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Research Papers: Natural and Mixed Convection

Analysis of Entropy Generation During Mixed Convective Heat Transfer of Nanofluids Past a Square Cylinder in Vertically Upward Flow

[+] Author and Article Information
Suvankar Ganguly

e-mail: suva_112@yahoo.co.in
Research and Development Division,
Tata Steel Ltd.,
Jamshedpur 831001, India

Amaresh Dalal

Department of Mechanical Engineering,
Indian Institute of Technology,
Guwahati, Guwahati 781039, India

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received October 13, 2011; final manuscript received August 1, 2012; published online October 5, 2012. Assoc. Editor: Giulio Lorenzini.

J. Heat Transfer 134(12), 122501 (Oct 05, 2012) (8 pages) doi:10.1115/1.4007411 History: Received October 13, 2011; Revised August 01, 2012

The present work demonstrates entropy generation due to laminar mixed convection of water-based nanofluid past a square cylinder in vertically upward flow. Streamline upwind Petrov–Galerkin (SUPG) based finite element method is used for numerical simulation. Nanosized copper (Cu) and alumina (Al2O3) particles suspended in water are used with Prandtl number (Pr) = 6.2. The range of nanoparticle volume fractions considered is 0–20%. Computations are carried out at a representative Reynolds number (Re) of 100 with Richardson number (Ri) range −0.5 < Ri < 0.5, both values inclusive. For both the nanofluids (Al2O3–water and Cu–water nanofluids), total entropy generation decreases with increasing nanoparticle volume fractions. It is found that for the present case of mixed convection flows with nanofluids, thermal irreversibility is much higher than that of frictional irreversibility. The Bejan number decreases with increasing nanoparticle volume fractions.

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Figures

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Fig. 1

Schematic of problem geometry

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Fig. 2

Time-averaged entropy generation contours for Al2O3–water nanofluids at Ri = 0.5 and for different ϕ; (a) frictional entropy and (b) thermal entropy

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Fig. 3

Time-averaged entropy generation contours for Cu–water nanofluids at Ri = 0.5 and for different ϕ; (a) frictional entropy and (b) thermal entropy

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Fig. 4

Variation of thermal conductivity ratio (keff/kf) with particle volume fraction (ϕ) for both Cu–water and Al2O3–water nanofluids

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Fig. 5

Time-averaged contours of isotherms at Ri = 0.5 and ϕ = 20%; (a) Al2O3–water nanofluids and (b) Cu–water nanofluids

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Fig. 6

Variation of (a) total entropy generation due to fluid friction, (b) total entropy generation heat transfer, and (c) global total entropy generation, with ϕ for different nanofluids and Richardson numbers

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Fig. 7

Variation of Bejan number with ϕ for different nanofluids and Richardson numbers

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Fig. 8

Variation of time-averaged local Nusselt number over the cylinder surface for different nanofluids at Ri = 0.15 and for increasing ϕ

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