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1.
Hydrogen production using a thermochemical cycle
Jurij Avsec, Urška Novosel, Dušan Strušnik, 2022, original scientific article

Abstract: 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.
Keywords: thermodynamics, energy, hydrogen production, solid phase, fluid phase
Published in DKUM: 30.10.2023; Views: 60; Downloads: 4
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2.
Simulation of automotive air-conditioning system in 1D simulation software : diplomsko delo
Marko Copot, 2019, undergraduate thesis

Abstract: The development of state-of-the-art vehicles requires advanced simulations tools in heating, ventilation and air-conditioning (HVAC). The focus of this thesis is the construction of an automotive HVAC model, its calibration and the simulation of the behaviour of the HVAC model in various ambient conditions. The theoretical background of refrigeration system as part of the HVAC system is presented. The model is constructed with following components: compressor, condenser, throttling device, evaporator and battery chiller, which is a heat exchanger between coolant and refrigerant. The description and role of each component in the HVAC model is presented. All heat exchangers are calibrated, which is done with multiple simulations that have defined input data. The results are compared to experimental data. With addition of vehicle cabin with air recirculation, HVAC control logic is implemented. The behaviour of the system is simulated in defined environmental conditions. The results of the simulations are presented in graphs and tables.
Keywords: 1D simulations, air-conditioning, HVAC, calibration, thermodynamics, cooling
Published in DKUM: 23.09.2019; Views: 1166; Downloads: 93
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3.
The calculation of specific heats for some important solid components in hydrogen production process based on CuCl cycle
Jurij Avsec, 2014, original scientific article

Abstract: Hydrogen is one of the most promising energy sources of the future enabling direct production of power and heat in fuel cells, hydrogen engines or furnaces with hydrogen burners. One of the last remainder problems in hydrogen technology is how to produce a sufficient amount of cheap hydrogen. One of the best options is large scale thermochemical production of hydrogen in combination with nuclear power plant. copper-chlorine (CuCl) cycle is the most promissible thermochemical cycle to produce cheap hydrogen.This paper focuses on a CuCl cycle, and the describes the models how to calculate thermodynamic properties. Unfortunately, for many components in CuCl cycle the thermochemical functions of state have never been measured. This is the reason that we have tried to calculate some very important thermophysical properties. This paper discusses the mathematical model for computing the thermodynamic properties for pure substances and their mixtures such as CuCl, HCl, Cu2OCl2 important in CuCl hydrogen production in their fluid and solid phase with an aid of statistical thermodynamics. For the solid phase, we have developed the mathematical model for the calculation of thermodynamic properties for polyatomic crystals. In this way, we have used Debye functions and Einstein function for acoustical modes and optical modes of vibrations to take into account vibration of atoms. The influence of intermolecular energy we have solved on the basis of Murnaghan equation of state and statistical thermodynamics.
Keywords: thermodynamics, molecular crystals, mathematical models, statistical thermodynamics
Published in DKUM: 07.07.2017; Views: 2152; Downloads: 416
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4.
Sensor for injection rate measurements
Milan Marčič, 2006, original scientific article

Abstract: A vast majority of the medium and high speed Diesel engines are equipped with multi-hole injection nozzles nowadays. Inaccuracies in workmanship and changing hydraulic conditions in the nozzles result in differences in injection rates between individual injection nozzle holes. The new deformational measuring method described in the paper allows injection rate measurement in each injection nozzle hole. The differences in injection rates lead to uneven thermal loads of Diesel engine combustion chambers. All today known measuring method, such as Bosch and Zeuch give accurate results of the injection rate in diesel single-hole nozzles. With multihole nozzles they tellus nothing about possible differences in injection rates between individual holes of the nozzle. At deformational measuring method, the criterion of the injected fuel is expressed by the deformation of membrane occurring due to the collision of the pressure wave against the membrane. The pressure wave is generated by the injection of the fuel into the measuring space. For each hole of the nozzle the measuring device must have a measuring space of its own into which fuel is injected as well as its measuring membraneand its own fuel outlet. During measurements procedure the measuring space must be filled with fuel to maintain an overpressure of 5 kPa. Fuel escaping from the measuring device is conducted into the graduated cylinders for measuring the volumetric flow through each hole of the nozzle.The membrane deformation is assessed by strain gauges. They are glued to the membrane and forming the full Wheatstonećs bridge. We devoted special attention to the membrane shape and temperature compensation of the strain gauges.
Keywords: thermodynamics, sensors, Diesel engines, nozzles, injection, measurements
Published in DKUM: 22.06.2017; Views: 1481; Downloads: 333
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5.
The maximum entropy production principle and linear irreversible processes
Paško Županović, Domagoj Kuić, Željana Bonačić Lošić, Dražen Petrov, Davor Juretić, Milan Brumen, 2010, original scientific article

Abstract: It is shown that Onsager’s principle of the least dissipation of energy is equivalent to the maximum entropy production principle. It is known that solutions of the linearized Boltzmann equation make extrema of entropy production. It is argued, in the case of stationary processes, that this extremum is a maximum rather than a minimum.
Keywords: entropy production, linear nonequilibrium thermodynamics, linearized Boltzmann equation
Published in DKUM: 21.06.2017; Views: 986; Downloads: 379
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6.
On the problem of formulating principles in nonequilibrium thermodynamics
Paško Županović, Domagoj Kuić, Davor Juretić, Andrej Dobovišek, 2010, original scientific article

Abstract: In this work, we consider the choice of a system suitable for the formulation of principles in nonequilibrium thermodynamics. It is argued that an isolated system is a much better candidate than a system in contact with a bath. In other words, relaxation processes rather than stationary processes are more appropriate for the formulation of principles in nonequilibrium thermodynamics. Arguing that slow varying relaxation can be described with quasi-stationary process, it is shown for two special cases, linear nonequilibrium thermodynamics and linearized Boltzmann equation, that solutions of these problems are in accordance with the maximum entropy production principle.
Keywords: thermodynamics, entropy, relaxation, stationary process, entropy production
Published in DKUM: 07.06.2012; Views: 1411; Downloads: 385
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7.
Enzymatic fatty ester synthesis
Simona Pečnik, Željko Knez, 1992, original scientific article

Abstract: Fatty ester synthesis with immobilized 1,3-specific lipase from Mucor Miehei is described. 1,2-Isopropylidene glycerol was peoduced by condensation of glycerol with acetone was esterified with oleic acid in the presence of a Mucor Miehei lipaze (Lipozyme TM) to obtain 1,2 isopropylidene- 3-oleoyl glycerol. The effects of various process parameters (temperature and pressure)and various ratios (enzyme/substrate) have been investigated to determine optimal conditions for the esterification process. The highest conversion of oleic acid (80% w/w) was obtained at 55 oC and 57.057 bar, while the optimal addition of lipase to substrate was determined to be 0,096 g per gram of reaction mixture. The esterification can be modelled successfully as a reverse second order reaction. Thermodynamic properties of the reaction system at 55 oC and 0.057 bar were also determined. Activation energy was 20.82 kJ/mole, entropy of activation -0,26 kJ/(Kmole) and free energy of activation was 103.32 kJ/mole.
Keywords: chemical engineering, biotechnology, esterification, syntheses, esters, enzymes, lipase, Mucor miehei, reaction kinetics, reaction thermodynamics, 1, 2-isopropylidene-3-oleoyl glycerol
Published in DKUM: 06.06.2012; Views: 2219; Downloads: 95
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9.
Influence of vacuum energy on scattering
Milan Marčič, 1997, original scientific article

Abstract: We deal with photon-electron scattering which occurs between two uncharged conducting parallel plates moving away from each other at a constant velocity. The electromagnetic vacuum field between the two plates is defined by the configuration of space and also interacts with the electrons. We show the relevant operators for both the photon and the electron fields and the computation of the corresponding Feynman propagator, S-matrix and scattering cross section, taking into account the influence of the changeable vacuum field. Correction terms in the computed S-matrix and scattering cross section manifest the influence of the changeable vacuum field. We analyze an example for low-energy scattering of the influence of the changeable vacuum field uponthe scattering cross section.
Keywords: physics, quantum electrodynamics, statistical thermodynamics
Published in DKUM: 01.06.2012; Views: 2214; Downloads: 87
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10.
Calculation of thermophysical and thermochemical properties during hydrocarbon combustion
Jurij Avsec, Franc Zgaga, Milan Marčič, 2002, original scientific article

Abstract: A mathematical model is presented for computing the chemical and thermophysical properties in the process of combustion of natural gas. To identify the parameters of state of combustion products, their composition hasto be known, which may be determined from chemical equilibrium. The computation is performed with the use of chemical potentials and statistical thermodynamics, featuring all important molecular contributions (translation, rotation, vibration, and intermolecular potential energy). A thermal equation of state with two virial terms is used. The real gas mixture is treated as consisting of four components: carbon dioxide, nitrogen, carbon monoxide, and water. Virial coefficients are dependent on temperature and mole fractions of the real components. Mixed terms are taken into account. The caloric equation of state is based on statistical thermodynamics for an ideal gas. Corrections are made in accordance with the second law of thermodynamics and the thermal equation of state. As the whole computation is based on matrix algebra, increasing the number of components presents no problems. We tested our model in the high-pressure region (100 bar) and the low-pressure region (1 bar), in the temperature range 500 - 6000°K. Our model is compared with other analytical models presented in the literature and shows relatively good agreement. At the same time we tested the influence of real conditions on the chemical and thermophysical properties of combustion products.
Keywords: statistical thermodynamics, thermodynamical properties, combustion of natural gas, mathematical models, thermodynamic functions of state, equation of state, virial coefficients
Published in DKUM: 01.06.2012; Views: 2086; Downloads: 118
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