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Research Papers: Evaporation, Boiling, and Condensation

Effect of Surface Roughness on Pool Boiling Heat Transfer of Water on a Superhydrophilic Aluminum Surface

[+] Author and Article Information
Jinsub Kim

Extreme Mechanical Engineering Research
Division,
Korea Institute of Machinery and Materials,
156 Gajeongbuk-Ro, Yuseong-Gu,
Daejeon 34103, South Korea
e-mail: jskim129@kimm.re.kr

Seongchul Jun

Mechanical Engineering Department,
University of Texas at Dallas,
800 W. Campbell Road,
Richardson, TX 75080
e-mail: sxj142030@utdallas.edu

Jungho Lee

Extreme Mechanical Engineering
Research Division,
Korea Institute of Machinery and Materials,
156 Gajeongbuk-Ro, Yuseong-Gu,
Daejeon 34103, South Korea
e-mail: jungho@kimm.re.kr

Juan Godinez

Mechanical Engineering Department,
University of Texas at Dallas,
800 W. Campbell Road,
Richardson, TX 75080
e-mail: jxg129530@utdallas.edu

Seung M. You

Mem. ASME
Professor
Mechanical Engineering Department,
University of Texas at Dallas,
800 W. Campbell Road,
Richardson, TX 75080
e-mail: you@utdallas.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received September 20, 2016; final manuscript received April 19, 2017; published online May 23, 2017. Assoc. Editor: Debjyoti Banerjee.

J. Heat Transfer 139(10), 101501 (May 23, 2017) (9 pages) Paper No: HT-16-1593; doi: 10.1115/1.4036599 History: Received September 20, 2016; Revised April 19, 2017

The effect of surface roughness on the pool boiling heat transfer of water was investigated on superhydrophilic aluminum surfaces. The formation of nanoscale protrusions on the aluminum surface was confirmed after immersing it in boiling water, which modified surface wettability to form a superhydrophilic surface. The effect of surface roughness was examined at different average roughness (Ra) values ranging from 0.11 to 2.93 μm. The boiling heat transfer coefficients increased with an increase in roughness owing to the increased number of cavities. However, the superhydrophilic aluminum surfaces exhibited degradation of the heat transfer coefficients when compared with copper surfaces owing to the flooding of promising cavities. The superhydrophilic aluminum surfaces exhibited a higher critical heat flux (CHF) than the copper surfaces. The CHF was 1650 kW/m2 for Ra = 0.11 μm, and it increased to 2150 kW/m2 for Ra = 0.35 μm. Surface roughness is considered to affect CHF as it improves the capillary wicking on the superhydrophilic surface. However, further increase in surface roughness above 0.35 μm did not augment the CHF, even at Ra = 2.93 μm. This upper limit of the CHF appears to result from the hydrodynamic limit on the superhydrophilic surface, because the roughest surface with Ra = 2.93 μm still showed a faster liquid spreading speed.

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References

Figures

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Fig. 1

Pool boiling test chamber

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Fig. 2

Test heater design

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Fig. 3

Scanning electron microscope images of aluminum surfaces after hot water treatment

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Fig. 4

Static contact angle variation according to the immersion time in boiling water

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Fig. 5

Comparison of boiling curves between aluminum and copper [19] surfaces

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Fig. 6

Comparison of nanostructures on aluminum and copper surfaces

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Fig. 7

Boiling curves of superhydrophilic aluminum compared with copper surfaces [19]

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Fig. 8

Boiling heat transfer coefficients of aluminum surfaces with difference roughness values compared with copper surfaces [19]: (a) q″ = 500 kW/m2 and (b) q″ = 1000 kW/m2

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Fig. 9

Captured images of bubble behaviors on superhydrophilic aluminum surfaces with different surface roughness values at q″ = 80 kW/m2

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Fig. 10

Critical heat flux on superhydrophilic aluminum surfaces with different surface roughness values

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Fig. 11

Comparison of droplet impact and spreading on the aluminum surfaces with different surface roughness characteristics (drop height = 6 mm)

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Fig. 12

Quantitative comparison of droplet spreading on three aluminum surfaces with different surface roughness values

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Fig. 13

Critical heat flux chart representing surface effects of wettability and surface roughness

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