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Technical Brief

A Numerical Case Study: Effect of Heat Leakage on Thermodynamic Efficiency of Cylinders in Cross-Flow

[+] Author and Article Information
Mustafa Erguvan

Department of Mechanical Engineering,
University of Alabama,
Tuscaloosa, AL 35401
e-mail: merguvan@crimson.ua.edu

David W. MacPhee

Department of Mechanical Engineering,
University of Alabama,
Tuscaloosa, AL 35401
e-mail: dwmacphee@ua.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received March 7, 2018; final manuscript received November 21, 2018; published online December 17, 2018. Assoc. Editor: Sara Rainieri.

J. Heat Transfer 141(2), 024505 (Dec 17, 2018) (7 pages) Paper No: HT-18-1137; doi: 10.1115/1.4042156 History: Received March 07, 2018; Revised November 21, 2018

Numerical and thermodynamic analyses have been undertaken in this study to examine energy and exergy efficiencies of in-line tube banks for unsteady cross-flow. Pitch ratio (PR) and the number of in-line tubes are varied for Reynolds numbers of 500 and 10,000, and artificial heat leakages are modeled as a source term. Numerical results are compared with published values, and good agreements are obtained regarding Nusselt number and pressure drop. Whereas the energy efficiency varied between 72% and 99%, the exergy efficiency ranged from 40% to 70%. It was found that while viscous dissipation has a low effect on energy and exergy efficiencies for the lower Reynolds number, it has a significant effect for the higher Reynolds number. On the other hand, heat leakage had a greater effect on exergy efficiency compared to energy efficiency, especially for the lower Reynolds number case. Overall, this study verified how heat leakage could play a vital role on efficiency for low-inlet temperature heat recovery systems.

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References

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Figures

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Fig. 1

Geometry and boundary conditions

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Fig. 2

Detailed mesh near cylindrical surface

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Fig. 3

Grid and time-step size independence studies

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Fig. 4

Temperature contour for 0.01 s time-step size

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Fig. 5

Nusselt number validation: (a) Re = 500 and (b) Re = 10,000

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Fig. 6

Pressure drop validation: (a) Re = 500 and (b) Re = 10,000

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Fig. 7

Energy efficiency for (a) eight tubes, (b) four tubes, (c) three tubes varying PR for different heat leakages for Re  =  500. Subfigures (d), (e), and (f) show the same eight, four, and three tube cases for Re  = 10,000.

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Fig. 8

Exergy efficiency for (a) eight tubes, (b) four tubes, (c) three tubes varying PR for different heat leakages for Re  =  500. Subfigures (d), (e), and (f) show the same eight, four, and three tube cases for Re  = 10,000.

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Fig. 9

Heat leakage effect on energy and exergy: (a) Re = 500 and (b) Re = 10,000

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