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, original scientific article Abstract: 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.
Keywords: natural convection, heat transfer, nanofluid, Nusselt number
Published in DKUM: 07.07.2017; Views: 1293; Downloads: 363
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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, original scientific article Abstract: 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.
Keywords: natural convection, CMC-Au nanofluid, heat transfer, Nusslet number
Published in DKUM: 16.03.2017; Views: 1388; Downloads: 96
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3. Numerical study of heat-transfer enhancement of homogeneous water-Au nanofluid under natural convectionPrimož Ternik, Rebeka Rudolf, Zoran Žunič, 2012, original scientific article Abstract: 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.
Keywords: natural convection, nanofluid, heat transfer, numerical modelling
Published in DKUM: 10.07.2015; Views: 1363; Downloads: 141
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4. Numerical study of Rayleigh-Bénard natural-convection heat-transfer characteristics of water-based Au nanofluidsPrimož Ternik, Rebeka Rudolf, Zoran Žunič, 2013, original scientific article Abstract: 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.
Keywords: Rayleigh-Bénard natural convection, water-Au nanofluid, heat transfer, numerical modelling
Published in DKUM: 10.07.2015; Views: 1435; Downloads: 118
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