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Open AccessArticle

Analyses of the Instabilities in the Discretized Diffusion Equations via Information Theory

by

Maxence Bigerelle

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Hakim Naceur

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Alain Iost

Entropy 2016, 18(4), 155; https://doi.org/10.3390/e18040155 - 21 Apr 2016

Viewed by 3747

Abstract

In a previous investigation (Bigerelle and Iost, 2004), the authors have proposed a physical interpretation of the instability λ = Δt/Δx² > 1/2 of the parabolic partial differential equations when solved by finite differences. However, our results were obtained [...] Read more.

In a previous investigation (Bigerelle and Iost, 2004), the authors have proposed a physical interpretation of the instability λ = Δt/Δx² > 1/2 of the parabolic partial differential equations when solved by finite differences. However, our results were obtained using integration techniques based on erf functions meaning that no statistical fluctuation was introduced in the mathematical background. In this paper, we showed that the diffusive system can be divided into sub-systems onto which a Brownian motion is applied. Monte Carlo simulations are carried out to reproduce the macroscopic diffusive system. It is shown that the amount of information characterized by the compression ratio of information of the system is pertinent to quantify the entropy of the system according to some concepts introduced by the authors (Bigerelle and Iost, 2007). Thanks to this mesoscopic discretization, it is proved that information on each sub-cell of the diffusion map decreases with time before the unstable equality λ = 1/2 and increases after this threshold involving an increase in negentropy, i.e., a decrease in entropy contrarily to the second principle of thermodynamics. Full article

(This article belongs to the Special Issue Entropy Generation in Thermal Systems and Processes 2015)

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Open AccessArticle

Energetic and Exergetic Analysis of a Heat Exchanger Integrated in a Solid Biomass-Fuelled Micro-CHP System with an Ericsson Engine

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Entropy 2016, 18(4), 154; https://doi.org/10.3390/e18040154 - 20 Apr 2016

Cited by 4 | Viewed by 4659

Abstract

A specific heat exchanger has been developed to transfer heat from flue gas to the working fluid (hot air) of the Ericsson engine of a solid biomass-fuelled micro combined heat and power (CHP). In this paper, the theoretical and experimental energetic analyses of [...] Read more.

A specific heat exchanger has been developed to transfer heat from flue gas to the working fluid (hot air) of the Ericsson engine of a solid biomass-fuelled micro combined heat and power (CHP). In this paper, the theoretical and experimental energetic analyses of this heat exchanger are compared. The experimental performances are described considering energetic and exergetic parameters, in particular the effectiveness on both hot and cold sides. A new exergetic parameter called the exergetic effectiveness is introduced, which allows a comparison between the real and the ideal heat exchanger considering the Second Law of Thermodynamics. A global analysis of exergetic fluxes in the whole micro-CHP system is presented, showing the repartition of the exergy destruction among the components. Full article

(This article belongs to the Special Issue Entropy Generation in Thermal Systems and Processes 2015)

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Open AccessArticle

Exergy Analysis of Complex Ship Energy Systems

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Entropy 2016, 18(4), 127; https://doi.org/10.3390/e18040127 - 08 Apr 2016

Cited by 12 | Viewed by 6411

Abstract

With multiple primary and secondary energy converters (diesel engines, steam turbines, waste heat recovery (WHR) and oil-fired boilers, etc.) and extensive energy networks (steam, cooling water, exhaust gases, etc.), ships may be considered as complex energy systems. Understanding and optimizing such [...] Read more.

With multiple primary and secondary energy converters (diesel engines, steam turbines, waste heat recovery (WHR) and oil-fired boilers, etc.) and extensive energy networks (steam, cooling water, exhaust gases, etc.), ships may be considered as complex energy systems. Understanding and optimizing such systems requires advanced holistic energy modeling. This modeling can be done in two ways: The simpler approach focuses on energy flows, and has already been tested, approved and presented; a new, more complicated approach, focusing on energy quality, i.e., exergy, is presented in this paper. Exergy analysis has rarely been applied to ships, and, as a general rule, the shipping industry is not familiar with this tool. This paper tries to fill this gap. We start by giving a short reminder of what exergy is and describe the principles of exergy modeling to explain what kind of results should be expected from such an analysis. We then apply these principles to the analysis of a large two-stroke diesel engine with its cooling and exhaust systems. Simulation results are then presented along with the exergy analysis. Finally, we propose solutions for energy and exergy saving which could be applied to marine engines and ships in general. Full article

(This article belongs to the Special Issue Entropy Generation in Thermal Systems and Processes 2015)

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Open AccessArticle

Thermodynamic Analysis of the Irreversibilities in Solar Absorption Refrigerators

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Emma Berrich Betouche

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Entropy 2016, 18(4), 107; https://doi.org/10.3390/e18040107 - 24 Mar 2016

Cited by 3 | Viewed by 4186

Abstract

A thermodynamic analysis of the irreversibility on solar absorption refrigerators is presented. Under the hierarchical decomposition and the hypothesis of an endoreversible model, many functional and practical domains are defined. The effect of external heat source temperature on the entropy rate and on [...] Read more.

A thermodynamic analysis of the irreversibility on solar absorption refrigerators is presented. Under the hierarchical decomposition and the hypothesis of an endoreversible model, many functional and practical domains are defined. The effect of external heat source temperature on the entropy rate and on the inverse specific cooling load (ISCL) multiplied by the total area of the refrigerator A/Q_e are studied. This may help a constructor to well dimension the solar machine under an optimal technico-economical criterion A/Q_e and with reasonable irreversibility on the refrigerator. The solar concentrator temperature effect on the total exchanged area, on the technico-economical ratio A/Q_e, and on the internal entropy rate are illustrated and discussed. The originality of these results is that they allow a conceptual study of a solar absorption refrigeration cycle. Full article

(This article belongs to the Special Issue Entropy Generation in Thermal Systems and Processes 2015)

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Open AccessArticle

Hierarchical Decomposition Thermodynamic Approach for the Study of Solar Absorption Refrigerator Performance

by

Emma Berrich Betouche

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Entropy 2016, 18(3), 82; https://doi.org/10.3390/e18030082 - 04 Mar 2016

Cited by 1 | Viewed by 4144

Abstract

A thermodynamic approach based on the hierarchical decomposition which is usually used in mechanical structure engineering is proposed. The methodology is applied to an absorption refrigeration cycle. Thus, a thermodynamic analysis of the performances on solar absorption refrigerators is presented. Under the hypothesis [...] Read more.

A thermodynamic approach based on the hierarchical decomposition which is usually used in mechanical structure engineering is proposed. The methodology is applied to an absorption refrigeration cycle. Thus, a thermodynamic analysis of the performances on solar absorption refrigerators is presented. Under the hypothesis of an endoreversible model, the effects of the generator, the solar concentrator and the solar converter temperatures, on the coefficient of performance (COP), are presented and discussed. In fact, the coefficient of performance variations, according to the ratio of the heat transfer areas of the high temperature part (the thermal engine 2) A_h and the heat transfer areas of the low temperature part (the thermal receptor) A_r variations, are studied in this paper. For low values of the heat-transfer areas of the high temperature part and relatively important values of heat-transfer areas of the low temperature part as for example A_h equal to 30% of A_r, the coefficient of performance is relatively important (approximately equal to 65%). For an equal-area distribution corresponding to an area ratio A_h/A_r of 50%, the COP is approximately equal to 35%. The originality of this deduction is that it allows a conceptual study of the solar absorption cycle. Full article

(This article belongs to the Special Issue Entropy Generation in Thermal Systems and Processes 2015)

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Open AccessArticle

Fractal Representation of Exergy

by

Yvain Canivet

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Diogo Queiros-Condé

and

Lavinia Grosu

Entropy 2016, 18(2), 56; https://doi.org/10.3390/e18020056 - 06 Feb 2016

Cited by 3 | Viewed by 4007

Abstract

We developed a geometrical model to represent the thermodynamic concepts of exergy and anergy. The model leads to multi-scale energy lines (correlons) that we characterised by fractal dimension and entropy analyses. A specific attention will be paid to overlapping points, rising interesting remarks [...] Read more.

We developed a geometrical model to represent the thermodynamic concepts of exergy and anergy. The model leads to multi-scale energy lines (correlons) that we characterised by fractal dimension and entropy analyses. A specific attention will be paid to overlapping points, rising interesting remarks about trans-scale dynamics of heat flows. Full article

(This article belongs to the Special Issue Entropy Generation in Thermal Systems and Processes 2015)

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Open AccessArticle

Preliminary Numerical Investigations of Entropy Generation in Electric Machines Based on a Canonical Configuration

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Entropy 2015, 17(12), 8187-8206; https://doi.org/10.3390/e17127874 - 15 Dec 2015

Cited by 3 | Viewed by 4106

Abstract

The present paper analyzes numerically the entropy generation induced by forced convection in a canonical configuration. The configuration itself includes two well known fluid dynamic problems: (1) an external flow (flow around a cylinder, Kármán flow); and (2) an internal flow (flow between [...] Read more.

The present paper analyzes numerically the entropy generation induced by forced convection in a canonical configuration. The configuration itself includes two well known fluid dynamic problems: (1) an external flow (flow around a cylinder, Kármán flow); and (2) an internal flow (flow between two concentric rotating cylinders, Couette flow). In many daily engineering issues (e.g., cooling of electric machines), a combination of these problems occurs and has to be investigated. Using the canonical configuration, the fields of entropy generation are analyzed in this work for a constant wall heat flux but varying two key parameters (Reynolds numbers Re_∞ and Re₀). The entropy generation due to conduction shows an absolute minimum around Re₀ = 10,000. The same minima can be found by a detailed analysis of the temperature profile. Thus, entropy generation seems to be a suitable indicator for optimizing heat exchange processes and delivers a large amount of information concerning fluid and heat transport. Full article

(This article belongs to the Special Issue Entropy Generation in Thermal Systems and Processes 2015)

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Open AccessArticle

Comparison Based on Exergetic Analyses of Two Hot Air Engines: A Gamma Type Stirling Engine and an Open Joule Cycle Ericsson Engine

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Entropy 2015, 17(11), 7331-7348; https://doi.org/10.3390/e17117331 - 28 Oct 2015

Cited by 6 | Viewed by 8496

Abstract

In this paper, a comparison of exergetic models between two hot air engines (a Gamma type Stirling prototype having a maximum output mechanical power of 500 W and an Ericsson hot air engine with a maximum power of 300 W) is made. Referring [...] Read more.

In this paper, a comparison of exergetic models between two hot air engines (a Gamma type Stirling prototype having a maximum output mechanical power of 500 W and an Ericsson hot air engine with a maximum power of 300 W) is made. Referring to previous energetic analyses, exergetic models are set up in order to quantify the exergy destruction and efficiencies in each type of engine. The repartition of the exergy fluxes in each part of the two engines are determined and represented in Sankey diagrams, using dimensionless exergy fluxes. The results show a similar proportion in both engines of destroyed exergy compared to the exergy flux from the hot source. The compression cylinders generate the highest exergy destruction, whereas the expansion cylinders generate the lowest one. The regenerator of the Stirling engine increases the exergy resource at the inlet of the expansion cylinder, which might be also set up in the Ericsson engine, using a preheater between the exhaust air and the compressed air transferred to the hot heat exchanger. Full article

(This article belongs to the Special Issue Entropy Generation in Thermal Systems and Processes 2015)

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Open AccessArticle

A Thermodynamic Entropy Approach to Reliability Assessment with Applications to Corrosion Fatigue

by

Anahita Imanian

and

Mohammad Modarres

Entropy 2015, 17(10), 6995-7020; https://doi.org/10.3390/e17106995 - 16 Oct 2015

Cited by 32 | Viewed by 6037

Abstract

This paper outlines a science-based explanation of damage and reliability of critical components and structures within the second law of thermodynamics. The approach relies on the fundamentals of irreversible thermodynamics, specifically the concept of entropy generation as an index of degradation and damage [...] Read more.

This paper outlines a science-based explanation of damage and reliability of critical components and structures within the second law of thermodynamics. The approach relies on the fundamentals of irreversible thermodynamics, specifically the concept of entropy generation as an index of degradation and damage in materials. All damage mechanisms share a common feature, namely energy dissipation. Dissipation, a fundamental measure for irreversibility in a thermodynamic treatment of non-equilibrium processes, is quantified by entropy generation. An entropic-based damage approach to reliability and integrity characterization is presented and supported by experimental validation. Using this theorem, which relates entropy generation to dissipative phenomena, the corrosion fatigue entropy generation function is derived, evaluated, and employed for structural integrity and reliability assessment of aluminum 7075-T651 specimens. Full article

(This article belongs to the Special Issue Entropy Generation in Thermal Systems and Processes 2015)

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Open AccessArticle

Entropy Generation through Deterministic Spiral Structures in a Corner Boundary-Layer Flow

by

LaVar King Isaacson

Entropy 2015, 17(8), 5304-5332; https://doi.org/10.3390/e17085304 - 27 Jul 2015

Cited by 1 | Viewed by 3967

Abstract

It is shown that nonlinear interactions between boundary layers on adjacent corner surfaces produce deterministic stream wise spiral structures. The synchronization properties of nonlinear spectral velocity equations of Lorenz form yield clearly defined deterministic spiral structures at several downstream stations. The computational procedure [...] Read more.

It is shown that nonlinear interactions between boundary layers on adjacent corner surfaces produce deterministic stream wise spiral structures. The synchronization properties of nonlinear spectral velocity equations of Lorenz form yield clearly defined deterministic spiral structures at several downstream stations. The computational procedure includes Burg’s method to obtain power spectral densities, yielding the available kinetic energy dissipation rates within the spiral structures. The singular value decomposition method is applied to the nonlinear time series solutions yielding empirical entropies, from which empirical entropic indices are then extracted. The intermittency exponents obtained from the entropic indices allow the computation of the entropy generation through the spiral structures to the final dissipation of the fluctuating kinetic energy into background thermal energy, resulting in an increase in the entropy. The entropy generation rates through the spiral structures are compared with the entropy generation rates within an empirical turbulent boundary layer at several stream wise stations. Full article

(This article belongs to the Special Issue Entropy Generation in Thermal Systems and Processes 2015)

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Open AccessArticle

Modeling and Analysis of Entropy Generation in Light Heating of Nanoscaled Silicon and Germanium Thin Films

by

José Ernesto Nájera-Carpio

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Federico Vázquez

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Aldo Figueroa

Entropy 2015, 17(7), 4786-4808; https://doi.org/10.3390/e17074786 - 09 Jul 2015

Viewed by 4467

Abstract

In this work, the irreversible processes in light heating of Silicon (Si) and Germanium (Ge) thin films are examined. Each film is exposed to light irradiation with radiative and convective boundary conditions. Heat, electron and hole transport and generation-recombination processes of electron-hole pairs [...] Read more.

In this work, the irreversible processes in light heating of Silicon (Si) and Germanium (Ge) thin films are examined. Each film is exposed to light irradiation with radiative and convective boundary conditions. Heat, electron and hole transport and generation-recombination processes of electron-hole pairs are studied in terms of a phenomenological model obtained from basic principles of irreversible thermodynamics. We present an analysis of the contributions to the entropy production in the stationary state due to the dissipative effects associated with electron and hole transport, generation-recombination of electron-hole pairs as well as heat transport. The most significant contribution to the entropy production comes from the interaction of light with the medium in both Si and Ge. This interaction includes two processes, namely, the generation of electron-hole pairs and the transferring of energy from the absorbed light to the lattice. In Si the following contribution in magnitude comes from the heat transport. In Ge all the remaining contributions to entropy production have nearly the same order of magnitude. The results are compared and explained addressing the differences in the magnitude of the thermodynamic forces, Onsager’s coefficients and transport properties of Si and Ge. Full article

(This article belongs to the Special Issue Entropy Generation in Thermal Systems and Processes 2015)

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