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Technical Brief

Experimental Verification of a Prediction Model for Pool Boiling Enhanced by the Electrohydrodynamic Effect and Surface Wettability

[+] Author and Article Information
Ichiro Kano

Mem. ASME
Graduate School of Science and Engineering,
Yamagata University,
Yonezawa 992-8510,
Yamagata, Japan
e-mail: kano@yz.yamagata-u.ac.jp

Naoki Okamoto

Graduate School of Science and Engineering,
Yamagata University,
Yonezawa 992-8510,
Yamagata, Japan
e-mail: tah58620@st.yamagata-u.ac.jp

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received October 17, 2015; final manuscript received December 28, 2016; published online April 11, 2017. Assoc. Editor: Debjyoti Banerjee.

J. Heat Transfer 139(8), 084501 (Apr 11, 2017) (7 pages) Paper No: HT-15-1659; doi: 10.1115/1.4036040 History: Received October 17, 2015; Revised December 28, 2016

Enhancing of boiling heat transfer by combining the electrohydrodynamic (EHD) effect and surface wettability has been shown to remove the high heat fluxes from electrical devices such as laser diodes, light emitting diodes, and central processing units. However, this phenomenon is not well understood. Our previous studies on the critical heat flux (CHF) of pool boiling have shown that CHF greatly increases with the application of an electric field and that the wall temperature can be decreased to a level with the safe operation of the electrical devices by using a low contact angle with the boiling surface. To verify the earlier prediction model, CHF enhancement by changing the contact angle with the boiling surface and by the application of an electric field was investigated. A fluorinated dielectric liquid (Asahi Glass Co. Ltd, Tokyo, Japan, AE-3000) was selected as the working fluid. To allow the contact angle between the boiling surface and the dielectric liquid to be changed, several different materials (Cu, Cr, NiB, Sn) and a surface coated with a mixture of 1.5 and 5 μm diamond particles were used as boiling surfaces. The CHFs at different contact angles were 20.5–26.9 W/cm2, corresponding to 95–125% of that for a polished Cu surface (21.5 W/cm2). Upon application of a −5 kV/mm electric field to the microstructured surface (the mixture of 1.5 μm and 5 μm diamond particles), a CHF of 99 W/cm2 at a superheat of 33.5 K was obtained. Based on this experimental evidence, we normalized the CHF and contact angle using our previously developed hydrodynamic instability model and semi-empirical model derived from the interfacial area density close to the boiling surface. This procedure allowed us to develop a general model that predicted CHF well, including the CHF for the de-ionized (DI) water.

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References

Figures

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Fig. 1

Vapor removal configuration through a slit electrode [22]

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Fig. 2

Schematic diagram of experimental facility: ① top of boiling chamber, ② middle of boiling chamber, ③ bottom of boiling chamber, ④ Teflon block, ⑤ copper block, ⑥ main heater, ⑦ condenser, ⑧ preheater, ⑨ subheater, ⑩ electrode, high DC supply, resistance (100kΩ), Ⓣ T-type thermocouple, Ⓟ pressure transducer, and Ⓥ voltmeter

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Fig. 3

SEM image of a boiling surface electrically deposited with 1.5 and 5 μm diamond particles

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Fig. 4

Electrode geometry. This electrode was designed using the basic concept of the previous paper [22].

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Fig. 5

Boiling curves for various surface materials without electrode

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Fig. 6

CHFs for various surface materials as functions of contact angle; no electrode is present

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Fig. 7

Normalized CHFs as functions of contact angle. Contact angle of ϕ1,AE3000 at normalized CHF = 1 is 15 deg, and ϕ1,Water is 27.5 deg.

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Fig. 8

Normalized CHFs as functions of normalized contact angle

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Fig. 10

HTCs for polished Cu surfaces with application of electric fields

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Fig. 9

Effects of electric field on boiling curves for polished Cu surface with application of electric fields

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Fig. 11

Boiling curves for 1.5 and 5 μm diamond-particle surfaces with application of electric fields

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Fig. 12

HTCs for 1.5 and 5 μm diamond-particle surface with application of electric fields

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Fig. 13

Normalized CHFs as functions of normalized contact angle

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