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1.
Numerical analysis of fluid flow in a vial : [master thesis]
Žiga Časar, 2019, magistrsko delo

Opis: Lyophilization or freeze-drying is a widely used process in the pharmaceutical and food industry. In the process the solvent will be removed under extreme conditions of low temperature and low system pressures, whereby sublimation happens, the transition from the solid phase to the gas phase, with skipping the liquid phase, which happens bellow the triple point. This study focuses on numerical modeling at the start of the process, the so called primary drying. For this stage the highest mass flow rates of vapor are typical, since the driving force of the process is the pressure difference between the sublimation front and surrounding area. In this stage the non-bonded solvent is removed. Because of the extreme conditions the typical computational fluid dynamics approach is not suitable anymore and has to be corrected. One way to do this is to use additional models for fluid behavior at the solid wall. The study focuses on the influence of different boundary conditions on the solid wall, No-Slip, Free Slip and Maxwell Slip, and their effect on fluid flow inside the vial. A quantitative and qualitative comparison of the results is presented.
Ključne besede: Lyophilization, Knudsen number, computational fluid dynamics, fluid flow, numerical modeling, slip boundary condition
Objavljeno v DKUM: 09.07.2019; Ogledov: 1049; Prenosov: 165
.pdf Celotno besedilo (2,66 MB)

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Aerodynamic analysis of an oscillating airfoil in a power-extraction regime using the compressible Navier-Stokes equations with efficient and accurate low-speed preconditioning
Jernej Drofelnik, 2012, diplomsko delo

Opis: A wing that is simultaneously heaving and pitching may extract energy from an oncoming air flow, thus acting as turbine. The purpose of this study was to analyse the relationship between the aerodynamics and the theoretical performance of this device by means of timedependent laminar flow simulations performed with a research compressible finite volume Navier-Stokes solver COSA. In presented analyses, which confirm the findings of another independent study, the efficiency of the power extraction of this device can be of the order of 35 %, and such an efficient operating condition is characterized due to the favourable effects of a strong dynamic stall. This study is a part of a wider research programme of Dr. Campobasso’s group at University of Glasgow, aiming to develop a general-purpose computational framework for unsteady aerodynamic and aeroacoustic wind energy engineering. In view of aeroacoustic applications, the developed flow solver uses the compressible formulation of the Navier-Stokes equations with carefully optimized low-speed preconditioning. To demonstrate the modeling capabilities, the accuracy and the high computational performance of the developed low-speed preconditioning technology, the unsteady aerodynamics of the energy-extracting device is simulated by using a computationally challenging freestream Mach number of 0.001. A mixed preconditioning strategy that maintains both the nominal accuracy and the computational efficiency of the solver also for time-dependent low-speed problems is presented. A fundamental element of novelty of this study is a thorough assessment of the proposed approach partly based on the challenging and realistic problem associated with the oscillating wing device.
Ključne besede: Low-speed preconditioning, compressible multigrid Navier-Stokes solver, energy-extracting oscillating wing, computational fluid dynamics.
Objavljeno v DKUM: 06.07.2012; Ogledov: 2232; Prenosov: 158
.pdf Celotno besedilo (2,40 MB)

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Computational fluid dynamics by boundary-domain integral method
Leopold Škerget, Matjaž Hriberšek, G. Kuhn, 1999, izvirni znanstveni članek

Opis: A boundary-domain integral method for the solution of general transport phenomena incompressible fluid motion given by the Navier-Stokes equation set is presented. Velocity-vorticity formulation of the conservations is employed. Different integral representations for conservation field functions based on different fundamental solutions are developed. Special attention is given to the use of subdomain technique and Krylov subspace iterative solvers. The computed solutions of several benchmark problems agree well with available experimental and other computational results.
Ključne besede: fluid mechanics, fluid dynamics, numerical methods, boundary domain integral method, viscous fluid, heat transfer, diffusion-convective solution
Objavljeno v DKUM: 01.06.2012; Ogledov: 1910; Prenosov: 71
URL Povezava na celotno besedilo

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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 v DKUM: 01.06.2012; Ogledov: 2135; Prenosov: 97
URL Povezava na celotno besedilo

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Natural convection flows in complex cavities by BEM
Leopold Škerget, Matjaž Hriberšek, Zoran Žunič, 2003, izvirni znanstveni članek

Opis: A numerical method for the solution of Navier-Stokes equations is developed using an integral representation of the conservation equations. The velocity- vorticity formulation is employed, where the kinematics is given with the Poisson equation for a velocity vector, while the kinetics is represented with the vorticity transport equation. The corresponding boundary-domain integral equations are presented along with discussions of the kinetics and kinematics of the fluid flow problem. THE BEM formulation is developed and tested for natural convection flows in closed cavities with complex geometries.
Ključne besede: fluid dynamics, natural convection, boundary element method, differential equations, closed cavity
Objavljeno v DKUM: 01.06.2012; Ogledov: 1709; Prenosov: 78
URL Povezava na celotno besedilo

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The wavelet transform for BEM computational fluid dynamics
Jure 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: 1788; Prenosov: 89
URL Povezava na celotno besedilo

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