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Research Papers: Forced Convection

Thermohydraulics of Laminar Flow Through Rectangular and Square Ducts With Axial Corrugation Roughness and Twisted Tapes With Oblique Teeth

[+] Author and Article Information
Sujoy Kumar Saha1

ENEA Casaccia Research Centre, Institute of Thermal Fluid Dynamics, Office Building F-20, Via Anguillarese 301, 00123 S. M. Galeria, Rome, Italysujoy_k_saha@hotmail.com

1

Corresponding author. On leave from Mechanical Engineering Department, Bengal Engineering and Science University, Shibpur Howrah 711 103, West Bengal, India.

J. Heat Transfer 132(8), 081701 (Jun 02, 2010) (12 pages) doi:10.1115/1.4001313 History: Received July 16, 2009; Revised January 28, 2010; Published June 02, 2010; Online June 02, 2010

The heat transfer and the pressure drop characteristics of laminar flow of viscous oil (175<Pr<538) through rectangular and square ducts with combined internal axial corrugations on all the surfaces of the ducts and with twisted-tape inserts with and without oblique teeth have been studied experimentally. The axial corrugations in combination with both twisted tapes with and without oblique teeth have been found to perform better than either axial corrugations or twisted-tape inserts acting alone. The heat transfer and the pressure drop measurements have been taken in separate test sections. Heat transfer tests were carried out in electrically heated stainless steel ducts incorporating uniform wall heat flux boundary conditions. Pressure drop tests were carried out in acrylic ducts. The flow friction and thermal characteristics are governed by duct aspect ratio, corrugation angle, corrugation pitch, twist ratio, space ratio, length, tooth horizontal length and tooth angle of the twisted tapes, Reynolds number, and Prandtl number. Correlations developed for friction factor and Nusselt number have predicted the experimental data satisfactorily. The performance of the geometry under investigation has been evaluated. It has been found that based on constant pumping power, up to 45% heat duty increase occurs for the combined axial corrugation and twisted-tape insert case compared with the individual axial corrugation and twisted-tape insert cases in the measured experimental parameters space. On the constant heat duty basis, the pumping power has been reduced up to 30% for the combined enhancement geometry than the individual enhancement geometries.

Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 11

Effect of tooth horizontal length on friction factor short length twisted-tape: tooth angle=10 deg; corrugation angle=60 deg, P/e=2.0437, AR=0.5

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Figure 12

Effect of tooth angle on friction factor short length twisted-tape: thl=0.01538; corrugation angle=30 deg, P/e=5.6481, AR=0.5

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Figure 13

Effect of tooth horizontal length on friction factor full-length twisted-tape: tooth angle=10 deg; corrugation angle=60 deg, P/e=2.0437, AR=0.5

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Figure 1

Square duct with internal axial corrugation

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Figure 2

Different types of twisted tapes: (a) full-length twisted-tape insert inside a duct, (b) regularly spaced twisted-tape elements, (c) full-length twisted-tape with oblique teeth, and (d) detail A of (c)

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Figure 3

Schematic of the experimental setup

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Figure 4

Square corrugated duct connected with end flange

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Figure 5

Full-length, short length, and regularly spaced twisted-tape elements with and without oblique teeth

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Figure 6

Comparison of the present experimental friction factor data with the correlation (validation of the experimental setup)

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Figure 7

Comparison of the present experimental Nusselt number data with the correlation (validation of the experimental setup)

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Figure 8

Effect of Duct aspect ratio on friction factor short length twisted-tape: tooth angle=10 deg, thl=0.03077; corrugation angle=60 deg, P/e=2.0437

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Figure 9

Effect of corrugation angle on friction factor short length twisted-tape: tooth angle=10 deg, thl=0.01538, P/e=2.0437, AR=0.5

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Figure 10

Effect of corrugation pitch on friction factor short length twisted-tape: tooth angle=10 deg, thl=0.01538; corrugation angle=30 deg, AR=0.5

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Figure 14

Effect of tooth angle on friction factor full-length twisted-tape: thl=0.01538; corrugation angle=30 deg, P/e=5.6481, AR=0.5

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Figure 15

Regularly spaced twisted-tape elements: effect of tooth angle on friction factor; corrugation angle=30 deg, P/e=2.0437, thl=0.01538

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Figure 16

Comparison of present experimental friction factor data with the experimental friction factor data, Eq. 2 of Abdel-Kariem and Fletcher (4)

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Figure 17

Effect of duct aspect aspect ratio on nu short length twisted-tape: tooth angle=10 deg, thl=0.01538; corrugation angle=30 deg, P/e=2.0437

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Figure 18

Effect of corrugation angle on Nu full-length twisted-tape: tooth angle=10 deg, thl=0.01538, P/e=2.0437, AR=0.5

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Figure 19

Effect of corrugation pitch on Nu full-length twisted-tape: tooth angle=10 deg, thl=0.01538; corrugation angle=30 deg, AR=0.5

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Figure 20

Regularly spaced twisted-tape elements: effect of tooth angle on Nu; corrugation angle=30 deg, P/e=2.0437, thl=0.01538

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Figure 21

Regularly spaced twisted-tape elements: effect of thl on Nu; corrugation angle=30 deg, P/e=2.0437, tooth angle=10 deg

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Figure 22

Comparison present Nusselt number data with the experimental friction factor data, Eq. 1 of Abdel-Kariem and Fletcher (4)

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Figure 23

Comparison of experimental friction factor data with that predicted from correlation

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Figure 24

Comparison of experimental Nusselt number data with that predicted from correlation

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