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Brestrnica, Slovenia

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. Source


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. Source


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. Source


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. Source


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. Source

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