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An evaluation of marine sediments in terms of their usability in the brick industry
Patrik Baksa, Franka Cepak, Rebeka Kovačič Lukman, Vilma Ducman, 2018, original scientific article

Abstract: A dredging process is essential for the development of harbours and ports, allowing the functional daily operation of the port. The management of dredged material represents a worldwide challenge, especially considering unwanted deposition of material. Because of their chemical, petrographic, mineralogical and homogeneity composition, marine sediments could represent an appropriate raw material for the brick industry, particularly for the production of clay blocks, roofing and ceramic tiles. In this study dredged material from Port of Koper was tested for such use, thus various analyses were carried out in order to determine if the dredged material is environmentally friendly and suitable for use in the brick industry. These included: chemical analysis, mineralogical analysis, particle size analysis, chloride content analysis and tests of firing in a gradient furnace. Furthermore, tests of mechanical properties, as well as tests of the frost-resistance of the samples were carried out. On the basis of the primary analyses and samples prepared in a laboratory, it was confirmed that marine sediments from the Port of Koper, without any additives are only conditionally suitable as a source material for producing brick products, because without additives they exhibit too much shrinkage on drying and firing, as well as high water absorption, this can be improved by the incorporation of suitable additives, for example, virgin clay or other suitable waste material. The approach described herewith can also be followed to assess sediments from other ports and rivers regarding its potential use in clay brick sector.
Keywords: dredge marine sediment, recycling, clay bricks, mechanical properties, chemical analysis
Published: 21.12.2017; Views: 1245; Downloads: 90
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Zbirka nalog iz Matematičnih metod II z rešitvami
Maja Žulj, 2017, other educational material

Abstract: Zbirka nalog vsebuje naloge namenjene študentom za utrjevanje snovi pri predmetu Matematične metode II. Naloge sledijo razporeditvi snovi v učbeniku Matematične metode II, zato je pred nalogami vselej navedeno poglavje iz učbenika, na katero se naloge nanašajo (Diferencialne enačbe, Funkcije več spremenljivk, Ravnine in premice v prostoru, Vektorska analiza, Trigonometrične vrste, Verjetnostni račun in Linearno programiranje). Za razumevanje snovi je potrebno poznati vsaj osnove, ki so bile podane pri predmetu Matematične metode I in v istoimenskem učbeniku. Naloge imajo rešitve zapisane na koncu vsakega poglavja. Rešitve prvih nekaj nalog poglavja so podane z vsemi vmesnimi koraki in potrebno teorijo, da lahko tudi bralec, ki se prvič srečuje s podobnimi nalogami, sledi postopku in pride do pravilne rešitve.
Keywords: diferencialne enačbe, funkcije več spremenljivk, premice in ravnine, verjetnost, linearno programiranje
Published: 16.11.2017; Views: 1006; Downloads: 316
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Underground coal gasification - the Velenje coal mine energy and economic calculations
Damjan Konovšek, Zdravko Praunseis, Jurij Avsec, Gorazd Berčič, Andrej Pohar, Simon Zavšek, Milan Medved, 2017, original scientific article

Abstract: Underground coal gasification (UCG) is a viable possibility for the exploitation of vast coal deposits that are unreachable by conventional mining and can meet the energy, economic and environmental demands of the 21st century. Due to the complexity of the process, and the site-specific coal and seam properties, it is important to acknowledge all the available data and past experiences, in order to conduct a successful UCG operation. Slovenia has huge unmined reserves of coal, and therefore offers the possibility of an alternative use of this domestic primary energy source. According to the available underground coal gasification technology, the energy and economic assessment for the exploitation of coal to generate electricity and heat was made. A new procedure for the estimation of the energy efficiency of the coal gasification process, which is also used to compare the energy analyses for different examples of coal exploitation, was proposed, as well as the technological schemes and plant operating mode in Velenje, and the use of produced synthetic coal gas (syngas). The proposed location for the pilot demonstration experiment in Velenje Coal Mine was reviewed and the viability of the underground coal gasification project in Velenje was determined.
Keywords: underground coal gasification, syngas, clean coal technology, energy analysis, economic analysis
Published: 31.08.2017; Views: 1453; Downloads: 263
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Limit cycle bifurcated from a center in a three dimensional system
Bo Sang, Brigita Ferčec, Qin-Long Wang, 2016, original scientific article

Abstract: Based on the pseudo-division algorithm, we introduce a method for computing focal values of a class of 3-dimensional autonomous systems. Using the $Є^1$-order focal values computation, we determine the number of limit cycles bifurcating from each component of the center variety (obtained by Mahdi et al). It is shown that at most four limit cycles can be bifurcated from the center with identical quadratic perturbations and that the bound is sharp.
Keywords: algorithms, three dimensional systems, focal value, limit cycle, Hopf bifurcation, center
Published: 08.08.2017; Views: 1289; Downloads: 99
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Exergy analysis of a Brayton cycle with variable physical properties and variable composition of working substance
Marija Živić, Antun Galović, Jurij Avsec, Mario Holik, 2016, original scientific article

Abstract: The exergy analysis of a Brayton cycle is performed in the paper. The four input variables: the ratio of the compressor exit and inlet pressures, the ratio of inlet temperature of gases in turbine and inlet temperature of air in compressor and the isentropic efficiencies of the compressor and turbine are analysed. The temperature ratio is varied in a way that the compressor inlet temperature of air is maintained constant, while the turbine inlet temperature of flue gases is varied from 900 to 1200°C. In the combustion chamber methane is completely combusted with excess air ratio which is determined by the temperature of flue gases at the turbine inlet. The analysis further includes variability of the molar heat capacities of air and flue gases with temperature and variability of their heat capacity ratios. The exergy destruction in turbine, compressor and combustion chamber and also total exergy efficiency of the cycle are considered in the analysis.
Keywords: Brayton cycle, variable physical properties, variable composition of working substance, maximum work output, maximum thermal efficiency
Published: 12.07.2017; Views: 1143; Downloads: 240
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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: 07.07.2017; Views: 1343; Downloads: 308
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Optimalno sledenje sončnih modulov Soncu ob upoštevanju izgub pogonskega sklopa
Sebastijan Seme, Gorazd Štumberger, Jože Voršič, 2013, original scientific article

Abstract: V delu je obravnavan dvo-osni sledilni sistem za sledenje sončnih modulov trajektoriji Sonca. Pri tem je predstavljena nova metoda za optimalno sledenje trajektoriji Sonca, ki upošteva tudi izgube pogonskega sklopa dvo-osnega sledilnega sistema. Cilj optimalnega sledenja je maksimalna pretvorba energije sončnega sevanja v električno energijo upoštevajoč na električne izgube pogonskega sklopa. Določitev trajektorije sledilnega sistema predstavlja v optimizaciji nelinearni in omejen problem, kjer ciljna funkcija ni na voljo v eksplicitni obliki. Za optimizacijski postopek se je uporabila stohastična metoda imenovana diferenčna evolucija. Pri tem je ciljna funkcija podana z napovedjo razpoložljivega sončnega sevanja, izgubami pogonskega sklopa in izkoristkom sončne elektrarne. Omejitve problema predstavljajo konstantna hitrost premikanja in minimalna sprememba kota premika pogonskega sklopa sledilnega sistema. Podani rezultati kažejo, da je optimalna trajektorija sledilnega sistema, odvisna predvsem od razpoložljivega sončnega sevanja, izkoristka sončne elektrarne, izgub pogonskega sklopa in omejitev, ki jih upoštevamo v sami optimizaciji.
Keywords: sončne elektrarne, fotonapetostni sistem, optimiranje, sončno sevanje, izgube
Published: 21.12.2015; Views: 1899; Downloads: 70
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Experimental analysis of the impact of particles on the cavitating flow
Boštjan Gregorc, Andrej Predin, Drago Fabijan, Roman Klasinc, 2012, original scientific article

Abstract: The purpose of this paper is to present an analysis of the impact of solid particles on the development of cavitating flow conditions around a hydrofoil. Experimental studies have been conducted in a cavitation tunnel with three different mixtures of particles and water. We used a particle-like properties, such as are found in river water, and with increasing mass concentration. We performed measurements of torque and the relative noise in the hydrofoil. The point in the formation of vapour phase on the hydrofoil and the pronounced frequency effect were determined by measuring the relative noise. Based on the analysis the results show that the particles increase the intensity and extent of cavitation.
Keywords: particles, cavitation, noise, measurements
Published: 10.07.2015; Views: 5001; Downloads: 62
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