Abstract
Flow and heat transfer property of Oldroyd-B-fluid-based nanofluids containing cylindrical particles are studied in a pipe with circular cross-section in the range of Reynolds number (Re) from 100 to 2000, Weissenberg number (We) from 0.1 to 2, particle aspect ratio (β) from 2 to 16 and particle volume concentration (Φ) from 0.1% to 2.5%. The motion equation of Oldroyd-B fluid with particles, the equation for probability density function of particle orientation and convection-diffusion equation for particles are solved numerically. The numerical method used in the simulation is validated by comparing with the available results. The effects of Re, We, β and Φ on the friction factor (f), Nusselt number (Nu) and ratio of energy performance evaluation criterion (PECt/PECf) for Oldroyd-B-fluid-based nanofluids to that for Oldroyd-B fluids are discussed. The results showed that the values of f and Nu of Oldroyd-B-fluid-based nanofluids are larger than that of water-based nanofluids and that of pure Oldroyd-B fluids. The values of f increase with increasing Re, We and Φ, but with decreasing β. The values of Nu and PECt/PECf are enhanced with increasing Re, We, β and Φ. The increase of f is larger than that of Nu at lower Re, but is less than that of Nu at higher Re. It is more effective to use Oldroyd-B-fluid-based nanofluids with cylindrical nanoparticles to improve the heat transfer at the conditions of higher Re, We, β and Φ. Finally, the correlation formula of PECt/PECf as a function of Re, We, β and Φ is derived.
Highlights
Mechanical and heat transfer characteristics of non-Newtonian fluids are of great interest due to its wide engineering applications, for example, polymer extrusion, glass manufacturing, tailings, paper-making [1,2]
The difference in the friction factor between nanofluids and pure water decreases with increasing Reynolds number (Re) because the viscosity of nanofluids decreases with Re as well as the shear rate, which is consistent with the experimental results in water-based ZnO nanofluids [30] and in aqueous suspensions of carbon nanotubes [31]
In order to understand the heat transfer property of Oldroyd-B-fluid-based nanofluids containing cylindrical particles, we explore the effects of various factors on the Nusselt number (Nu) which is defined as the ratio of convective heat transfer to fluid conduction heat transfer as shown in Equation (20)
Summary
Mechanical and heat transfer characteristics of non-Newtonian fluids are of great interest due to its wide engineering applications, for example, polymer extrusion, glass manufacturing, tailings, paper-making [1,2]. In order to improve the flow and heat transfer of the base fluids, nanoparticles are immersed into the base fluids, i.e., nanofluids. A growing number of attentions have been paid to the potentials of nanofluids in the applications [3]. Most of these studies use Newtonian fluids as the base fluids, and many valuable conclusions are obtained. Water-Al2 O3 and -SiO2 nanofluids had the best effect for the flow and heat transfer in a spiral double-pipe heat exchanger with the Reynolds numbers of 10,551~17,220 and 17,220~31,910, respectively [6]
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