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Influence of Heat Treatments on Microstructure of Electron Beam Additive Manufactured Ti-6Al-4V Alloy
Damir Skuhala, 2020, magistrsko delo

Opis: Additive manufacturing of metallic parts is increasing in popularity and starting to emerge as a new competitive manufacturing process. Printed structures from Ti-6Al-4V titanium alloy, produced by electron beam additive manufacturing (EBAM), possess columnar prior β grains and layer bands, alongside an ultrafine lamellar microstructure, which is prone to low ductility and thus requiring thermal post-processing. Several heat treatments were performed in α + β and β field, in one or multiple stages. The results showed that bi-lamellar microstructure can be obtained, and that selection of annealing temperature and cooling rate determines the morphology, thickness, and distribution of both primary and secondary α features. Mechanical properties were evaluated on three selected heat treatments. Annealing of the As-built condition was performed at 710°C (HT1) and 870°C (HT2), resulting in lamellar microstructure with basketweave morphology. In two-stage heat treatment (HT3), the temperature in the first stage has exceeded β transus, while in the second, annealing was performed again at 870°C. The microstructure was characterized as a mixture of lamellar and bi-lamellar with large α colonies inside the rearranged prior β grains. Air cooling was performed in all HT from the final annealing stage. Strength and hardness have decreased with increasingly coarser microstructural features, while fracture toughness was improved, except in HT1, where the decrease in the fracture toughness was mainly attributed to reduced intrinsic toughening. As-built and HT1 conditions were effected by microstructural texture, causing inconsistent fracture morphology, reduced crack roughness and scattering in results. The influence of texture was decreased by coarser microstructure in HT2, while crack tortuosity was increased. Very unpredictable fracture behaviour was observed in HT3 due to large α colonies, as their orientation determines the areas of ductile or cleavage crack propagation.
Ključne besede: Titanium alloys, Ti-6Al-4V, additive manufacturing, EBAM, heat treatments, microstructural optimization, mechanical properties, fracture toughness
Objavljeno: 11.05.2020; Ogledov: 395; Prenosov: 108
.pdf Celotno besedilo (25,14 MB)

Analytical modelling of achieving energy efficiency with green walls
Dejan Tasić, 2019, magistrsko delo

Opis: In the last years, energy efficiency has become an important issue for the EU and Slovenia, who both strive for more sustainable use of energy in buildings. As an innovative approach to such matter, green walls are vertical structures that can serve both as a façade or an insulation layer as well as an aesthetic design for building application. This thesis contains calculated annual heat (transmission) losses through different wall assemblies with and without a constructed green wall in front of them. The goal is to compare values of heat losses between those wall assemblies and the explanation of such results which will determine if green walls present a viable energy-efficient structure for buildings.
Ključne besede: energy efficiency, green wall, heat losses, modelling
Objavljeno: 18.11.2019; Ogledov: 659; Prenosov: 62
.pdf Celotno besedilo (3,83 MB)

Simulation of flow conditions in nuclear power plant reactor pressure vessel lower plenum experimental facility
Blaž Kamenik, 2019, magistrsko delo

Opis: The flow conditions during the experiment LIVE2D on reactor core melt behaviour in the lower plenum of a reactor pressure vessel, performed at the Karlsruhe Institute of Technology (Germany), were simulated with a Computational Fluid Dynamics computer code. In this hypothetical severe accident scenario in a pressurized water reactor nuclear power plant, the melt is divided into an oxidic layer and a metallic layer on top of it, and the oxidic layer is volumetrically heated due to decay heat. In the experiment, oil and salt were used as simulant materials for metallic and oxidic melt, respectively. The main goal of performed simulations was to investigate the so-called “focusing effect”, where a thin layer of the reactor vessel steel wall is exposed to high heat flux. Due to the length of experiment, which exceeds 100 hours, only intervals of the melt behaviour were simulated. Four cases were simulated. The first case investigated different boundary conditions for the oil layer behaviour for layer thickness 35 mm. The second case investigated the same conditions with added modelling of the reactor vessel steel wall and salt crust from the lower layer. The third case used similar modelling as the second case to investigate the oil layer behaviour for layer thickness 75 mm. The fourth case investigated both salt and oil layers for oil layer thickness 75 mm. Different analytical and numerical calculations were performed to determine heat losses from simulant liquids to the surroundings, which played an important part in the experiment.
Ključne besede: nuclear power plant, severe accident, reactor core melt, lower plenum, heat flux focusing effect
Objavljeno: 17.09.2019; Ogledov: 383; Prenosov: 63
.pdf Celotno besedilo (6,83 MB)

High-Perssure process design for polymer treatment and heat transfer enhancement
Gregor Kravanja, 2018, doktorska disertacija

Opis: The doctoral thesis presents the design of several high-pressure processes involving »green solvents« so-called supercritical fluids for the eco-friendly and sustainable production of new products with special characteristics, fewer toxic residues, and low energy consumption. The thesis is divided into three main parts: polymer processing and formulation of active drugs, measurements of transport properties form pendant drop geometry, and study of heat transfer under supercritical conditions. In the first part, special attention is given to using biodegradable polymers in particle size reduction processes that are related to pharmaceutical applications for controlled drug release. The PGSSTM micronization process was applied to the biodegradable carrier materials polyoxyethylene stearyl ether (Brij 100 and Brij 50) and polyethylene glycol (PEG 4000) for the incorporation of the insoluble drugs nimodipine, fenofibrate, o-vanillin, and esomeprazole with the purpose of improving their bioavailability and dissolution rate. In order to optimize and design micronization process, preliminary transfer and thermodynamic experiments of water-soluble carriers (Brij and PEG)/ SCFs system were carried out. It was observed that a combination of process parameters, including particle size reduction and interactions between drugs and hydrophilic carriers, contributed to enhancing the dissolution rates of precipitated solid particles. In the second part, a new optimized experimental setup based on pendant drop tensiometry was developed and a mathematical model designed to fit the experimental data was used to determine the diffusion coefficients of binary systems at elevated pressures and temperatures. Droplet geometry was examined by using a precise computer algorithm that fits the Young–Laplace equation to the axisymmetric shape of a drop. The experimental procedure was validated by a comparison of the experimental data for the water-CO2 mixture with data from the literature. For the first time, interfacial tension of CO2 saturated solution with propylene glycol and diffusion coefficients of propylene glycol in supercritical CO2 at temperatures of 120°C and 150°C in a pressure range from 5 MPa, up to 17.5 MPa were measured. Additionally, the drop tensiometry method was applied for measuring systems that are of great importance in carbon sequestration related applications. The effect of argon as a co-contaminant in a CO2 stream on the interfacial tension, diffusion coefficients, and storage capacity was studied. In the third part, comprehensive investigation into the heat transfer performance of CO2, ethane and their azeotropic mixture at high pressures and temperatures was studied. A double pipe heat exchanger was developed and set up to study the effects of different operating parameters on heat transfer performance over a wide range of temperatures (25 °C to 90 °C) and pressures (5 MPa to 30 MPa). Heat flux of supercritical fluids was measured in the inner pipe in the counter-current with water in the outer pipe. For the first time, the heat transfer coefficients (HTC) of supercritical CO2, ethane and their azeotropic mixture in water loop have been measured and compared. A brief evaluation is provided of the effect of mass flux, heat flux, pressure, temperature and buoyancy force on heat transfer coefficients. Additionally, to properly evaluate the potential and the performance of azeotropic mixture CO2-ethane, the coefficients of performance (COP) were calculated for the heat pump working cycle and compared to a system containing exclusively CO2.
Ključne besede: supercritical fluids, PGSSTM, formulation of active drugs, biodegradable polymers, transport and thermodynamic data, pendant drop method, carbon sequestration, heat transfer coefficients
Objavljeno: 28.05.2018; Ogledov: 827; Prenosov: 126
.pdf Celotno besedilo (5,51 MB)

Matevž Frajnkovič, 2017, magistrsko delo

Opis: This master’s thesis deals with heat transfer in a specific cellular structure, called UniPore cellular structure. Said structure has been developed at Japan’s Kumamoto university. The structure is manufactured using the technique of explosion welding. Due to longitudinal orientation of the pores and high thermal conductivity of materials, the thermal properties of the structure as a heat exchanger have been analysed. Influence of different boundary conditions on the effectiveness of heat transfer in the structure has been analysed. The results are compared and analysed. It has been concluded, that the structure itself might be suitable when dealing with dirty liquids. Usage of the structure in such systems would enable a quick and efficient cleaning process of the waste, that deposits on the walls over time.
Ključne besede: Heat transfer, cellular structure, porous materials, CFD
Objavljeno: 24.08.2017; Ogledov: 668; Prenosov: 147
.pdf Celotno besedilo (2,59 MB)

Multiple-effect evaporation in aluminosilicate technology
Dušan Klinar, Janvit Golob, 2001, strokovni članek

Opis: The article presents an engineering approach to the development of an alternative production with the existing equipment. Zeolite production is becoming an alternative to the old »Bayer« process for aluminum hydrate production. By applying appropriate know-how old equipment was used for an economically as well as ecologically acceptable production. In this equipment adaptation among other production steps the multistage evaporation battery was the most critical part of the process. We applied semi empirical approach on the basis of Z. Rant ideas to find heat transfer coefficients and to determine which equipment elements are more relevant for efficient performance and need serious maintenance.
Ključne besede: chemical engineering, evaporation in silicate technology, bauxite alumina production, evaporators, process optimization, heat transfer, heat flow, empirical equations, heat transfer coefficients, zeolites
Objavljeno: 24.08.2017; Ogledov: 608; Prenosov: 67
.pdf Celotno besedilo (354,14 KB)
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A multiscale approach to deformation and fracture of heat-resistant steel under static and cyclic loading
P. O. Maruščak, Denys Baran, Vladimir Gliha, 2013, izvirni znanstveni članek

Opis: Regularities of static and cyclic deformation, damage and fracture of heat-resistant steel 25Kh1M1F, based on the approaches of physical mesomechanics and 3D interferometry method, are presented in this paper. The applicability of these techniques for different hierarchy levels of deformation was studied. The investigation of scanning microscope photos was conducted for several dissipative structures, fragmentation of the material, localisation of macrodeformation and subsequent failure on macro- and mesolevel. It is shown that the used modern techniques of experimental analysis are very efficient in understanding deformation and damage evolution in materials.
Ključne besede: fracture, heat-resistant steel, cyclic loading, fatigue, plastic deformation
Objavljeno: 18.08.2017; Ogledov: 516; Prenosov: 253
.pdf Celotno besedilo (2,42 MB)
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Dependence of warm or cold feeling and heat retention ability of knitwear from digital print parameters
Mladen Stančić, Dragana Grujić, Dragoljub Novaković, Nemanja Kašiković, Branka Ružičić, Jelka Geršak, 2014, izvirni znanstveni članek

Opis: Textile materials are increasingly being subjected to the process of printing. The printing process with its parameters significantly affects the properties of textile materials and clothes made from these materials. This paper examines the effect of the parameters of digital printing on thermo-physiological characteristics of printed textile materials. As the essential print parameters were selected tone value and a different number of passes. In this research were used knitted fabric materials of 100% cotton fibers (100% CO), 100% polyester fibers (100% PES) and their mixture (50%CO/50% PES). The influence of print parameters to thermo-physiological properties of the material is evaluated through a warm or cold feeling and heat retention ability. Results of the research demonstrated that, in addition to material composition, the printing process with its parameters have a significant influence on the thermo-physiological characteristics of textile materials.
Ključne besede: digital printing, textile materials, thermo-physiological comfort, warm of cold feeling, heat retention ability
Objavljeno: 09.08.2017; Ogledov: 526; Prenosov: 55
.pdf Celotno besedilo (934,30 KB)
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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, izvirni znanstveni članek

Opis: 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.
Ključne besede: welding simulations, numerical analysis, thermal analysis, simulations, transient heat conduction, moving heat source
Objavljeno: 07.07.2017; Ogledov: 556; Prenosov: 302
.pdf Celotno besedilo (975,43 KB)
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Geothermal heat potential - the source for heating greenhouses in Southestern Europe
Danijela Urbancl, Peter Trop, Darko Goričanec, 2016, izvirni znanstveni članek

Opis: The paper presents economically evaluated solutions for heating greenhouses with geothermal potential, if the same greenhouse is placed in two different locations in Southeastern Europe, one in Slovenia and the other in Serbia. The direct geothermal water exploitation using heat exchangers is presented and the remaining heat potential of already used geothermal water is exploited using high temperature heat pumps. Energy demands for heating greenhouses are calculated considering climatic parameters of both locations. Furthermore, different constructions materials are taken into account, and energy demands are evaluated if the same greenhouse is made of 4 mm toughened single glass, double insulated glass or polycarbonate plates. The results show that the geothermal energy usage is economically feasible in both locations, because payback periods are in range from two to almost eight years for different scenarios.
Ključne besede: geothermal heat exploitation, greenhouses energy demands, high temperature heat pump, economic analysis
Objavljeno: 07.07.2017; Ogledov: 613; Prenosov: 284
.pdf Celotno besedilo (1,02 MB)
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