1. A regenerator used in the installation of magnetic refrigeration devicesDorin Botoc, Jurij Avsec, Adrian Plesca, 2020, strokovni članek Opis: In this article, the mechanism and functioning of a refrigeration system based on the magnetic system and the magnetocaloric effect are examined. Magnetic refrigeration plants operate based on a state-of-the-art technology that does not contain any toxic refrigerant that is harmful to the environment and the ozone layer. The magnetocaloric effect is created by a rare earth metal called gadolinium. We have studied the benefits of using this type of mechanism for both domestic and industrial needs. High efficiency, net energy consumption lower than the classic, silent systems, and a lack of typical refrigerant characterize this type of installation. The following layout describes the initial prototype for AMR in magnetocaloric refrigeration. Ključne besede: energy efficiency, gadolinium material, magnetocaloric effect, alternative technology, AMR Objavljeno v DKUM: 01.12.2023; Ogledov: 20; Prenosov: 0
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2. The properties of the material gadolinium and the working agent used in the installation of magnetic refrigeration devicesDorin Botoc, Jurij Avsec, Adrian Plesca, Georgel Gabor, Rusu Ionut, 2020, strokovni članek Opis: Much remains to be done to understand better and thus achieve better control over magnetic materials to maximize their magnetocaloric properties and performance, specifically for gadolinium. A clear path forward is highlighted by thorough experiments coupled with theory, in which the latter is tested and re%ned against the former, thus resulting in discoveries of new and improved materials and bringing near-room-temperature magnetic refrigeration technology to fruition in the near future. Ključne besede: Gadolinium, heat transfer, magneto-calorific, magnetic field Objavljeno v DKUM: 01.12.2023; Ogledov: 23; Prenosov: 0
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3. A review of the use of Rankine cycle systems for hydrogen productionUrška Novosel, Jurij Avsec, 2020, izvirni znanstveni članek Opis: The vast majority of steam power plants in the world are based on the Rankine cycle. It is a wellknown, trustworthy process that uses water or water vapour as a working medium, which supplies heat from various primary energy sources: fossil fuels, renewable energy sources (solar energy, energy from wood biomass, etc.) or a combination of both. With the Rankine cycle, energy sources other than electricity can be produced, which can be used as the primary energy source for various applications. The present article focuses on the production of hydrogen in addition to electricity; therefore, two energy sources are obtained from the same system with a few modifications of the existing power plant for further exploitation. There are several processes for hydrogen production using the Rankine cycle; in the present article, two processes are focused on: using part of the electricity produced and obtaining hydrogen by electrolysis of water or using part of high quality steam (basically heat energy) in combination with electricity and obtaining hydrogen by a thermochemical copper-chlorine process. Each of these processes has its advantages and disadvantages, which are presented in the present article with an example model of a power plant. Ključne besede: Rankine cycle, hydrogen production, electrolysis, thermochemical process Objavljeno v DKUM: 01.12.2023; Ogledov: 19; Prenosov: 0
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4. Multi-purpose use and lifecycle analysis of solar panelsDušan Strušnik, Urška Novosel, Jurij Avsec, 2020, izvirni znanstveni članek Opis: The combined use of renewable energy technologies and alternative energy technologies is a promising approach to reduce global warming effects throughout the world. In this paper, the solar panel is used in combination with a heat pump or with biomass sources to obtain heat, electricity, and hydrogen. Based on the Rankine thermodynamic cycle, hydrogen could be obtained from water with electrolysis and the CuCl thermochemical cycle. Furthermore, this study contains a life cycle analysis of solar panels. Ključne besede: heat pump, life cycle analysis, Rankine cycle, solar panel, thermochemical cycle Objavljeno v DKUM: 01.12.2023; Ogledov: 18; Prenosov: 0
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5. Modelling of magnetic regenerator and heat transfer agent in microchannelsDorin Botoc, Bianca Eliza Oneata, Rusu Ionut, Alexandru Salceanu, Jurij Avsec, 2021, izvirni znanstveni članek Opis: In this article, a brief introduction of conventional refrigeration is given, followed by a description and history of magnetic refrigeration. The active magnetic regenerator comprises 12 parallel plates of magnetocaloric material (gadolinium (Gd)), through which circulates the heat transfer fluid (water, in this case). At both ends of the regenerator are the heat exchangers. The hot heat exchanger (HHEX) and the cold heat exchanger (CHEX) connects the fluid to the heat sources. The principle of operation of a magnetic refrigeration installation is based on exploiting the magnetocaloric effect from the materials that possess these properties (in this case, Gd). Ključne besede: magnetic refrigeration, active magnetic regenerator, magnetocaloric material Objavljeno v DKUM: 10.11.2023; Ogledov: 57; Prenosov: 2
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6. Design of thermal power plant modernization and rehabilitation model for the new market demands and challengesMartin Bricl, Jurij Avsec, 2021, izvirni znanstveni članek Opis: The article presents the model for the rehabilitation of existing conventional thermal power plants in order to lower the consumption of fossil fuels. Instead of them, the model uses an alternative energy source - sun irradiation. The proposed rehabilitation model is theoretically calculated and designed. The model in the software environment Matlab Simulink was developed, based on previous calculations and determined parameters. In this article, it is presented the combination of Clausius - Rankine process and solar central receiver system. The model enables simultaneous calculations of exit model parameters for the complete model, based on predetermined entering parameters of the model. Ključne besede: Clausius Rankine process, solar central receiver system, modeling, analysis, Matlab Simulink software environment Objavljeno v DKUM: 10.11.2023; Ogledov: 41; Prenosov: 6
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7. Energy analysis of hydrogen use in road transport of the Republic of CroatiaFranco Krog, Jurij Avsec, 2022, strokovni članek Opis: In this paper, we will calculate the needs for hydrogen if all traffic in Croatia was driven by hydrogen. In the article, we will determine the required amount in several ways. First, we will briefly describe fuel cell cars and the extent to which the amount of exhaust gases would be reduced. We will then explain the ways of obtaining hydrogen, its transport and what the purchase costs would be. Finally, we will compare the results and draw some conclusions. Ključne besede: hydrogen, hydrogen technologies, hydrogen acquisition, transport Objavljeno v DKUM: 30.10.2023; Ogledov: 120; Prenosov: 7
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8. Energo-economics payback investment calculation modelling of gas-steam combined cycle power plantDušan Strušnik, Jurij Avsec, 2022, izvirni znanstveni članek Opis: The paper deals with energo-economic payback calculation modelling of the combined gassteam cycle operation, demonstrating the basic characteristic properties of cycle behaviour in different operating regimes and calculating the payback period of the investment. The calculation of the payback period of the investment is based on the calculation of the net present value and with actual obtaining data sets from a recently built gas-steam combined cycle power plant. The results of the calculation modelling show that the gas-steam combined cycle power plant can achieve a useful efficiency of up to 88% in the back-pressure operation of the steam turbine. The useful efficiency of the gas turbine is up to 40%. The payback period of the investment depends on the investment costs, the quantity and market price of the consumed fuel, the quantity and market price of the generated electricity and thermal energy. The results show that with a price ratio fuel/electricity of 0.36, the payback period of the investment is 4 years, with a price ratio fuel/electricity of 0.54, the payback period of the investment is as much as 17 years. Ključne besede: calculation, efficiency, investment, market, modelling, payback Objavljeno v DKUM: 30.10.2023; Ogledov: 123; Prenosov: 3
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9. Off-design flow analysis of cogeneration steam turbine with real process dataDušan Strušnik, Igor Kuštrin, Jurij Avsec, 2022, izvirni znanstveni članek Opis: This paper presents the concept of reconstruction of the existing coal-fired combined heat and power plant to comply with new European environmental policies. The existing coal-fired boiler will be replaced by two new dual pressure heat recovery steam generators, which will utilize the exhaust gas heat from two new gas turbines. The steam from the heat recovery steam generators will be fed to the existing steam turbine. After the reconstruction, the nominal turbine inlet steam mass-flow of 40 kg/s will be reduced to 30 kg/s. During periods of low heat demand, only one gas turbine and one heat recovery steam generator will be in operation and the live steam mass-flow may drop even to 12 kg/s. Prior to the reconstruction, dedicated tests of the existing steam turbine were carried out using the steam from the existing coal-fired boiler. The goal of the test was to verify the viability of operation with such an extremely low mass-flow. The results of tests show that such operation is possible but inefficient from a power generation point of view. Besides this, the turbine control algorithm needs to be accommodated to this extreme operating regime and additional measures like displacement of the extraction points and steam cooling will be required to control the temperature of the steam extractions. The novelty of this paper is using real prereconstruction process data for the assessment of feasibility and efficiency of the post-reconstruction operation of a combined heat and power turbine. Ključne besede: cogeneration, control valves, exhaust gas, heat recovery, steam turbine Objavljeno v DKUM: 30.10.2023; Ogledov: 48; Prenosov: 3
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10. Hydrogen production using a thermochemical cycleJurij Avsec, Urška Novosel, Dušan Strušnik, 2022, izvirni znanstveni članek Opis: Sustainable methods of clean fuel production are needed throughout the world due to depleting oil reserves and the need to reduce carbon dioxide emissions. The technology based on fuel cells for electricity production or the transport sector has already been developed. However, a key missing element is a large-scale method of hydrogen production. The copper-chlorine (CuCI) combined thermochemical cycle is a promising thermochemical cycle that can produce large amounts of cheap hydrogen. A particularly promising part of this process is its use in combination with nuclear or thermal power plants. This paper focuses on a CuCl cycle and describes the models used to calculate thermodynamic and transport properties. This paper discusses the mathematical model for computing the thermodynamic properties for pure HCl and CuCl2. The mathematical model developed for the solid phase takes into account vibrations of atoms in molecules and intermolecular forces. This mathematical model can be used for the calculation of the thermodynamic properties of polyatomic crystals on the basis of the Einstein and Debye equations. The authors of this paper developed the model in the low temperature and high temperature region. All the analytical data have been compared with some experimental results and show a relatively good match. For the solid phase, the authors developed a model to calculate thermal conductivity based on electron and phonon contributions. Ključne besede: thermodynamics, energy, hydrogen production, solid phase, fluid phase Objavljeno v DKUM: 30.10.2023; Ogledov: 60; Prenosov: 4
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