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Research Papers: Natural and Mixed Convection

# Three-Dimensional Numerical Investigation of Thermodynamic Performance Due to Conjugate Natural Convection From Horizontal Cylinder With Annular Fins

[+] Author and Article Information
Jnana Ranjan Senapati

Department of Mechanical Engineering,
Indian Institute of Technology Kharagpur,
Kharagpur 721302, India
e-mail: jnanabharat270@gmail.com

Sukanta Kumar Dash, Subhransu Roy

Department of Mechanical Engineering,
Indian Institute of Technology Kharagpur,
Kharagpur 721302, India

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received September 5, 2016; final manuscript received January 25, 2017; published online April 11, 2017. Assoc. Editor: Debjyoti Banerjee.

J. Heat Transfer 139(8), 082501 (Apr 11, 2017) (7 pages) Paper No: HT-16-1555; doi: 10.1115/1.4035968 History: Received September 05, 2016; Revised January 25, 2017

## Abstract

Entropy generation due to natural convection has been computed for a wide range of Rayleigh numbers based on fin spacing, RaS in the entire laminar range $5≤RaS≤108$, and diameter ratio 2 ≤ D/d ≤ 5 for an isothermal horizontal cylinder fitted with vertical annular fins. Entropy generation in the tube-fin system is predominantly due to heat transfer rather than fluid friction. The results demonstrate that the degree of irreversibility is higher in the case of the finned configuration when compared with the unfinned one. With the deployment of a merit function combining the first and second laws of thermodynamics, we have tried to show the thermodynamic performance of finned cylinder with natural convection. So, we have defined the ratio (I/Q)finned/(I/Q)unfinned which gets its minimum value at optimum fin spacing where heat transfer is maximum. A detailed view of the entropy generation around the finned cylinder has been shown for various S/d (fin spacing to tube diameter ratio) at a particular D/d (fin to tube diameter ratio) and Rayleigh number, which explains the nature and reason of entropy production.

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## Figures

Fig. 1

Schematic diagram of cylindrical computational domain

Fig. 2

Schematic diagram of cylindrical computational domain (side view)

Fig. 3

Variation of NuS with (a) computational cells and (b) domain diameter

Fig. 4

Variation of Nusselt number with Rayleigh number: a comparison between the present computation and available correlations. For D/d = 5, S/d = 1.0292.

Fig. 5

Variation of fin effectiveness, Q/Q0 with nondimensional fin spacing, S/d for different diameter ratio, D/d, and Ra

Fig. 6

Variation of the ratio (I/Q)finned/(I/Q)unfinned with nondimensional fin spacing, S/d for different values diameter ratio, D/d, and Ra

Fig. 7

Variation of heat transfer irreversibility (a) and fluid friction irreversibility (b) with nondimensional fin spacing, S/d for different values of Ra, with D/d = 5

Fig. 8

Contours of entropy generation rate per unit volume with varying fin spacing, S/d at D/d = 5, and Ra = 80,703

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