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Research Papers: Heat Transfer Enhancement

An Experimental Study of Passive and Active Heat Transfer Enhancement in Microchannels

[+] Author and Article Information
Yoav Peles

e-mail: pelesy@rpi.edu
Mechanical, Aerospace,
and Nuclear Engineering (MANE),
Rensselaer Polytechnic Institute,
Troy, NY 12180

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received February 12, 2013; final manuscript received August 29, 2013; published online November 15, 2013. Assoc. Editor: Sujoy Kumar Saha.

J. Heat Transfer 136(3), 031901 (Nov 15, 2013) (11 pages) Paper No: HT-13-1076; doi: 10.1115/1.4025558 History: Received February 12, 2013; Revised August 29, 2013

An experimental study on single-phase heat transfer and fluid flow downstream a single microscale pillar in a microchannel was conducted. A secondary jet flow was issued from slits formed along the pillar. A comparison of the thermal performances of a plain microchannel, a microchannel with a pillar, and a microchannel with a jet issued from a pillar was performed to elucidate the merits of this heat transfer enhancement technique. It was found that the presence of a pillar upstream the heater enhanced the heat transfer; the addition of jet flow issued from a pillar further enhanced the heat transfer. At a Reynolds number of 730, an improvement of spatially averaged Nusselt number of 80% was achieved due to the combined effect of the pillar and the jet compared with the corresponding plain channel. Micro particle image velocimetry (μPIV) measurements provided planar velocity fields at two planes along the channel height, and allowed flow structure visualization. Turbulent kinetic energy (TKE) was used to measure flow mixing and to quantify the hydrodynamic effect of the jet. It was shown that the TKE is closely related to the Nusselt number.

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Figures

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Fig. 1

Schematics of (a) microdevice and (b) microdevice zoom-in; (c) SEM image of the micropillar and slits

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Fig. 2

Schematics of the assembly of the fixture; the jet flow was introduced from the bottom

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Fig. 3

(a) Schematic of the closed heat transfer flow loop. (b) Schematic of the μPIV flow loop.

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Fig. 4

Averaged Nusselt numbers of the plain microchannel with thermal heating length, x of 1 mm and hydraulic diameter, Dh of 391 μm

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Fig. 5

Nusselt numbers for the plain microchannel (hollow dots) and the channel with a pillar (solid dots)

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Fig. 6

Nusselt numbers for the plain microchannel without a jet, the channel with a pillar without a jet, and the channel with a jet issued from the pillar at a jet-to-crossflow momentum coefficient of 10%

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Fig. 7

Nusselt numbers for the channel with a pillar without a jet and the channel with a jet issued from the pillar at jet-to-crossflow momentum coefficients of 3%, 5%, 8%, and 10% at Re = 320, 524, and 730

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Fig. 8

The variation of the heat transfer enhancement, E, as a function of the jet momentum coefficient, at Re = 320, 524, and 730

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Fig. 9

Time averaged velocity field contours at Re = 322 in the 1/8 plane ((a)–(c)) and middle plane ((d)–(f)) with three jet-to-crossflow momentum coefficients. The velocities were normalized by the main flow mean velocity.

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Fig. 10

Schematic of the evolution of the jet and its interaction with the main flow in top view (a) and side view (b). And the corresponding velocity fields contours in 1/8 plane near the wall (c) and the middle plane (d).

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Fig. 11

Instantaneous velocity field contours and streamlines in the middle plane at Re = 730 at two different time instances, t1 ((a)–(c)) and t2 ((d)–(f)) with three jet-to-crossflow momentum coefficients

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Fig. 12

TKE contours downstream the pillar at Re = 730 in two planes for flow without a jet ((a) and (b)) and with a jet of  = 10% ((c) and (d)). The squares in four contours denote the position of the heaters.

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Fig. 13

TKE contours downstream the pillar for flow in two planes at Re = 322 ((a) and (b)), 524 ((c) and (d)), and 730 ((e) and (f)) with a same jet momentum coefficient,  = 10%

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Fig. 14

Variation of total TKEs with jet momentum coefficients in two planes at Re = 320, 524, and 730

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Fig. 15

Variation of Nusselt numbers and total TKEs in the 1/8 plane with jet momentum coefficients at Re = 320, 524, and 730

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