Investigation of Laminar Convective Heat Transfer for Al2O3-Water Nanofluids Flowing through a Square Cross-Section Duct with a Constant Heat Flux

Hsien-Hung Ting,Shuhn-Shyurng Hou

doi:10.3390/ma8085246

Abstract

The objective of this study is to numerically investigate the convective heat transfer of water-based Al2O3 nanofluids flowing through a square cross-section duct with a constant heat flux under laminar flow conditions. The effects of nanoparticle concentration and Peclet number on the heat transfer characteristics of Al2O3-water nanofluids are investigated. The nanoparticle diameter is 25 nm and six particle concentrations (0.2, 0.5, 1, 1.5, 2, and 2.5 vol.%) are considered. The numerical results show that the heat transfer coefficients and Nusselt numbers of Al2O3-water nanofluids increase with increases in the Peclet number as well as particle volume concentration. The heat transfer coefficient of nanofluids is increased by 25.5% at a particle volume concentration of 2.5% and a Peclet number of 7500 as compared with that of the base fluid (pure water). It is noteworthy that at the same particle volume concentration of 2.5%, the enhancement of the convective heat transfer coefficient of Al2O3-water nanofluid (25.5%) is much higher than that of the effective thermal conductivity (9.98%). Thus, the enhancement of the convective heat transfer cannot be solely attributed to the enhancement of the effective thermal conductivity. Additionally, the numerical results coincide well with the published experimental data.

Highlights

Nanofluids, a new class of heat transfer fluids, are liquid suspensions of nanometer-sized particles.Typically, nanofluids contain nanoparticles with sizes of 1 to 100 nm dispersed in a conventional liquid such as water [1,2], ethylene glycol [3], methanol [4], and engine oil [5]
Bianco et al [1] reported an analysis based on the second law of thermodynamics applied to a water-Al2 O3 nanofluid in turbulent convection inside a circular tube subjected to constant wall temperature
The present study numerically investigates the characteristics of the convective heat transfer of water-based Al2 O3 nanofluids flowing through a square cross-section duct with a constant heat flux under laminar flow conditions

Summary

Introduction

Nanofluids, a new class of heat transfer fluids, are liquid suspensions of nanometer-sized particles. Nanofluids contain nanoparticles with sizes of 1 to 100 nm dispersed in a conventional liquid such as water [1,2], ethylene glycol [3], methanol [4], and engine oil [5]. The thermal conductivities of nanofluids with suspended metallic or nonmetallic particles are expected to be significantly higher than those of traditional heat transfer fluids. The suspended nanoparticles can significantly change the transport and thermal properties of a conventional liquid (base fluid). The remarkable enhancement of forced convective heat transfer has been extensively investigated in Cu-water- [6,7,8,9], CuO-water- [10,11], TiO2 -water- [8,10], Al2 O3 -water- [1,2,8], and carbon nanotube-water-based [12]. At a constant Reynolds number, there is an increase of entropy generation, whereas at a constant mass flow rate or velocity, entropy generation decreases

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Conclusion