1. Optimizacija postopka ekstrakcije učinkovin iz arnike arnica montana in formulacija produktov : master's thesisÁlvaro Pequeno Alonso, 2022, magistrsko delo Opis: Arnica Montana je obetaven vir bioaktivnih spojin, predvsem fenolov, ki zaradi svoje antioksidativne aktivnosti izkazujejo koristi za zdravje ljudi. Da bi dosegli stopnjo farmacevtske uporabe, je treba cvetove Arnice Montana predelati v izdelek, ki je primeren za preživetje. V ta namen so bile izvedene različne ekstrakcijske tehnike z različnimi topili: hladna maceracija, ultrazvok, Soxhlet in superkritični CO2; uporabljena topila so bila etanol, metanol in mešanica etanola in vode 95:5 (v:v). Analiza, ki je vključevala ultravijolično/vidno spektrometrijo, je bila opravljena za merjenje antioksidativne aktivnosti in celotne vsebnosti fenolov v ekstraktih. Končno je bil organogel oblikovan z uporabo izvlečka, olja konoplje in voska riževih otrobov ter testiran glede njegove stabilnosti. V okviru tega dela je bil prvič formuliran organogel z visoko stabilnostjo, saj do sedaj v znanstveni literaturi ni bilo podatkov o tovrstni formulaciji. Za določitev njegovih reoloških lastnosti in topnosti v različnih topilih pri različnih temperaturnih pogojih bodo potrebne dodatne študije. Ključne besede: Arnica Montana, organogels, solvent extraction, phenolic compounds, isolation, formulation Objavljeno v DKUM: 13.07.2022; Ogledov: 420; Prenosov: 31 Celotno besedilo (2,03 MB) |
2. High-Perssure process design for polymer treatment and heat transfer enhancementGregor Kravanja, 2018, doktorska disertacija Opis: 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. Ključne besede: supercritical fluids, PGSSTM, formulation of active drugs, biodegradable polymers, transport and thermodynamic data, pendant drop method, carbon sequestration, heat transfer coefficients Objavljeno v DKUM: 28.05.2018; Ogledov: 1521; Prenosov: 220 Celotno besedilo (5,51 MB) |
3. Least metameric recipe formulationBoris Sluban, Olivera Šauperl, 2003, izvirni znanstveni članek Opis: The paper describes a variant of multi-illuminant strategy of colour match prediction calculation for the cases of CMC (l:c) and CIE94 colour differences. This strategy tries to minimize the colour differences (against a given standard) under several different illuminants. In case when a given standard, using the usual single-illuminant matching strategy, can not be matched non-metamerically by the colorants available, the multi-illuminant matching strategy tries to produce a more acceptable match by balancing the colour differences under several different illuminants. The theoretical concepts are illustrated by the colorimetric data of the corresponding laboratory samples produced by either strategy. The multi-illuminant-strategy regularly produced lower metamerism than the single-illuminant strategy did. Ključne besede: colorimetry, colour matching, recipe formulation, computer aided reciping, metamerism, colour differences Objavljeno v DKUM: 05.07.2017; Ogledov: 1297; Prenosov: 116 Celotno besedilo (104,42 KB) Gradivo ima več datotek! Več... |
4. Mixed boundary elements for laminar flowsMatjaž Ramšak, Leopold Škerget, 1999, izvirni znanstveni članek Opis: This paper presents a mixed boundary element formulation of the boundary domain integral method (BDIM) for solving diffusion-convective transport problems. The basic idea of mixed elements is the use of a continuos interpolation polynomial for conservative field function approximation and a discontinuous interpolation polynomial for its normal derivative along the boundary element. In this way, the advantages of continuous field function approximation are retained and its conservation is preserved while the normal flux values are approximated by interpolation nodal points with a uniquely defined normal direction. Due to the use of mixed boundary elements, the final discretized matrix system is overdetermined and a special solver based on the least squares method is applied. Driven cavity, natural and forced convection in a closed cavity are studied. Driven caviaty results at Re=100, 400 and 1000 agree better with the benchmark solution than Finite Element Method of Finite Volume Method results for the same grid density with 21 x 21 degrees of freedom. The average Nusselt number values for natural convection ▫$10^3$▫▫$le$▫Ra▫$le$▫▫$10^6$▫ agree better than 0.1% with benchmark solutions for maximal calculated grid desities 61 x 61 degrees for freedom. Ključne besede: fluid mechanics, incompressible fluid, laminar flow, velocity vorticity formulation, boundary element method, mixed boundary elements Objavljeno v DKUM: 01.06.2012; Ogledov: 2108; Prenosov: 94 Povezava na celotno besedilo |
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6. The wavelet transform for BEM computational fluid dynamicsJure Ravnik, Leopold Škerget, Matjaž Hriberšek, 2004, izvirni znanstveni članek Opis: A wavelet matrix compression technique was used to solve systems of linear equations resulting from BEM applied to fluid dynamics. The governing equations were written in velocity-vorticity formulation and solutions of the resulting systems of equations were obtained with and without wavelet matrix compression. A modification of the Haar wavelet transform, which can transformvectors of any size, is proposed. The threshold, used for making fully populated matrices sparse, was written as a product of a user defined factor and the average value of absolute matrix elements values. Numerical tests were performed to assert, that the error caused by wavelet compression depends linearly on the factor , while the dependence of the error on the share of thresholded elements in the system matrix is highly non-linear. The results also showed that the increasing non-linearity (higher Ra and Re numbervalues) limits the extent of compression. On the other hand, higher meshdensity enables higher compression ratios. Ključne besede: fluid mechanics, computational fluid dynamics, boundary element method, wavelet transform, linear systems of equations, velocity vorticity formulation, driven cavity, natural convection, system matrix compression Objavljeno v DKUM: 01.06.2012; Ogledov: 2042; Prenosov: 94 Povezava na celotno besedilo |
7. Numerical simulation of dilute particle laden flows by wavelet BEM-FEMJure Ravnik, Leopold Škerget, Matjaž Hriberšek, Zoran Žunič, 2008, izvirni znanstveni članek Opis: A wavelet transform based BEM and FEM numerical scheme was used to simulate laminar viscous flow. The velocity-vorticity formulation of the Navier-Stokes equations was used. The flow simulation algorithm was coupled with a Lagrangian particle tracking scheme for dilute suspensions of massless particles and particles without inertia. The proposed numerical approach was used to simulate flow and particle paths for two test cases: flow over a backward-facing step and flow past a circular cylinder. We present methods of calculating the pressure and stream function field at the end of each time step. The pressure field was used to calculate drag and lift coefficients, which enable qualitative comparison of our results with the benchmark. The stream function enabled the comparison of streamlines and massless particle paths in steady state low Reynolds number value flow fields, and thus provided an estimate on the accuracy of the particle tracking algorithm. Unsteady higher Reynolds number value flows were investigated in terms of particle distributions in vortex streets in the wake of the cylinder and behind the step. Sedimentation of particles without inertia was studied in the flow field behind a backward-facing step at Reynolds number value 5000. Ključne besede: boundary element method, velocity-vertocity formulation, discrete wavelet transform, Lagrangian particle tracking, backward-facing step, bluff body flow, dilute particle suspension Objavljeno v DKUM: 01.06.2012; Ogledov: 1957; Prenosov: 96 Povezava na celotno besedilo |
8. A multidomain boundary element method for unsteady laminar flow using stream function-vorticity equationsMatjaž Ramšak, Leopold Škerget, Matjaž Hriberšek, Zoran Žunič, 2005, izvirni znanstveni članek Opis: The paper deals with the Boundary Element Method (BEM) for modelling 2D unsteady laminar flow using stream function-vorticity formulation of the Navier-Stokes equations. The numerical algorithm for solving a general parabolic diffusion-convection equation is based on linear mixed elements and a multidomain model also known as subdomain technique. Robustness, accuracy and economy of the developed numerical algorithm is shown on a standard case of steady backward facing step flow and a periodic flow past a circular cylinder test case. Ključne besede: fluid mechanics, viscous fluid, unsteady laminar flow, boundary element method, multidomain model, stream function, vorticity formulation, backward facing step flow, flow past a cylinder Objavljeno v DKUM: 01.06.2012; Ogledov: 2104; Prenosov: 103 Povezava na celotno besedilo |
9. A multidomain boundary element method for two equation turbulence modelsMatjaž Ramšak, Leopold Škerget, 2005, izvirni znanstveni članek Opis: The paper deals with the multidomain Boundary Element Method (BEM) for modelling 2D complex turbulent flow using low Reynolds two equation turbulence models. While the BEM is widely accepted for laminar flow this is the first case, where this method is applied for complex flow problems using ▫$k-epsilon$▫ turbulence model. The integral boundary domain equations are discretised using mixed boundary elements and a multidomain method also known as subdomain technique. The resulting system matrix is overdetermined, sparse, block banded and solved using fast iterative linear least squares solver. The simulation of turbulent flow over a backward step is in excellent agreement with the finite volume method using the same turbulent model. Ključne besede: fluid mechanics, turbulent flow, boundary element method, incompressible viscous fluid, stream function-vorticity formulation, two equation turbulence model, backward facing step flow Objavljeno v DKUM: 01.06.2012; Ogledov: 2039; Prenosov: 98 Povezava na celotno besedilo |
10. Boundary domain integral method for high Reynolds viscous fluid flows in complex planar geometriesMatjaž Hriberšek, Leopold Škerget, 2005, izvirni znanstveni članek Opis: The article presents new developments in boundary domain integral method (BDIM) for computation of viscous fluid flows, governed by the Navier-Stokes equations. The BDIM algorithm uses velocity-vorticity formulation and is basedon Poisson velocity equation for flow kinematics. This results in accurate determination of boundary vorticity values, a crucial step in constructing an accurate numerical algorithm for computation of flows in complex geometries, i.e. geometries with sharp corners. The domain velocity computations are done by the segmentation technique using large segments. After solving the kinematics equation the vorticity transport equation is solved using macro-element approach. This enables the use of macro-element based diffusion-convection fundamental solution, a key factor in assuring accuracy of computations for high Reynolds value laminar flows. The versatility and accuracy of the proposed numerical algorithm is shown for several test problems, including the standard driven cavity together with the driven cavity flow in an L shaped cavity and flow in a Z shaped channel. The values of Reynolds number reach 10,000 for driven cavity and 7500 for L shapeddriven cavity, whereas the Z shaped channel flow is computed up to Re = 400. The comparison of computational results shows that the developed algorithm is capable of accurate resolution of flow fields in complex geometries. Ključne besede: fluid mechanics, numerical methods, boundary domain integral method, algorithms, incompressible fluid flow, Navier-Stokes equations, velocity vorticity formulation, segmentation technique, driven cavity flow Objavljeno v DKUM: 01.06.2012; Ogledov: 2003; Prenosov: 86 Povezava na celotno besedilo |