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Research Papers: Heat Exchangers

# Heat Transfer and Friction Factor of Coil-Springs Inserted in the Horizontal Concentric Tubes

[+] Author and Article Information
Haydar Eren

Department of Mechanical Engineering, University of Firat, Elazig 23119, Turkeyhaydar@firat.edu.tr

Nevin Celik1

Department of Mechanical Engineering, University of Minnesota, MN 55455nevincelik23@gmail.com

Seyba Yildiz

Department of Mechanical Engineering, University of Firat, Elazig 23119, Turkeyseybayildiz@yahoo.com

Aydın Durmus

Department of Mechanical Engineering, University of Ondokuz Mayis, Samsun 55139, Turkeyadurmus@omu.edu.tr

1

Corresponding author.

J. Heat Transfer 132(1), 011801 (Oct 30, 2009) (11 pages) doi:10.1115/1.3194771 History: Received December 29, 2008; Revised June 19, 2009; Published October 30, 2009

## Abstract

The goal of this investigation is to obtain definitive information about the heat transfer characteristics of circular coil-spring turbulators. This is achieved by measuring the wall temperatures on the inner tube of the exchanger. Also the inlet and outlet temperatures and pressure loss of the fluid are measured. These results are parametrized by Reynolds numbers $(2500, outer diameters of the springs ($Ds=7.2 mm$, 9.5 mm, 12 mm, and 13 mm), numbers of the springs ($n=4$, 5, and 6), and the incline angles of the springs ($θ=0 deg$, 7 deg, and 10 deg). Additionally, another goal of this work is to quantify the friction factor $f$ of the turbulated heat exchanger system with respect to aforementioned parametric values. As a result, it is found that increasing spring number, spring diameter, and incline angle result in significant augmentation on heat transfer, comparatively 1.5–2.5 times of the results of a smooth empty tube. By the way, friction factor increases 40–80 times of the results found for a smooth tube. Furthermore, as a design parameter, the incline angle has the dominant effect on heat transfer and friction loss while spring number has the weakest effect.

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## Figures

Figure 1

Schematic view of the whole setup

Figure 2

Specifications of the springs: (a) dimensions of the springs and (b) incline angle of the springs

Figure 3

Verification of the results for a smooth tube and empirical correlations: (a) Nu number results versus Dittus–Boelter correlation’s results, and (b) f friction factor results versus Blasius correlation’s results

Figure 4

Nu number versus Re number with respect to (a) incline angles, for Ds=13 mm and n=6; (b) number of springs, for Ds=7.2 mm and θ=0 deg; and (c) diameter of the springs, for n=5 and θ=7 deg

Figure 5

Correlation results for predicted Nu number versus observed Nu number

Figure 6

Friction factor f versus Re number with respect to (a) incline angles, for Ds=13 mm and n=6; (b) number of springs, for Ds=7.2 mm and θ=0 deg; and (c) diameter of the springs, for n=5 and θ=7 deg

Figure 7

Correlation results for predicted friction factor versus observed friction factor

Figure 8

Ratio of augmented Nu number to the smooth tube Nu number, Nu/Nu0: (a) Ds=7.2 mm, (b) Ds=9.5 mm, (c) Ds=12 mm, and (d) Ds=13 mm

Figure 9

Ratio of augmented friction factor to the smooth tube friction factor, f/f0: (a) Ds=7.2 mm, (b) Ds=9.5 mm, (c) Ds=12 mm, and (d) Ds=13 mm

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