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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, objavljeni znanstveni prispevek na konferenci

Opis: 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.
Ključne besede: roll bond solar absorbers, thermal analysis, solar systems, heat pump systems, heating and cooling in residential buildings
Objavljeno v DKUM: 04.12.2023; Ogledov: 108; Prenosov: 7
.pdf Celotno besedilo (18,06 MB)
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Fractal geometry as an effective heat sink
Matjaž Ramšak, 2022, izvirni znanstveni članek

Opis: "How long is the coast of Britain?" was the question stated by Mandelbrot. Using smaller and smaller rulers the coast length limits to infinity. If this logic is applied to the fractal heat sink geometry, infinite cooling capacity should be obtained using fractals with mathematically infinite surface area. The aim of this article is to check this idea using Richardson extrapolation of numerical simulation results varying the fractal element length from one to zero. As expected, the extrapolated heat flux has a noninfinite limit. The presented fractal heat sink geometry is non-competitive to the straight fins.
Ključne besede: fractal heat sink, LED cooling, CPU cooling, conjugate heat transfer, laminar flow, boundary element method, Koch snowflake
Objavljeno v DKUM: 14.07.2023; Ogledov: 512; Prenosov: 11
.pdf Celotno besedilo (3,00 MB)
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Empirical modeling of liquefied nitrogen cooling impact during machining Inconel 718
Matija Hriberšek, Lucijano Berus, Franci Pušavec, Simon Klančnik, 2020, izvirni znanstveni članek

Opis: This paper explains liquefied nitrogen’s cooling ability on a nickel super alloy called Inconel 718. A set of experiments was performed where the Inconel 718 plate was cooled by a moving liquefied nitrogen nozzle with changing the input parameters. Based on the experimental data, the empirical model was designed by an adaptive neuro-fuzzy inference system (ANFIS) and optimized with the particle swarm optimization algorithm (PSO), with the aim to predict the cooling rate (temperature) of the used media. The research has shown that the velocity of the nozzle has a significant impact on its cooling ability, among other factors such as depth and distance. Conducted experimental results were used as a learning set for the ANFIS model’s construction and validated via k-fold cross-validation. Optimization of the ANFIS’s external input parameters was also performed with the particle swarm optimization algorithm. The best results achieved by the optimized ANFIS structure had test root mean squared error (test RMSE) = 0.2620, and test R$^2$ = 0.8585, proving the high modeling ability of the proposed method. The completed research contributes to knowledge of the field of defining liquefied nitrogen’s cooling ability, which has an impact on the surface characteristics of the machined parts.
Ključne besede: cryogenic machining, cooling impact, Inconel 718, machine learning, adaptive neuro-fuzzy inference system, particle swarm optimization
Objavljeno v DKUM: 14.07.2023; Ogledov: 315; Prenosov: 14
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Simulation of automotive air-conditioning system in 1D simulation software : diplomsko delo
Marko Copot, 2019, diplomsko delo

Opis: 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.
Ključne besede: 1D simulations, air-conditioning, HVAC, calibration, thermodynamics, cooling
Objavljeno v DKUM: 23.09.2019; Ogledov: 1263; Prenosov: 95
.pdf Celotno besedilo (1,54 MB)

Ground-sourced energy wells for heating and cooling of buildings
Heinz Brandl, Dietmar Adam, Roman Markiewicz, 2006, izvirni znanstveni članek

Opis: Energy wells are thermo-active elements for an economical extraction or storage of ground energy, similar to energy piles and other deep foundation elements also used as heat exchangers. Heating and/or cooling of buildings requires a primary and secondary thermo-active circuit, commonly connected by a heat pump. The paper gives several design aspects of energy wells which can be also used for the design of deep energy foundations. Thermal response tests have proved suitable for the in-situ determination of thermal ground properties required for an optimised design. Moreover, different systems of energy wells are discussed, and a comprehensive pilot research project is described.
Ključne besede: energy wells, energy foundations, geothermal geotechnics, geothermal heating/cooling, thermo-active structures, thermal ground properties, field testing
Objavljeno v DKUM: 17.05.2018; Ogledov: 928; Prenosov: 115
.pdf Celotno besedilo (4,24 MB)
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Cooling analysis of a light emitting diode automotive fog lamp
Matej Zadravec, Matjaž Ramšak, Jure Ravnik, Matjaž Hriberšek, Jernej Slanovec, 2017, izvirni znanstveni članek

Opis: Efficiency of cooling fins inside of a light emitting diode fog lamp is studied using computational fluid dynamics. Diffusion in heat sink, natural convection and radiation are the main principles of the simulated heat transfer. The Navier-Stokes equations were solved by the computational fluid dynamics code, including Monte Carlo radiation model and no additional turbulence model was needed. The numerical simulation is tested using the existing lamp geometry and temperature measurements. The agreement is excellent inside of few degrees at all measured points. The main objective of the article is to determine the cooling effect of various heat sink parts. Based on performed simulations, some heat sink parts are found to be very ineffective. The geometry and heat sink modifications are proposed. While radiation influence is significant, compressible effects are found to be minor.
Ključne besede: heat transfer, cooling of electronic devices, cooling fins, light emitting diode automotive lamp, compressible flow
Objavljeno v DKUM: 07.07.2017; Ogledov: 1351; Prenosov: 374
.pdf Celotno besedilo (2,09 MB)
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Weldability investigation steel P 91 by weld thermal cycle simulation
Marko Dunđer, Ivan Samardžić, Tomaž Vuherer, 2015, izvirni znanstveni članek

Opis: This paper elaborates results of hardness and impact energy of thermal cycle simulated specimens of high-alloy steel P 91 and their dependence on cooling time from 800 to 500 °C. Results were obtained by measuring hardness HV 1 and by experimental testing of Charpy notched specimens. Metallographic analysis of samples was performed on scanning electronic microscope.
Ključne besede: welding, P 91, hardness, impact energy, cooling
Objavljeno v DKUM: 03.07.2017; Ogledov: 2226; Prenosov: 111
.pdf Celotno besedilo (512,44 KB)
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The microstructure and properties of materials at the fusion line
Vladimir Gliha, 2005, izvirni znanstveni članek

Opis: In this paper, the formation of the HAZ that is caused by the thermal effects of welding is investigated from the theoretical and experimental points of view. Samples of the material found at the fusion line were prepared by simulating the thermal regimes that occur during welding. A number of CCT diagrams that are valid for the conditions during welding were designed, and the hardness and impact-toughness of the samples were measured. This information was then related to the results of metallographic examinations. The maximum temperature and the cooling rate of the applied thermal cycles were found to be decisive in terms of the properties of HAZ.
Ključne besede: welding, HAZ, thermal cycle, cooling rate, fusion line
Objavljeno v DKUM: 03.07.2017; Ogledov: 2033; Prenosov: 106
.pdf Celotno besedilo (270,09 KB)
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Impact energy analysis of quenched and tempered fine grain structural steel specimens after weld thermal cycle simulation
Marko Dunđer, Tomaž Vuherer, Ivan Samardžić, 2014, izvirni znanstveni članek

Opis: The paper presents impact energy results of thermal cycle simulated specimens of quenched and tempered fine grain structural steel S960QL. These results are obtained by examining notched Charpy specimens. Upon performed metallographic analysis and measured hardness, total impact energy is separated into ductile and brittle components.
Ključne besede: quenched and tempered fine grain structural steel, welding thermal cycle, impact energy, cooling time t8/5
Objavljeno v DKUM: 03.07.2017; Ogledov: 1123; Prenosov: 131
.pdf Celotno besedilo (1,18 MB)
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Effect of cooling rate on the microstructure of an Al94Mn2Be2Cu2 alloy
Tonica Bončina, Boštjan Markoli, Franc Zupanič, 2012, izvirni znanstveni članek

Opis: In this study the effect of the cooling rate on the microstructure of Al94 Mn2 Be2 Cu2 alloy was investigated. The vacuum induction melted and cast alloy was exposed to different cooling rates. The slowest cooling rate was achieved by the DSC (10 K·min^−1), the moderate cooling rate succeeded by casting in the copper mould (≈1 000 K·s−1) and the rapid solidification was performed by melt spinning (up to 10^6 K·s^−1). The microstructure of the DSC-sample consisted of α-Al matrix, and several intermetallics: τ1-Al29 Mn6 Cu4 , Al4 Mn, θ-Al2 Cu and Be4 Al(Mn,Cu). The microstructures of the alloy at moderate and rapid cooling consisted of the α-Al matrix, i-phase and θ-Al2 Cu. Particles of i-phase and θ-Al2 Cu were much smaller and more uniformly distributed in melt-spun ribbons.
Ključne besede: Al-alloy, metallography, microstructure, cooling rate, solidification
Objavljeno v DKUM: 03.07.2017; Ogledov: 878; Prenosov: 97
.pdf Celotno besedilo (231,30 KB)
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