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Application of gas condensing boilers in domestic heating
Marija Živić, Antun Galović, Jurij Avsec, Antun Barac, 2019, original scientific article

Abstract: A growing number of households have had condensing boilers built in to be used for the heating of spaces and for the hot water supply. The use of condensing boilers is justified from the point of view of energy because they achieve higher thermal efficiency than traditional boilers. Condensation of water vapour occurs in the flue gases, whereby the heat released by condensation is used to heat the water in the boiler. How much water vapour will condense depends on the temperature to which the flue gases are cooled. In this paper, a thermodynamic analysis of thirteen built-in gas condensing boilers was performed; data on the flue gas composition and temperature, as well as on the excess air required for combustion were obtained for that purpose. The calculation results consisting of the amount of condensed water, the thermal efficiency of the boiler, and the volume flow rates of the air and fuel are presented in tables. The analysis identified the cases in which the water vapour condensation occurred and determined the amount of the condensed water. The cases without water vapour condensation were also identified.
Keywords: gas condensing boilers, thermodynamic analysis, thermal efficiency of the boiler
Published in DKUM: 22.02.2024; Views: 206; Downloads: 8
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An alternative method of increasing the transmission performance of a conventional 110 kV cable line
Dardan Klimenta, Dragan Tasić, Miroljub S. Jevtić, 2019, professional article

Abstract: The purpose of this paper is to show that a significant increase in the ampacity of a 110 kV underground cable line is achievable, if a hydronic asphalt pavement system is applied along the entire line, and if the cable trench is completely filled with high thermal conductivity bedding in order to improve the conduction of heat between the line and the surface of the earth. In such a way, it would be possible to simultaneously collect and then store heat from the sun and cable line. The mutual thermal effects between the 110 kV cable line and the hydronic asphalt pavement, in the presence of solar radiation, wind-driven convection and heat emission along the earth surface, are simulated using FEM-based models for the most unfavourable summer conditions and the most common winter conditions. An adequate experimental background is also provided based on the existing measurements relevant to the thermal analysis performed. It was found that, compared to the associated base cases, the cable ampacity can be increased up to 92.3% for the most unfavourable summer conditions, and up to 60.3% for the most common winter conditions.
Keywords: ampacity, finite-element method, hydronic asphalt pavement, power cable, thermal analysis
Published in DKUM: 05.12.2023; Views: 302; Downloads: 4
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Production, thermal analysis and application of roll bond solar absorbers for heating and cooling in residential buildings
Jurij Avsec, Daniel Brandl, Helmut Schober, Urška Novosel, Janko Ferčec, 2019, published scientific conference contribution

Abstract: The effects of global warming are a crucial issue in the near future. The combination of renewable energy sources (RES) and the use of alternative energy technology such as heat pumps and hydrogen technology could solve major ecological problems. In Central Europe, the energy demand for heating and cooling in residential buildings is clearly higher than for generation of electricity or energy for trucking e.g. In this paper, a new solar thermal absorber has been analysed which is produced by using the so called "roll bond" technology (ABS Network, 2018). The focus of this study lies on the determination of the energy efficiency by combining this solar thermal absorber with heat pumps and biomass or geothermal systems in the region of Central Europe.
Keywords: roll bond solar absorbers, thermal analysis, solar systems, heat pump systems, heating and cooling in residential buildings
Published in DKUM: 04.12.2023; Views: 265; Downloads: 14
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Synthesis, crystal structure and magnetic properties of a new hydroxylammonium fluoroferrate
Brina Dojer, Matjaž Kristl, Zvonko Jagličić, Amalija Golobič, Marta Kasunič, Mihael Drofenik, 2012, original scientific article

Abstract: This paper reports on the synthesis of a new hydroxylammonium fluoroferrate, with the formula $(NH_3OH)_3FeF_6$, obtained after dissolving iron powder in hydrofluoric acid and adding solid $NH_3OHF$. This new compound has been characterized by chemical and thermal analysis, single-crystal X-ray diffraction, and magnetic measurements. The title compound crystallizes trigonal, R3c, with cell parameters a = 11.4154(2) Å, c = 11.5720(2) Å, Z = 6. The structure consists of $NH_3OH^+$ cations and isolated $FeF_6^{3–}$ octahedra in which the central ion lies on a threefold axis. The oxygen and nitrogen atoms of the hydroxylammonium cations are donors of hydrogen bonds to fluoride anions, resulting in a network of hydrogen bonds between counterions. The effective magnetic moment $µ_{eff}$ = 5.8 BM was calculated and perfectly matches the expected value of high-spin Fe(III) ions. The thermal decomposition of the compound was studied by TG, DSC, and X-ray powder diffraction.
Keywords: inorganic chemistry, crystallography, coordination compounds, synthesis, crystal structure, characterization of compounds, determination of the structure of compounds, X-ray diffraction, magnetic measurements, thermal analysis, TG, DSC, hydrogen bond, metal complexes, hydroxylammonium fluoromethalatehydroxylammonium, fluoroferrate
Published in DKUM: 25.08.2017; Views: 2005; Downloads: 67
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Ammoniumbis(hydroxylammonium) pentafluoridooxidovanadate(IV) : synthesis and characterisation of a new fluorovanadate
Brina Dojer, Matjaž Kristl, Zvonko Jagličić, Mihael Drofenik, Anton Meden, 2008, original scientific article

Abstract: Turquoise crystals of a new hydroxylammonium compound with the formula $NH_4(NH_3OH)_2[VOF_5]$ have been synthesized by the reaction of solid $NH_3OHF$ and the aqueous solution of vanadium in HF. The compound crystallizes monoclinic, $P2_1/n$, with cell parameters: a = 10.5658(2) Å, b = 6.6143(1) Å, c = 11.6618(2) Å, β = 96.282(1). Magnetic susceptibility was measured using a SQUID device over a temperature range 2–300 K at magnetic field $10^3 Oe$ giving the result $µ_{eff}$ = 1.65 BM. The thermal decomposition was studied by TG and DSC analysis. $NH_4(NH_3OH)_2[OF_5V]$ decomposes above 354 K in three steps, obtaining $NH_4VOF_3$ after the first step and $V_2O_5$ as the final residue.
Keywords: hydroxylammonium fluorovanadates, x-ray powder diffraction, x-ray structure determination, thermal analysis
Published in DKUM: 17.08.2017; Views: 1766; Downloads: 106
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Numerical analysis of temperature field during hardfacing process and comparison with experimental results
Vukić Lazić, Ivana Ivanović, Aleksandar Sedmak, Rebeka Rudolf, Mirjana Lazić, Zoran Radaković, 2014, original scientific article

Abstract: The three-dimensional transient nonlinear thermal analysis of the hard facing process is performed by using the finite element method. The simulations were executed on the open source Salome platform using the open source finite element solver Code Aster. The Gaussian double ellipsoid was selected in order to enable greater possibilities for the calculation of the moving heat source. The numerical results were compared with available experimental results.
Keywords: welding simulations, numerical analysis, thermal analysis, simulations, transient heat conduction, moving heat source
Published in DKUM: 07.07.2017; Views: 1430; Downloads: 383
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Comparison of NiTi orthodontic archwires and a determination of the charasteristic properties
Janko Ferčec, Matija Kos, Mihael Brunčko, Ivan Anžel, Branislav Glišić, Evgenija Marković, Rebeka Rudolf, 2014, original scientific article

Abstract: The aim of this paper was to analyse the characteristic properties of six different, commercially available nickel-titaniumorthodontic wires with a diameter of 0.305 mm (0.014"). The characteristic properties were determined by usingsemi-quantitative EDX analyses, DSC analyses for a determination of the phase temperatures, and a tensile test to obtain themechanical properties of the wires. The investigation of the chemical composition showed an equiatomic NiTi alloy. Analysesof phase temperatures showed that the nickel-titanium orthodontic wires were, in an austenitic microstructure, exhibiting asuperelastic effect in the oral environment. The uniaxial tensile stressstrain curves showed different values for the beginningand the end of the transformation range during the loading.
Keywords: shape-memory alloy, phase transformation, thermal analysis, tensile test
Published in DKUM: 21.12.2015; Views: 1478; Downloads: 106
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Hydroxylammonium fluorogermanates
Irena Ban, Matjaž Kristl, Mihael Drofenik, Arkadije Popović, 2004, original scientific article

Abstract: A new hydroxylammonium compound (NH3OH)2GeF6, has been synthesized by the addition of solid NH3OHF to a solution of GeO2 dissolved in 20% HF. The compound was characterized by chemical analysis and X-ray powder diffraction, the thermal decomposition was studied by thermal analysis and mass spectrometry. (NH3OH)2GeF6 crystallizes monoclinic. Two endothermic and two exothermic peaks have been observed on the DSC curve, the decomposition product at 500 °C is GeO2.
Keywords: inorganic chemistry, synthesis, characterisation, hydroxylammonium fluorogermanates, x-ray powder diffraction, mass spectroscopy, thermal analysis
Published in DKUM: 01.06.2012; Views: 3232; Downloads: 112
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