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1.
Hydrogen production using a thermochemical cycle
Jurij Avsec, Urška Novosel, Dušan Strušnik, 2022, izvirni znanstveni članek

Opis: Sustainable methods of clean fuel production are needed throughout the world due to depleting oil reserves and the need to reduce carbon dioxide emissions. The technology based on fuel cells for electricity production or the transport sector has already been developed. However, a key missing element is a large-scale method of hydrogen production. The copper-chlorine (CuCI) combined thermochemical cycle is a promising thermochemical cycle that can produce large amounts of cheap hydrogen. A particularly promising part of this process is its use in combination with nuclear or thermal power plants. This paper focuses on a CuCl cycle and describes the models used to calculate thermodynamic and transport properties. This paper discusses the mathematical model for computing the thermodynamic properties for pure HCl and CuCl2. The mathematical model developed for the solid phase takes into account vibrations of atoms in molecules and intermolecular forces. This mathematical model can be used for the calculation of the thermodynamic properties of polyatomic crystals on the basis of the Einstein and Debye equations. The authors of this paper developed the model in the low temperature and high temperature region. All the analytical data have been compared with some experimental results and show a relatively good match. For the solid phase, the authors developed a model to calculate thermal conductivity based on electron and phonon contributions.
Ključne besede: thermodynamics, energy, hydrogen production, solid phase, fluid phase
Objavljeno v DKUM: 30.10.2023; Ogledov: 185; Prenosov: 4
.pdf Celotno besedilo (685,49 KB)
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2.
Sustainable processing of materials using supercritical fluids : doktorska disertacija
Dragana Borjan, 2022, doktorska disertacija

Opis: Supercritical fluids (SCFs) are powerful solvents with many unique properties. They have great potential for many processes, from extraction to chemical reactions and recycling. Accordingly, phase equilibrium data and thermodynamic and transport properties measurements in systems with a supercritical phase, as well as reliable and versatile mathematical models of the phase equilibrium thermodynamics, are needed for the process design and economic feasibility studies. The dissertation focuses on the benefits of supercritical fluid technology and consists of three main sections. The first section includes studies of the phase equilibria of the binary gas-alcohol and gas-urea derivatives. The influence of pressure and temperature on the system behaviour (solubility, viscosity, density, interfacial tension, melting point curve) was investigated. Most of the experiments were carried out with a high-pressure optical view cell, with minor modifications of the apparatus and measurement principle to determine mentioned thermodynamic and transport properties. The second part of the dissertation deals with the recovery of extracts from natural materials. Special interest is oriented towards supercritical fluid extracts, characterised by strong biological activities, especially antimicrobial and antioxidant properties. Supercritical fluid extraction has been performed on a semi-continuous apparatus (at pressures of 150 bar and 250 bar and temperatures of 313.15 K and 333.15 K for oregano extraction; and at pressures of 100 bar and 300 bar and temperatures of 313.15 K and 333.15 K for red beetroot extraction) and various methods such as the microdilution method and the DPPH method were used to determine antimicrobial and antioxidant activity. In the third part, an overview of different methods for recycling carbon fibre reinforced composites is given, including chemical recycling with supercritical fluids. This field has not been well explored, and the approach is relatively new but very interesting from a sustainable point of view. For an economically feasible process design, the thermodynamic and mass transfer data have to be determined. The principles of the future lab- and pilot-scale operations demand these supporting data be known. The results obtained in the frame of this study represent the high added value in the scientific field. They are essential to design and modify processes that yield products that cannot be achieved with conventional production processes.
Ključne besede: supercritical fluids, alcohols, urea, phase equilibria, viscosity, density, interfacial tension, modified capillary method, isolation methods, supercritical fluid extraction, pharmacological activity, carbon fiber reinforced composites, recycling techniques
Objavljeno v DKUM: 11.10.2022; Ogledov: 763; Prenosov: 114
.pdf Celotno besedilo (4,64 MB)

3.
Analysis of the effect of the swirl flow intensity on combustion characteristics in liquid fuel powered confined swirling flames
Marko Klančišar, Tim Schloen, Matjaž Hriberšek, Niko Samec, 2016, izvirni znanstveni članek

Opis: This article examines the implementation of CFD technology in the design of the industrial liquid fuel powered swirl flame burner. The coupling between the flow field and the combustion model is based on the eddy dissipation model. The choice of the LES (Large Eddy Simulation) turbulence model over standard RANS (Reynolds Averaged Navier-Stokes) offers a possibility to improve the quality of the combustion-flow field interaction. The Wall Adapting Local Eddy-Viscosity (WALE) sub-grid model was used. The reaction chemistry is a simple infinitely fast one step global irreversible reaction. The computational model was setup with the Ansys-CFX software. Through the detailed measurements of industrial size burner, it was possible to determine the natural operational state of the burner according to the type of fuel used. For the inlet conditions, axial and radial velocity components were calculated from known physical characteristics of both the fuel and air input, with the initial tangential velocity of the fuel assumed as 18% of the initial axial fuel velocity. Different swirl number (S) values were studied. Addition of a surplus (in comparison to conventional flame stabilization) of tangential air velocity component (W), the rotational component increases itself with a considerably high magnitude, contributing to the overall flame stabilization. The level of S especially influences the turbulent energy, its dissipation rate and turbulent (Reynolds) stresses. In the case of high swirl number values (S > 0,65) it is possible to divide the flow field in three principle areas: mixing area (fuel-air), where exothermal reactions are taking place, central recirculation area and outer recirculation area, which primarily contains the flow of burnt flue gases. The described model was used to determine the flow and chemical behavior, whereas the liquid atomization was accounted for by LISA (Linear Instability Sheet Atomization) model incorporating also the cavitation within injection boundary condition. The boundary conditions were determined based on the data from the experimental hot water system. Depending on system requirements, especially with continuous physical processes as well as the results of experimental measurements, the paper reports on determination of the mixing field and its intensity in the turbulent flow, the description of heat release and interaction of turbulent flow field and chemical kinetics in the case of confined swirling flames.
Ključne besede: CFD, fluid dispersion, combustion, industrial burner, confined swirling flame, two-phase flow
Objavljeno v DKUM: 04.08.2017; Ogledov: 1312; Prenosov: 381
.pdf Celotno besedilo (1,08 MB)
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4.
Weakly coupled analysis of a blade in multiphase mixing vessel
Matej Vesenjak, Zoran Ren, Matjaž Hriberšek, 2004, kratki znanstveni prispevek

Opis: Two or more physical systems frequently interact with each other, where the independent solution of one system is impossible without a simultaneous solution of the others. An obvious coupled system is that of a dynamic fluid-structure interaction. š8đ In this paper a computational analysis of thefluid-structure interaction in a mixing vessel is presented. In mixing vessels the fluid can have a significant influence on the deformation of blades during mixing, depending on speed of mixing blades and fluid viscosity.For this purpose a computational weakly coupled analysis has been performed to determine the multiphase fluid influences on the mixing vessel structure. The multiphase fluid field in the mixing vessel was first analyzed with the computational fluid dynamics (CFD) code CFX. The results in the form of pressure were then applied to the blade model, which was the analysed with the structural code MSC.visualNastran forWindows, which is based on the finiteelement method (FEM).
Ključne besede: fluid mechanics, solid mechanics, coupled problems, computational analysis, two-phase fluid, mixing blade, pressure distribution, finite volume method, finite element method
Objavljeno v DKUM: 01.06.2012; Ogledov: 1661; Prenosov: 91
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