Research Papers: Natural and Mixed Convection

Analysis of Entropy Generation During Mixed Convective Heat Transfer of Nanofluids Past a Rotating Circular Cylinder

[+] Author and Article Information
Sandip Sarkar

Department of Mechanical Engineering,
Indian Institute of Science Bangalore,
Bangalore 560012, India

Suvankar Ganguly

Research and Development Division,
Tata Steel Ltd.,
Jamshedpur 831007, India
e-mail: suva_112@yahoo.co.in

Amaresh Dalal

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

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received June 22, 2013; final manuscript received January 2, 2014; published online March 7, 2014. Assoc. Editor: Giulio Lorenzini.

J. Heat Transfer 136(6), 062501 (Mar 07, 2014) (10 pages) Paper No: HT-13-1321; doi: 10.1115/1.4026470 History: Received June 22, 2013; Revised January 02, 2014

The entropy generation due to mixed convective heat transfer of nanofluids past a rotating circular cylinder placed in a uniform cross stream is investigated via streamline upwind Petrov–Galerkin based finite element method. Nanosized copper (Cu) particles suspended in water are used with Prandtl number (Pr) = 6.9. The computations are carried out at a representative Reynolds number (Re) of 100. The dimensionless cylinder rotation rate, α, is varied between 0 and 2. The range of nanoparticle volume fractions (ϕ) considered is 0 ≤ ϕ ≤ 5%. Effect of aiding buoyancy is brought about by considering two fixed values of the Richardson number (Ri) as 0.5 and 1.0. A new model for predicting the effective viscosity and thermal conductivity of dilute suspensions of nanoscale colloidal particles is presented. The model addresses the details of the agglomeration–deagglomeration in tune with the pertinent variations in the effective particulate dimensions, volume fractions, as well as the aggregate structure of the particulate system. The total entropy generation is found to decrease sharply with cylinder rotation rates and nanoparticle volume fractions. Increase in nanoparticle agglomeration shows decrease in heat transfer irreversibility. The Bejan number falls sharply with increase in α and ϕ.

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Fig. 1

Variation in relative viscosity of Al2O3-water nanofluid as a function of nanoparticle volume fraction

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Fig. 2

Schematic of the cylinder and the physical domain

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Fig. 3

Time-averaged contours of (a) frictional and (b) thermal entropy for different α at n = 5, ϕ = 5%, and Ri = 0.5

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Fig. 4

Time-averaged vector plots at Ri = 1.0, ϕ = 3%, n = 1, and for various α; (a) α = 0, (b) α = 1, and (c) α = 2

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Fig. 5

Time-averaged contours of (a) frictional and (b) thermal entropy for different n at α = 1.5, ϕ = 3%, and Ri = 1.0

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Fig. 6

Time-averaged contours of (a) streamlines and (b) isotherms for α = 1.5, n = 5, ϕ = 3%, and Ri = 1.0. (c) Time-averaged isotherms at α = 0, ϕ = 3%, n = 5, and Ri = 1.0.

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Fig. 7

Variation of ST: (a) with α at ϕ = 5% for various n, Ri and (b) with ϕ at α = 1.5 for various n, Ri

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Fig. 8

Variation of Bejan number (Be): (a) with α at ϕ = 5% for various n, Ri and (b) with ϕ at α = 1.5 for various n, Ri

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Fig. 9

Time-averaged local Nusselt number distribution over the cylinder surface at Ri = 1.0 for (a) various α at n = 5, ϕ = 5%; (b) various ϕ at n = 3, α = 1.5; and (c) various n at α = 1, ϕ = 4%




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