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Research Papers: Forced Convection

Mixing and Heat Transfer Enhancement in Microchannels Containing Converging-Diverging Passages

[+] Author and Article Information
J. Q. Yong

Department of Mechanical Engineering,
National University of Singapore,
9 Engineering Drive 1,
Singapore 117576, Singapore

C. J. Teo

Department of Mechanical Engineering,
National University of Singapore,
9 Engineering Drive 1,
Singapore 117576, Singapore
e-mail: mpeteocj@nus.edu.sg

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received January 27, 2013; final manuscript received November 18, 2013; published online January 31, 2014. Assoc. Editor: Sujoy Kumar Saha.

J. Heat Transfer 136(4), 041704 (Jan 31, 2014) (11 pages) Paper No: HT-13-1047; doi: 10.1115/1.4026090 History: Received January 27, 2013; Revised November 18, 2013

Fully-developed flow and heat transfer in periodic converging-diverging channels with rectangular cross sections are studied using computational fluid dynamics (CFD) simulations for Reynolds numbers ranging from 50 to 200. Experimental laser sheet flow visualizations have also been utilized with the aid of an enlarged transparent Perspex model, which serves as a form of secondary verification of the CFD results. The CFD investigations focus on two principal configurations of converging-diverging channels, namely the constant curvature and sinusoidal converging-diverging channel. Heat transfer simulations have been carried out under constant wall temperature conditions using liquid water as the coolant. It is found that due to the fluid mixing arising from a pair of recirculating vortices in the converging-diverging channels, the heat transfer performance is always significantly more superior to that of straight channels with the same average cross sections; at the same time the pressure drop penalty of the converging-diverging channels can be much smaller than the heat transfer enhancement. The effects of channel aspect ratio and amplitude of the converging-diverging profiles have been systematically investigated. The results show that for a steady flow, the flow pattern is generally characterized by the formation of a pair of symmetrical recirculating vortices in the two furrows of the converging-diverging channel. Both the optimal aspect ratio and channel amplitude are being presented with the support of CFD analyses. Experimental flow visualizations have also been utilized and it was found that the experimental results agrees favorably with the CFD results. The present study shows that these converging-diverging channels have prominent advantages over straight channels. The most superior configuration considered in this paper has been found to yield an improvement of up to 60% in terms of the overall thermal-hydraulic performance compared to microchannels with straight walls, thus serving as promising candidates for incorporation into efficient heat transfer devices.

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References

Figures

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Fig. 2

Characteristic dimensions of typical converging-diverging channel (single period, plan, and isometric views)

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Fig. 5

Tracking of particles released at channel inlet for the converging-diverging channel (left) and the straight channel (right)

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Fig. 6

Enhancement in friction factor for constant curvature converging-diverging channels of several aspect ratios at various Reynolds numbers

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Fig. 4

Static temperature contour at mid-plane cross section for constant curvature converging-diverging channel with A/L = 0.075 and (b) straight channel of AR = 1.0 at Re = 100

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Fig. 3

Streamline plots for constant curvature converging-diverging channel with A/L = 0.075 and AR = 1.0 (streamline plots along mid-plane of channel height) at Re = 100

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Fig. 7

Enhancement in Nusselt number for constant curvature converging-diverging channels of several aspect ratios at various Reynolds numbers

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Fig. 8

Performance factor for constant curvature converging-diverging channels of several aspect ratios at various Reynolds numbers

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Fig. 9

Iso-surface plots mapping out the fluid recirculation zones in the constant curvature converging-diverging channels of various aspect ratios

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Fig. 10

Streamline plots along mid-plane of channel height for various amplitude ratios of the constant curvature converging-diverging channel at Re = 100

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Fig. 11

Enhancement in Nusselt number for constant curvature converging-diverging channels of several amplitude ratios at various Reynolds numbers

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Fig. 12

Enhancement in friction factor for constant curvature converging-diverging channels of several amplitude ratios at various Reynolds numbers

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Fig. 16

Enhancement in Nusselt number for sinusoidal converging-diverging channels of several amplitude ratios at various Reynolds numbers

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Fig. 13

Performance factor for constant curvature converging-diverging channels of several amplitude ratios at various Reynolds numbers

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Fig. 14

Streamline plots along mid-plane of channel height for various amplitude ratios of the sinusoidal converging-diverging channel at Re = 100

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Fig. 15

Enhancement in friction factor for sinusoidal converging-diverging channels of several amplitude ratios at various Reynolds numbers

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Fig. 19

Streamline plots at channel's upper furrow for sinusoidal (left) and constant curvature (right) converging-diverging channel of various amplitude ratios at Re = 100

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Fig. 17

Enhancement in performance factor for sinusoidal converging-diverging channels of several amplitude ratios at various Reynolds numbers

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Fig. 18

Performance factor for sinusoidal and constant curvature converging-diverging channels at several amplitude ratios for Re = 50, 100, 150, and 200

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Fig. 22

Laser sheet flow visualization set up

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Fig. 23

Laser sheet flow visualization results for Re = 100 and Re = 200

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Fig. 24

CFD results for streamline plots at Re = 100 and Re = 200

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Fig. 20

Longitudinal plane of laser sheet flow visualization along mid plane of channel height

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Fig. 21

Experiment set up of converging-diverging channel

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Fig. 1

CAD illustration of the proposed microchannel heat sink design containing converging-diverging flow passages

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