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Research Papers: Micro/Nanoscale Heat Transfer

Entropy Generation Analysis for Nanofluid Flow in Microchannels

[+] Author and Article Information
Jie Li

Department of Mechanical and Aerospace Engineering, NC State University, Raleigh, NC 27695

Clement Kleinstreuer1

Department of Mechanical and Aerospace Engineering, NC State University, Raleigh, NC 27695ck@eos.ncsu.edu

1

Corresponding author.

J. Heat Transfer 132(12), 122401 (Sep 17, 2010) (8 pages) doi:10.1115/1.4002395 History: Received April 30, 2009; Revised May 06, 2010; Published September 17, 2010; Online September 17, 2010

Employing a validated computer simulation model, entropy generation is analyzed in trapezoidal microchannels for steady laminar flow of pure water and CuO-water nanofluids. Focusing on microchannel heat sink applications, local and volumetric entropy rates caused by frictional and thermal effects are computed for different coolants, inlet temperatures, Reynolds numbers, and channel aspect ratios. It was found that there exists an optimal Reynolds number range to operate the system due to the characteristics of the two different entropy sources, both related to the inlet Reynolds number. Microchannels with high aspect ratios have a lower suitable operational Reynolds number range. The employment of nanofluids can further minimize entropy generation because of their superior thermal properties. Heat transfer induced entropy generation is dominant for typical microheating systems while frictional entropy generation becomes more and more important with the increase in fluid inlet velocity/Reynolds number.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

System sketch: (a) validation test tube and (b) investigated trapezoidal channel

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Figure 2

Model validation: (a) dimensionless entropy generation rate profiles in radial direction and (b) local heat transfer coefficients in the tubular entrance region for both pure water and nanofluid flows

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Figure 3

Entropy generation contours due to friction for pure water flow: (a) trapezoidal microchannel case 1, (b) trapezoidal microchannel case 2, and (c) trapezoidal microchannel case 3

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Figure 4

Entropy generation contours due to heat transfer for pure water flow: (a) trapezoidal microchannel case 1, (b) trapezoidal microchannel case 2, and (c) trapezoidal microchannel case 3

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Figure 5

Entropy generation contours due to both sources for pure water flow: (a) trapezoidal microchannel case 1, (b) trapezoidal microchannel case 2, and (c) trapezoidal microchannel case 3

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Figure 6

Entropy generation rate developing along the channel axis for pure water flow: (a) developing frictional irreversibilities, (b) developing thermal irreversibilities, and (c) total irreversibilities

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Figure 7

System entropy generation versus fluid inlet temperature

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Figure 8

System entropy generation versus volume fraction

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Figure 9

System entropy generation versus Reynolds number

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Figure 10

System entropy generation as a function of aspect ratios and Reynolds number

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