Thermo

30 pages, 2113 KiB

Open AccessReview

Linking Solution Microstructure and Solvation Thermodynamics of Mixed-Solvent Systems: Formal Results, Critical Observations, and Modeling Pitfalls

by Ariel A. Chialvo

Thermo 2024, 4(3), 407-432; https://doi.org/10.3390/thermo4030022 - 22 Sep 2024

Viewed by 330

Abstract

This review provides a critical assessment of the current state of affairs regarding the solvation thermodynamics involving mixed-solvent systems. It focuses specifically on (i) its rigorous molecular-based foundations, (ii) the underlying connections between the microstructural behavior of the mixed-solvent [...] Read more.

This review provides a critical assessment of the current state of affairs regarding the solvation thermodynamics involving mixed-solvent systems. It focuses specifically on (i) its rigorous molecular-based foundations, (ii) the underlying connections between the microstructural behavior of the mixed-solvent environment and its thermodynamic responses, (iii) the microstructural characterization of the behavior of the mixed-solvent environment around the dilute solute via unique fundamental structure-making/-breaking functions and the universal preferential solvation function, (iv) the discussion of potential drawbacks associated with the molecular simulation-based determination of thermodynamic preferential interaction parameters, and (v) the forensic examination of frequent modeling pitfalls behind the interpretation of preferential solvation from experimental data of Gibbs free energy of solute transfer. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Molecular Simulation and Thermodynamics)

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13 pages, 3140 KiB

Open AccessArticle

A New Numerically Improved Transient Technique for Measuring Thermal Properties of Anisotropic Materials

by Svetozár Malinarič, Peter Bokes and Goran Bulatovič

Thermo 2024, 4(3), 394-406; https://doi.org/10.3390/thermo4030021 - 10 Sep 2024

Viewed by 419

Abstract

A new transient technique of the thermal conductivity and diffusivity measurement for anisotropic materials is presented and validated. It is based on measuring the through-plane properties using the extended dynamic plane source (EDPS) method and in-plane conductivity employing the transient plane source (TPS) [...] Read more.

A new transient technique of the thermal conductivity and diffusivity measurement for anisotropic materials is presented and validated. It is based on measuring the through-plane properties using the extended dynamic plane source (EDPS) method and in-plane conductivity employing the transient plane source (TPS) and modified dynamic plane source (MDPS) methods. The key advantage of this technique is that only one pair of specimens is required for measurements. While the EDPS method is implemented on real measurements, the TPS and MDPS are applied to the finite elements method (FEM) simulation of the experiment. The accuracy of the results is enhanced by the application of the FEM and is better than 1% for materials with through-plane conductivity of less than 2 W m⁻¹ K⁻¹ and a specimen thickness of 9 mm. Full article

(This article belongs to the Special Issue Thermal Processes and Thermal Properties of Sustainable Polymeric Materials)

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12 pages, 2636 KiB

Open AccessReview

Effect of Fin Type and Geometry on Thermal and Hydraulic Performance in Conditions of Combined-Cycle Nuclear Power Plant with High-Temperature Gas-Cooled Reactors

by Khaled A. A. Ramadan and Konstantin V. Slyusarskiy

Thermo 2024, 4(3), 382-393; https://doi.org/10.3390/thermo4030020 - 9 Aug 2024

Viewed by 768

Abstract

One method of nuclear energy development involves using helium. Its properties make using extended surfaces obligatory. However, currently nuclear technology does not typically use finned tubes. This study explores ways of enhancing heat transfer efficiency in a high-temperature gas-cooled reactor system by using [...] Read more.

One method of nuclear energy development involves using helium. Its properties make using extended surfaces obligatory. However, currently nuclear technology does not typically use finned tubes. This study explores ways of enhancing heat transfer efficiency in a high-temperature gas-cooled reactor system by using novel fin designs in the heat exchanger for residual heat removal. Four different types of fins were studied: annular, serrated, square, and helical. The effect of fin height, thickness, and number was evaluated. Serrated and helical fins demonstrated superior performance compared to conventional annular fin designs, which was expressed in enhanced efficiency. The thickness of fins was found to have the strongest influence on the efficiency, while the height and number of fins per meter had weaker effects. In addition, the study emphasized the significance of considering complex effects when optimizing fin design, like the effect of fin geometry on the velocity of helium. The findings highlight the potential of creative fin designs to greatly enhance the efficiency and dependability of gas-cooled reactor systems, opening up possibilities for advancements in nuclear power plant technology. Full article

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9 pages, 617 KiB

Open AccessArticle

Misinterpretation of Thermodynamic Parameters Evaluated from Activation Energy and Preexponential Factor Determined in Thermal Analysis Experiments

by Sergey Vyazovkin

Thermo 2024, 4(3), 373-381; https://doi.org/10.3390/thermo4030019 - 5 Aug 2024

Cited by 1 | Viewed by 776

Abstract

Thermogravimetry (TGA) and differential scanning calorimetry (DSC) are used broadly to study the kinetics of thermally stimulated processes such as thermal decomposition (pyrolysis) or thermal polymerization. These studies typically yield the activation energy (E) and preexponential factor (A). The [...] Read more.

Thermogravimetry (TGA) and differential scanning calorimetry (DSC) are used broadly to study the kinetics of thermally stimulated processes such as thermal decomposition (pyrolysis) or thermal polymerization. These studies typically yield the activation energy (E) and preexponential factor (A). The resulting experimental values of E and A are oftentimes used to determine the so-called “thermodynamic parameters”, i.e., the enthalpy, entropy, and Gibbs free energy. Attention is called to the persistent and mistaken trend to interpret the resulting quantities as the thermodynamic parameters of the conversion of reactants to products. In fact, these quantities are specific to the conversion of reactants to the activated complex and, as such, provide no insights into the thermodynamics of the conversion of reactants to products. The basics of the activated complex (transition state) theory are provided to explain the meaning of the equations used for evaluating the thermodynamic parameters from the experimental values of E and A. Typical examples of misinterpretation are highlighted and discussed briefly. The applicability of the theory to the systems studied by the thermal analysis kinetics is also discussed. Full article

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27 pages, 5900 KiB

Open AccessTechnical Note

Artificial Intelligence Applied to Microwave Heating Systems: Prediction of Temperature Profile through Convolutional Neural Networks

by Victor Rosario Núñez, Alfonso Hernández, Iván Rodríguez, Ignacio Fernández-Pacheco Ruiz and Luis Acevedo

Thermo 2024, 4(3), 346-372; https://doi.org/10.3390/thermo4030018 - 3 Aug 2024

Viewed by 755

Abstract

Microwave heating, which is caused by the interaction of electromagnetic radiation and materials, has become an important component in industrial operations across numerous industries. Despite their importance, conventional numerical simulations of microwave heating are computationally intensive. Concurrently, advances in artificial intelligence (AI), particularly [...] Read more.

Microwave heating, which is caused by the interaction of electromagnetic radiation and materials, has become an important component in industrial operations across numerous industries. Despite their importance, conventional numerical simulations of microwave heating are computationally intensive. Concurrently, advances in artificial intelligence (AI), particularly machine learning algorithms, have transformed data processing by increasing accuracy while decreasing computational time. This study tackles the difficulty of efficient and accurate modelling in microwave heating by combining convolutional neural networks (CNNs) with traditional simulation techniques. The major goal of this research is to use CNNs to forecast temperature profiles in a variety of industrial materials, including susceptors, semi-transparent, and microwave-transparent materials, under varying power settings and heating periods. This unique strategy greatly reduces prediction times, with up to 60-fold speed increases over standard methods. Our research is based on examining the electromagnetic and thermal responses of these materials under microwave heating. This study’s findings emphasise the need for extensive datasets and show the transformational potential of CNNs in optimising material processing. It uses artificial intelligence to pave the way for more effective and exact simulations, supporting breakthroughs in industrial microwave heating applications. Full article

(This article belongs to the Special Issue Numerical Simulations for Thermal Engineering and Thermodynamic Systems)

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31 pages, 2615 KiB

Open AccessArticle

Unified Classical Thermodynamics: Primacy of Dissymmetry over Free Energy

by Lin-Shu Wang

Thermo 2024, 4(3), 315-345; https://doi.org/10.3390/thermo4030017 - 19 Jul 2024

Viewed by 565

Abstract

In thermodynamic theory, free energy (i.e., available energy) is the concept facilitating the combined applications of the theory’s two fundamental laws, the first and the second laws of thermodynamics. The critical step was taken by Kelvin, then by Helmholtz and Gibbs—that in natural [...] Read more.

In thermodynamic theory, free energy (i.e., available energy) is the concept facilitating the combined applications of the theory’s two fundamental laws, the first and the second laws of thermodynamics. The critical step was taken by Kelvin, then by Helmholtz and Gibbs—that in natural processes, free energy dissipates spontaneously. With the formulation of the second law of entropy growth, this may be referred to as the dissymmetry proposition manifested in the spontaneous increase of system/environment entropy towards equilibrium. Because of Kelvin’s pre-entropy law formulation of free energy, our concept of free energy is still defined, within a framework on the premise of primacy of energy, as “body’s internal energy or enthalpy, subtracted by energy that is not available”. This primacy of energy is called into question because the driving force to cause a system’s change is the purview of the second law. This paper makes a case for an engineering thermodynamics framework, instead, to be based on the premise of the primacy of dissymmetry over free energy. With Gibbsian thermodynamics undergirded with dissymmetry proposition and engineering thermodynamics with a dissymmetry premise, the two branches of thermodynamics are unified to become classical thermodynamics. Full article

(This article belongs to the Special Issue Annual Thermodynamics Education Issue: Methods & Results)

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20 pages, 5620 KiB

Open AccessArticle

Packed Bed Thermal Energy Storage System: Parametric Study

by Ayah Marwan Rabi’, Jovana Radulovic and James M. Buick

Thermo 2024, 4(3), 295-314; https://doi.org/10.3390/thermo4030016 - 10 Jul 2024

Viewed by 1090

Abstract

The use of thermal energy storage (TES) contributes to the ongoing process of integrating various types of energy resources in order to achieve cleaner, more flexible, and more sustainable energy use. Numerical modelling of hot storage packed bed storage systems has been conducted [...] Read more.

The use of thermal energy storage (TES) contributes to the ongoing process of integrating various types of energy resources in order to achieve cleaner, more flexible, and more sustainable energy use. Numerical modelling of hot storage packed bed storage systems has been conducted in this paper in order to investigate the optimum design of the hot storage system. In this paper, the effect of varying design parameters, including the diameter of the packed bed, the storage material, the void fraction, and the aspect ratio of the packed bed, on storage performance was investigated. COMSOL Multiphysics 5.6 software has been used to design, simulate, and validate an axisymmetric model, which was then applied to evaluate the performance of the storage system based on the total energy stored, the heat transfer efficiency, and the capacity factor. In this paper, a novel-packed bed was proposed based on the parametric analysis. This involved a 0.2 void fraction, 4 mm porous media particle diameter, and Magnesia as the optimum storage material with air as the heat transfer fluid. Full article

(This article belongs to the Special Issue Numerical Simulations for Thermal Engineering and Thermodynamic Systems)

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Thermo, Volume 4, Issue 3 (September 2024) – 7 articles

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