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1.
Sustainable processing of materials using supercritical fluids : doktorska disertacija
Dragana Borjan, 2022, doctoral dissertation

Abstract: 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.
Keywords: 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
Published in DKUM: 11.10.2022; Views: 940; Downloads: 133
.pdf Full text (4,64 MB)

2.
Tok vode in onesnaževal skozi nenasičeno sredino
Simon Hajnc, 2016, master's thesis

Abstract: V magistrskem delu smo naredili simulacije toka padavinske vode in onesnaževala skozi nenasičeno cono vodonosnika na Apaškem polju s programom HYDRUS 1D. V ta namen smo pregledali obstoječo zakonodajo in navedli pomembne člene posamičnih uredb. Prav tako smo opisali teoretično dogajanje v nenasičeni coni, podrobneje obravnavali dušikov cikel v njej in fizikalni princip toka tekočine in transporta onesnaževala. Kot onesnaževalo smo v magistrski nalogi upoštevali razpadajoče gnojilo urea. Gnojilo urea razpade vse do nitrata, kateri je problematičen v vodonosniku na Apaškem polju. Izdelana je bila tudi validacija modela na primeru nitrifikacijske verige. Simulacije smo naredili za dva različna profila tal, in sicer za profil tal v Podgradu in profil tal v Segovcih ob Muri.
Keywords: HYDRUS 1D, simulacija toka vode in onesnaževala skozi nenasičeno cono, veriga razpada urea, nitrifikacija, nitrat v podzemni vodi, Apaško polje
Published in DKUM: 02.09.2016; Views: 2024; Downloads: 205
.pdf Full text (2,47 MB)

3.
Vpliv kontrolne enote in modela zgorevanja na tranzietno delovanje motorja
Aleš Cvikl, 2016, master's thesis

Abstract: Ena izmed glavnih težav osebnega dizelskega vozila so emisije in prav na tem področju se v bližnji prihodnosti obetajo morebitne spremembe. Zaradi visokih stroškov razvoja novih sistemov je sprva smiselno preveriti možnost zmanjšanja emisij zgolj s kontrolno enoto motorja. Tako je glavna ideja magistrskega dela prikaz izboljšanja izpusta emisij NOx pri hladnem zagonu, kjer je pretvorba emisij zaradi nizke temperature katalizatorja najslabša. Prikazano je, da lahko z zamikom vbrizga in vbrizganjem ogljikovodikov pred katalizator zmanjšamo izpust NOx pri hladnem zagonu z zgolj nekoliko povišano porabo goriva.
Keywords: EGR, emisije, SCR, UREA, NEDC, NOx
Published in DKUM: 31.03.2016; Views: 1047; Downloads: 149
.pdf Full text (3,38 MB)

4.
Primerjava fizikalnih modelov Adblue tekočine pri SCR sistemih ter vpliv mrež različnih gostot
Teo Milošič, 2013, undergraduate thesis

Abstract: Diplomska naloga predstavlja primerjavo fizikalnih modelov Adblue tekočine pri SCR sistemih. AdBlue tekočina je enkrat obravnavana kot več-komponentna zmes (vodna raztopina uree – UWS), drugič kot eno-komponentna zmes (voda), primerjava pa je pokazala vpliv izbire modela na rezultate CFD simulacije. Izvedena je bila tudi primerjava računskih mrež različnih gostot in s tem predstavljen vpliv velikosti celice računske mreže na rezultate. Simulacije in analize so bile narejene s programskim paketom AVL FIRE v2011.1. Analiza rezultatov simulacij vpliva izbire modela Adblue tekočine je pokazala, da je pri simulacijah SCR sistemov pravilneje uporabiti model, ki jo definira kot več-komponentno zmes (UWS). Analiza rezultatov simulacij z računskimi mrežami različnih velikosti celice pa je pokazala vpliv izbire velikosti celice na natančnost rezultatov.
Keywords: AdBlue, SCR sistemi, urea, redukcija NOx, metoda končnih volumnov, računalniška dinamika tekočin
Published in DKUM: 11.11.2013; Views: 2386; Downloads: 223
.pdf Full text (3,72 MB)

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