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Evaporation, Boiling, and Condensation

Investigation of Pool Boiling Critical Heat Flux Enhancement on a Modified Surface Through the Dynamic Wetting of Water Droplets

[+] Author and Article Information
Ho Seon Ahn

Division of Advanced Nuclear Engineering, POSTECH, Pohang 790-784, Republic of Korea

Joonwon Kim

Department of Mechanical Engineering, POSTECH, Pohang 790-784, Republic of Korea

Moo Hwan Kim1

Division of Advanced Nuclear Engineering, POSTECH, Pohang 790-784, Republic of Koreamhkim@postech.ac.kr

1

1 Corresponding author.

J. Heat Transfer 134(7), 071504 (May 24, 2012) (13 pages) doi:10.1115/1.4006113 History: Received August 21, 2011; Revised December 20, 2011; Published May 24, 2012; Online May 24, 2012

Dynamic wetting behaviors of water droplet on the modified surface were investigated experimentally. Dynamic contact angles were measured as a characterization method to explain the extraordinary pool boiling critical heat flux (CHF) enhancement on the zirconium surface by anodic oxidation modification. The sample surface is rectangular zirconium alloy plates (20 × 25 × 0.7 mm), and 12 μl of deionized water droplets were fallen from 40 mm of height over the surface. Dynamic wetting movement of water on the surface showed different characteristics depending on static contact angle (49.3 deg–0 deg) and surface temperature (120 °C–280 °C). Compared with bare surface, wettable and spreading surface had no-receding contact angle jump and seemed stable evaporating meniscus of liquid droplet in dynamic wetting condition on hot surface. This phenomenon could be explained by the interaction between the evaporation recoil and the surface tension forces. The surface tension force increased by micro/nanostructure of the modified zirconium surface suppresses the vapor recoil force by evaporation which makes the water layer unstable on the heated surface. Thus, such increased surface force could sustain the water layer stable in pool boiling CHF condition so that the extraordinary CHF enhancement could be possible.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 3

Detachable zirconium alloy test section [15]

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Figure 4

The schematic diagram of the experimental facility for the dynamic wetting

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Figure 5

The motion of water droplet on the bare and the modified zirconium alloy. All frames have the interval of 1 ms.

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Figure 6

Dynamic contact angle on the bare and the modified zirconium alloy with the wall temperature of 27 °C.

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Figure 7

(a) The water boiling curve of bare zirconium alloy for repeatability and (b) the fine bubble nucleation on the heated surface

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Figure 8

(a) The boiling curves of bare and modified zirconium alloy, (b) CHF enhancement ratio (%) based on the bare zirconium alloy (inset: Liquid spreading ability of each surface under the contact angle of 10 deg)

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Figure 9

The dynamic wetting of water droplet on a bare zirconium alloy surface at 120 °C, 160 °C, 200 °C, 240 °C, and 280 °C

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Figure 10

The dynamic contact angles of bare zirconium alloy surface with the wall temperature increasing

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Figure 11

The dynamic wetting of water droplet on a modified zirconium alloy surface (the contact angle of 22.6 deg) at 120 °C, 160 °C, 200 °C, 240 °C, and 280 °C

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Figure 12

The dynamic contact angles of modified zirconium alloy surface (the contact angle of 22.6 deg) with the wall temperature increasing

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Figure 13

The dynamic wetting of water droplet on a modified zirconium alloy surface (the contact angle of 0 deg) at 120 °C, 160 °C, 200 °C, 240 °C, and 280 °C

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Figure 14

The dynamic contact angles of modified zirconium alloy surface (the contact angle of 0 deg) with the wall temperature increasing

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Figure 2

Schematic diagram of pool boiling experimental facility

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Figure 1

SEM images, contact angle, and liquid spreading of test surfaces: (a) 49.3 deg–0 s of anodic oxidation time (bare zirconium alloy), (b) 32.4 deg–20 s, (c) 22.6 deg–40 s, (d) 21.7 deg–60 s, (e) 8.2 deg–240 s, (f) 2.1 deg–360 s, (g) 0 deg–480 s, and (h) 0 deg–600 s

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