1. Underground coal gasification - the Velenje coal mine energy and economic calculationsDamjan 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: 71; Downloads: 6 Full text (1,32 MB) |
2. Limit cycle bifurcated from a center in a three dimensional systemBo 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: 76; Downloads: 1 Full text (236,33 KB) |
3. Exergy analysis of a Brayton cycle with variable physical properties and variable composition of working substanceMarija 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: 167; Downloads: 4 Full text (789,62 KB) |
4. The calculation of specific heats for some important solid components in hydrogen production process based on CuCl cycleJurij 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: 195; Downloads: 8 Full text (266,80 KB) |
5. Optimalno sledenje sončnih modulov Soncu ob upoštevanju izgub pogonskega sklopaSebastijan Seme, Jože Voršič, Gorazd Štumberger, 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: 821; Downloads: 28 Full text (0,00 KB) |
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7. Experimental analysis of the impact of particles on the cavitating flowBoštjan 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: 611; Downloads: 3 Full text (0,00 KB) |
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10. Graphʼs theory approach for searching the shortest routing path in RIP protocolSaša Klampfer, Amor Chowdhury, Jože Mohorko, Žarko Čučej, 2012, original scientific article Abstract: Routing is a problem domain with an infinite number of final-solutions. One of the possible approaches to solving such problems is using graph theory. This paper presents mathematical analysis methodologies based on circular graphs for solving a shortest path routing problem. The problem is focused on searching for the shortest path within a circular graph. Such a search coincides with the network routing problem domain. In this paper, we introduce in the detail all necessary parts needed to understand such an approach. This includes: definition of the routing problem domain, introduction to circular graphs and their usage, circular graphʼs properties, definition of walks through a circular graph, searching and determining the shortest path within a circular graph, etc. The state of the art routing methods, implemented in contemporary highly sophisticated routers, includes well-known weight-based algorithms and distance-vectors-based algorithms. The proposed solution can be placed between the two abovementioned methods. Each of these known methods strives for optimal results, but each of them also has its own deficiencies, which should be rectified with the proposed new method. This theoretically presented method is argued by a practical example and compared with the RIP (Routing Information Protocol) technique, where we look for the shortest path and possible walks through a specified circular graph. Keywords: circular graphs, shortest path, graph diameter, walk through, CIGRP, connectivity matrix, network topology, symmetry, fully connected graph Published: 10.07.2015; Views: 544; Downloads: 14 Full text (0,00 KB) |