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Research Papers: Natural and Mixed Convection

Entropy Generation in Water-Based Natural Circulation Loop

[+] Author and Article Information
Sugun Tej Inampudi

Department of Mechanical Engineering,
Birla Institute of Technology & Science Pilani,
Pilani 333031, Rajasthan, India
e-mail: f2014417@pilani.bits-pilani.ac.in

Baji Marthi

Department of Mechanical Engineering,
Birla Institute of Technology & Science Pilani,
Pilani 333031, Rajasthan, India
e-mail: f2014385@pilani.bits-pilani.ac.in

Satyabrata Sahoo

Department of Mechanical Engineering,
Indian Institute of Technology (ISM) Dhanbad,
Dhanbad 826004, Jharkhand, India
e-mail: satyabrata111sahoo4@gmail.com

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received August 21, 2017; final manuscript received March 14, 2018; published online May 22, 2018. Assoc. Editor: Amitabh Narain.

J. Heat Transfer 140(9), 092501 (May 22, 2018) (11 pages) Paper No: HT-17-1485; doi: 10.1115/1.4039764 History: Received August 21, 2017; Revised March 14, 2018

Natural circulation loop (NCL) based secondary fluid systems are simple, reliable, and inexpensive due to the absence of any moving components such as pumps. Water-based NCLs are widely used in applications such as solar collectors and nuclear reactors. Also, most of the studies on NCLs do not consider the three-dimensional (3D) variation of the field variables. In the subject work, 3D steady flow simulation of water based, single-phase rectangular NCL with isothermal source and sink has been carried out to study the effects of different design and operating parameters such as loop height, temperature lift, in plane and out of plane tilt angles on the rate of heat transfer, and the rate of entropy generation due to both fluid flow and heat transfer. The rate of entropy generation due to both heat transfer and fluid flow for turbulent flow regimes in a NCL is calculated for a wide range of design and operating parameters. In turbulent flow regimes, the rate of entropy generation due to fluid flow is significant although the rate of entropy generation due to heat transfer is dominant. All the above-mentioned design and operating parameters have significant effect on the rate of entropy generation and the rate of heat transfer as well. With increases in loop height and temperature lift, the rate of entropy generation increases. As the tilt angle increases in the XY plane, the rate of the entropy generation initially increases but after certain tilt angle it starts decreasing.

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Figures

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Fig. 1

(a) Physical model of the NCL used for simulation, (b) rotation of loop about the Z-axis (tilt of gravity vector in the XY plane), and (c) rotation of loop about the X-axis (tilt of gravity vector in the YZ plane)

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Fig. 2

Comparison of simulated results with the existing results from the literature

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Fig. 3

Rate of entropy generation due to fluid flow versus temperature lift for different loop heights

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Fig. 4

Rate of total entropy generation versus temperature lift for different loop heights

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Fig. 5

Rate of total heat transfer versus temperature lift for different loop heights

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Fig. 6

Velocity vectors at the cross section of source center for loop heights of 124.5 cm, 300 cm, and 500 cm, respectively

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Fig. 7

Rate of entropy generation due to fluid flow versus temperature lift for different tilt angles in the YZ plane

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Fig. 8

Rate of total entropy generation versus temperature lift for different tilt angles in the YZ plane

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Fig. 9

Rate of total heat transfer versus temperature lift for different tilt angles in the YZ plane

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Fig. 10

Velocity vectors at the cross section of source center for tilt angles of 0 deg, 30 deg, 45 deg, and 60 deg, respectively, in the YZ plane

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Fig. 11

Rate of entropy generation due to fluid flow versus temperature lift for different tilt angles in the XY plane

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Fig. 12

Rate of total entropy generation versus temperature lift for different tilt angles in the XY plane

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Fig. 13

Rate of total heat transfer versus temperature lift for different tilt angles in the XY plane

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Fig. 14

Velocity vectors at the cross section of source center for tilt angles of 0 deg, 30 deg, 60 deg, and 90 deg, respectively, in the XY plane

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Fig. 15

Variation of Q/I with loop height

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Fig. 16

Variation of Q/I with tilt angle in the YZ plane and the XY plane

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