissance towards ORC research in the last decade, ORC architectures have received relatively little attention. Several barriers can be listed. First, there is the difficulty in assessing the additional complexity of the system. While several advanced cycle designs appear promising from a thermodynamic viewpoint, it is not clear that these represent viable economic solutions. Secondly, there is a lack of experimental data from open literature. Additionally, there is the challenge of coping with various boundary conditions from literature, which makes an objective comparison difficult. In this article an overview is presented of ORC architectures. The performance evaluation criteria and boundary conditions are clearly stated. As well, an overview of the available experimental data is given.
529 citations
Cites background from "An examination of exergy destructio..."
...Especially for low waste heat temperatures, these have a significant impact on the subcritical heat exchange process [46, 47]....
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...85 n/a n/a WHR 100 kWe [46] 177 25 B+RG 0....
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...[46], between 40....
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...Furthermore, zeotropic mixtures are already used in cryogenic refrigeration [46]....
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TL;DR: In this article, a comparative study of different geothermal power plant concepts, based on the exergy analysis for high-temperature geothermal resources, is presented, and the performance of each cycle has been discussed in terms of second-law efficiency, exergy destruction rate, and first-law efficiencies.
355 citations
Cites background or methods from "An examination of exergy destructio..."
...An interesting approach, which is in fact the basis for the system presented in this paper, has been proposed by Mago et al. [9, 10 ] and Yari [11] the ‘‘regenerative organic Rankine cycle’’....
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...For the case of the binary geothermal power plants (ORCs), the numerical model was validated by using previously published data from references [2,9, 10 ,18]....
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TL;DR: In this paper, a small-scale combined solar heat and power (CSHP) system based on an organic rankine cycle (ORC) was investigated for the combined provision of heating and power for domestic use in the UK.
239 citations
Cites background from "An examination of exergy destructio..."
...[39], it is evident that: (1) the exergy efficiency of the ORC components in the present study are on the whole lower; and (2) the relative percentages of exergy destroyed are also different,...
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...[39] in a study of a non-regenerative ORC system....
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TL;DR: In this paper, the authors proposed a thermal efficiency model theoretically based on an ideal ORC to analyze the influence of working fluid properties on the thermal efficiency, the optimal operation condition and exergy destruction for various heat source temperatures were also evaluated utilizing pinch point analysis and ex-ergy analysis.
217 citations
TL;DR: In this paper, the second law efficiency of a non-superheated subcritical organic rankine cycle with zeotropic mixtures as working fluids is evaluated. But the results show that the evaporator accounts for the highest exergy loss.
187 citations
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TL;DR: Entropy generation minimization (finite time thermodynamics, or thermodynamic optimization) is the method that combines into simple models the most basic concepts of heat transfer, fluid mechanics, and thermodynamics as mentioned in this paper.
Abstract: Entropy generation minimization (finite time thermodynamics, or thermodynamic optimization) is the method that combines into simple models the most basic concepts of heat transfer, fluid mechanics, and thermodynamics. These simple models are used in the optimization of real (irreversible) devices and processes, subject to finite‐size and finite‐time constraints. The review traces the development and adoption of the method in several sectors of mainstream thermal engineering and science: cryogenics, heat transfer, education, storage systems, solar power plants, nuclear and fossil power plants, and refrigerators. Emphasis is placed on the fundamental and technological importance of the optimization method and its results, the pedagogical merits of the method, and the chronological development of the field.
1,516 citations
TL;DR: In this article, the second law of thermodynamics is used as a basis for evaluating the irreversibility associated with simple heat transfer processes, such as heat augmentation techniques, heat exchanger design, and thermal insulation systems.
612 citations
TL;DR: In this article, a Rankine cycle using organic fluids as working fluids was investigated in recovering low enthalpy containing heat sources and it was shown that p-Xylene showed the highest efficiency while Benzene showed the lowest.
542 citations
TL;DR: In this article, an analysis of regenerative organic Rankine cycles using dry organic fluids, to convert waste energy to power from low-grade heat sources is presented, and the evaluation for both configurations will be performed using a combined first and second law analysis by varying certain system operating parameters at various reference temperatures and pressures.
520 citations
TL;DR: In this paper, the authors outline the fundamentals of the methods of exergy analysis and entropy generation minimization (or thermodynamic optimization) subject to finite-size constraints and specified environmental conditions, and illustrate the accounting for exergy flows and accumulation in closed systems, open systems, heat transfer processes, and power and refrigeration plants.
Abstract: This paper outlines the fundamentals of the methods of exergy analysis and entropy generation minimization (or thermodynamic optimization—the minimization of exergy destruction). The paper begins with a review of the concept of irreversibility, entropy generation, or exergy destruction. Examples illustrate the accounting for exergy flows and accumulation in closed systems, open systems, heat transfer processes, and power and refrigeration plants. The proportionality between exergy destruction and entropy generation sends the designer in search of improved thermodynamic performance subject to finite-size constraints and specified environmental conditions. Examples are drawn from energy storage systems for sensible heat and latent heat, solar energy, and the generation of maximum power in a power plant model with finite heat transfer surface inventory. It is shown that the physical structure (geometric configuration, topology) of the system springs out of the process of global thermodynamic optimization subject to global constraints. This principle generates structure not only in engineering but also in physics and biology (constructal theory). Copyright © 2002 John Wiley & Sons, Ltd.
494 citations