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

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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Flow Boiling Heat Transfer and Two-Phase Flow Instability of Nanofluids in a Minichannel

Journal of Heat Transfer ◽

10.1115/1.4029647 ◽

2015 ◽

Vol 137 (5) ◽

Cited By ~ 21

Author(s):

Leyuan Yu ◽

Aritra Sur ◽

Dong Liu

Keyword(s):

Heat Transfer ◽

Boiling Heat Transfer ◽

Two Phase Flow ◽

Flow Instability ◽

Flow Boiling ◽

Nucleate Boiling ◽

Flow Instabilities ◽

Phase Flow ◽

Two Phase ◽

Flow Boiling Heat Transfer

Single-phase convective heat transfer of nanofluids has been studied extensively, and different degrees of enhancement were observed over the base fluids, whereas there is still debate on the improvement in overall thermal performance when both heat transfer and hydrodynamic characteristics are considered. Meanwhile, very few studies have been devoted to investigating two-phase heat transfer of nanofluids, and it remains inconclusive whether the same pessimistic outlook should be expected. In this work, an experimental study of forced convective flow boiling and two-phase flow was conducted for Al2O3–water nanofluids through a minichannel. General flow boiling heat transfer characteristics were measured, and the effects of nanofluids on the onset of nucleate boiling (ONB) were studied. Two-phase flow instabilities were also explored with an emphasis on the transition boundaries of onset of flow instabilities (OFI). It was found that the presence of nanoparticles delays ONB and suppresses OFI, and the extent is correlated to the nanoparticle volume concentration. These effects were attributed to the changes in available nucleation sites and surface wettability as well as thinning of thermal boundary layers in nanofluid flow. Additionally, it was observed that the pressure-drop type flow instability prevails in two-phase flow of nanofluids, but with reduced amplitude in pressure, temperature, and mass flux oscillations.

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TWO-PHASE FLOW INSTABILITIES IN HORIZONTAL AND VERTICAL IN - TUBE FLOW BOILING SYSTEMS

International Symposium on Transient Convective Heat Transfer ◽

10.1615/ichmt.1996.transientconvheattransf.150 ◽

1996 ◽

Author(s):

Sadik Kakac ◽

Claudia O. Gavrilescu

Keyword(s):

Two Phase Flow ◽

Flow Boiling ◽

Flow Instabilities ◽

Phase Flow ◽

Tube Flow ◽

Two Phase

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Flow Boiling Heat Transfer and Two-Phase Flow Instability of Nanofluids in a Minichannel

Volume 2: Heat Transfer Enhancement for Practical Applications; Heat and Mass Transfer in Fire and Combustion; Heat Transfer in Multiphase Systems; Heat and Mass Transfer in Biotechnology ◽

10.1115/ht2013-17154 ◽

2013 ◽

Cited By ~ 1

Author(s):

Leyuan Yu ◽

Dong Liu

Keyword(s):

Heat Transfer ◽

Boiling Heat Transfer ◽

Two Phase Flow ◽

Flow Instability ◽

Flow Boiling ◽

Nucleate Boiling ◽

Flow Instabilities ◽

Phase Flow ◽

Two Phase ◽

Flow Boiling Heat Transfer

Recent studies of single-phase convective heat transfer of nanofluids reveal that, unlike the promising hypohesis in the early works, there is no significant improvement in the overall thermal performance of nanofluids over that of the base fluids when both heat transfer and hydrodynamic characteristics are considered. Meanwhile, very few studies have been devoted to investigating two-phase heat transfer of nanofluids, and it remains inconclusive whether the same pessimistic outlook should be expected. In this work, an experimental study of forced convective flow boiling and two-phase flow was conducted for Al2O3-water nanofluids through a minichannel. General flow boiling heat transfer characteristics were measured, and the effects of nanofluids on the onset of nucleate boiling (ONB) were studied. Two-phase flow instabilities were also explored with an emphasis on the transition boundaries of onset of flow instabilities (OFI). It was found that the presence of nanoparticles delays ONB and suppresses OFI, and the extent is correlated to the nanoparticle volume concentration. These effects were attributed to the change of surface wettability and the thinning of thermal boundary layer in the nanofluid flow. Additionally, it was observed that the pressure-drop type flow instability prevails in nanofluid two-phase flow, however, the oscillation amplitudes of the pressure, temperature and mass flux measurements are reduced.

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