TY - JOUR AU - Farkas, Csaba AU - Gál, László AU - Csiszár, András AU - Grennerat, Vincent AU - Jeannin, Pierre-Olivier AU - Xavier, Pascal AU - Rigler, Dániel AU - Krammer, Olivér AU - Plachy, Zbynek AU - Dusek, Karel AU - Kovács, Róbert Sándor AU - Fehér, Anna Éva AU - Géczy, Attila TI - Sustainable printed circuit board substrates based on flame-retarded PLA/flax composites to reduce environmental load of electronics: Quality, reliability, degradation and application tests JF - SUSTAINABLE MATERIALS AND TECHNOLOGIES J2 - SUSTAINABLE MATERIALS TECHNOLOGIES VL - 40 PY - 2024 PG - 15 SN - 2214-9929 DO - 10.1016/j.susmat.2024.e00902 UR - https://m2.mtmt.hu/api/publication/34746761 ID - 34746761 N1 - Funding Agency and Grant Number: National Research, Development and Innovation Office - NKFIH; Ministry of Culture and Innovation of Hungary from the National Research, Development and Innovation Fund [242519/0579]; Interdisciplinary mission of the French CNRS [FK 132186]; [TKP2021-EGA] Funding text: The authors would like to acknowledge the support of: Fedrigoni (htt ps://paper.fedrigoni.com /fra/) , Cisteme (https://cisteme.net/) and the help of UniPCB Kft. colleagues and Istvan Hajdu. The support of the National Research, Development and Innovation Office - NKFIH, FK 132186 project, related to vapour phase soldering studies was necessary to conduct the reported soldering studies. Project no. TKP2021-EGA-02 has been implemented with the support provided by the Ministry of Culture and Innovation of Hungary from the National Research, Development and Innovation Fund, financed under the TKP2021-EGA funding scheme. The project received some funding from the Interdisciplinary mission of the French CNRS with the acronym CIRCABIO (number 242519/0579) under the call "Frugality-Sobriety 2023". AB - The present paper introduces a novel, sustainable approach to produce an eco-friendly Printed Circuit Board (PCB) substrate; a substitute for traditional substrates, to significantly reduce e-waste. We present the prepreg technology, the road to actual circuit assembly with application studies, life cycle analysis (LCA), and sustainability analysis. The flame-retarded prepregs and resulting PCB assemblies were based on polylactic acid (PLA), the structure is reinforced with flax textiles. After copper lamination, subtractive PCB production was performed, and thermal and mechanical reliability was investigated in the case of both laminated and bare substrates. Steps of surface roughness, peel and thermal analysis followed. After a new set of assemblies, the post-assembly analysis was extended with further shear strength analysis on the soldered components and mass analysis regarding thermal processes. The evaluation showed that PLA/Flax substrates provide reliable structural performance up to 200 °C in the reflow soldering process; this allows limited but stabilized application possibilities with specific eco-friendly lead-free solders. A basic blinker circuit and a field programmable gate array (FPGA)–based design was produced and tested; the latter has the general complexity of a commercial circuit. A vol% and wt% analysis extended our discussion with a reduction of harmful components in waste in the range of 90%, which is a disruptive and significant result. Life cycle analysis (LCA) quantified the ecological impact of the assembly, highlighting a significant ease on environmental load (∼10%) for the total assembly. Finally, a qualitative degradation study was introduced to the prepared samples to investigate short-term stability with mechanical-, colour-, mass- and scanning electron microscopy (structure) analysis. Early results show that the boards can withstand the harsh environment of a composting bin for a few days, but in the time of a few weeks, degradation starts, pointing to eventual decomposition. The work directly connects with multiple sustainability development goals. © 2024 The Authors LA - English DB - MTMT ER - TY - JOUR AU - Fehér, Anna Éva AU - Maróti, János Endre AU - Takács, Donát M. AU - Orbulov, Imre Norbert AU - Kovács, Róbert Sándor TI - Thermal and mechanical properties of AlSi7Mg matrix syntactic foams reinforced by Al2O3 or SiC particles in matrix JF - INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER J2 - INT J HEAT MASS TRANS VL - 226 PY - 2024 PG - 12 SN - 0017-9310 DO - 10.1016/j.ijheatmasstransfer.2024.125446 UR - https://m2.mtmt.hu/api/publication/34755651 ID - 34755651 LA - English DB - MTMT ER - TY - JOUR AU - Fehér, Anna Éva AU - Kovács, Róbert Sándor AU - Sudár, Ákos AU - Barnaföldi, Gergely Gábor TI - Challenges in the thermal modeling of highly porous carbon foams JF - JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY J2 - J THERM ANAL CALORIM VL - 149 PY - 2024 IS - 8 SP - 3605 EP - 3616 PG - 12 SN - 1388-6150 DO - 10.1007/s10973-024-12927-w UR - https://m2.mtmt.hu/api/publication/34691294 ID - 34691294 AB - The heat pulse (flash) experiment is a well-known, widely used method to determine thermal diffusivity. However, for heterogeneous, highly porous materials, neither the measurement nor the evaluation methodologies are straightforward. In the present paper, we focus on two open-cell carbon foam types, differing in their porosity but having the same sample size. Recent experiments showed that a non-Fourier behavior, called ’over-diffusive’ propagation, can be present for such a complex structure. The (continuum) Guyer–Krumhansl equation stands as a promising candidate to model such transient thermal behavior. In order to obtain a reliable evaluation and thus reliable thermal parameters, we utilize a novel, state-of-the-art evaluation procedure developed recently using an analytical solution of the Guyer–Krumhansl equation. Based on our observations, it turned out that the presence of high porosity alone is necessary but not satisfactory for non-Fourier behavior. Additionally, the mentioned non-Fourier effects are porosity-dependent; however, porous samples can also follow the Fourier law on a particular time scale. These data serve as a basis to properly identify the characteristic heat transfer mechanisms and their corresponding time scales, which altogether result in the present non-Fourier behavior. Based on these, we determined the validity region of Fourier’s law in respect of time scales. LA - English DB - MTMT ER - TY - JOUR AU - Fehér, Anna Éva AU - Kovács, Róbert Sándor AU - Kun-Balog, Attila AU - Maróti, János Endre AU - Orbulov, Imre Norbert AU - Sztankó, Krisztián Endre AU - Szücs, Mátyás AU - Balog, Róbert AU - Takács, Donát M. TI - Szintaktikus fémhabok termikus és mechanikai tulajdonságai, valamint alkalmazhatóságuk fázisváltó hőtároló rendszerekben JF - ENERGIAGAZDÁLKODÁS J2 - ENGA VL - 65 PY - 2024 IS - 5-6 SP - 6 EP - 11 PG - 6 SN - 0021-0757 UR - https://m2.mtmt.hu/api/publication/35659955 ID - 35659955 N1 - Közlemény:35472736 utánközlése. LA - Hungarian DB - MTMT ER - TY - JOUR AU - Fehér, Anna Éva AU - Kovács, Róbert Sándor AU - Kun-Balog, Attila AU - Maróti, János Endre AU - Orbulov, Imre Norbert AU - Sztankó, Krisztián Endre AU - Szücs, Mátyás AU - Balog, Róbert AU - Takács, Donát M. TI - Szintaktikus fémhabok termikus és mechanikai tulajdonságai, valamint alkalmazhatóságuk fázisváltó hőtároló rendszerekben JF - ENERGIAGAZDÁLKODÁS J2 - ENGA VL - 65 PY - 2024 IS - Klsz. SP - 34 EP - 39 PG - 6 SN - 0021-0757 UR - https://m2.mtmt.hu/api/publication/35472736 ID - 35472736 N1 - További megjelenése In: ENERGIAGAZDÁLKODÁS (0021-0757 ): 65 5-6 pp 6-11 (2024) [35659955] LA - Hungarian DB - MTMT ER - TY - JOUR AU - Fehér, Anna Éva AU - Kovács, Róbert Sándor TI - On the dynamic thermal conductivity and diffusivity observed in heat pulse experiments JF - JOURNAL OF NON-EQUILIBRIUM THERMODYNAMICS J2 - J NON-EQUIL THERMODY VL - 49 PY - 2024 IS - 2 SP - 161 EP - 170 PG - 10 SN - 0340-0204 DO - 10.1515/jnet-2023-0119 UR - https://m2.mtmt.hu/api/publication/34733253 ID - 34733253 AB - Determining the thermal properties of materials with complex structures is still a major engineering challenge today. The well-known heat pulse experiment can be used to determine the thermal diffusivity by measuring the temperature history as a thermal response for a fast excitation. However, the evaluation of the measurements can be challenging, especially when dealing with non-homogeneous samples. The thermal behavior of such heterogeneous materials may exhibit a response including two-time scales. Therefore, the Fourier equation is not necessarily applicable. The simplest possible alternatives are the 2-temperature models the Guyer–Krumhansl and Jeffreys heat equations. In the present paper, we focus on the interpretation of the Jeffreys heat equation; studying its analytical solution, we present a fitting method for determining the unknown parameters. We also discuss its relation with the other two heat equations, and we offer an interpretation of how to characterize the transient response of heterogeneous materials. LA - English DB - MTMT ER - TY - JOUR AU - Gál, Márton AU - Samaniego Andrade, Samantha Kathiuska AU - Fehér, Anna Éva AU - Farkas, Attila AU - Madarász, János AU - Horváth, Lili AU - Gordon, Péter AU - Kovács, Róbert Sándor AU - Nagyné László, Krisztina TI - Thermal diffusity in copper benzene-1,3,5-tricarboxylate–reduced graphite oxide mechanical composites JF - JOURNAL OF THERMAL ANALYSIS AND CALORIMETRY J2 - J THERM ANAL CALORIM VL - 149 PY - 2024 IS - 12 SP - 5971 EP - 5983 PG - 13 SN - 1388-6150 DO - 10.1007/s10973-024-13021-x UR - https://m2.mtmt.hu/api/publication/34772009 ID - 34772009 AB - Metal organic frameworks (MOFs) and particularly copper benzene-1,3,5-tricarboxylate (HKUST-1) are excellent materials for gas storage (e.g., CH 4 , N 2 , H 2 adsorption) and gas separation. In this work, reduced graphene oxide (RGO)–HKUST-1 mechanical mixtures were studied in order to reveal the effect of RGO content on the pressure tolerance of the texture and heat conductivity. HKUST-1 was obtained by two different synthesis routes. Air-dried MOF and RGO were thoroughly mixed prior to the compression. Powder XRD and Raman spectroscopy were used to characterize the response of the crystal structure, while low-temperature nitrogen adsorption was used the follow the adsorption properties of the pellets. Finally, the "flash" heat pulse method was used to assess the thermal properties. The gas adsorption isotherms revealed that the adsorption capacity decreases when RGO is added. Based on Raman and XRD results, we found that the synthesis route has an effect on multiple scales. We experimentally confirmed that evaluation of the thermal diffusivity requires a model more complex than the simple Fourier equation, due to the inherent heterogeneous structure of the material. A good approximation of the Fourier coefficient of thermal diffusivity was obtained using the parameters of the Guyer–Krumhansl equation. The heat pulse experiments also revealed possible size-dependent behavior. LA - English DB - MTMT ER - TY - JOUR AU - Kovács, Róbert Sándor TI - Heat equations beyond Fourier: From heat waves to thermal metamaterials JF - PHYSICS REPORTS-REVIEW SECTION OF PHYSICS LETTERS J2 - PHYS REP VL - 1048 PY - 2024 SP - 1 EP - 75 PG - 75 SN - 0370-1573 DO - 10.1016/j.physrep.2023.11.001 UR - https://m2.mtmt.hu/api/publication/34297744 ID - 34297744 LA - English DB - MTMT ER - TY - JOUR AU - Munafò, C.F. AU - Rogolino, P. AU - Kovács, Róbert Sándor TI - Nonlinear thermal analysis of two-dimensional materials with memory JF - INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER J2 - INT J HEAT MASS TRANS VL - 219 PY - 2024 PG - 19 SN - 0017-9310 DO - 10.1016/j.ijheatmasstransfer.2023.124847 UR - https://m2.mtmt.hu/api/publication/34225898 ID - 34225898 AB - A nonlinear hyperbolic heat transport equation has been proposed based on the Cattaneo model without mechanical effects. We analyze the two-dimensional Maxwell-Cattaneo-Vernotte heat equation in a medium subjected to homogeneous and non-homogeneous boundary conditions and with thermal conductivity and relaxation time linearly dependent on temperature. Since these nonlinearities are essential from an experimental point of view, it is necessary to establish an effective and reliable way to solve the system of partial differential equations and study the behavior of temperature evolution. A numerical scheme of finite differences for the solution of the two-dimensional non-Fourier heat transfer equation is introduced and studied. We also investigate the attributes of the numerical method from the aspects of stability, dissipation and dispersive errors. LA - English DB - MTMT ER - TY - JOUR AU - Ramos, Anderson AU - Campelo, Anderson AU - Freitas, Mirelson AU - Kovács, Róbert Sándor TI - Numerical analysis of the Maxwell-Cattaneo-Vernotte nonlinear model JF - JOURNAL OF THERMAL STRESSES J2 - J THERM STRESSES VL - 47 PY - 2024 IS - 9 SP - 1262 EP - 1276 PG - 15 SN - 0149-5739 DO - 10.1080/01495739.2024.2391749 UR - https://m2.mtmt.hu/api/publication/35180177 ID - 35180177 N1 - Funding Agency and Grant Number: Ministry of Culture and Innovation of Hungary from the National Research Funding text: No Statement Available LA - English DB - MTMT ER - TY - JOUR AU - Tóth, Balázs AU - Molnár, Zsombor AU - Kovács, Róbert Sándor TI - Two-field mixed hp-finite elements for time-dependent problems in the refined theories of thermodynamics JF - CONTINUUM MECHANICS AND THERMODYNAMICS J2 - CONTINUUM MECH THERM VL - 36 PY - 2024 SP - 825 EP - 838 PG - 14 SN - 0935-1175 DO - 10.1007/s00161-024-01300-9 UR - https://m2.mtmt.hu/api/publication/34757577 ID - 34757577 AB - Modern manufacturing technologies allow heterogeneous materials with complex inner structures (e.g., foams) to be easily produced. However, their utilization is not straightforward, as the classical constitutive laws are not necessarily valid. According to various experimental observations, the Guyer–Krumhansl equation is a promising candidate for modeling such complex structures. However, practical applications need a reliable and efficient algorithm capable of handling both complex geometries and advanced heat equations. In the present paper, we derive new two-field variational formulations which treat the temperature and the heat flux as independent field variables, and we develop new, advanced hp -type mixed finite element methods, which can be reliably applied. We investigate their convergence properties for various situations, challenging in relation to stability and the treatment of fast propagation speeds. That algorithm is also proved to be outstandingly efficient, providing solutions four magnitudes faster than commercial algorithms. LA - English DB - MTMT ER - TY - CHAP AU - Fehér, Anna Éva AU - Kovács, Róbert Sándor ED - Kózelné Székely, Edit TI - Analytical evaluation of non–Fourier heat pulse experiments on room temperature T2 - 19th European Meeting on Supercritical Fluids PB - Budapest University of Technology and Economics CY - Budapest SN - 9789634219248 PY - 2023 SP - 162 EP - 162 PG - 1 UR - https://m2.mtmt.hu/api/publication/34042297 ID - 34042297 LA - English DB - MTMT ER - TY - CHAP AU - Fehér, Anna Éva AU - Kovács, Róbert Sándor ED - Takács, Donát M. ED - Ván, Péter ED - Vásárhelyi, Balázs TI - Általánosított termodinamikai modellek kísérleti kiértékelési módszertana [An evaluation procedure of experimental data for generalized thermodynamic models] T2 - Kőzetmechanika és termodinamika [Rock mechanics and thermodynamics] PB - Egyesület a Tudomány és Technológia Egységéért CY - Budapest SN - 9786158015783 T3 - Mérnökgeológia-Kőzetmechanika Kiskönyvtár, ISSN 1789-0454 ; 26. PY - 2023 SP - 3 EP - 16 PG - 14 UR - https://m2.mtmt.hu/api/publication/33766899 ID - 33766899 LA - Hungarian DB - MTMT ER - TY - CONF AU - Fehér, Anna Éva AU - Kovács, Róbert Sándor TI - Non-Fourier heat pulse experiments and evaluation for heterogeneous materials T2 - Joint European Thermodynamics Conference 2023 PY - 2023 SP - 75 EP - 75 PG - 1 UR - https://m2.mtmt.hu/api/publication/34042770 ID - 34042770 LA - English DB - MTMT ER - TY - JOUR AU - Kovács, Róbert Sándor TI - Transient non-Fourier behavior of large surface bodies JF - INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER J2 - INT COMMUN HEAT MASS VL - 148 PY - 2023 PG - 10 SN - 0735-1933 DO - 10.1016/j.icheatmasstransfer.2023.107028 UR - https://m2.mtmt.hu/api/publication/34139488 ID - 34139488 LA - English DB - MTMT ER - TY - BOOK ED - Kovács, Róbert Sándor ED - Rogolino, Patrizia ED - Oliveri, Francesco TI - Mathematical Aspects in Non-equilibrium Thermodynamics PB - MDPI CY - Basel PY - 2023 SP - 90 SN - 9783036577623 DO - 10.3390/books978-3-0365-7763-0 UR - https://m2.mtmt.hu/api/publication/34058066 ID - 34058066 N1 - This is a Reprint of the Special Issue Mathematical Aspects in Non-equilibrium Thermodynamics that was published in Symmetry. AB - Non-equilibrium thermodynamics is a relatively new field of research, and one which is also becoming increasingly important in engineering applications. However, despite the many approaches developed in recent decades, they all raise questions from a mathematical point of view, for instance on the proper definitions of initial and boundary conditions, analytical and numerical solution methods, and geometrical background. These questions cover numerous topics, including the mathematical analysis of various thermodynamic approaches, the investigation of the resulting governing equations, symmetry analysis of the solutions, and how the numerical methods can be built on the geometrical background. The aim of this Special Issue is to discuss and present up-to-date problems that may not be constrained to the previously mentioned aspects but must be connected to non-equilibrium thermodynamics. Thus, in the present Special Issue we aim to present the open mathematical questions on and characteristics of different thermodynamic approaches. LA - English DB - MTMT ER - TY - CONF AU - Kovács, Róbert Sándor AU - Fehér, Anna Éva TI - Emergence of non-Fourier heat conduction for heterogeneous materials T2 - Joint European Thermodynamics Conference 2023 PY - 2023 SP - 76 EP - 76 PG - 1 UR - https://m2.mtmt.hu/api/publication/34042794 ID - 34042794 LA - English DB - MTMT ER - TY - JOUR AU - Kovács, Róbert Sándor AU - Rogolino, Patrizia AU - Oliveri, Francesco TI - Mathematical Aspects in Non-Equilibrium Thermodynamics JF - SYMMETRY (BASEL) J2 - SYMMETRY-BASEL VL - 15 PY - 2023 IS - 4 PG - 2 SN - 2073-8994 DO - 10.3390/sym15040929 UR - https://m2.mtmt.hu/api/publication/33766579 ID - 33766579 LA - English DB - MTMT ER - TY - GEN AU - Kovács, Róbert Sándor TI - Heat equations beyond Fourier: from heat waves to thermal metamaterials PY - 2023 DO - 10.52843/cassyni.j4rmf8 UR - https://m2.mtmt.hu/api/publication/34429307 ID - 34429307 AB - In the past few decades, numerous heat conduction models extending beyond Fourier's have been developed to account for large gradients, fast phenomena, wave propagation, and heterogeneous material structures typical of biological systems, superlattices, and thermal metamaterials. Navigating through these models has become challenging due to their varying thermodynamic backgrounds and potential compatibility issues. Furthermore, recent discoveries in the field of non-Fourier heat conduction have complicated the interpretation and utilization of specific non-Fourier heat equations, especially when designing materials for the new generation of thermal metamaterials. The situation is further compounded by the existence of numerous modeling strategies in the literature, each offering different interpretations of even the same heat equation. This complexity makes it increasingly difficult to gain a comprehensive understanding of this research field. Therefore, this review aims to facilitate the navigation of advanced heat equations beyond Fourier by discussing their properties and potential practical applications in the context of experiments. We begin with the simplest models and their fundamental principles, progressing toward more complex, coupled phenomena, such as ballistic heat conduction. We do not delve into the often intricate technical details of each thermodynamic framework or aim to compare each approach from a methodological perspective. Instead, we focus on reviewing models primarily from the Rational Extended Thermodynamics, Extended Irreversible Thermodynamics, and Non-Equilibrium Thermodynamics with Internal Variables frameworks. Additionally, we discuss relevant models from kinetic theory, fractional derivatives, thermomass, and phase lag approaches. We provide background information on these models to highlight their origins, any limitations they may have, and the corresponding stability conditions, if applicable. Furthermore, as the field of non-Fourier heat conduction has become quite segmented, this paper also seeks to establish a common foundation, promoting a comprehensive mutual understanding of the fundamentals of each model and the phenomena to which they can be applied. LA - English DB - MTMT ER - TY - JOUR AU - Környey, Tamás AU - Kiss, László AU - Ván, Péter AU - Fülöp, Tamás AU - Kovács, Róbert Sándor AU - Szücs, Mátyás TI - Hőtechnikai és irreverzibilis termodinamikai kutatások és alkalmazásaik JF - ENERGIAGAZDÁLKODÁS J2 - ENGA VL - 64 PY - 2023 IS - különszám SP - 24 EP - 27 PG - 4 SN - 0021-0757 UR - https://m2.mtmt.hu/api/publication/34023946 ID - 34023946 LA - Hungarian DB - MTMT ER - TY - JOUR AU - Ramos, A.J.A. AU - Miranda, L.G.R. AU - Freitas, M.M. AU - Kovács, Róbert Sándor TI - Non-negativity and maximum principle: Revisiting the Guyer–Krumhansl heat equation JF - INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER J2 - INT J HEAT MASS TRANS VL - 211 PY - 2023 PG - 7 SN - 0017-9310 DO - 10.1016/j.ijheatmasstransfer.2023.124288 UR - https://m2.mtmt.hu/api/publication/33858746 ID - 33858746 LA - English DB - MTMT ER - TY - JOUR AU - Ramos, A.J.A. AU - Kovács, Róbert Sándor AU - Freitas, M.M. AU - Almeida Júnior, D.S. TI - Mathematical analysis and numerical simulation of the Guyer–Krumhansl heat equation JF - APPLIED MATHEMATICAL MODELLING J2 - APPL MATH MODEL VL - 115 PY - 2023 SP - 191 EP - 202 PG - 12 SN - 0307-904X DO - 10.1016/j.apm.2022.10.054 UR - https://m2.mtmt.hu/api/publication/33228605 ID - 33228605 LA - English DB - MTMT ER - TY - CONF AU - Takács, Donát M. AU - Kovács, Róbert Sándor AU - Szücs, Mátyás AU - Pozsár, Áron AU - Fülöp, Tamás TI - Thermodynamically extended symplectic numerical simulation of viscoelastic, thermal expansion and heat conduction phenomena in solids T2 - Joint European Thermodynamics Conference 2023 PY - 2023 SP - 68 EP - 68 PG - 1 UR - https://m2.mtmt.hu/api/publication/34042764 ID - 34042764 LA - English DB - MTMT ER - TY - CHAP AU - Takács, Donát M. AU - Fülöp, Tamás AU - Pozsár, Áron AU - Kovács, Róbert Sándor AU - Szücs, Mátyás AU - Ván, Péter ED - Schubert, Wulf ED - Kluckner, Alexander TI - Modelling time-dependent processes resulting from thermo-viscoelastic behaviour of rocks T2 - Proceedings of the ISRM 15th International Congress on Rock Mechanics and Rock Engineering & 72nd Geomechanics Colloquium PB - Austrian Society for Geomechanics CY - Salzburg SN - 9783950389838 PY - 2023 SP - 2091 EP - 2096 PG - 6 UR - https://m2.mtmt.hu/api/publication/33686972 ID - 33686972 LA - English DB - MTMT ER - TY - GEN AU - Fehér, Anna Éva AU - Fülöp, Tamás AU - Kovács, Róbert Sándor AU - Pozsár, Áron AU - Szücs, Mátyás AU - Takács, Donát M. AU - Ván, Péter TI - Recent results by the Irreversible Thermodynamics Research Group of Budapest University of Technology and Economics PY - 2022 PG - 1 UR - https://m2.mtmt.hu/api/publication/33908905 ID - 33908905 LA - English DB - MTMT ER -