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The properties of the material gadolinium and the working agent used in the installation of magnetic refrigeration devices
Dorin Botoc, Jurij Avsec, Adrian Plesca, Georgel Gabor, Rusu Ionut, 2020, professional article

Abstract: Much remains to be done to understand better and thus achieve better control over magnetic materials to maximize their magnetocaloric properties and performance, specifically for gadolinium. A clear path forward is highlighted by thorough experiments coupled with theory, in which the latter is tested and re%ned against the former, thus resulting in discoveries of new and improved materials and bringing near-room-temperature magnetic refrigeration technology to fruition in the near future.
Keywords: Gadolinium, heat transfer, magneto-calorific, magnetic field
Published in DKUM: 01.12.2023; Views: 315; Downloads: 4
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Geometry design and analysis of an electric bus for the interior ther-mal modelling
Costica Nituca, Gabriel Chiriac, Georgel Gabor, Ilie Nucǎ, Vadim Cazac, Marcel Burduniuc, 2021, original scientific article

Abstract: The heating, ventilation and air-conditioning (HVAC) system represents the main auxiliary load for any type of bus. Being the most significant energy-consuming auxiliary load for the electric bus, it must be given special attention in an electric bus system design. To study the heat transfer and thermal optimization for passenger comfort in the electric bus computer-aided design (CAD) is used. The geometry of an electric bus interior is designed considering the main components of the vehicle: passenger cabin, driver’s cabin, windows, walls, and seats. Materials of the same type as those used in the real bus are considered for the geometry model. Based on the heat transfer theory, a thermal model and simulations are made for the heat transfer inside the electric bus. The simulated data are compared with measurement data, and based on these, it can be concluded that the thermal model of the electric bus can be validated and used further for a wide variety of thermal simulation types.
Keywords: heat transfer, electric bus, passenger comfort, geometry design, thermal modelling
Published in DKUM: 13.11.2023; Views: 195; Downloads: 3
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Static model of temperature distribution in a photovoltaic module
Klemen Sredenšek, Sebastijan Seme, Gorazd Hren, 2021, original scientific article

Abstract: The primary objective of this paper is to present a static model for calculating the temperature distribution in a photovoltaic module using the finite element method. The paper presents in more detail the theoretical background of solar radiation, heat transfer, and the finite element method. The results of the static model are evaluated using temperature measurements of a photovoltaic model, which were performed at the Institute of Energy Technology, Faculty of Energy Technology, University of Maribor. The results of the regression analysis show a good concurrence between the measured and modelled values of the temperature of the photovoltaic module, especially on days with a higher share of the direct component of solar radiation.
Keywords: photovoltaic module, temperature distribution, heat transfer, finite element method
Published in DKUM: 13.11.2023; Views: 172; Downloads: 5
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Fractal geometry as an effective heat sink
Matjaž Ramšak, 2022, original scientific article

Abstract: "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.
Keywords: fractal heat sink, LED cooling, CPU cooling, conjugate heat transfer, laminar flow, boundary element method, Koch snowflake
Published in DKUM: 14.07.2023; Views: 585; Downloads: 14
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Measurements of material heat transfer properties : master study programme
Miha Donša, 2022, master's thesis

Abstract: An experimental setup was created to observe temperature change at two points inside the experimental body. Such an experimental setup created data that was used as an anchor point of optimization that was coupled with numerical models to find unknown variables of heat conductivity and specific heat of the materials. Two numerical models were created. A 1D numerical model was created for possibilities of fast optimization ignoring the insulation and heat transfer through it. Such a model did not manage to describe the experimental setup accurately. Therefore, a 3D numerical model was created simulating the whole experimental setup and yielded much more promising results. Problems with the model were soon seen when experimental data was compared to the numerical solution where variables that were initially not taken into the account showed a much greater effect than first anticipated. Therefore, the 3D numerical model was adjusted to describe the experimental setup as accurately as possible. The experiment was done with two different materials. The materials were picked based on their heat conductivity (high and low). High heat conductivity material was easy to understand and to find a solution to it. With low conductivity material, some problems were quickly observed and as such created a lot of questions as to why and how to find the unknown variables of the material. It was then shown that the masses of the materials in the experiment and the length of the experiment played the most important role in the experiment and quickly explained why and how the experimental setup should be modified to obtain better results.
Keywords: heat transfer, material heat transfer properties, specific heat, heat conductivity, optimization, numerical simulation of heat transfer
Published in DKUM: 07.07.2022; Views: 721; Downloads: 41
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High-Perssure process design for polymer treatment and heat transfer enhancement
Gregor Kravanja, 2018, doctoral dissertation

Abstract: 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.
Keywords: supercritical fluids, PGSSTM, formulation of active drugs, biodegradable polymers, transport and thermodynamic data, pendant drop method, carbon sequestration, heat transfer coefficients
Published in DKUM: 28.05.2018; Views: 1578; Downloads: 221
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Matevž Frajnkovič, 2017, master's thesis

Abstract: 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.
Keywords: Heat transfer, cellular structure, porous materials, CFD
Published in DKUM: 24.08.2017; Views: 1633; Downloads: 205
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Multiple-effect evaporation in aluminosilicate technology
Dušan Klinar, Janvit Golob, 2001, professional article

Abstract: 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.
Keywords: chemical engineering, evaporation in silicate technology, bauxite alumina production, evaporators, process optimization, heat transfer, heat flow, empirical equations, heat transfer coefficients, zeolites
Published in DKUM: 24.08.2017; Views: 1485; Downloads: 105
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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, original scientific article

Abstract: 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.
Keywords: heat transfer, cooling of electronic devices, cooling fins, light emitting diode automotive lamp, compressible flow
Published in DKUM: 07.07.2017; Views: 1433; Downloads: 375
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Conduction and convection heat transfer characteristics of water-based Au nanofluids in a square cavity with differentially heated side walls subjected to constant temperatures
Primož Ternik, Rebeka Rudolf, 2014, original scientific article

Abstract: The present work deals with the natural convection in a square cavity filled with the water-based Au nanofluid. The cavity is heated on the vertical and cooled from the adjacent wall, while the other two horizontal walls are adiabatic. The governing differential equations have been solved by the standard finite volume method and the hydrodynamic and thermal fields were coupled together using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticles' volume fraction on the heat transfer characteristics of Au nanofluids at the given base fluid's (i.e. water) Rayleigh number. Accurate results are presented over a wide range of the base fluid Rayleigh number and the volume fraction of Au nanoparticles. It is shown that adding nanoparticles in a base fluid delays the onset of convection. Contrary to what is argued by many authors, we show by numerical simulations that the use of nanofluids can reduce the heat transfer rate instead of increasing it.
Keywords: natural convection, heat transfer, nanofluid, Nusselt number
Published in DKUM: 07.07.2017; Views: 1196; Downloads: 358
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