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Research Papers: Micro/Nanoscale Heat Transfer

Formation Mechanism and Characteristics of a Liquid Microlayer in Microchannel Boiling System

[+] Author and Article Information
Yaohua Zhang

Graduate School of Engineering, Yokohama National University, Tokiwadai, Hodogaya, Yokohama 240-8501, Japand08sb191@ynu.ac.jp

Yoshio Utaka

Faculty of Engineering, Yokohama National University, Tokiwadai, Hodogaya, Yokohama 240-8501, Japanutaka@ynu.an.jp

Yuki Kashiwabara

 Tokyo Electric Power Company, 2-1377 Soga-cho, Chuo-ku 260-0822Chiba, Japankashiwabara1986@hotmail.co.jp

J. Heat Transfer 132(12), 122403 (Sep 20, 2010) (7 pages) doi:10.1115/1.4002365 History: Received October 23, 2009; Revised May 17, 2010; Published September 20, 2010; Online September 20, 2010

Experiments were performed using the laser extinction method to measure the thickness of the liquid film formed by growing flattened bubbles in a microchannel for gap sizes of 0.5 mm, 0.3 mm, and 0.15 mm. Water, ethanol, and toluene were used as test fluids. A high-speed camera was also used to simultaneously measure the bubble growth process. It was confirmed that the gap size and bubble forefront velocity determined the initial microlayer thickness. The variation trend of the microlayer thickness relative to the velocity of the interface was divided into two regions: region I, where the velocity is small and the thickness increases linearly with increasing velocity, and region II, where the thickness is almost constant or decreased slightly with increasing velocity. Furthermore, a nondimensional correlation for investigating the effects of test materials and gap sizes on microlayer thickness is presented. An analysis of the results showed that the boundaries of the two regions correspond to a Weber number of approximately 110, and in the region where the Weber number was smaller than 110, the thickness of the microlayer was thinner for the liquid whose value of ρ0.62ν0.42σ0.62 was relatively small. However, for the region where Weber number was larger than 110, the smaller the kinematic viscosity of the liquid, the thinner the microlayer became.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic diagram of bubble

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Figure 2

Experimental apparatus for measuring microlayer thickness

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Figure 3

Error of microlayer thickness measurement due to variation in ambient temperature

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Figure 4

Microlayer thicknesses versus local bubble forefront velocity for water, ethanol, and toluene

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Figure 5

Relationship between microlayer thickness and ratio of I to I0

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Figure 6

Microlayer thickness versus viscous boundary layer thickness

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Figure 7

Effect of bubble forefront traveling distance

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Figure 8

Nondimensional viscous microlayer thickness versus Weber number for all test liquids and gaps

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Figure 11

Comparison between the prediction and the experiment

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Figure 10

Effect of fluid properties on initial microlayer thickness for s=0.5 mm, 0.3 mm, and 0.15 mm

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Figure 9

Nondimensional microlayer thickness versus Weber number for water and toluene to examine the effect of gap sizes

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