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Evaporation, Boiling, and Condensation

Experimental Study of Nucleate Boiling Heat Transfer Using Enhanced Space-Confined Structures

[+] Author and Article Information
Xuehu Ma1

Institute of Chemical Engineering,  Dalian University of Technology, Dalian 116012, Chinaxuehuma@dlut.edu.cn

Chunjian Yu, Zhong Lan, Donghui Wang, Tao Bai

Institute of Chemical Engineering,  Dalian University of Technology, Dalian 116012, Chinaxuehuma@dlut.edu.cn

1

Corresponding author.

J. Heat Transfer 134(6), 061501 (May 08, 2012) (10 pages) doi:10.1115/1.4006018 History: Received April 18, 2011; Revised November 04, 2011; Published May 08, 2012; Online May 08, 2012

For narrow space boiling, it is difficult to release bubbles from the narrow space, especially on a large-area surface. To solve this problem, a new structure is designed in the present paper. An experimental study of pool boiling on the novel copper enhanced structure, with the separate ordinary confined spaces and the open channels between them, was conducted with water and ethanol. High-speed visualizations are performed to elucidate the bubble flow. The results show that the boiling performance of both water and ethanol can be enhanced effectively. The visualizations indicated that most active nucleation sites emerged in the confined channels and rarely appeared at the bare surfaces not covered by enhanced structures even at high superheat. The bubble diameter, the bubble departure frequency, and the numbers of nucleation sites are obtained using statistical methods. The results suggest that the magnitudes of bubble diameter of water are almost the same on the smooth and enhanced surfaces. The amount of nucleation sites on the enhanced surfaces is remarkably increased, indicating its key role in the boiling enhancement of water. The bubble departure frequency is increased on one of the enhanced surfaces while not increased on another, showing that it is also a significant factor for heat transfer enhancement under certain conditions. While for ethanol, all the three parameters are increased on the enhanced surfaces.

Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

Schematic of the enhanced structure

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Figure 2

Schematic diagram of experimental apparatus: (a) Layout of the elements and (b) details of the open and confined space

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Figure 3

Reliability tests of the experimental system: (a) boiling curve in unconfined pool boiling and (b) temperature measurements

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Figure 4

Boiling curves of deionized water on enhanced structures

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Figure 5

Boiling curves of ethanol on enhanced structures

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Figure 6

Horizontal view of boiling water on the smooth copper surface: (a) q = 33.3 kW/m2 ; (b) q = 163.6 kW/m2 ; (c) q = 248.9 kW/m2 ; and (d) q = 288.9 kW/m2

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Figure 7

Horizontal view of boiling water on E0.5 surface: (a) q = 54.1 kW/m2 ; (b) q = 127.2 kW/m2 ; (c) q = 200.2 kW/m2 ; (d) q = 288.9 kW/m2 ; (e) q = 346.2 kW/m2 ; (f) q = 421.3 kW/m2 ; and (g) film boiling

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Figure 8

Horizontal view of boiling of water on E0.15 surface: (a) q = 54.2 kW/m2 ; (b) q = 126.2 kW/m2 ; (c) q = 202.2 kW/m2 ; (d) q = 298.7 kW/m2 ; (e) q = 337.5 kW/m2 ; and (f) film boiling status

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Figure 9

Horizontal view of boiling of ethanol on the smooth surface: (a) q = 13.3 kW/m2 ; (b) q = 18.9 kW/m2 ; (c) q = 24.7 kW/m2 ; (d) q = 31.1 kW/m2 ; (e) q = 82.3 kW/m2 ; and (f) q = 115.1 kW/m2 .

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Figure 10

Horizontal view of boiling of ethanol on E0.5 surface: (a) q = 26.7 kW/m2 ; (b) q = 61.1 kW/m2 ; (c) q = 168.3 kW/m2 ; and (d) q = 344.3 kW/m2

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Figure 11

Horizontal view of boiling of ethanol on E0.15 surface: (a) q = 33.1 kW/m2 ; (b) q = 83.3 kW/m2 ; (c) q = 190.2 kW/m2 ; and (d) q = 372 kW/m2

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Figure 12

Photographs from side view for ethanol boiling on E0.5 surface: (a) q = 26.7 kW/m2 and (b) q = 72.3 kW/m2

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Figure 13

Boiling curves with different D, f = 40 s−1 , n = 1 cm−2

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Figure 14

Boiling curves with different n, D = 4 mm, f = 40 s−1

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Figure 15

Boiling curves with different f, D = 4 mm, n = 2 cm−2

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Figure 16

The statistical data for bubble diameter: (a) water and (b) ethanol

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Figure 17

Schematic diagram of bubble on free (left) and confined (right) surfaces

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Figure 18

The statistical data for the numbers of nucleation sites: (a) water and (b) ethanol

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Figure 19

The statistical data for bubble departure frequency: (a) water and (b) ethanol

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