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The development of a new process for gentle drying, micronisation and formulation of a high viscous biopoymer
Christian Reibe, 2011, doktorska disertacija

Opis: Biopolymers are characterised by their biodegradable behaviour in certain environments. Especially the development of natural biopolymers from renewable resources is gathering increasing interest in the scientific as well as in the industrial sectors . Since Biopolymers may be tailored to specific requirements, the encapsulation of pharmaceutical compounds or flavours in biopolymers would open wide avenues for the production of controlled- release systems. Most common mechanical pulverisation processes are milling and grinding. With these processes it is not possible to produce specific morphologies like foams or hollow spheres, but always splintered edges. Encapsulation is carried out by common precipitation techniques. Gelatine, as a widely applied biopolymer, represents one example of those substances of large interest, but it is difficult to process. Especially gelatines with high molecular mass are difficult or almost impossible to be pulverized by spray drying techniques, due to their high viscosity. In the frame of this research work, an integrated high-pressure spraying, drying and pulverization process for high viscous gelatine was developed, based on a combination of the water removing effects "Evaporation" and "Gas-solubility". The resulting products were dry, free-flowing gelatine powders, still exhibiting high molecular masses. Due to the new, gentle method of processing, a completely new gelatine product with unique properties was obtained. Even the encapsulation of edible oil in high ratios was found to be possible with this new process. The characterisation was carried out by standard methods for gelatine on the one hand side, and standard procedures for characterising powders on the other hand side. The developed process was patented under the identifier "WO 002009135601 A1".
Ključne besede: High Pressure Process, Supercritical Fluids, High molecular mass Gelatine, Micronisation, CO-2 - spray drying, Encapsulation, Gelatine Powder
Objavljeno: 26.01.2011; Ogledov: 2158; Prenosov: 56
.pdf Polno besedilo (24,89 MB)

Analytical calculation of nanofluid flow in rectangular mini-channels and micro-channels
Jurij Avsec, Maks Oblak, 2006, objavljeni povzetek znanstvenega prispevka na konferenci

Ključne besede: therodynamics, statistical nano-mechanics, fluid flow, nanofluids, thermal conductivity, pure fluids, mathematical model
Objavljeno: 30.05.2012; Ogledov: 1205; Prenosov: 3
URL Polno besedilo (0,00 KB)

Influence of temperature and pressure during PGSS[sup]TM micronization and storage time on degree of crystallinity and crystal forms of monostearate and tristearate
Zoran Mandžuka, Željko Knez, 2008, izvirni znanstveni članek

Opis: For controlling the degree of crystallinity and crystal form during particle formation using supercritical fluids, knowledge of pressure influence on solid-liquid-gas (S-L-G) equilibrium and solubility data of the system is crucial. S-L-G equilibrium data were determined in pressure range from 50 to 600 bar for systems monostearate/CO2 and tristearate/CO2 using a high-pressure view cell. Results showed a temperature minimum for both systems.The solubilities of CO2 in liquid glycerides were high: maximum solubilities, which were determined at temperatures 70 and 90 °C and pressure range from 50 to 450 bar, were from 50 to 90 mol%. Physical characteristics of micronized monostearate and tristearate samples were studied in detail after micronization and after 3 months of storage at 20 °C.
Ključne besede: chemical processing, high pressure technology, supercritical fluids, micronization, fine particles, Particles from Gas Saturated Solution, degree of crystallinity
Objavljeno: 31.05.2012; Ogledov: 792; Prenosov: 11
URL Polno besedilo (0,00 KB)

Comparison of the performances of absorption refrigeration cycles
Zvonimir Črepinšek, Darko Goričanec, Jurij Krope, 2009, izvirni znanstveni članek

Opis: This paper compares the performance of absorption refrigeration cycles that are used for refrigeration temperatures below 0°C. Since the most common vapor absorption refrigeration systems use ammonia-water solution with ammonia as the refrigerant and water as the absorbent, research has been devoted to improvement of the performance of ammonia-water absorption refrigeration systems in recent years. In this paper the performances of the ammonia-water and possible alternative cycles as ammonia-lithium nitrate, ammonia-sodium thiocyanate, monomethylamine-water, R22-DMEU, R32-DMEU, R124-DMEU, R152a-DMEU,R125-DMEU, R134a-DMEU, trifluoroethanol (TFE)-tetraethylenglycol dimethylether (TEGDME), methanol-TEGDME and R134a-DMAC are compared in respect of the coefficient of performance (COP) and circulation ratio (f). The highest COP and the lowest f, were found as a function of the generator, condenser, absorber and evaporating temperature.
Ključne besede: absorption, refrigeration, working fluids, COP, circulation ratio, waste heat
Objavljeno: 31.05.2012; Ogledov: 975; Prenosov: 7
URL Polno besedilo (0,00 KB)

Magnetic particle separation in viscous flows by BEM
Matjaž Hriberšek, Jure Ravnik, Primož Kocutar, 2011, objavljeni znanstveni prispevek na konferenci

Opis: A boundary element method based solver for particle motion simulation in dilute suspensions under the influence of hydrodynamic and magnetic forces was applied. The Euler-Lagrangian formulation for simulation of dilute two-phase flow was applied. The algorithm solves the incompressible Navier-Stokes equations written in velocity-vorticity formulation. The non uniform magnetic field was defined analytically for the case of a set of long thin wires. The particle trajectories were computed by applying the 4th order Runge-Kutta method. The computed test case consisted of a narrow channel under the influence of a nonuniform magnetic field, where magnetite and aluminium particles were suspended in water. The results of computations show the distributions of particles along the channel and confirms the suitability of the proposed configuration as a separation device under ideal conditions.
Ključne besede: boundary element method, laminar flow, magnetic particles, viscous fluids
Objavljeno: 01.06.2012; Ogledov: 772; Prenosov: 3
URL Polno besedilo (0,00 KB)

Turning of high quality aluminium alloys with minimum costs
Marko Reibenschuh, Franc Čuš, Uroš Župerl, 2011, izvirni znanstveni članek

Opis: Turning is one of the most common metal cutting procedures used. To optimize such a cutting process, some adaptations must be made. Implementing tool wear conditioning and the use of dry cutting can significantly lower the production cost. This research focuses on the cost effectiveness of using dry cutting in comparison with the use of cutting fluids and the use of different tool geometry. A series of tests was conducted and in the end the results are given.
Ključne besede: aluminium, cutting fluids, production costs, turning
Objavljeno: 01.06.2012; Ogledov: 562; Prenosov: 1
.pdf Polno besedilo (315,97 KB)

Influence of material pre-treatment with supercritical fluids on extraction efficiency of flavonoids
Katja Makovšek, Mojca Škerget, Željko Knez, 2012, objavljeni znanstveni prispevek na konferenci

Ključne besede: materials, supercritical fluids, flavonooids
Objavljeno: 01.06.2012; Ogledov: 821; Prenosov: 14
URL Polno besedilo (0,00 KB)

Enzymatic reactions in dense gases
Željko Knez, 2009, pregledni znanstveni članek

Opis: The developments on applications of supercritical fluids as alternative solvents for biocatalytic processes that have taken place over the past two decades have been reviewed. An overview of process parameters influencing enzyme activity and stability, the influence of process parameters on reaction rates and productivity are presented. Applications of various types of reactors for enzymatic reaction in dense fluids, limitations of using enzymes as biocatalyst in supercritical fluids as well as future trends are presented. Main advantages of using dense gases as solvents for biocatalyzed reactions are the tunability of solvent properties and simple down stream processing features that can be readily combined with other unit operations. Although many enzymes are stable in supercritical fluids (SCFs) one should pay considerable attention to finding the correct reaction conditions for each substrate/enzyme/SCF system. One of the persistent problems is the instability and deactivation of enzymes under pressure and temperature. At present the most stable enzymes are hydrolases (lipases and esterases) for which pressure effect is lower than temperature deactivation.
Ključne besede: biocatalysis, supercritical fluids, enzyme bioreactors, heterogeneous biocatalysis
Objavljeno: 01.06.2012; Ogledov: 802; Prenosov: 2
URL Polno besedilo (0,00 KB)

Phase equilibria in systems containing [alpha]-tocopherol and dense gas
Mojca Škerget, Petra Kotnik, Željko Knez, 2003, izvirni znanstveni članek

Opis: Solubility of ▫$alpha$▫-tocopherol in CO2 and propane was determined at temperatures 303, 313, 333 and 353 K and over a pressure range from 79 to 286 bar for CO2 and 16 to 112 bar for propane. A static-analytic method was applied. The solubility of ▫$alpha$▫-tocopherol in dense CO2 under the conditions investigated was in the range of 0.2-17.0 mg/g CO2. The maximal solubilities of ▫$alpha$▫-tocopherol in propane were approximately up to ten times higher than in CO2 and were in the range from 38.9 to 171.9 mg/g propane. Phase equilibrium data for Milk Thistle seed oil in supercritical CO2 were determined at temperatures 313, 333 and 353 K and pressures ranging from 100 to 300 bar. The oil was previously additionally vitaminized and contained 1.9 wt.% of ▫$alpha$▫-tocopherol and 1.7 wt.% of free fatty acids (FFA). The solubility of oil in CO2 was in the range from 1.3 to 17.9 mg/g CO2. The distribution coefficients of ▫$alpha$▫-tocopherol and FFA between light and heavy phase were determined on a solvent free basis. The obtained separation factors increased with temperature and pressure to approximately 160-200 bar and decreased with a further increase of pressure.
Ključne besede: chemical processing, supercritical fluids, phase equilibria, separation factors, vitamin E, CO2, dense gases
Objavljeno: 01.06.2012; Ogledov: 769; Prenosov: 4
URL Polno besedilo (0,00 KB)

Multifunctional composites by high-pressure spray processes
Eckhard 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: 01.06.2012; Ogledov: 982; Prenosov: 1
URL Polno besedilo (0,00 KB)

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