41. Volumetric properties of ethanol-water mixtures under high pressureAljana Petek, Darja Pečar, Valter Doleček, 2001, izvirni znanstveni članek Opis: Densities of ethanol-water mixtures have been measured using a vibrating tube densimeter and a different arrangement high-pressure experimental set-up. Measurements were carried out at 298,15 K in a pressure range from 0.1 MPa to 5MPa. Partial molar volumes, excess molar volumes and coefficients of isothermal compressibility were calculated. The molar volumes of alcohol and its partial molar volumes in mixtures with water are found to decrease monotonously with increasing pressure. Excess molar volumes are negative at all pressures. The numerical P-V relations at each composition are correlated satisfactorily as a function of pressure by the Hayward equation.
Ključne besede: chemistry, high-pressure vibrating tube densimeter, excess molar values, isothermal compressibility
Objavljeno v DKUM: 10.07.2015; Ogledov: 1507; Prenosov: 109
 Celotno besedilo (424,02 KB)
Gradivo ima več datotek! Več... |
42. Pressure stability of lipases and their use in different systemsMaja Leitgeb, Željko Knez, 2001, izvirni znanstveni članek Opis: For the investigation of the solvent impact on the enzymes, lipases from different sources (Pseudomonas fluorescences, Rhizopus javanicus, Rhizopus niveus, Candida rugose and Porcine pancreas) were used. Stability and activity of these lipases in aqueous medium in supercritical $CO_2$ and liquid propane at 100 bar and 40°C were studied.
On the basis of previous results lipases were used for their application in two different systems. The application of the polysulphone membrane in the continuous stirred tank membrane reactor was studied on the model system of the hydrolysis of oleyl oleate in propane at high pressure. As a catalyst the Candida rugosa lipase was used. The next utilization of lipases was the use of on silica arerogel self-immobilized lipase from Porcine pancreas as catalyst for esterification reaction in near-critical propane at 40°C and 100 bar.
Ključne besede: chemical processing, supercritical fluids, lipases, enzyme stability, high pressure membrane reactor
Objavljeno v DKUM: 10.07.2015; Ogledov: 1541; Prenosov: 198
Celotno besedilo (608,04 KB)
Gradivo ima več datotek! Več... |
43. Temperature and pressure dependence of volumetric properties for binary mixtures of n-heptane and n-octaneDarja Pečar, Valter Doleček, 2007, izvirni znanstveni članek Opis: The densities of n-heptane, n-octane and their binary mixtures were measured at 298.15, 323.15 and 348.15 K and within the pressure range 0.1 to 40 MPa using a vibrating tube densimeter. The reliability of this technique has been verified in our previous works. The partial molar volumes, excess molar volumes, isothermal compressibilities, isobaric thermal expansivities and internal pressures were calculated from the obtained densities. This study presents the dependence of densities, partial molar volumes, excess molar volumes, isothermal compressibilities, isobaric thermal expansivities and internal pressures on composition, temperature and pressure.
Ključne besede: density measurements, partial molar volume, excess molar volume, isothermal compressibility, isobaric thermal expansivity, internal pressure, n-heptane, n-octane
Objavljeno v DKUM: 10.07.2015; Ogledov: 1689; Prenosov: 125
Celotno besedilo (191,46 KB)
Gradivo ima več datotek! Več... |
44. |
45. Karakterizacija mehanskih lastnosti visokozmogljivih materialov za letalske aplikacije pri udarnih obremenitvahNika Sajko, 2012, magistrsko delo Opis: Določene komponente sodobnih tehnoloških napravah so pogosto izpostavljene udarnim obremenitvam. Če želimo optimirati takšne naprave (npr. turbine letalskih motorjev), moramo poznati mehanske lastnosti materiala pri visokih hitrostih obremenjevanja, saj te za večino kovin niso enake kot pri statičnih obremenitvah.
V magistrskem delu smo predstavili metodo za določanje dinamičnih lastnosti materiala in zasnovali napravo za testiranje kovinskih preizkušancev, t.i. Split Hopkinson Pressure Bar (SHPB), ki jo bomo v prihodnosti postavili na Fakulteti za strojništvo v Mariboru. Pripravili smo numerični model SHPB, na podlagi katerega lahko napovemo, kakšne napetostne signale lahko proizvedemo med testiranjem. Konstruirali smo tudi različne nove oblike preizkušancev, ki smo jih prav tako numerično preizkusili, in na podlagi rezultatov simulacij izbrali najbolj primerno obliko dog-bone preizkušanca. Ugotovili smo, da s spremembo geometrije preizkušanca vplivamo na napetostno stanje v njem, z dodanim utorom v preizkušancu ustvarimo namesto enoosnega večosno napetostno stanje. Predstavljen je tudi celotni eksperimentalni postopek in rezultati testiranj za dva različna materiala. Testiranja smo izvedli v Impact Engineering Laboratory na univerzi v Oxfordu.
Ključne besede: Split Hopkinson Pressure Bar, udarne obremenitve, karakterizacija materiala, numerične simulacije, LS-DYNA, dog-bone preizkušanci
Objavljeno v DKUM: 25.09.2012; Ogledov: 2585; Prenosov: 366
Celotno besedilo (5,62 MB) |
46. Donnan equilibrium and osmotic pressure in hollow polyelectrolyte microcapsulesDavid Haložan, Gleb B. Sukhorukov, Milan Brumen, Edwin Donath, Helmuth Möhwald, 2007, izvirni znanstveni članek Opis: A simple theoretical model of the Donnan equilibrium is applied to studies of distributions of ions between the external and internal volumes of hollow polyelectrolyte capsules as well as of concomitant osmotic pressure load on a capsule wall resulting from these distributions and the presence of polyanion. The model system consist of dispersed polyelectrolyte capsules in an electrolyte solution whereby two cases are considered with respect to the presence of the polyanion, either in the inner or external solution. It is assumed that the capsule wall is impermeable to polyanion, but water and all ions can freely penetrate. The model predictions are summarized by presenting the difference between the external pH, the pH of the inner solution and the osmotic pressure difference across the capsule wall, both in the dependence of sodium chloride concentration.
Ključne besede: biophysics, polyelectrolytes, polyelectrolyte capsules, Donnan equilibrium, osmotic pressure
Objavljeno v DKUM: 07.06.2012; Ogledov: 2176; Prenosov: 128
Celotno besedilo (141,11 KB)
Gradivo ima več datotek! Več... |
47. Particles formation and particle design using supercritical fluidsŽeljko Knez, Eckhard Weidner, 2003, pregledni znanstveni članek Opis: Major recent advances. Particle formation and design of solid particles and powdery composites with unique properties is at the moment a major developmentof supercritical fluids (synonymsČ dense gasses, dense fluids, highpressure) applications. This review will focus on recent advances and on fundamentals of these processes and their applications.
Ključne besede: chemical processing, high pressure technology, micronization, supercritical fluids, micro-particles, nano-particles, powder generation, crystallization, particles from gas saturated solutions
Objavljeno v DKUM: 01.06.2012; Ogledov: 3777; Prenosov: 110
 Povezava na celotno besedilo |
48. Multifunctional composites by high-pressure spray processesEckhard Weidner, Marcus Petermann, Željko Knez, 2003, pregledni znanstveni članek Opis: A series of spraying processes designed to generate powders and composites using supercritical fluids have been proposed in the past 15 years. In this review, thermo- and fluid-dynamic aspects and engineering principles are discussed and advantages of such technologies are demonstrated. These new techniques display convincing advantages, producing competitive high-quality products with tailor-made properties. Initial industrial applications have been achieved in the production of food products and fine-chemicals.
Ključne besede: chemical processing, high pressure technology, micronization, supercritical fluids, particles, powder generation, thermodynamics, fluid dynamics, PGSS
Objavljeno v DKUM: 01.06.2012; Ogledov: 2658; Prenosov: 105
Povezava na celotno besedilo |
49. Weakly coupled analysis of a blade in multiphase mixing vesselMatej Vesenjak, Zoran Ren, Matjaž Hriberšek, 2004, drugi znanstveni članki 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: 1877; Prenosov: 93
Povezava na celotno besedilo |
50. Preparation of WO[sub]3 aerogel catalysts using supercritical CO[sub]2Zoran Novak, Petra Kotnik, Željko Knez, 2004, izvirni znanstveni članek Opis: Single tungsten oxide aerogels (WO3), binary oxide aerogels (WO3-Al2O3) and ternary oxide aerogels (WO3-SiO2-Al2O3) were prepared using standard sol-gel route. Tungsten oxide tetraethoxide (WO(OCH2CH3)4) was used as the sol-gel precursor. The excellent properties of the gels obtained by the sol-gel synthesis were preserved upon supercritical drying with CO2. After supercritical drying at 40 °C and 100 bar, all aerogels were calcined to 800 °C. The influence of the synthesis parameters on the catalytic activity of WO3as supported on silica andžor alumina aerogels was investigated through thetransformation of N-(phosphonomethyl)iminodiacetic acid to N-(phosphonomethyl)glycine. Despite including WO3 into single and mixed silicaand alumina aerogels, high specific surface areas (284-653 m2 g-1) were preserved. Higher conversion was obtained for catalysts with higher ratios of WO3 in the mixed silica-alumina aerogels that were calcined at 800 °C.
Ključne besede: chemical processing, aerogels, catalysts, tungsten oxides, preparation of aerogels, characterisation of aerogels, supercritical CO2, supercritical drying, high pressure technology
Objavljeno v DKUM: 01.06.2012; Ogledov: 2113; Prenosov: 46
Povezava na celotno besedilo |
