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Research Papers: Heat Transfer Enhancement

Role of Chamfering Angles and Flow Through Slit on Heat Transfer Augmentation Behind a Surface-Mounted Rib

[+] Author and Article Information
Md Shaukat Ali

Mechanical Engineering Department,
College of Engineering,
Qassim University,
Buraidah 51452, Saudi Arabia
e-mail: shaukat779@gmail.com

Andallib Tariq

Mechanical and Industrial
Engineering Department,
Indian Institute of Technology Roorkee,
Roorkee 247667, India
e-mail: tariqfme@iitr.ac.in

B. K. Gandhi

Mechanical and Industrial
Engineering Department,
Indian Institute of Technology Roorkee,
Roorkee 247667, India
e-mail: bkgmefme@iitr.ac.in

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received September 20, 2015; final manuscript received June 1, 2016; published online June 28, 2016. Assoc. Editor: Danesh / D. K. Tafti.

J. Heat Transfer 138(11), 111901 (Jun 28, 2016) (16 pages) Paper No: HT-15-1612; doi: 10.1115/1.4033747 History: Received September 20, 2015; Revised June 01, 2016

Abstract

Detailed heat transfer and flow field investigations behind a surface-mounted slitted trapezoidal rib have been performed using liquid crystal thermography (LCT) and particle image velocimetry (PIV). In the accomplished experiments, the effects of varying the chamfering angle over the trailing edge of a rib with a centrally placed longitudinal continuous slit carrying an open area ratio equivalent to 25% were studied. The chamfering angle has been varied from 0 to 20 deg in a step of 5 deg. Experiments were carried out for four different Reynolds numbers ranging in between 9400 and 61,480, which were based upon the hydraulic diameter of the rectangular duct. The motive behind the present work is to systematically study the effect of change in chamfering angle of a trapezoidal rib with a centrally placed continuous slit over the flow and heat transfer parameters. Emphasis was made to identify the flow parameters responsible for augmentation in surface heat transfer coefficients (HTCs). Results are presented in terms of mean and rms velocity fields, stream traces, Reynolds stress, vorticity, and surface- and spanwise-averaged augmentation Nusselt number distribution. The reattachment length and the average augmentation Nusselt number have been evaluated for all of the different configurations. Entire configurations under selected range of Reynolds number led to the rise in heat transfer enhancement as against the flat surface without the rib. It is observed that slitted ribs cause shorter reattachment length and better heat transfer enhancement in the downstream vicinity of the rib. Further, the recirculation area behind the rib is enlarged to the point of spanning the nearby downstream vicinity of the rib ($x/e<4$), which signifies the zone of maximum heat transfer enhancement due to the effect of flow coming out of the slit. Salient critical points and foci of secondary recirculation patterns are extracted, which provides clues to the physical process occurring in the flow, which were responsible for the mixing enhancement behind slitted trapezoidal rib geometries.

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Figures

Fig. 1

Complete experimental facility for PIV and LCT measurements along with the details of rib configuration and heating section

Fig. 2

Comparison of span-averaged augmentation Nusselt number variation behind solid and slitted trapezoidal rib for varying chamfering angle at different Reynolds numbers

Fig. 3

Distribution of time-averaged normalized velocity magnitude (U/Ur) with stream traces behind solid and slitted trapezoidal ribs at the lowest and the highest Reynolds numbers under investigation

Fig. 4

Distribution of time-averaged normalized v-velocity (v/Ur) behind solid and slitted trapezoidal ribs at the lowest and the highest Reynolds numbers under investigation

Fig. 5

Close-up view of normalized velocity magnitude (U/Ur) with stream traces behind slitted trapezoidal ribs at different Reynolds numbers under investigation

Fig. 6

Normalized stresses distribution and turbulent kinetic energy fluctuation field behind a solid and slitted trapezoidal ribs of varying chamfering angle at a typical Reynolds number of Re = 44,600

Fig. 7

Normalized Reynolds stress distribution behind a solid and slitted trapezoidal ribs of varying chamfering angle at a typical Reynolds number of Re = 44,600

Fig. 8

Instantaneous velocity vectors and corresponding vorticity distributions behind slitted trapezoidal ribs of varying chamfering angle at a typical Reynolds number of Re = 44,600

Fig. 9

Normalized z-vorticity distribution behind solid and slitted ribs of varying chamfering angle at a typical Reynolds number of Re = 44,600

Fig. 10

Surface augmentation Nusselt number distribution behind slitted trapezoidal ribs of varying chamfering angle at different Reynolds numbers

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