Bresterniska ulica 163

Brestrnica, Slovenia

Bresterniska ulica 163

Brestrnica, Slovenia
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Ternik P.,Bresterniska ulica 163 | Zadravec M.,University of Zagreb | Rudolf R.,University of Zagreb | Rudolf R.,Zlatarna Celje d.d.
Science of Sintering | Year: 2017

The present study deals with the numerical analysis of the solidification process of a NiTi binary alloy. The physical medium is taken as an incompressible fluid where the heat is transferred by conduction and convection, including the thermal phase change phenomenon. The energy equation, which includes both convection-diffusion heat transfer and a mushy region for the phase-change (solidification), is modelled by using an enthalpy-based formulation. The numerical approach is based on the finite volume method in body fitted coordinates with a PISO scheme to couple the pressure and velocity fields. The results are presented for the temperature field, as well as for the NiTi mass fraction during the solidification process. © 2016 Authors.


Raic K.T.,University of Belgrade | Rudolf R.,University of Maribor | Ternik P.,Bresterniska ulica 163 | Zunic Z.,AVL AST | And 3 more authors.
Materiali in Tehnologije | Year: 2011

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.


Ternik P.,Bresterniska ulica 163 | Rudolf R.,University of Maribor | Rudolf R.,Zlatarna Celje d.d.
International Journal of Simulation Modelling | Year: 2012

Numerical analysis is performed to examine the heat transfer enhancement of Au, Al 2O 3, Cu and TiO 2 water-based nanofluids. The analysis uses a two-dimensional enclosure under natural convection heat transfer conditions and has been carried out for the Rayleigh number range 10 3 ≤ Ra ≤ 10 5, and for the nanoparticles' volume fraction range 0 ≤ φ ≤ 0,10. The governing equations were solved with the standard finite-volume method and the hydrodynamic and thermal fields were coupled together using the Boussinesq approximation. Highly accurate numerical results are presented in the form of average Nusselt number and heat transfer enhancement. The results indicate clearly that the average Nusselt number is an increasing function of both, Rayleigh number and volume fraction of nanoparticles. The results also indicate that heat transfer enhancement is possible using nanofluids in comparison to conventional fluids, resulting in the compactness of many industrial devices. However, low Rayleigh numbers show more enhancement compared to high Rayleigh numbers. © 2012 DAAAM International Vienna.


Ternik P.,Bresterniska ulica 163 | Rudolf R.,University of Maribor | Zunic Z.,AVL AST
Materiali in Tehnologije | Year: 2013

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. The governing 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 nanoparticles' 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 % ≤ φ ≤ 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 numericalsimulations, that the use of nanofluids can reduce the heat transfer instead of increasing it.


Ternik P.,Bresterniska ulica 163 | Rudolf R.,University of Maribor | Zunic Z.,AVL AST
Materiali in Tehnologije | Year: 2012

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 10 3 ≤ Ra ≤ 10 5, and for the Au nanoparticles' volume-fraction range of 0 ≤ φ ≤ 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.


Ternik P.,Bresterniska ulica 163 | Rudolf R.,University of Maribor
International Journal of Simulation Modelling | Year: 2013

The present work deals with the laminar natural convection in a square cavity with differentially heated side walls subjected to constant temperatures and filled with homogenous 0,4 wt. % aqueous solution of carboxymethyl cellulose (CMC) based Au, Al2O3, Cu and TiO2 nanofluids obeying the Power law rheological model. The governing differential equations have been solved by the standard finite volume method and the hydrodynamic and thermal fields are coupled together using the Boussinesq approximation. The main objective of this study is to investigate the influence of the nanoparticles' volume fraction (0% ≤ φ ≤ 10%) on the heat transfer characteristics of CMC based nanofluids over a wide range of nanofluid Rayleigh number (103 ≤ Ranf ≤ 106). Accurate numerical results are presented in the form of dimensionless temperature and velocity variations, isotherms, mean Nusselt number and heat transfer enhancement. The results indicate clearly that the heat and momentum transfer characteristics are affected only by the nanofluid Rayleigh number, while the type of nanoparticles (i.e. thermo-phyisical properties) and their volume fraction have effect only on the heat transfer enhancement. © 2013 DAAAM International Vienna all rights reserved.


Bilus I.,University of Maribor | Ternik P.,Bresterniska ulica 163 | Zunic Z.,AVL AST D.O.O.
Journal of Fluids and Structures | Year: 2011

The steady flow of generalized Newtonian fluid around a stationary cylinder placed between two parallel plates was studied numerically. Finite volume method was applied to solve the momentum equations along with the continuity equation and the Power law rheological model within the laminar flow regime for a range of the Reynolds number Re and the Power law index n values. The values of the Reynolds number, based on physical and rheological properties, cylinder radius and bulk velocity, were varied between 0.0001≤Re≤10, while the Power law index values mapped the 0.50≤n≤1.50 range, allowing for the investigation of both shear-thinning and shear-thickening effects at the creeping as well as slowly moving fluid flow conditions. We report accurate results of a systematic study with a focus on the most important characteristics of fluid flow past circular cylinder. It is shown that for the creeping flow regime there exist finite sized redevelopment length, drag and loss coefficient. Last but not least, the present numerical results indicate that the shear-thinning viscous behaviour decreases the onset of flow separation. © 2011 Elsevier Ltd.


Ternik P.,Bresterniska ulica 163
International Journal of Heat and Mass Transfer | Year: 2015

The present work deals with the steady-state natural convection in a cubic enclosure filled with the water-Au nanofluid. The enclosure is heated on the vertical and cooled from the adjacent wall, while the other 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 effects of the volume fraction of nanoparticles in the range 0%≤φ≤5% on the heat transfer characteristics of Au nanofluids are investigated for the nominal values of base-fluid Rayleigh number 101≤ Rabf≤106. 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 mean Nusselt number Nu¯ values for nanofluids φ>0% are smaller than those obtained in the case of pure fluid with the same nominal value of Rayleigh number Rabfdue to the weakening of convective transport. © 2014 Elsevier Ltd.


The steady flow of generalized Newtonian fluid in a two-dimensional 1:3 sudden expansion was studied numerically. Finite volume method was applied to solve the momentum equations along with the continuity equation and the Power law rheological model within the laminar flow regime for a range of Reynolds number and Power law index values. The values of generalized Reynolds number, based on physical and rheological properties, upstream channel height and bulk velocity, were varied between 0.0001≤Regen≤10, while the Power law index values mapped the 0.60≤n≤1.40 range, allowing for the investigation of both shear-thinning and shear-thickening effects at creeping as well as slowly moving fluid flow conditions. We report accurate results of a systematic study with a focus on most important characteristics of recirculating fluid flow in the downstream section of sudden expansion geometry. It is shown that for the creeping flow regime there exist finite sized redevelopment length, extra pressure drop (Couette correction) and recirculation zones (also called as Moffatt vortices) that are influenced by the non-Newtonian viscous behaviour. © 2010 Elsevier B.V.

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