Extended irreversible thermodynamics is a theory that expands the classical framework of nonequilibrium thermodynamics by going beyond the local-equilibrium assumption. A notable example of this is the Maxwell–Cattaneo heat flux model, which introduces a time lag in the heat flux response to temperature gradients. In this paper, we develop a variational formulation of the equations of extended irreversible thermodynamics by introducing an action principle for a nonequilibrium Lagrangian that treats thermodynamic fluxes as independent variables. A key feature of this approach is that it naturally extends both Hamilton’s principle of reversible continuum mechanics and the earlier variational formulation of classical irreversible thermodynamics. The variational principle is initially formulated in the material (Lagrangian) description, from which the Eulerian form is derived using material covariance (or relabeling symmetries). The tensorial structure of the thermodynamic fluxes dictates the choice of objective rate in the Eulerian description, and plays a central role in the emergence of nonequilibrium stresses – arising from both viscous and thermal effects – that are essential to ensure thermodynamic consistency. This framework naturally results in the Cattaneo–Christov model for heat flux. We also investigate the extension of the approach to accommodate higher-order fluxes and the general form of entropy fluxes. The variational framework presented in this paper has promising applications in the development of structure-preserving and thermodynamically consistent numerical methods. It is particularly relevant for modeling systems where entropy production is a delicate issue that requires careful treatment to ensure consistency with the laws of thermodynamics.
{"title":"A variational principle for extended irreversible thermodynamics: heat conducting viscous fluids","authors":"François Gay-Balmaz","doi":"10.1515/jnet-2025-0022","DOIUrl":"https://doi.org/10.1515/jnet-2025-0022","url":null,"abstract":"Extended irreversible thermodynamics is a theory that expands the classical framework of nonequilibrium thermodynamics by going beyond the local-equilibrium assumption. A notable example of this is the Maxwell–Cattaneo heat flux model, which introduces a time lag in the heat flux response to temperature gradients. In this paper, we develop a variational formulation of the equations of extended irreversible thermodynamics by introducing an action principle for a nonequilibrium Lagrangian that treats thermodynamic fluxes as independent variables. A key feature of this approach is that it naturally extends both Hamilton’s principle of reversible continuum mechanics and the earlier variational formulation of classical irreversible thermodynamics. The variational principle is initially formulated in the material (Lagrangian) description, from which the Eulerian form is derived using material covariance (or relabeling symmetries). The tensorial structure of the thermodynamic fluxes dictates the choice of objective rate in the Eulerian description, and plays a central role in the emergence of nonequilibrium stresses – arising from both viscous and thermal effects – that are essential to ensure thermodynamic consistency. This framework naturally results in the Cattaneo–Christov model for heat flux. We also investigate the extension of the approach to accommodate higher-order fluxes and the general form of entropy fluxes. The variational framework presented in this paper has promising applications in the development of structure-preserving and thermodynamically consistent numerical methods. It is particularly relevant for modeling systems where entropy production is a delicate issue that requires careful treatment to ensure consistency with the laws of thermodynamics.","PeriodicalId":16428,"journal":{"name":"Journal of Non-Equilibrium Thermodynamics","volume":"78 1","pages":""},"PeriodicalIF":6.6,"publicationDate":"2025-09-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144928613","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Umar Farooq, Hafiz Hamza Riaz, Tauqir Muhammad, Samar Ali, Tzu Chi Chan
Despite advancements in cooling solutions for electronic devices, heat dissipation remains the primary challenge in optimizing heat sink performance in a competitive industry. The current study numerically investigates the performance of plate-fin heat sink (PHS) and pin-fin heat sink (PnHS) using a hybrid nanofluid (GnP-MWCNT/Water) as the working fluid. Key performance parameters, including pressure drop, thermal resistance, effectivity, and turbulent kinetic energy, are analyzed across different Re and nanofluid concentrations. Findings indicate that while the PnHS exhibits higher convective heat transfer due to increased flow disturbances, it also suffers from greater thermal resistance and pressure drop. In contrast, the PHS offers an adequate balance between heat dissipation and flow efficiency, leading to higher overall effectiveness. At Re = 5,334, the pressure drop for 0.20 % nanofluid is 88.5 Pa in the PnHS and 73 Pa in the PHS. Additionally, at Re = 1,333, the effectiveness values for PHS are 0.333 (water) and 0.354 (nanofluid), while for PnHS, they are lower at 0.186 and 0.195, respectively. The current study highlights the interplay between enhanced heat transfer and increased flow resistance, emphasizing the importance of optimizing fin design and nanofluid concentration for efficient thermal management.
{"title":"Heat transfer analysis of plate versus pin fin heat sinks with GnP-MWCNT/water hybrid nanofluid","authors":"Umar Farooq, Hafiz Hamza Riaz, Tauqir Muhammad, Samar Ali, Tzu Chi Chan","doi":"10.1515/jnet-2025-0033","DOIUrl":"https://doi.org/10.1515/jnet-2025-0033","url":null,"abstract":"Despite advancements in cooling solutions for electronic devices, heat dissipation remains the primary challenge in optimizing heat sink performance in a competitive industry. The current study numerically investigates the performance of plate-fin heat sink (PHS) and pin-fin heat sink (PnHS) using a hybrid nanofluid (GnP-MWCNT/Water) as the working fluid. Key performance parameters, including pressure drop, thermal resistance, effectivity, and turbulent kinetic energy, are analyzed across different Re and nanofluid concentrations. Findings indicate that while the PnHS exhibits higher convective heat transfer due to increased flow disturbances, it also suffers from greater thermal resistance and pressure drop. In contrast, the PHS offers an adequate balance between heat dissipation and flow efficiency, leading to higher overall effectiveness. At Re = 5,334, the pressure drop for 0.20 % nanofluid is 88.5 Pa in the PnHS and 73 Pa in the PHS. Additionally, at Re = 1,333, the effectiveness values for PHS are 0.333 (water) and 0.354 (nanofluid), while for PnHS, they are lower at 0.186 and 0.195, respectively. The current study highlights the interplay between enhanced heat transfer and increased flow resistance, emphasizing the importance of optimizing fin design and nanofluid concentration for efficient thermal management.","PeriodicalId":16428,"journal":{"name":"Journal of Non-Equilibrium Thermodynamics","volume":"31 1","pages":""},"PeriodicalIF":6.6,"publicationDate":"2025-08-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144899995","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The current trend of reducing the size of electronic devices in the industry has extensively increased the demand for effective heat dissipation, thereby intensifying the need for high-performance heat-dissipating devices. A promising approach to solve this challenge is the use of single-phase (SP), two-phase (TP), and supercritical fluids in micro-channels (MCs). Two-phase cooling is applicable only to those devices in which the tip temperature is high enough to allow the cooling fluid to convert into a two-phase state. In all other cases, only single-phase cooling can be utilized. In this work, numerical and experimental investigations on MC have been performed using water as the working fluid to predict TP behavior and heat dissipation from electronic devices using SP and TP flow. A numerical model of flow boiling heat transfer was developed based on conservation equations, which is solved to identify the existence of single and two-phase regions in the MC and to study the variation of pressure along its length at different heating powers. Further, experiments were performed in both SP and TP conditions to observe the nature of flow regimes and the impact of various parameters on effective heat dissipation through MCs well as temperature distribution. Numerical results were validated with experimental results, which showed good agreement. Several experiments were also carried out to develop an empirical correlation between mass flow rate and heat power to maintain the electronic device temperature below 40 °C. The developed correlation is experimentally validated at three different heat powers 6 W, 8 W and 10 W.
{"title":"Numerical and experimental heat transfer analysis of two-phase flow through microchannel for development of heat dissipation correlation","authors":"Santosh Kumar Rai, Vikas Goyat, Mahesh Kumar Gupta, Gyander Ghangas, Dhowmya Bhatt, Arun Uniyal, Pardeep Kumar, Nikhil Vivek Shrivas","doi":"10.1515/jnet-2025-0044","DOIUrl":"https://doi.org/10.1515/jnet-2025-0044","url":null,"abstract":"The current trend of reducing the size of electronic devices in the industry has extensively increased the demand for effective heat dissipation, thereby intensifying the need for high-performance heat-dissipating devices. A promising approach to solve this challenge is the use of single-phase (SP), two-phase (TP), and supercritical fluids in micro-channels (MCs). Two-phase cooling is applicable only to those devices in which the tip temperature is high enough to allow the cooling fluid to convert into a two-phase state. In all other cases, only single-phase cooling can be utilized. In this work, numerical and experimental investigations on MC have been performed using water as the working fluid to predict TP behavior and heat dissipation from electronic devices using SP and TP flow. A numerical model of flow boiling heat transfer was developed based on conservation equations, which is solved to identify the existence of single and two-phase regions in the MC and to study the variation of pressure along its length at different heating powers. Further, experiments were performed in both SP and TP conditions to observe the nature of flow regimes and the impact of various parameters on effective heat dissipation through MCs well as temperature distribution. Numerical results were validated with experimental results, which showed good agreement. Several experiments were also carried out to develop an empirical correlation between mass flow rate and heat power to maintain the electronic device temperature below 40 °C. The developed correlation is experimentally validated at three different heat powers 6 W, 8 W and 10 W.","PeriodicalId":16428,"journal":{"name":"Journal of Non-Equilibrium Thermodynamics","volume":"69 1","pages":""},"PeriodicalIF":6.6,"publicationDate":"2025-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144778550","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Lactose permease, a secondary active transporter from Escherichia coli, facilitates the co-transport of protons and lactose across the cytoplasmic membrane. Unlike passive diffusion mechanisms, lactose permease operates via conformational switching that alternately exposes the binding pocket to either membrane side. In this study, we present a theoretical treatment combining irreversible thermodynamic principles and kinetic modeling to quantify its operation. Onsager’s reciprocity is applied to analyze proton-lactose coupling, and a bisubstrate kinetic scheme is employed to simulate system behavior under various proton gradients and lactose concentrations. The complete catalytic cycle is characterized by associated rate constants and energetic transitions, highlighting that lactose permease exhibits a dissipative nature as a hallmark of secondary active transport. Altogether, this study provides a novel thermodynamic perspective on lactose permease, aiming to bridge molecular transport kinetics with the formalism of irreversible processes. This work is the first to integrate Onsager relations with the Michaelis-Menten kinetic model to quantify the energetic efficiency of lactose permease.
{"title":"Applying irreversible thermodynamics to the paradigmatic secondary transporter: lactose permease (LacY)","authors":"Jordi H. Borrell","doi":"10.1515/jnet-2025-0054","DOIUrl":"https://doi.org/10.1515/jnet-2025-0054","url":null,"abstract":"Lactose permease, a secondary active transporter from <jats:italic>Escherichia coli</jats:italic>, facilitates the co-transport of protons and lactose across the cytoplasmic membrane. Unlike passive diffusion mechanisms, lactose permease operates via conformational switching that alternately exposes the binding pocket to either membrane side. In this study, we present a theoretical treatment combining irreversible thermodynamic principles and kinetic modeling to quantify its operation. Onsager’s reciprocity is applied to analyze proton-lactose coupling, and a bisubstrate kinetic scheme is employed to simulate system behavior under various proton gradients and lactose concentrations. The complete catalytic cycle is characterized by associated rate constants and energetic transitions, highlighting that lactose permease exhibits a dissipative nature as a hallmark of secondary active transport. Altogether, this study provides a novel thermodynamic perspective on lactose permease, aiming to bridge molecular transport kinetics with the formalism of irreversible processes. This work is the first to integrate Onsager relations with the Michaelis-Menten kinetic model to quantify the energetic efficiency of lactose permease.","PeriodicalId":16428,"journal":{"name":"Journal of Non-Equilibrium Thermodynamics","volume":"159 1","pages":""},"PeriodicalIF":6.6,"publicationDate":"2025-08-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144786588","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
High-temperature proton exchange membrane fuel cells (HT-PEMFCs) inherently produce waste heat, leading to component degradation, increased cooling demands, and reduced efficiency and longevity. To mitigate these challenges, this study introduces isopropanol-acetone-hydrogen chemical heat pumps (IAH-CHPs), selected for their proven ability to efficiently upgrade and store the waste heat from HT-PEMFCs in a high-value form. Grounded in thermodynamic and electrochemical principles, a comprehensive mathematical model, incorporating key irreversible losses, is developed to evaluate the potential. Numerical calculations predict a 29 % increase in the hybrid system’s maximum power density compared to a standalone HT-PEMFC operating at 443 K, along with corresponding enhancements of 14.17 % in energy efficiency and 14.16 % in exergy efficiency. Preliminary predictions confirm the feasibility of this approach, and the optimal operating ranges for maximizing power density are identified. Additionally, exhaustive parametric studies reveal the impacts of various structural and operational parameters – such as leakage current density, phosphoric acid doping, relative humidity, operating temperatures, and critical factors within the heat pump cycle – on the system’s thermodynamic performance and key current density indicators. Local sensitivity analyses highlight effective performance regulation strategies. These results provide essential insights for mitigating waste heat challenges, enhancing system efficiency, and extending the operational lifespan for HT-PEMFCs.
{"title":"A Hydrogen-fueled hybrid system based on HT-PEMFCs for simultaneous electrical power generation and high-value heat storage","authors":"Houcheng Zhang, Han Wang, Min Kuang, Yejian Xue","doi":"10.1515/jnet-2024-0122","DOIUrl":"https://doi.org/10.1515/jnet-2024-0122","url":null,"abstract":"High-temperature proton exchange membrane fuel cells (HT-PEMFCs) inherently produce waste heat, leading to component degradation, increased cooling demands, and reduced efficiency and longevity. To mitigate these challenges, this study introduces isopropanol-acetone-hydrogen chemical heat pumps (IAH-CHPs), selected for their proven ability to efficiently upgrade and store the waste heat from HT-PEMFCs in a high-value form. Grounded in thermodynamic and electrochemical principles, a comprehensive mathematical model, incorporating key irreversible losses, is developed to evaluate the potential. Numerical calculations predict a 29 % increase in the hybrid system’s maximum power density compared to a standalone HT-PEMFC operating at 443 K, along with corresponding enhancements of 14.17 % in energy efficiency and 14.16 % in exergy efficiency. Preliminary predictions confirm the feasibility of this approach, and the optimal operating ranges for maximizing power density are identified. Additionally, exhaustive parametric studies reveal the impacts of various structural and operational parameters – such as leakage current density, phosphoric acid doping, relative humidity, operating temperatures, and critical factors within the heat pump cycle – on the system’s thermodynamic performance and key current density indicators. Local sensitivity analyses highlight effective performance regulation strategies. These results provide essential insights for mitigating waste heat challenges, enhancing system efficiency, and extending the operational lifespan for HT-PEMFCs.","PeriodicalId":16428,"journal":{"name":"Journal of Non-Equilibrium Thermodynamics","volume":"1 1","pages":""},"PeriodicalIF":6.6,"publicationDate":"2025-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144747576","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Fuzhang Wang, Isaac Lare Animasaun, Taseer Muhammad
Accurately predicting turbulent water flow in duct systems remains a challenging problem, particularly when anisotropic turbulence effects are significant. Bridging the gap between industrial applications and academic research requires a deeper understanding of such complex flows. This study investigates a less commonly analyzed configuration involving a horizontal aluminum duct transitioning into a converging wavy duct. The wavy section consists of 2.5 full sinusoidal periods, ending in a reduced outlet diameter. In addition, the effect of incorporating four minor/secondary inlets, arranged as branches at different angles, was examined and presented herein. Aluminum was selected for its low density and corrosion resistance, which are beneficial in experimental and industrial setups. Initially, the duct was analyzed in an unbranched configuration. The study then progressed to include the four secondary/minor branch inlets at various angles. The simulation results were validated by comparison with a solution for a simple flow in a 70 mm duct. Additional verification was provided by employing other CFD codes, along with grid convergence index and mesh sensitivity analyses, improving the confidence in the simulation results. Branch angles influences turbulence intensity depending on flow conditions and angle magnitude. Sharper branch angles are particularly effective, inducing greater turbulence at the converged outlet. Higher inlet temperatures and velocities lead to increased Reynolds stress due to enhanced energy transfer and elevated turbulent kinetic energy. Specifically, an increase in inlet velocity at a 45° branch angle further augments turbulent momentum transfer, resulting in more controlled mixing along the duct.
{"title":"Anisotropic turbulent flow of water through converging wavy-aluminum-circular pipe with five half-cycles: insight into the significance of four-branch minor-inlet angle","authors":"Fuzhang Wang, Isaac Lare Animasaun, Taseer Muhammad","doi":"10.1515/jnet-2025-0046","DOIUrl":"https://doi.org/10.1515/jnet-2025-0046","url":null,"abstract":"Accurately predicting turbulent water flow in duct systems remains a challenging problem, particularly when anisotropic turbulence effects are significant. Bridging the gap between industrial applications and academic research requires a deeper understanding of such complex flows. This study investigates a less commonly analyzed configuration involving a horizontal aluminum duct transitioning into a converging wavy duct. The wavy section consists of 2.5 full sinusoidal periods, ending in a reduced outlet diameter. In addition, the effect of incorporating four minor/secondary inlets, arranged as branches at different angles, was examined and presented herein. Aluminum was selected for its low density and corrosion resistance, which are beneficial in experimental and industrial setups. Initially, the duct was analyzed in an unbranched configuration. The study then progressed to include the four secondary/minor branch inlets at various angles. The simulation results were validated by comparison with a solution for a simple flow in a 70 mm duct. Additional verification was provided by employing other CFD codes, along with grid convergence index and mesh sensitivity analyses, improving the confidence in the simulation results. Branch angles influences turbulence intensity depending on flow conditions and angle magnitude. Sharper branch angles are particularly effective, inducing greater turbulence at the converged outlet. Higher inlet temperatures and velocities lead to increased Reynolds stress due to enhanced energy transfer and elevated turbulent kinetic energy. Specifically, an increase in inlet velocity at a 45<jats:italic>°</jats:italic> branch angle further augments turbulent momentum transfer, resulting in more controlled mixing along the duct.","PeriodicalId":16428,"journal":{"name":"Journal of Non-Equilibrium Thermodynamics","volume":"69 1","pages":""},"PeriodicalIF":6.6,"publicationDate":"2025-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144533270","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Yasir Ul Umair Bin Turabi, Zeshan Faiz, Shahzad Munir, Shafee Ahmad, M.M. Alam, Hakim AL Garalleh
Enclosure design is essential for thermal engineering technology and applications, including electronics, heat transfer equipment, power reactors, cooling mechanisms, solar energy systems, and nuclear power plants. This study aims to analyze the numerical and Response Surface Methodology (RSM) optimization for natural convection and entropy generation in a wavy triangular cavity with Casson fluid under inclined magnetohydrodynamic and radiation influences. The finite element approach (FEM) is utilized to compute the numerical solution for the simulation framework, while RSM is applied to determine the optimal heat transfer rate among four different parameters. The study presents streamlines, velocity profiles, isothermal lines, total entropy generation, and average Nusselt number in graphically and tabularly. The results show that an increase in the number of undulations and the Casson parameter leads to an increase in the thermal transfer rate and total entropy generation, whereas the Hartmann number has a decreasing effect on both. The Nusselt number rises with the rising number of undulations and the radiation parameter. The peak stream function is observed at an inclination angle of 60°. The significant R2 value of 0.9967 shows a good agreement between the expected and actual values.
{"title":"Numerical and optimization analysis of natural convection and entropy-generation in wavy triangular cavity with Casson fluid under magnetohydrodynamics and radiation","authors":"Yasir Ul Umair Bin Turabi, Zeshan Faiz, Shahzad Munir, Shafee Ahmad, M.M. Alam, Hakim AL Garalleh","doi":"10.1515/jnet-2024-0101","DOIUrl":"https://doi.org/10.1515/jnet-2024-0101","url":null,"abstract":"Enclosure design is essential for thermal engineering technology and applications, including electronics, heat transfer equipment, power reactors, cooling mechanisms, solar energy systems, and nuclear power plants. This study aims to analyze the numerical and Response Surface Methodology (RSM) optimization for natural convection and entropy generation in a wavy triangular cavity with Casson fluid under inclined magnetohydrodynamic and radiation influences. The finite element approach (FEM) is utilized to compute the numerical solution for the simulation framework, while RSM is applied to determine the optimal heat transfer rate among four different parameters. The study presents streamlines, velocity profiles, isothermal lines, total entropy generation, and average Nusselt number in graphically and tabularly. The results show that an increase in the number of undulations and the Casson parameter leads to an increase in the thermal transfer rate and total entropy generation, whereas the Hartmann number has a decreasing effect on both. The Nusselt number rises with the rising number of undulations and the radiation parameter. The peak stream function is observed at an inclination angle of 60°. The significant <jats:italic>R</jats:italic> <jats:sup>2</jats:sup> value of 0.9967 shows a good agreement between the expected and actual values.","PeriodicalId":16428,"journal":{"name":"Journal of Non-Equilibrium Thermodynamics","volume":"26 1","pages":""},"PeriodicalIF":6.6,"publicationDate":"2025-06-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144488465","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper addresses the theoretical analysis of a piezothermoelastic problem involving an unbounded thermopiezoelectric medium with a spherical cavity subjected to pulse heating flux. The generalized piezo-thermo-elastic formulations of Lord and Shulman with thermal relaxation effects are used in this work. Unlike previous studies, which often consider simplified boundary conditions or steady-state thermal loading, our work incorporates generalized piezo-thermo-elastic formulations based on the Lord and Shulman model, accounting for thermal relaxation effects under dynamic thermal loading conditions. The numerical solution of the governing equations is done using the finite element approach, and temporal evolution is solved using the implicit scheme. New numerical results provide insight into the dynamic behavior of the piezoelectric medium subjected to thermal conditions. Thermal relaxation time and pulse heating flux are analyzed in their influence on the coupled thermal, mechanical and electrical fields and, thus, on the response of the system.
{"title":"Finite element analysis on generalized piezothermoelastic interactions in an unbounded piezoelectric medium containing a spherical cavity","authors":"Ibrahim Abbas, Areej Almuneef, Zuhur Alqahtani","doi":"10.1515/jnet-2025-0034","DOIUrl":"https://doi.org/10.1515/jnet-2025-0034","url":null,"abstract":"This paper addresses the theoretical analysis of a piezothermoelastic problem involving an unbounded thermopiezoelectric medium with a spherical cavity subjected to pulse heating flux. The generalized piezo-thermo-elastic formulations of Lord and Shulman with thermal relaxation effects are used in this work. Unlike previous studies, which often consider simplified boundary conditions or steady-state thermal loading, our work incorporates generalized piezo-thermo-elastic formulations based on the Lord and Shulman model, accounting for thermal relaxation effects under dynamic thermal loading conditions. The numerical solution of the governing equations is done using the finite element approach, and temporal evolution is solved using the implicit scheme. New numerical results provide insight into the dynamic behavior of the piezoelectric medium subjected to thermal conditions. Thermal relaxation time and pulse heating flux are analyzed in their influence on the coupled thermal, mechanical and electrical fields and, thus, on the response of the system.","PeriodicalId":16428,"journal":{"name":"Journal of Non-Equilibrium Thermodynamics","volume":"45 1","pages":""},"PeriodicalIF":6.6,"publicationDate":"2025-05-30","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144184113","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Non-equilibrium thermal energy transfer in small scale films pairs, composing of different film materials, is important for designing semiconductor devices or thermoelectric energy generators. The present study examines thermal energy transfer in low size silicon-diamond film pairs with the quantum dots in placed. Equation for Phonon Radiative Transport (EPRT) is used to predict the distribution of phonon intensities via adopting the discrete ordinate method. Thermal energy transport is quantified in the form phonon energies via using integral form of equilibrium phonon intensities. Because of the mismatch of properties between silicon and diamond films, interface conditions are formulated after considering energy balance across both films. Findings reveal that equivalent equilibrium temperature decays gradually in the film for small size quantum dots. As the quantum dot size increases, equivalent equilibrium temperature decays sharply because films edges behave like heat sink reducing equilibrium phonon intensities in the region of film edges. Temperature jump, due to mismatch properties of the films, signifies at the mid-section of the interface and it increases slightly with increasing quantum dot size. The magnitude of heat flux vector remains higher in diamond than silicon film. The effective thermal conductivity predicted is in agreement with the previous data for silicon film.
{"title":"Thermal transport in a silicon/diamond micro-flake with quantum dots inserts","authors":"Saad Bin Mansoor, Bekir Sami Yilbas","doi":"10.1515/jnet-2025-0025","DOIUrl":"https://doi.org/10.1515/jnet-2025-0025","url":null,"abstract":"Non-equilibrium thermal energy transfer in small scale films pairs, composing of different film materials, is important for designing semiconductor devices or thermoelectric energy generators. The present study examines thermal energy transfer in low size silicon-diamond film pairs with the quantum dots in placed. Equation for Phonon Radiative Transport (EPRT) is used to predict the distribution of phonon intensities via adopting the discrete ordinate method. Thermal energy transport is quantified in the form phonon energies via using integral form of equilibrium phonon intensities. Because of the mismatch of properties between silicon and diamond films, interface conditions are formulated after considering energy balance across both films. Findings reveal that equivalent equilibrium temperature decays gradually in the film for small size quantum dots. As the quantum dot size increases, equivalent equilibrium temperature decays sharply because films edges behave like heat sink reducing equilibrium phonon intensities in the region of film edges. Temperature jump, due to mismatch properties of the films, signifies at the mid-section of the interface and it increases slightly with increasing quantum dot size. The magnitude of heat flux vector remains higher in diamond than silicon film. The effective thermal conductivity predicted is in agreement with the previous data for silicon film.","PeriodicalId":16428,"journal":{"name":"Journal of Non-Equilibrium Thermodynamics","volume":"80 1","pages":""},"PeriodicalIF":6.6,"publicationDate":"2025-05-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144122396","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Ivan Sukin, Alexandr Mazikov, Anatoly Tsirlin, Ruben Gevorkyan
Authors give a review of the methods of finite-time thermodynamics in problems of obtaining the limiting capabilities of two- and multi-flow heat exchange systems. The boundaries of their physical reachability are constructed. The case of flows with changing heat capacity and, in particular, flows with a change in phase state is considered. The conditions for minimum heat exchange dissipation are obtained for different kinetics at fixed heat transfer coefficient and heat load. The concept of thermodynamically equivalent heat exchange systems is introduced and a method for transition from a multi-flow system to an equivalent two-flow heat exchanger in which heat capacities of the flows depend on temperature is proposed. Based on the obtained results, an algorithm for synthesis of multi-flow heat exchange systems is proposed. The synthesis takes into account the limitations on the temperatures of all or part of the flows. The synthesis of the system involves the calculation and minimization of the number of two-flow heat exchangers and the selection of the contact structure, the values of flow parameters, the distribution of contact surfaces and heat loads between two-flow heat exchange cells. In the design procedure the limitations on the temperatures of all or part of the flows are taken into account. Using thermodynamic criteria instead of technical and economic ones allows us to radically simplify the problem of designin the system.
{"title":"Approaches of finite-time thermodynamics in conceptual design of heat exchange systems","authors":"Ivan Sukin, Alexandr Mazikov, Anatoly Tsirlin, Ruben Gevorkyan","doi":"10.1515/jnet-2024-0118","DOIUrl":"https://doi.org/10.1515/jnet-2024-0118","url":null,"abstract":"Authors give a review of the methods of finite-time thermodynamics in problems of obtaining the limiting capabilities of two- and multi-flow heat exchange systems. The boundaries of their physical reachability are constructed. The case of flows with changing heat capacity and, in particular, flows with a change in phase state is considered. The conditions for minimum heat exchange dissipation are obtained for different kinetics at fixed heat transfer coefficient and heat load. The concept of thermodynamically equivalent heat exchange systems is introduced and a method for transition from a multi-flow system to an equivalent two-flow heat exchanger in which heat capacities of the flows depend on temperature is proposed. Based on the obtained results, an algorithm for synthesis of multi-flow heat exchange systems is proposed. The synthesis takes into account the limitations on the temperatures of all or part of the flows. The synthesis of the system involves the calculation and minimization of the number of two-flow heat exchangers and the selection of the contact structure, the values of flow parameters, the distribution of contact surfaces and heat loads between two-flow heat exchange cells. In the design procedure the limitations on the temperatures of all or part of the flows are taken into account. Using thermodynamic criteria instead of technical and economic ones allows us to radically simplify the problem of designin the system.","PeriodicalId":16428,"journal":{"name":"Journal of Non-Equilibrium Thermodynamics","volume":"127 1","pages":""},"PeriodicalIF":6.6,"publicationDate":"2025-04-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"143863007","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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