Editorial

3 pages, 179 KiB

Open AccessEditorial

The Carnot Cycle and Heat Engine Fundamentals and Applications II

by Michel Feidt

Entropy 2022, 24(2), 230; https://doi.org/10.3390/e24020230 - 02 Feb 2022

Cited by 1 | Viewed by 1354

This editorial introduces the second Special Issue entitled “Carnot Cycle and Heat Engine Fundamentals and Applications II” https://www [...] Full article

(This article belongs to the Special Issue Carnot Cycle and Heat Engine Fundamentals and Applications II)

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9 pages, 639 KiB

Open AccessFeature PaperArticle

A New Step in the Optimization of the Chambadal Model of the Carnot Engine

by Michel Feidt and Monica Costea

Entropy 2022, 24(1), 84; https://doi.org/10.3390/e24010084 - 04 Jan 2022

Cited by 5 | Viewed by 1284

Abstract

This paper presents a new step in the optimization of the Chambadal model of the Carnot engine. It allows a sequential optimization of a model with internal irreversibilities. The optimization is performed successively with respect to various objectives (e.g., energy, efficiency, or power [...] Read more.

This paper presents a new step in the optimization of the Chambadal model of the Carnot engine. It allows a sequential optimization of a model with internal irreversibilities. The optimization is performed successively with respect to various objectives (e.g., energy, efficiency, or power when introducing the duration of the cycle). New complementary results are reported, generalizing those recently published in the literature. In addition, the new concept of entropy production action is proposed. This concept induces new optimums concerning energy and power in the presence of internal irreversibilities inversely proportional to the cycle or transformation durations. This promising approach is related to applications but also to fundamental aspects. Full article

(This article belongs to the Special Issue Carnot Cycle and Heat Engine Fundamentals and Applications II)

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19 pages, 530 KiB

Open AccessArticle

Chemical and Mechanical Aspect of Entropy-Exergy Relationship

by Pierfrancesco Palazzo

Entropy 2021, 23(8), 972; https://doi.org/10.3390/e23080972 - 28 Jul 2021

Cited by 3 | Viewed by 1540

Abstract

The present research focuses the chemical aspect of entropy and exergy properties. This research represents the complement of a previous treatise already published and constitutes a set of concepts and definitions relating to the entropy–exergy relationship overarching thermal, chemical and mechanical aspects. The [...] Read more.

The present research focuses the chemical aspect of entropy and exergy properties. This research represents the complement of a previous treatise already published and constitutes a set of concepts and definitions relating to the entropy–exergy relationship overarching thermal, chemical and mechanical aspects. The extended perspective here proposed aims at embracing physical and chemical disciplines, describing macroscopic or microscopic systems characterized in the domain of industrial engineering and biotechnologies. The definition of chemical exergy, based on the Carnot chemical cycle, is complementary to the definition of thermal exergy expressed by means of the Carnot thermal cycle. These properties further prove that the mechanical exergy is an additional contribution to the generalized exergy to be accounted for in any equilibrium or non-equilibrium phenomena. The objective is to evaluate all interactions between the internal system and external environment, as well as performances in energy transduction processes. Full article

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18 pages, 6466 KiB

Open AccessArticle

Performance Optimizations with Single-, Bi-, Tri-, and Quadru-Objective for Irreversible Diesel Cycle

by Shuangshuang Shi, Lingen Chen, Yanlin Ge and Huijun Feng

Entropy 2021, 23(7), 826; https://doi.org/10.3390/e23070826 - 28 Jun 2021

Cited by 28 | Viewed by 2798

Abstract

Applying finite time thermodynamics theory and the non-dominated sorting genetic algorithm-II (NSGA-II), thermodynamic analysis and multi-objective optimization of an irreversible Diesel cycle are performed. Through numerical calculations, the impact of the cycle temperature ratio on the power density of the cycle is analyzed. [...] Read more.

Applying finite time thermodynamics theory and the non-dominated sorting genetic algorithm-II (NSGA-II), thermodynamic analysis and multi-objective optimization of an irreversible Diesel cycle are performed. Through numerical calculations, the impact of the cycle temperature ratio on the power density of the cycle is analyzed. The characteristic relationships among the cycle power density versus the compression ratio and thermal efficiency are obtained with three different loss issues. The thermal efficiency, the maximum specific volume (the size of the total volume of the cylinder), and the maximum pressure ratio are compared under the maximum power output and the maximum power density criteria. Using NSGA-II, single-, bi-, tri-, and quadru-objective optimizations are performed for an irreversible Diesel cycle by introducing dimensionless power output, thermal efficiency, dimensionless ecological function, and dimensionless power density as objectives, respectively. The optimal design plan is obtained by using three solution methods, that is, the linear programming technique for multidimensional analysis of preference (LINMAP), the technique for order preferences by similarity to ideal solution (TOPSIS), and Shannon entropy, to compare the results under different objective function combinations. The comparison results indicate that the deviation index of multi-objective optimization is small. When taking the dimensionless power output, dimensionless ecological function, and dimensionless power density as the objective function to perform tri-objective optimization, the LINMAP solution is used to obtain the minimum deviation index. The deviation index at this time is 0.1333, and the design scheme is closer to the ideal scheme. Full article

(This article belongs to the Special Issue Carnot Cycle and Heat Engine Fundamentals and Applications II)

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26 pages, 3592 KiB

Open AccessArticle

Optimization Modeling of Irreversible Carnot Engine from the Perspective of Combining Finite Speed and Finite Time Analysis

by Monica Costea, Stoian Petrescu, Michel Feidt, Catalina Dobre and Bogdan Borcila

Entropy 2021, 23(5), 504; https://doi.org/10.3390/e23050504 - 22 Apr 2021

Cited by 8 | Viewed by 1906

Abstract

An irreversible Carnot cycle engine operating as a closed system is modeled using the Direct Method and the First Law of Thermodynamics for processes with Finite Speed. Several models considering the effect on the engine performance of external and internal irreversibilities expressed as [...] Read more.

An irreversible Carnot cycle engine operating as a closed system is modeled using the Direct Method and the First Law of Thermodynamics for processes with Finite Speed. Several models considering the effect on the engine performance of external and internal irreversibilities expressed as a function of the piston speed are presented. External irreversibilities are due to heat transfer at temperature gradient between the cycle and heat reservoirs, while internal ones are represented by pressure losses due to the finite speed of the piston and friction. Moreover, a method for optimizing the temperature of the cycle fluid with respect to the temperature of source and sink and the piston speed is provided. The optimization results predict distinct maximums for the thermal efficiency and power output, as well as different behavior of the entropy generation per cycle and per time. The results obtained in this optimization, which is based on piston speed, and the Curzon–Ahlborn optimization, which is based on time duration, are compared and are found to differ significantly. Correction have been proposed in order to include internal irreversibility in the externally irreversible Carnot cycle from Curzon–Ahlborn optimization, which would be equivalent to a unification attempt of the two optimization analyses. Full article

(This article belongs to the Special Issue Carnot Cycle and Heat Engine Fundamentals and Applications II)

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11 pages, 4171 KiB

Open AccessArticle

Power and Thermal Efficiency Optimization of an Irreversible Steady-Flow Lenoir Cycle

by Ruibo Wang, Yanlin Ge, Lingen Chen, Huijun Feng and Zhixiang Wu

Entropy 2021, 23(4), 425; https://doi.org/10.3390/e23040425 - 02 Apr 2021

Cited by 18 | Viewed by 2299

Abstract

Using finite time thermodynamic theory, an irreversible steady-flow Lenoir cycle model is established, and expressions of power output and thermal efficiency for the model are derived. Through numerical calculations, with the different fixed total heat conductances (

U_{T}

) of two heat [...] Read more.

Using finite time thermodynamic theory, an irreversible steady-flow Lenoir cycle model is established, and expressions of power output and thermal efficiency for the model are derived. Through numerical calculations, with the different fixed total heat conductances (

U_{T}

) of two heat exchangers, the maximum powers (

P_{\max}

), the maximum thermal efficiencies (

η_{\max}

), and the corresponding optimal heat conductance distribution ratios (

u_{L_{P} (o p t)}

) and (

u_{L_{η} (o p t)}

) are obtained. The effects of the internal irreversibility are analyzed. The results show that, when the heat conductances of the hot- and cold-side heat exchangers are constants, the corresponding power output and thermal efficiency are constant values. When the heat source temperature ratio (

τ

) and the effectivenesses of the heat exchangers increase, the corresponding power output and thermal efficiency increase. When the heat conductance distributions are the optimal values, the characteristic relationships of

P - u_{L}

and

η - u_{L}

are parabolic-like ones. When

U_{T}

is given, with the increase in

τ

, the

P_{\max}

,

η_{\max}

,

u_{L_{P} (o p t)}

, and

u_{L_{η} (o p t)}

increase. When

τ

is given, with the increase in

U_{T}

,

P_{\max}

and

η_{\max}

increase, while

u_{L_{P} (o p t)}

and

u_{L_{η} (o p t)}

decrease. Full article

(This article belongs to the Special Issue Carnot Cycle and Heat Engine Fundamentals and Applications II)

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18 pages, 3275 KiB

Open AccessEditor’s ChoiceArticle

Stirling Refrigerating Machine Modeling Using Schmidt and Finite Physical Dimensions Thermodynamic Models: A Comparison with Experiments

by Cătălina Dobre, Lavinia Grosu, Alexandru Dobrovicescu, Georgiana Chişiu and Mihaela Constantin

Entropy 2021, 23(3), 368; https://doi.org/10.3390/e23030368 - 19 Mar 2021

Cited by 6 | Viewed by 2860

Abstract

The purpose of the study is to show that two simple models that take into account only the irreversibility due to temperature difference in the heat exchangers and imperfect regeneration are able to indicate refrigerating machine behavior. In the present paper, the finite [...] Read more.

The purpose of the study is to show that two simple models that take into account only the irreversibility due to temperature difference in the heat exchangers and imperfect regeneration are able to indicate refrigerating machine behavior. In the present paper, the finite physical dimensions thermodynamics (FPDT) method and 0-D modeling using the Schmidt model with imperfect regeneration were applied in the study of a β type Stirling refrigeration machine.The 0-D modeling is improved by including the irreversibility caused by imperfect regeneration and the finite temperature difference between the gas and the heat exchangers wall. A flowchart of the Stirling refrigerator exergy balance is presented to show the internal and external irreversibilities. It is found that the irreversibility at the regenerator level is more important than that at the heat exchangers level. The energies exchanged by the working gas are expressed according to the practical parameters, necessary for the engineer during the entire project. The results of the two thermodynamic models are presented in comparison with the experimental results, which leads to validation of the proposed FPDT model for the functional and constructive parameters of the studied refrigerating machine. Full article

(This article belongs to the Special Issue Carnot Cycle and Heat Engine Fundamentals and Applications II)

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13 pages, 497 KiB

Open AccessArticle

Simulating Finite-Time Isothermal Processes with Superconducting Quantum Circuits

by Jin-Fu Chen, Ying Li and Hui Dong

Entropy 2021, 23(3), 353; https://doi.org/10.3390/e23030353 - 16 Mar 2021

Cited by 8 | Viewed by 2122

Abstract

Finite-time isothermal processes are ubiquitous in quantum-heat-engine cycles, yet complicated due to the coexistence of the changing Hamiltonian and the interaction with the thermal bath. Such complexity prevents classical thermodynamic measurements of a performed work. In this paper, the isothermal process is decomposed [...] Read more.

Finite-time isothermal processes are ubiquitous in quantum-heat-engine cycles, yet complicated due to the coexistence of the changing Hamiltonian and the interaction with the thermal bath. Such complexity prevents classical thermodynamic measurements of a performed work. In this paper, the isothermal process is decomposed into piecewise adiabatic and isochoric processes to measure the performed work as the internal energy change in adiabatic processes. The piecewise control scheme allows the direct simulation of the whole process on a universal quantum computer, which provides a new experimental platform to study quantum thermodynamics. We implement the simulation on ibmqx2 to show the

1 / τ

scaling of the extra work in finite-time isothermal processes. Full article

(This article belongs to the Special Issue Carnot Cycle and Heat Engine Fundamentals and Applications II)

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34 pages, 7256 KiB

Open AccessArticle

Four-Objective Optimizations for an Improved Irreversible Closed Modified Simple Brayton Cycle

by Chenqi Tang, Lingen Chen, Huijun Feng and Yanlin Ge

Entropy 2021, 23(3), 282; https://doi.org/10.3390/e23030282 - 26 Feb 2021

Cited by 57 | Viewed by 2267

Abstract

An improved irreversible closed modified simple Brayton cycle model with one isothermal heating process is established in this paper by using finite time thermodynamics. The heat reservoirs are variable-temperature ones. The irreversible losses in the compressor, turbine, and heat exchangers are considered. Firstly, [...] Read more.

An improved irreversible closed modified simple Brayton cycle model with one isothermal heating process is established in this paper by using finite time thermodynamics. The heat reservoirs are variable-temperature ones. The irreversible losses in the compressor, turbine, and heat exchangers are considered. Firstly, the cycle performance is optimized by taking four performance indicators, including the dimensionless power output, thermal efficiency, dimensionless power density, and dimensionless ecological function, as the optimization objectives. The impacts of the irreversible losses on the optimization results are analyzed. The results indicate that four objective functions increase as the compressor and turbine efficiencies increase. The influences of the latter efficiency on the cycle performances are more significant than those of the former efficiency. Then, the NSGA-II algorithm is applied for multi-objective optimization, and three different decision methods are used to select the optimal solution from the Pareto frontier. The results show that the dimensionless power density and dimensionless ecological function compromise dimensionless power output and thermal efficiency. The corresponding deviation index of the Shannon Entropy method is equal to the corresponding deviation index of the maximum ecological function. Full article

(This article belongs to the Special Issue Carnot Cycle and Heat Engine Fundamentals and Applications II)

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15 pages, 3797 KiB

Open AccessArticle

Power and Efficiency Optimization for Open Combined Regenerative Brayton and Inverse Brayton Cycles with Regeneration before the Inverse Cycle

by Lingen Chen, Huijun Feng and Yanlin Ge

Entropy 2020, 22(6), 677; https://doi.org/10.3390/e22060677 - 17 Jun 2020

Cited by 26 | Viewed by 2601

Abstract

A theoretical model of an open combined cycle is researched in this paper. In this combined cycle, an inverse Brayton cycle is introduced into regenerative Brayton cycle by resorting to finite-time thermodynamics. The constraints of flow pressure drop and plant size are taken [...] Read more.

A theoretical model of an open combined cycle is researched in this paper. In this combined cycle, an inverse Brayton cycle is introduced into regenerative Brayton cycle by resorting to finite-time thermodynamics. The constraints of flow pressure drop and plant size are taken into account. Thirteen kinds of flow resistances in the cycle are calculated. On the one hand, four isentropic efficiencies are used to evaluate the friction losses in the blades and vanes. On the other hand, nine kinds of flow resistances are caused by the cross-section variances of flowing channels, which exist at the entrance of top cycle compressor (TCC), the entrance and exit of regenerator, the entrance and exit of combustion chamber, the exit of top cycle turbine, the exit of bottom cycle turbine, the entrance of heat exchanger, as well as the entrance of bottom cycle compressor (BCC). To analyze the thermodynamic indexes of power output, efficiency along with other coefficients, the analytical formulae of these indexes related to thirteen kinds of pressure drop losses are yielded. The thermodynamic performances are optimized by varying the cycle parameters. The numerical results reveal that the power output presents a maximal value when the air flow rate and entrance pressure of BCC change. In addition, the power output gets its double maximal value when the pressure ratio of TCC further changes. In the premise of constant flow rate of working fuel and invariant power plant size, the thermodynamic indexes can be optimized further when the flow areas of the components change. The effect of regenerator on thermal efficiency is further analyzed in detail. It is reported that better thermal efficiency can be procured by introducing the regenerator into the combined cycle in contrast with the counterpart without the regenerator as the cycle parameters change in the critical ranges. Full article

(This article belongs to the Special Issue Carnot Cycle and Heat Engine Fundamentals and Applications II)

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