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MICRO/NANOSCALE HEAT TRANSFER—PART II

Recent Work on Boiling and Condensation in Microchannels

[+] Author and Article Information
Ping Cheng1

School of Mechanical and Power Engineering, Shanghai Jiaotong University, 800 Dong Chuan Road, Shanghai 200240, P.R. Chinapingcheng@sjtu.edu.cn

Guodong Wang

School of Mechanical and Power Engineering, Shanghai Jiaotong University, 800 Dong Chuan Road, Shanghai 200240, P.R. Chinawangguodong@sjtu.edu.cn

Xiaojun Quan

School of Mechanical and Power Engineering, Shanghai Jiaotong University, 800 Dong Chuan Road, Shanghai 200240, P.R. Chinaquan_xiaojun@sjtu.edu.cn

1

Corresponding author.

J. Heat Transfer 131(4), 043211 (Mar 04, 2009) (15 pages) doi:10.1115/1.3072906 History: Received March 02, 2008; Revised August 03, 2008; Published March 04, 2009

Recent work on boiling of water and condensation of steam in single and parallel microchannels is reviewed in this paper. It is found that the amplitude and frequency of fluctuations of temperature and pressure during the unstable flow-boiling mode depend greatly on the inlet/outlet configurations and the exit vapor quality. By fabricating an inlet restriction on each microchannel or the installation of a throttling valve upstream of the test section, reversed flow of vapor bubbles can be suppressed resulting in a stable flow-boiling mode. Boiling heat transfer coefficient and pressure drop in microchannels under stable flow-boiling conditions are obtained. These data at high vapor qualities are found to be substantially different from the correlations obtained for flow-boiling in macrochannels. Microbubble emission boiling phenomena, which can defer the arrival of critical heat flux, exist in a partially heated Pyrex glass microchannel at sufficiently high heat flux and high inlet subcooling conditions. For condensation in a microchannel, transition from annular flow to slug/bubbly flow is investigated. The occurrence of the injection flow is owing to the instability of the liquid/vapor interface. The location, at which the injection flow occurs, depends on the mass flux and the cooling rate of steam. Increase in steam mass flux, decrease in cooling rate, and microchannel diameter tend to enhance the instability of the condensate film on the wall, resulting in the occurrence of injection flow further downstream at increasingly high frequency. The pressure drop in the condensing flow increases with the increase in mass flux and quality or with decreasing microchannel diameter. The existing correlations for pressure drop and heat transfer of condensing flow in macrochannels overestimate the experimental data in microchannels.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Parallel microchannels with two different types of inlet/outlet connections (15)

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Figure 2

Different flow-boiling patterns in parallel microchannels (Dh=186 μm) with vertical inlet/outlet connections (14) and with horizontal inlet/outlet connections (15)

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Figure 3

Measurements of inlet/outlet water and wall temperatures and inlet/outlet pressures in parallel microchannels (Dh=186 μm) in bubby/annular alternating flow-boiling regime: (a) horizontal inlet/outlet connections with q=485.5 kW/m2, G=364.9 kg/m2 s, and Tin=35°C(xe=0.096); (b) vertical inlet/outlet connection with q=497.8 kW/m2, G=368.9 kg/m2 s, and Tin=35°C(xe=0.099)(15)

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Figure 4

Microchannels with inlet restrictions (15)

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Figure 5

Temporal pressure and temperature variations during flow boiling of water in microchannels with inlet restrictions (Dh=186 μm) and photos of steady flow-boiling patterns at different locations for q=364.7 kW/m2, G=124 kg/m2 s, and Tin=35°C(xe=0.359)(15)

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Figure 6

Flow pattern map for stable flow boiling of R134a in microchannel (Dh=509 μm) at different mass fluxes (26)

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Figure 7

Pressure drop data for steady flow boiling of water in microchannels (Dh=186 μm) and its comparison with Mishima and Hibiki correlation for flow boiling in mini/microchannels at different heat fluxes (15)

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Figure 8

Local boiling heat transfer coefficient of water in microchannel (Dh=480 μm) at mass flux of 200 kg/m2 s(19)

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Figure 9

Comparison of boiling heat transfer coefficient data of water in microchannels (Dh=186 μm) with Kandlikar correlation at different heat fluxes (15)

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Figure 10

Effects of microchannels width on boiling curves of FC-77 and boiling heat transfer coefficient versus wall heat flux at G=700 kg/m2 s(22)

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Figure 11

Boiling heat transfer coefficient of R134a versus vapor quality at different mass fluxes and saturation pressures in a minichannel with Dh=1090 μm(23)

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Figure 12

Three-zone model for elongated bubble flow and cyclic variation in boiling heat transfer coefficient (24)

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Figure 13

Comparison of three-zone model with Agostini’s flow-boiling data of R134a in a 0.77 mm tube (25)

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Figure 14

Determination of saturated CHF of R134a at G=1000 kg/m2 s, Tsat=30°C, in a microtube having D=0.5 mm, Lh=70 mm(27)

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Figure 15

Effects of mass flux and heated length on saturated CHF of R134a in two microtubes of 0.5 mm and 0.8 mm in diameters (27)

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Figure 16

A microchannel integrated with a serpentine microheater (28)

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Figure 17

Effects of mass flux on subcooled flow boiling of water in a single microchannel (Dh=155 μm) with Tin=20°C(28)

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Figure 18

Photos of bubble behavior in a single microchannel (Dh=155 μm) in fully developed MEB of water at q=6.21 MW/m2, G=294.6 kg/m2 s, and Tin=20°C(28)

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Figure 19

Condensation flow regimes in minichannels (49) and microchannels (31)

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Figure 20

Effects of mass flux of steam on location of injection flow Z/L versus Co in parallel microchannels of 136 μm in diameter (29)

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Figure 21

Effects of steam mass fluxes on occurrence frequency of injection flow at different Co numbers in a single microchannel of 128 μm in diameter (29)

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Figure 22

Two-phase pressure drops in condensation of steam in two set of parallel microchannels of 109 μm and 151 μm in diameters (30)

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Figure 23

Variation in ΦL2 versus X in two sets of parallel microchannels having 109 μm and 259 μm in diameters (30)

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Figure 24

Variation in mean heat transfer coefficients along the microchannels with different cross-sectional geometry (35)

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Figure 25

Heat transfer coefficient for annular flow of steam condensing in single microchannel of 173 μm in diameter (31)

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