Flow Characteristics Of Nanofluids Research Articles

Unconfined laminar nanofluid flow and heat transfer around a square cylinder

The momentum and forced convection heat transfer for a laminar and steady free stream flow of nanofluids past an isolated square cylinder have been studied numerically. Different nanofluids consisting of Al 2O 3 and CuO with base fluids of water and a 60:40 (by mass) ethylene glycol and water mixture were selected to evaluate their superiority over conventional fluids. Recent correlations for the thermal conductivity and viscosity of nanofluids, which are functions of particle volumetric concentration as well as temperature, have been employed in this paper. The simulations have been conducted for Pe = 25, 50, 100 and 200, with nanoparticle diameters of 30 and 100 nm and particle volumetric concentrations ranging from 0% to 4%. The results of heat transfer characteristics of nanofluid flow over a square cylinder showed marked improvement comparing with the base fluids. This improvement is more evident in flows with higher Peclet numbers and higher particle volume concentration, while the particle diameter imposes an adverse effect on the heat transfer characteristics. In addition, it was shown that for any given particle diameter there is an optimum value of particle concentration that results in the highest heat transfer coefficient.

Flow Characteristics of Nanofluids According to Nanoparticles Shape

In this paper, flow characteristics of water-based Al2O3 nanofluids according to nanoparticles shape are experimentally investigated in fully developed laminar flow regime. Al2O3 nanofluids of 0.3 Vol. % with sphere-, rod-, blade-, platelet-and brick-shaped nanoparticles are manufactured by the two-step method. Nanoparticles shape dispersed in base fluid are also checked using TEM image. Zeta potential and sedimentation are measured to examine suspension and dispersion characteristics of Al2O3 nanofluids with nanoparticles of various shapes. Based on the experimental results, it is found that the pressure drop of Al2O3 nanofluids strongly depends on the shape of nanoparticles at the fixed volume fraction of 0.3%. We experimentally show that the pressure drop characteristics of Al2O3 nanofluids can be explained by both the surface area per unit mass and the size of nanoparticles which are related with the shape of nanoparticles.

Heat transfer enhancement for combined convection flow of nanofluids in a vertical rectangular duct considering radiation effects

AbstractIn this paper, combined convective heat transfer and nanofluids flow characteristics in a vertical rectangular duct are numerically investigated. This investigation covers Rayleigh numbers in the range of 2 × 106 ≤ Ra ≤ 2 × 107 and Reynolds numbers in the range of 200 ≤ Re ≤ 1000. Pure water and five different types of nanofluids such as Ag, Au, CuO, diamond, and SiO2 with a volume fraction range of 0.5% ≤ φ ≤ 3% are used. The three‐dimensional steady, laminar flow, and heat transfer governing equations are solved using finite volume method (FVM). The effects of Rayleigh number, Reynolds number, nanofluids type, nanoparticle volume fraction of nano‐ fluids, and effect of radiation on the thermal and flow fields are examined. It is found that the heat transfer is enhanced using nanofluids by 47% when compared with water. The Nusselt number increases as the Reynolds number and Rayleigh number increase and aspect ratio decreases. A SiO2 nanofluid has the highest Nusselt number and highest wall shear stress while the Au nanofluid has the lowest Nusselt number and lowest wall shear stress. The results also revealed that the wall shear stress increases as Reynolds number increases, aspect ratio decreases, and nanoparticle volume fraction increases. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library (wileyonlinelibrary.com/journal/htj). DOI 10.1002/htj.20354

Rheological and flow characteristics of nanofluids: Influence of electroviscous effects and particle agglomeration

Nanofluids have shown remarkable attraction in heat transfer community due to its reported enhanced thermal properties. One factor which can restrict nanofluids in heat transfer application is the increased viscosity value (compared to classical predictions). Particle aggregation occurring was the major reason for this observation. Even though majority of the aqueous nanofluids prepared in literature were stabilized electrostatically by adjusting the pH, studies on the effect of the electrical double layer thus created and its influence on viscosity increase has not been investigated for these nanofluids so far. Thus, in the present paper, rheological properties of alumina-water nanofluids, which are electrostatically stabilized, are measured and the increase in suspension viscosity due to presence of this electrical double layer causing additional electroviscous effects is brought out. Based on dynamic light scattering studies, particle agglomeration and its subsequent effect in increasing the viscosity of alumina-ethylene glycol nanofluid, where electroviscous effects are absent, are also considered. It is noted that the understanding of electroviscous effect is equally important as understanding the particle agglomeration effect and understanding both the effects is central to revealing the physics of nanofluid rheology. Further, hydrodynamic experiments are made, which show that nanofluids behaves almost like a homogeneous fluids under flow conditions, and by knowing their properties, such as viscosity and density, pressure drop can be predicted.