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Non-Newtonian fluid flow through a planar symmetric expansion: shear thickenning fluids
Primož Ternik, Jure Marn, Zoran Žunič, 2006, izvirni znanstveni članek

Opis: The incompressible non-Newtonian fluid flow through a symmetric sudden expansion is studied numerically in order to obtain Reynolds number critical value. The Quadratic model is employed to accommodate the shear-thickening behavior of corn-starch and water mixture. Numerical procedure is validated with results for the Newtonian fluid flow in a range of the Reynolds number Re=10,20,.,100. Results for the non-Newtonian fluid show that the shear-thickening behavior lowers the threshold of the transition from flow symmetry to its asymmetry (lowers the onset of the bifurcation and the critical value of the Reynolds number) and increases the reattachment length. In addition, the results for the Quadratic model are compared to the results obtained with the Power law.
Ključne besede: fluid mechanics, bifurcation, sudden expansion, shear thickenningfluid, quadratic model, powr law
Objavljeno: 31.05.2012; Ogledov: 968; Prenosov: 22
URL Povezava na celotno besedilo

3.
Laminar flow of a shear-thickening fluid in a 90° pipe bend
Jure Marn, Primož Ternik, 2006, izvirni znanstveni članek

Opis: The non-Newtonian fluid flow in a sharp 90 curved pipe is studied numerically to obtain the pressure loss coefficient prompted by disagreement between the existing empirical correlations and results obtained by computer codes. This disagreement results from presumption of fully developed flow throughout the curvature (correlations) while the actual flow is partially developed for the Newtonian and sharp 90 curved bend non-Newtonian flows, and fully developed for slightly bent 90 curvature non-Newtonian flow. The Quadratic model is employed to accommodate the shear-thickening behavior of an electrostatic ash and water mixture. Numerical results are obtained for different values of Reynolds number. Finally, results for local pressure loss coefficient are compared with values obtained for the Power law rheological model.
Ključne besede: shear-thickening fluid, fluid dynamics, rheological model, pipe bend flow, numerical modelling, pressure losses
Objavljeno: 30.05.2012; Ogledov: 1118; Prenosov: 46
URL Povezava na celotno besedilo

4.
Symmetry breaking phenomena of purely viscous shear-thinning fluid flow in a locally constricted channel
Primož 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: 31.05.2012; Ogledov: 913; Prenosov: 51
URL Povezava na celotno besedilo

5.
CFD analysis of exothermic reactions in Al-Au nano multi-layered foils
Karlo 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: 01.06.2012; Ogledov: 959; Prenosov: 56
.pdf Celotno besedilo (526,41 KB)
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6.
7.
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: 1385; Prenosov: 14
URL Povezava na celotno besedilo

8.
Heat-transfer characteristics of a non-newtonian Au nanofluid in a cubical enclosure with differentially heated side walls
Primož 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: 16.03.2017; Ogledov: 435; Prenosov: 44
.pdf Celotno besedilo (736,13 KB)
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9.
Numerical study of heat-transfer enhancement of homogeneous water-Au nanofluid under natural convection
Primož Ternik, Rebeka Rudolf, Zoran Žunič, 2012, izvirni znanstveni članek

Opis: A numerical analysis is performed to examine the heat transfer of colloidal dispersions of Au nanoparticles in water (Au nanofluids). The analysis used a two-dimensional enclosure under natural convection heat-transfer conditions and has been carried out for the Rayleigh number in the range of 103 < Ra < 105, and for the Au nanoparticles' volume-fraction range of 0 < j < 0.10. We report highly accurate numerical results indicating clearly that the mean Nusselt number is an increasing function of both Rayleigh number and volume fraction of Au nanoparticles. The results also indicate that a heat-transfer enhancement is possible using nanofluids in comparison to conventional fluids. However, low Rayleigh numbers show more enhancement compared to high Rayleigh numbers.
Ključne besede: natural convection, nanofluid, heat transfer, numerical modelling
Objavljeno: 10.07.2015; Ogledov: 475; Prenosov: 54
URL Povezava na celotno besedilo
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10.
Numerical study of Rayleigh-Bénard natural-convection heat-transfer characteristics of water-based Au nanofluids
Primož 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: 10.07.2015; Ogledov: 438; Prenosov: 55
.pdf Celotno besedilo (282,00 KB)
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