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Numerical analysis of fluid flow in a vial
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: 09.07.2019; Ogledov: 660; Prenosov: 111
.pdf Celotno besedilo (2,66 MB)

Analysis of the effect of the swirl flow intensity on combustion characteristics in liquid fuel powered confined swirling flames
Marko Klančišar, Tim Schloen, Matjaž Hriberšek, Niko Samec, 2016, izvirni znanstveni članek

Opis: This article examines the implementation of CFD technology in the design of the industrial liquid fuel powered swirl flame burner. The coupling between the flow field and the combustion model is based on the eddy dissipation model. The choice of the LES (Large Eddy Simulation) turbulence model over standard RANS (Reynolds Averaged Navier-Stokes) offers a possibility to improve the quality of the combustion-flow field interaction. The Wall Adapting Local Eddy-Viscosity (WALE) sub-grid model was used. The reaction chemistry is a simple infinitely fast one step global irreversible reaction. The computational model was setup with the Ansys-CFX software. Through the detailed measurements of industrial size burner, it was possible to determine the natural operational state of the burner according to the type of fuel used. For the inlet conditions, axial and radial velocity components were calculated from known physical characteristics of both the fuel and air input, with the initial tangential velocity of the fuel assumed as 18% of the initial axial fuel velocity. Different swirl number (S) values were studied. Addition of a surplus (in comparison to conventional flame stabilization) of tangential air velocity component (W), the rotational component increases itself with a considerably high magnitude, contributing to the overall flame stabilization. The level of S especially influences the turbulent energy, its dissipation rate and turbulent (Reynolds) stresses. In the case of high swirl number values (S > 0,65) it is possible to divide the flow field in three principle areas: mixing area (fuel-air), where exothermal reactions are taking place, central recirculation area and outer recirculation area, which primarily contains the flow of burnt flue gases. The described model was used to determine the flow and chemical behavior, whereas the liquid atomization was accounted for by LISA (Linear Instability Sheet Atomization) model incorporating also the cavitation within injection boundary condition. The boundary conditions were determined based on the data from the experimental hot water system. Depending on system requirements, especially with continuous physical processes as well as the results of experimental measurements, the paper reports on determination of the mixing field and its intensity in the turbulent flow, the description of heat release and interaction of turbulent flow field and chemical kinetics in the case of confined swirling flames.
Ključne besede: CFD, fluid dispersion, combustion, industrial burner, confined swirling flame, two-phase flow
Objavljeno: 04.08.2017; Ogledov: 877; Prenosov: 310
.pdf Celotno besedilo (1,08 MB)
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Mixed boundary elements for laminar flows
Matjaž 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: 01.06.2012; Ogledov: 1490; Prenosov: 70
URL Povezava na celotno besedilo

On new approach to rheological modeling of an electrostatic ash and water - quadratic law
Primož Ternik, 2002, objavljeni znanstveni prispevek na konferenci

Opis: In the paper a new rheological model for an electrostatic ash and water mixture is proposed. The fundamental equation of the rheological model was used to determine the relationship between the shear stress and the shear rate as well as the equation of a velocity profile for the flow through a straight pipe. Experimental results obtained from a capillary viscometer were used as the basis to determine the parameters for the proposed model by the non-linear regression analysis. With the Quadratic law a numerical analysis of a mixture flow through a capillary pipe with the finite volume method was performed. The derived equations for the velocity profile, shear stress and shear rate were validated through a comparison of numerically obtained and theoretical results. Finally, the compariosn between the Quadratic and the Power law is presented.
Ključne besede: fluid mechanics, non-Newtonian fluids, mixture of electrofilter ash and water, flow in pipes, capillary pipes, rheological model, velocity profile, shear stress, finite volume method, numerical analysis, quadratic law, power law, mehanika fluidov
Objavljeno: 01.06.2012; Ogledov: 1715; Prenosov: 28
URL Povezava na celotno besedilo

Boundary element method for natural convection in non-Newtonian fluid saturated square porous cavity
Renata Jecl, Leopold Škerget, 2003, izvirni znanstveni članek

Opis: The main purpose of this work is to present the use of the Boundary Element Method (BEM) in the analysis of the natural convection in the square porous cavity saturated by the non-Newtonian fluid. The results of hydrodynamic and heat transfer evaluations are reported for the configuration in which the enclosure is heated from a side wall while the horizontal walls are insulated.The flow in the porous medium is modelled using the modified Brinkman extended Darcy model taking into account the non-Darcy viscous effects. The governing equations are transformed by the velocity-vorticity variables formulation enabling the computation scheme to be partitioned into kinematic and kinetic parts. To analyse the effects of the available non-Newtonian viscosity and to evaluate the presented approach, the power law model for shear thinning fluids (n<1), for shear thickening fluids (n>1) and in the limit for the Newtonian fluids (n=1) is considered. Numerical model is tested also for the Carreau model adequate for many non-Newtonian fluids. Solutions for the flow and temperature fields and Nusselt numbers are obtainedin terms of a modified Rayleigh number Ra*, Darcy number Da, and the non-Newtonian model parameters. The agreement between the results obtained with finite difference method is very good indicating that BEM can be efficiently used for solving transport phenomena in saturated porous medium.
Ključne besede: natural convection, non-Newtonian fluid, porous medium, cavity flow, boundary element method, boundary domain integral method
Objavljeno: 01.06.2012; Ogledov: 1246; Prenosov: 76
URL Povezava na celotno besedilo

Integral formulation of a diffusive-convective transport equation for reacting flows
Niko Samec, Leopold Škerget, 2004, izvirni znanstveni članek

Opis: This peper deals with a numerical solution of a diffusive-convective transport equation for reacting flows based on boundary domain integral formulation for diffusive-convective fundamental solution. A great part of attention has been dedicated to the numerical treatment of the diffusive-convective transport equation for high Pe number and reaction term values as the convective or reaction term becomes dominant compared to the diffusion one. In this case, the hyperbolic character predominates the ellipticity or parabolicity of the governing transport equation, and stability problems arise in the numerical solution. Numerical efficiency of the developed numerical implementation is tested against analytical and numerical results for the typical test cases of diffusive-convective transport problems (i.e. multicomponent reacting flows).
Ključne besede: fluid mechanics, boundary element method, diffusion, convection, transport problems, reacting flow
Objavljeno: 01.06.2012; Ogledov: 1133; Prenosov: 79
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Combined single domain and subdomain BEM for 3D laminar viscous flow
Jure Ravnik, Leopold Škerget, Zoran Žunič, 2009, izvirni znanstveni članek

Opis: A subdomain boundary element method (BEM) using a continuous quadratic interpolation of function and discontinuous linear interpolation of flux is presented for the solution of the vorticity transport equation and the kinematics equation in 3D. By employing compatibility conditions between subdomains an over-determined system of linear equations is obtained, which is solved in a least squares manner. The method, combined with the single domain BEM, is used to solve laminar viscous flows using the velocity vorticity formulation of Navier-Stokes equations. The versatility and accuracy of the method are proven using the 3D lid driven cavity test case.
Ključne besede: subdomain boundary element method, laminar viscous fluid flow, velocity-vorticity fomulation, lid driven cavity
Objavljeno: 01.06.2012; Ogledov: 1283; Prenosov: 83
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A multidomain boundary element method for unsteady laminar flow using stream function-vorticity equations
Matjaž 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: 01.06.2012; Ogledov: 1643; Prenosov: 84
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