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Research Papers

Suppression of Two-Phase Flow Instabilities in Parallel Microchannels by Using Synthetic Jets

[+] Author and Article Information
Ruixian Fang

e-mail: fangr@cec.sc.edu

Jamil A. Khan

e-mail: khan@cec.sc.edu
Department of Mechanical Engineering,
University of South Carolina,
Columbia, SC 29208

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the Journal of Heat Transfer. Manuscript received July 1, 2012; final manuscript received February 13, 2013; published online September 23, 2013. Assoc. Editor: Sujoy Kumar Saha.

J. Heat Transfer 135(11), 111016 (Sep 23, 2013) (13 pages) Paper No: HT-12-1338; doi: 10.1115/1.4024624 History: Received July 01, 2012; Revised February 13, 2013

Two-phase flow instabilities in microchannels exhibit pressure and temperature fluctuations with different frequencies and amplitudes. An active way to suppress the dynamic instabilities in the boiling microchannels is to introduce synthetic jets into the channel fluid. Thus, the bubbles can be condensed before they clog the channel and expand upstream causing flow reversal. The present work experimentally investigated the effects of synthetic jets on microchannel flow boiling. An array of synthetic jets was introduced into the microchannel flow. The strength and frequency of the jets were controlled by changing the driving signals of the piezoelectric driven jet actuator. It is found that the bubbles were effectively condensed inside the jet cavity. The boiling flow reversals were notably delayed by the synthetic jets. Meanwhile, the pressure fluctuation amplitudes were suppressed to some extent. It was also observed that synthetic jets can help to uniformize the heat sink temperature distribution.

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References

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Figures

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Fig. 1

Schematic of flow loop for flow boiling

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Fig. 2

Test module exploded view (insulation blocks not shown)

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Fig. 3

Test module assemblies

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Fig. 4

Schematic of the jet array and their position

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Fig. 5

Cross section of a microchannel (not to scale)

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Fig. 6

(a) Heat loss correlation and (b) boiling curve. For G = 172 kg/m2 s

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Fig. 7

Comparison of temperature and pressures variations at unstable state (a) and (b) and stable states (c) and (d) for G = 172 kg/m2 s

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Fig. 8

Boling curves with and without synthetic jet, G = 172 kg/m2 s

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Fig. 9

Local wall temperature with synthetic jets, q″ = 55.9 W/cm2 and G = 172 kg/m2 s

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Fig. 10

(a) Fluid temperature fluctuations and (b) pressures fluctuations at the onset of unstable boiling with synthetic jets. q″ = 55.9 W/cm2 and G = 172 kg/m2 s

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Fig. 11

Schematic of the modified jet array

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Fig. 12

Boling curves with and without synthetic jets for the modified design. The jet actuator is operated at 160 V, and G = 172 kg/m2 s.

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Fig. 13

Boling curves for the modified design. The jet actuator is operated at 160 V, and G = 172 kg/m2 s.

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Fig. 14

Fluid temperature and pressure variations without jets (a) and (b) and with jets (c) and (d), G = 172 kg/m2 s. With synthetic jets, the actuator is operated at 160 V and 80 Hz.

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Fig. 15

Average heat transfer coefficient of the heat sink for the modified design. The jet actuator is operated at 160 V, and G = 172 kg/m2 s.

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Fig. 16

Boling curves with and without synthetic jets for the modified design. The jet actuator is operated at 160 V, and G = 325 kg/m2 s.

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Fig. 17

The concept of using synthetic jets to suppress flow boiling instabilities: (a) Bubble collapse during the discharge stroke; (b) Bubble collapse during the suction stroke.

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Fig. 18

Sequence images of bubble expansion into the jet cavity, the jet orifices shown are at fifth, sixth, and seventh columns. Jet actuator is operated at 160 V and 80 Hz; G = 172 kg/m2 s; q″ = 47.7 W/cm2.

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Fig. 19

Image of bubbles expansion into the jet cavity, orifices shown are at fifth, sixth, and seventh columns. Jet actuator is operated at 160 V and 80 Hz; G = 172 kg/m2 s; q″ = 80.7 W/cm2.

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Fig. 20

Local wall temperature distribution, G = 325 kg/m2 s. For tests with jets, the jet actuator is operated at 160 V and 80 Hz.

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Fig. 21

Subcooling effects on boiling curves for G = 172 kg/m2 s. Tests with synthetic jets only, the jet actuator is operated at 160 V and 200 Hz

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Fig. 22

Effect of synthetic jets on pressure drops. G = 325 kg/m2 s, the jet actuator is operated at 160 V and 80 Hz.

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