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Research Papers: Natural and Mixed Convection

Optimization of Free Convection Heat Transfer From Vertical Plates Using Nanofluids

[+] Author and Article Information
Massimo Corcione1

 DIAEE Sezione Fisica Tecnica—Sapienza Università di Roma, via Eudossiana 18, 00184 Rome, Italymassimo.corcione@uniroma1.it

Marta Cianfrini, Emanuele Habib, Alessandro Quintino

 DIAEE Sezione Fisica Tecnica—Sapienza Università di Roma, via Eudossiana 18, 00184 Rome, Italymassimo.corcione@uniroma1.it

1

Corresponding author.

J. Heat Transfer 134(4), 042501 (Feb 15, 2012) (8 pages) doi:10.1115/1.4005108 History: Received January 12, 2011; Revised August 22, 2011; Published February 15, 2012; Online February 15, 2012

Free convection heat transfer in nanofluids from vertical flat plates at uniform temperature is investigated theoretically. The main idea upon which the present work is based is that nanofluids behave more like single-phase fluids rather than like conventional solid–liquid mixtures. This assumption implies that all the convective heat transfer correlations available in the literature for single-phase flows can be extended to nanoparticle suspensions, provided that the thermophysical properties appearing in them are the nanofluid effective properties calculated at the reference temperature. In this connection, two empirical equations, based on a wide variety of experimental data reported in the literature, are used for the evaluation of the nanofluid effective thermal conductivity and dynamic viscosity. Conversely, the other effective properties are computed by the traditional mixing theory. The heat transfer enhancement that derives from the dispersion of nanosized solid particles into the base liquid is calculated for different operating conditions, nanoparticle diameters, and combinations of solid and liquid phases. The fundamental result obtained is the existence of an optimal particle loading for maximum heat transfer. In particular, for any assigned combination of suspended nanoparticles and base liquid, it is found that the optimal volume fraction increases as the nanofluid average temperature increases, the nanoparticle size decreases, and the Rayleigh number of the base fluid decreases.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Distributions of keff /kf versus ϕ for Al2 O3  + H2 O, with dp and T as parameters

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Figure 2

Distributions of μeff /μf versus ϕ for water-based nanofluids, with dp as a parameter

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Figure 3

Distributions of the other effective property ratios versus ϕ for Al2 O3  + H2 O at T = 309 K

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Figure 4

Distributions of E (%) versus ϕ for Al2 O3  + H2 O at Raf  = 104 for: (a) Tref  = 309 K and different values of dp and (b) dp  = 25 nm and different values of Tref

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Figure 5

Distributions of E (%) versus ϕ for Al2 O3 (dp  = 25 nm) + H2 O at Tref  = 309 K, with Raf as a parameter

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Figure 6

Distributions of ϕopt (%) versus Raf for Al2 O3  + H2 O, with dp and Tref as parameters

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Figure 7

Distributions of ϕopt (%) versus Raf for Al2 O3  + H2 O at Tref  = 309 K, with dp as a parameter

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Figure 8

Distributions of Emax (%) versus Raf for Al2 O3  + H2 O with: (a) dp  = 25 nm and different values of Tref and (b) dp  = 100 nm and different values of Tref

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Figure 9

Distributions of E (%) versus ϕ for different nanofluids, assumed Raf  = 104 , dp  = 25 nm, and Tref  = 324 K

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Figure 10

Comparison between Eqs. 10 - 12 and the theoretical data of ϕopt (%)

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