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A special issue of Entropy (ISSN 1099-4300). This special issue belongs to the section "Thermodynamics".

Deadline for manuscript submissions: 31 January 2026 | Viewed by 3430

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Dr. Adriano Viana Ensinas

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Department of Engineering, Federal University of Lavras, Lavras 37200-900, MG, Brazil
Interests: biofuels; biomass conversion; process integration; modeling and design of biorefineries
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Special Issue Information

Dear Colleagues,

This Special Issue on Thermodynamic Optimization of Energy Systems explores advanced methods for the design, optimization, and sustainability of energy systems in response to global energy and environmental challenges. Key topics include multi-objective optimization techniques, exergy and pinch analysis, life cycle assessment, and computational modeling for enhancing the efficiency of thermodynamic processes. Research covers biofuel production, hydrogen technology, and the integration of renewables, focusing on energy transitions in agricultural and industrial sectors. Emphasis is placed on innovative thermodynamic cycles, the optimization of energy conversion processes, emission reduction strategies, and resource management, offering critical insights for sustainable energy system design and operation.

Dr. Adriano Viana Ensinas
Guest Editor

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Keywords

thermodynamics
energy optimization
sustainable energy systems
multi-objective optimization
emission reduction strategies

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Published Papers (4 papers)

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Research

18 pages, 1930 KB

Open AccessArticle

Optimization of Exergy Output Rate in a Supercritical CO₂ Brayton Cogeneration System

by Jiachi Shan, Shaojun Xia and Qinglong Jin

Entropy 2025, 27(10), 1078; https://doi.org/10.3390/e27101078 (registering DOI) - 18 Oct 2025

Abstract

To address low energy utilization efficiency and severe exergy destruction from direct discharge of high-temperature turbine exhaust, this study proposes a supercritical CO₂ Brayton cogeneration system with a series-connected hot water heat exchanger for stepwise waste heat recovery. Based on finite-time thermodynamics, a physical model that provides a more realistic framework by incorporating finite temperature difference heat transfer, irreversible compression, and expansion losses is established. Aiming to maximize exergy output rate under the constraint of fixed total thermal conductance, the decision variables, including working fluid mass flow rate, pressure ratio, and thermal conductance distribution ratio, are optimized. Optimization yields a 16.06% increase in exergy output rate compared with the baseline design. The optimal parameter combination is a mass flow rate of 79 kg/s and a pressure ratio of 5.64, with thermal conductance allocation increased for the regenerator and cooler, while decreased for the heater. The obtained results could provide theoretical guidance for enhancing energy efficiency and sustainability in S-CO₂ cogeneration systems, with potential applications in industrial waste heat recovery and power generation. Full article

(This article belongs to the Special Issue Thermodynamic Optimization of Energy Systems)

27 pages, 1002 KB

Open AccessArticle

Exergy Efficiency of Closed and Unsteady-Flow Systems

by Yunus A. Çengel and Mehmet Kanoğlu

Entropy 2025, 27(9), 943; https://doi.org/10.3390/e27090943 - 10 Sep 2025

Viewed by 511

Abstract

Exergy efficiency is viewed as the degree of approaching reversible operation, with a value of 100 percent for a reversible process characterized by zero entropy generation or equivalently zero exergy destruction since X_destroyed = T₀S_gen. As such, exergy efficiency becomes a measure of thermodynamic perfection. There are different conceptual definitions of exergy efficiency, the most common ones being (1) the ratio of exergy output to exergy input η_ex = X_output/X_input = 1 − (X_destroyed + X_loss)/X_input, (2) the ratio of the product exergy to fuel exergy η_ex = X_product/X_fuel = 1 − (X_destroyed + X_loss)/X_fuel, and (3) the ratio of exergy recovered to exergy expended η_ex = X_recovered/X_expended = 1 − X_destroyed/X_expended. Most exergy efficiency definitions are formulated with steady-flow systems in mind, and they are generally applied to systems in steady operation such as power plants and refrigeration systems whose exergy content remains constant. If these definitions are to be used for closed and unsteady-flow systems, the terms need to be interpreted broadly to account for the exergy change of the systems as exergy input or output, as appropriate. In this paper, general exergy efficiency relations are developed for closed and unsteady-flow systems and their use is demonstrated with applications. Also, the practicality of the use of the term exergy loss X_loss is questioned, and limitations on the definition η_ex = W_act,out/W_rev,out are discussed. Full article

(This article belongs to the Special Issue Thermodynamic Optimization of Energy Systems)

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23 pages, 4430 KB

Open AccessArticle

Exergetic Analysis and Design of a Mechanical Compression Stage—Application for a Cryogenic Air Separation Plant

by Adalia Andreea Percembli (Chelmuș), Arthur Dupuy, Lavinia Grosu, Daniel Dima and Alexandru Dobrovicescu

Entropy 2025, 27(5), 532; https://doi.org/10.3390/e27050532 - 16 May 2025

Viewed by 572

Abstract

This study focuses on the compression area of a cryogenic air separation unit (ASU). The mechanism of exergy consumption in the compressor was revealed. The influence of the compression ratio and of the isentropic efficiency per stage give arguments for proper choice of these decisional parameters. For the purchase cost of the compressor, an exergoeconomic correlation based on the exergetic product represented by the compression ratio and the isentropic efficiency as the Second Law coefficient of performance was used instead of the common thermo-economic one based only on the cost of materials. The impact of the suction temperature on the compressor operating performance is shown, making the gap between the compression stage and the associated intercooler. After optimization of the global system, a specific exergy destruction is assigned to each inter-stage compression cooler. To fit this optimum exergy consumption, a design procedure for the inter-stages and final coolers based on the number of heat transfer units (NTU-ε) method and the number of exergy units destroyed (NEUD) is shown. Graphs are provided that make the application of the method straightforward and much easier to use compared to the usual logarithmic mean temperature difference. A 25% increase in the compression ratio per stage leads to a decrease in the exergy efficiency of 3%, while the purchase cost of the compressor rises by 80%. An increase in the isentropic efficiency of the compressor from 0.7 to 0.85 leads to an increase in the exergetic performance coefficient of 21%, while the compressor purchase cost triples. Full article

(This article belongs to the Special Issue Thermodynamic Optimization of Energy Systems)

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21 pages, 5719 KB

Open AccessArticle

Exergy Analysis of a Convective Heat Pump Dryer Integrated with a Membrane Energy Recovery Ventilator

by Anand Balaraman, Md Ashiqur Rahman, Davide Ziviani and David M. Warsinger

Entropy 2025, 27(2), 197; https://doi.org/10.3390/e27020197 - 13 Feb 2025

Cited by 1 | Viewed by 1878

Abstract

To increase energy efficiency, heat pump dryers and membrane dryers have been proposed to replace conventional fossil fuel dryers. Both conventional and heat pump dryers require substantial energy for condensing and reheating, while “active” membrane systems require vacuum pumps that are insufficiently developed. Lower temperature dehumidification systems make efficient use of membrane energy recovery ventilators (MERVs) that do not need vacuum pumps, but their high heat losses and lack of vapor selectivity have prevented their use in industrial drying. In this work, we propose an insulating membrane energy recovery ventilator for moisture removal from drying exhaust air, thereby reducing sensible heat loss from the dehumidification process and reheating energy. The second law analysis of the proposed system is carried out and compared with a baseline convective heat pump dryer. Irreversibilities in each component under different ambient temperatures (5–35 °C) and relative humidity (5–95%) are identified. At an ambient temperature of 35 °C, the proposed system substantially reduces sensible heat loss (47–60%) in the dehumidification process, resulting in a large reduction in condenser load (45–50%) compared to the baseline system. The evaporator in the proposed system accounts for up to 59% less irreversibility than the baseline system. A maximum of 24.5% reduction in overall exergy input is also observed. The highest exergy efficiency of 10.2% is obtained at an ambient condition of 35 °C and 5% relative humidity, which is more than twice the efficiency of the baseline system under the same operating condition. Full article

(This article belongs to the Special Issue Thermodynamic Optimization of Energy Systems)

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