1. Conduction and convection heat transfer characteristics of water-based Au nanofluids in a square cavity with differentially heated side walls subjected to constant temperaturesPrimož Ternik, Rebeka Rudolf, 2014, izvirni znanstveni članek Opis: The present work deals with the natural convection in a square cavity filled with the water-based Au nanofluid. The cavity is heated on the vertical and cooled from the adjacent wall, while the other two horizontal walls are adiabatic. The governing differential equations have been solved by the standard finite volume method and the hydrodynamic and thermal fields were coupled together using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticles' volume fraction on the heat transfer characteristics of Au nanofluids at the given base fluid's (i.e. water) Rayleigh number. Accurate results are presented over a wide range of the base fluid Rayleigh number and the volume fraction of Au nanoparticles. It is shown that adding nanoparticles in a base fluid delays the onset of convection. Contrary to what is argued by many authors, we show by numerical simulations that the use of nanofluids can reduce the heat transfer rate instead of increasing it. Ključne besede: natural convection, heat transfer, nanofluid, Nusselt number Objavljeno v DKUM: 07.07.2017; Ogledov: 1257; Prenosov: 361 Celotno besedilo (834,69 KB) Gradivo ima več datotek! Več... |
2. Heat-transfer characteristics of a non-newtonian Au nanofluid in a cubical enclosure with differentially heated side wallsPrimož Ternik, Rebeka Rudolf, Zoran Žunič, 2015, izvirni znanstveni članek Opis: The present work deals with the laminar natural convection in a cubical cavity filled with a homogenous aqueous solution of carboxymethyl cellulose (CMC) based gold (Au) nanofluid obeying the power-law rheological model. The cavity is heated on the vertical and cooled from the adjacent wall, while the other walls are adiabatic. The governing differential equations were solved with the standard finite-volume method and the hydrodynamic and thermal fields are coupled using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticle volume fraction on the heat-transfer characteristics of CMC-based Au nanofluid over a wide range of the base-fluid Rayleigh number. Accurate numerical results are presented in the form of dimensionless temperature and velocity variations, the mean Nusselt number and the heat-transfer rate. It is shown that adding nanoparticles to the base fluid delays the onset of natural convection. In addition, numerical simulations showed that, just after the onset of natural convection, adding nanoparticles reduces the mean Nusselt number value for any given base-fluid Rayleigh number. Ključne besede: natural convection, CMC-Au nanofluid, heat transfer, Nusslet number Objavljeno v DKUM: 16.03.2017; Ogledov: 1372; Prenosov: 93 Celotno besedilo (736,13 KB) Gradivo ima več datotek! Več... |
3. Tokovne razmere v avtomobilski lakirnici: numerična in eksperimentalna analizaJure Marn, Zoran Žunič, Matjaž Ramšak, Primož Ternik, 2002, izvirni znanstveni članek Opis: V prispevku smo analizirali tokovne razmere v avtomobilski lakirni komori. Za reševanje Navier-Stokesovih enačb prostorskega toka nestisljive izotermne tekočine smo uporabili metodo nadzornih prostornin (CFX 5.4). Podrobno smo opisali potek izračuna, uporabljene robne in začetne pogoje, uporabljene metode za stabilizacijo numeričnih nihanj ter druge parametre, pomembne za izračun. Predstavili smo rezultate za ravninski in prostorski primer izračuna. Robni pogoji so bili določeni z meritvami na realni komori in to za primer brez avtomobila in z njim. Filter komore je bil upoštevan kot porozna snov s kvadratno funkcijo upora po podatkih proizvajalca, ki smo jih preverili z lastnimi meritvami padca tlakov. Objavljeno v DKUM: 10.07.2015; Ogledov: 1336; Prenosov: 40 Povezava na celotno besedilo |
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5. Non-Newtonian blood flow around healthy and regurgitated aortic valve with coronary blood flow involvedJure Marn, Jurij Iljaž, Zoran Žunič, Primož Ternik, 2012, izvirni znanstveni članek Opis: Most numerical simulations about aortic valve are discussing about the blood flow through prosthetic valves, therefore this study covers a biological aortic valve. In this paper the simulation of blood flow around the regurgitated valve as well as around the health valve have been investigated and is showing how the regurgitation affects the heart function and coronary blood flow. Furthermore it also covers the coronary blood flow and its affect on the blood motion around the valve and consequently on the possible calcification. The physical problem has been treated for the period of closed valve, because of the regurgitation, which occurs at that time. For this restriction the assumption of non-elastic geometry has been used. Also the non-Newtonian Power Law model for the blood rheology has been used; because of the regions of slowly moving blood. Results are showing that the coronary blood flow does not have a high impact on the blood motion and thus the calcification is more probable as well that the regurgitation has a strong affect on the heart function, like aortic pressure drop, increased left ventricle volume, etc. The calcification reason has also been stated, but needs some further investigation. This paper covers in detail the geometry of computational domain and physics, so the results can be easily repeated. Ključne besede: aortna zaklopka, regurgitacija, dinamika tekočin, nenewtonska tekočina Objavljeno v DKUM: 10.07.2015; Ogledov: 1367; Prenosov: 103 Povezava na celotno besedilo |
6. Numerical study of Rayleigh-Bénard natural-convection heat-transfer characteristics of water-based Au nanofluidsPrimož Ternik, Rebeka Rudolf, Zoran Žunič, 2013, izvirni znanstveni članek Opis: The present work deals with the natural convection in a square cavity filled with a water-based Au nanofluid. The cavity is heated from the lower and cooled from the adjacent wall, while the other two walls are adiabatic. Theg overning differential equations have been solved with the standard finite volume method and the hydrodynamic and thermal fields have been coupled using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticlesć volume fraction on the heat-transfer characteristics of Au nanofluids at a given base-fluid (i.e., water) Rayleigh number Rabf. Accurate results are presented over a wide range of the base-fluid Rayleigh numbers (102 £ Rabf £ 105) and the volume fraction of Au nanoparticles (0 % £ j £ 10 %). It is shown that adding nanoparticles to the base fluid delays the onset of convection. Contrary to what is argued by many authors, we show, with numerical simulations, that the use of nanofluids can reduce the heat transfer instead of increasing it. Ključne besede: Rayleigh-Bénard natural convection, water-Au nanofluid, heat transfer, numerical modelling Objavljeno v DKUM: 10.07.2015; Ogledov: 1384; Prenosov: 115 Celotno besedilo (282,00 KB) Gradivo ima več datotek! Več... |
7. On new approach to rheological modeling of an electrostatic ash and water - quadratic lawPrimož 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 v DKUM: 01.06.2012; Ogledov: 2407; Prenosov: 46 Povezava na celotno besedilo |
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9. CFD analysis of exothermic reactions in Al-Au nano multi-layered foilsKarlo Raić, Rebeka Rudolf, Primož Ternik, Zoran Žunič, Vojkan Lazić, Dragoslav Stamenković, Tatjana Tanasković, Ivan Anžel, 2011, izvirni znanstveni članek Opis: This work presents the possibility of numerical modelling using Computational Fluid Dynamics (CFD) in the field of nano-foils. The governing equations were solved using a Finite Volume Methodology (FVM). The computational domain was discretized using a uniform Cartesian grid with the appropriate mesh size along the x and y directions employing the corresponding number of grid points. The field variables were discretized at the cell centres and the spatial, as well as the time, derivatives were approximated using the second-order accurate numerical scheme. The time-evolution of the temperature and concentration fields, as well as the atomic diffusion coefficient, will be presented for the appropriate Al-Au nano-foil geometry and boundary conditions. Ključne besede: Au-Al nano-foils, finite volume method, temperature transfer, concentration transfer Objavljeno v DKUM: 01.06.2012; Ogledov: 1884; Prenosov: 105 Celotno besedilo (526,41 KB) Gradivo ima več datotek! Več... |
10. Symmetry breaking phenomena of purely viscous shear-thinning fluid flow in a locally constricted channelPrimož Ternik, 2008, izvirni znanstveni članek Opis: The goal of a present study is to investigate the effects of generalized Newtonian fluids on the threshold of the transition from flow symmetry to its asymmetry for the flow through a locally constricted channel. We consider purely viscous shear-thinning fluid and compare it with the Newtonian fluid. Fluid flow is studied numerically by solving the two dimensional momentum equations along with the continuity equation and the Carreau-Yasuda rheological model. We report systematic results in a range of generalized Reynolds number 250▫$leq$▫Re▫$leq$▫150 with a focus on its critical value. Results indicate that the shear-thinning viscous behaviour decreases the onset of bifurcation phenomena and the critical value of Reynolds number. Last but not least, a systematic grid refinement analysis and numerical accuracy study is performed and present numerical results may be treated as the benchmark. Ključne besede: bifurcation, inelastic shear-thinning fluid, Carreau-Yasuda model, numerical modelling Objavljeno v DKUM: 31.05.2012; Ogledov: 1996; Prenosov: 138 Povezava na celotno besedilo |