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Research Papers: Evaporation, Boiling, and Condensation

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

[+] Author and Article Information
Leyuan Yu, Aritra Sur

Department of Mechanical Engineering,
University of Houston,
Houston, TX 77204-4006

Dong Liu

Department of Mechanical Engineering,
University of Houston,
Houston, TX 77204-4006
e-mail: dongliu@uh.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received June 16, 2014; final manuscript received January 10, 2015; published online February 10, 2015. Assoc. Editor: Robert D. Tzou.

J. Heat Transfer 137(5), 051502 (May 01, 2015) (11 pages) Paper No: HT-14-1408; doi: 10.1115/1.4029647 History: Received June 16, 2014; Revised January 10, 2015; Online February 10, 2015

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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Figures

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Fig. 1

Schematic of the experimental apparatus

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Fig. 2

Boiling curves of (a) water, (b) 0.01 vol. % nanofluid, and (c) 0.1 vol. % nanofluid

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Fig. 3

Comparison of the boiling curves at two inlet conditions: (a) G = 1364.3 kg/m2s, Tf,in = 90.6 °C and (b) G = 1545.0 kg/m2s, Tf,in = 85.5 °C

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Fig. 5

Size range of active nucleation sites as a function of wall temperature for different contact angles (Note: θ=20 deg is a hypothetical case to illustrate the effect of contact angle)

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Fig. 6

Time-dependence of mass flux (G), inlet and outlet pressures (Pin and Pout), pumping power (P), and inlet and outlet temperatures (Tin and Tout) of water at (a) G = 2038.7 kg/m2s, Tf,in = 92.3 °C, and qw'' = 29.9 W/cm2 (stable region); and (b) G = 1054.4 kg/m2s, Tf,in = 91.9 °C, and qw'' = 29.9 W/cm2

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Fig. 7

Time-dependence of mass flux (G), inlet and outlet pressures (Pin and Pout), pumping power (P), and inlet and outlet temperatures (Tin and Tout) of 0.01 vol. % nanofluids at (a) G = 2007.4 kg/m2s, Tf,in = 92.3 °C, and qw'' = 29.9 W/cm2 (stable region); and (b) G = 1052.4 kg/m2s, Tf,in = 92.7 °C, and qw'' = 29.9 W/cm2

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Fig. 8

Time-dependence of mass flux (G), inlet and outlet pressures (Pin and Pout), pumping power (P), and inlet and outlet temperatures (Tin and Tout) of 0.1 vol. % nanofluids at (a) G = 2028.5 kg/m2s, Tf,in = 92.3 °C, and qw'' = 29.9 W/cm2 (stable region); and (b) G = 1065.9 kg/m2s, Tf,in = 92.5 °C, and qw'' = 29.9 W/cm2

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Fig. 9

Two-phase flow oscillations at G = 1065.9 kg/m2s, Tf,in = 91.9–92.5 °C, and qw'' = 29.9 W/cm2

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Fig. 10

Two-phase flow characteristics under different heat fluxes: (a) water, (b) 0.01 vol. % nanofluid, and (c) 0.1 vol. % nanofluid (Tf,in = 92.5 °C)

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Fig. 11

Comparison of two-phase flow characteristics of water and nanofluids under different heat fluxes. (a) qw'' = 19.9 W/cm2, (b) qw'' = 23.2 W/cm2, (c) qw'' = 26.2 W/cm2, and (d) qw'' = 29.9 W/cm2.

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