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Research Papers: Evaporation, Boiling, and Condensation

Flow Boiling Enhancement in Microtubes With Crosslinked pHEMA Coatings and the Effect of Coating Thickness

[+] Author and Article Information
Taha Çıkım

Mechatronics Engineering Program,
Faculty of Engineering Science,
Orhanli – Tuzla/Istanbul 34956, Turkey
e-mail: tahacikim@sabanciuniv.edu

Efe Armağan

Material Science and Engineering Program,
Faculty of Engineering Science,
Orhanli – Tuzla/Istanbul 34956, Turkey
e-mail: efearmagan@sabanciuniv.edu

Gozde Ozaydin Ince

Material Science and Engineering Program,
Faculty of Engineering Science,
Orhanli – Tuzla/Istanbul 34956, Turkey
e-mail: gozdeince@sabanciuniv.edu

Ali Koşar

Mechatronics Engineering Program,
Faculty of Engineering Science,
Orhanli – Tuzla/Istanbul 34956, Turkey
e-mail: kosara@sabanciuniv.edu

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received September 16, 2013; final manuscript received March 28, 2014; published online May 2, 2014. Assoc. Editor: W. Q. Tao.

J. Heat Transfer 136(8), 081504 (May 02, 2014) (11 pages) Paper No: HT-13-1486; doi: 10.1115/1.4027352 History: Received September 16, 2013; Revised March 28, 2014

In this experimental study, flow boiling in mini/microtubes was investigated with surface enhancements provided by crosslinked polyhydroxyethylmethacrylate (pHEMA) coatings, which were used as a crosslinker coating type with different thicknesses (∼50 nm, 100 nm, and 150 nm) on inner microtube walls. Flow boiling heat transfer experiments were conducted on microtubes (with inner diameters of 249 μm, 507 μm, and 908 μm) coated with crosslinked pHEMA coatings. pHEMA nanofilms were deposited with initiated chemical vapor deposition (iCVD) technique. De-ionized water was utilized as the working fluid in this study. Experimental results obtained from coated microtubes were compared to their plain surface counterparts at two different mass fluxes (5000 kg/m2 s and 20,000 kg/m2 s), and significant enhancements in critical heat flux (up to 29.7%) and boiling heat transfer (up to 126.2%) were attained. The enhancement of boiling heat transfer was attributed to the increase in nucleation site density and incidence of bubbles departing from surface due to porous structure of crosslinked pHEMA coatings. The underlying mechanism was explained with suction-evaporation mode. Moreover, thicker pHEMA coatings resulted in larger enhancements in both CHF and boiling heat transfer.

Copyright © 2014 by ASME
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References

Figures

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Fig. 1

Schematic of iCVD system and the components

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Fig. 2

Schematic of the heat transfer experiment setup

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Fig. 3

Schematic of the test section

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Fig. 4

Raman spectrum taken from the inner surface of the untreated sample microtube having 249 μm inner diameter

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Fig. 5

Raman spectrum taken from the inner surface of the treated sample microtube having 249 μm inner diameter

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Fig. 9

Boiling curves for plain surface microtubes and pHEMA coated microtubes (50 nm, 100 nm, and 150 nm thick coatings) with an inner diameter of 998 μm at the mass flux of 5000 kg/m2 s

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Fig. 10

Boiling curves for plain surface microtubes and pHEMA coated microtubes (50 nm, 100 nm, and 150 nm thick coatings) with an inner diameter of 249 μm at the mass flux of 20,000 kg/m2 s

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Fig. 11

Boiling curves for plain surface microtubes and pHEMA coated microtubes (50 nm, 100 nm, and 150 nm thick coatings) with an inner diameter of 507 μm at the mass flux of 20,000 kg/m2 s

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Fig. 12

Boiling curves for plain surface microtubes and pHEMA coated microtubes (50 nm, 100 nm, and 150 nm thick coatings) with an inner diameter of 998 μm at the mass flux of 20,000 kg/m2 s

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Fig. 13

(a) Two-phase heat transfer coefficient for plain surface microtubes and pHEMA coated microtubes (50 nm, 100 nm, and 150 nm thick coatings) with an inner diameter of 249 μm at the mass flux of 5000 kg/m2 s. (b) Two-phase heat transfer coefficient for plain surface microtubes and pHEMA coated microtubes (50 nm, 100 nm, and 150 nm thick coatings) with an inner diameter of 507 μm at the mass flux of 5000 kg/m2 s. (c) Two-phase heat transfer coefficient for plain surface microtubes and pHEMA coated microtubes (50 nm, 100 nm, and 150 nm thick coatings) with an inner diameter of 998 μm at the mass flux of 5000 kg/m2 s.

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Fig. 14

(a) Two-phase heat transfer coefficient for plain surface microtubes and pHEMA coated microtubes (50 nm, 100 nm, and 150 nm thick coatings) with an inner diameter of 249 μm at the mass flux of 20,000 kg/m2 s. (b) Two-phase heat transfer coefficient for plain surface microtubes and pHEMA coated microtubes (50 nm, 100 nm, and 150 nm thick coatings) with an inner diameter of 507 μm at the mass flux of 20,000 kg/m2 s. (c) Two-phase heat transfer coefficient for plain surface microtubes and pHEMA coated microtubes (50 nm, 100 nm, and 150 nm thick coatings) with an inner diameter of 998 μm at the mass flux of 20,000 kg/m2 s.

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Fig. 15

The schematic of the experimental setup for visualization

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Fig. 8

Boiling curves for plain surface microtubes and pHEMA coated microtubes (50 nm, 100 nm, and 150 nm thick coatings) with an inner diameter of 507 μm at the mass flux of 5000 kg/m2 s

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Fig. 7

Boiling curves for plain surface microtubes and pHEMA coated microtubes (50 nm, 100 nm, and 150 nm thick coatings) with an inner diameter of 249 μm at the mass flux of 5000 kg/m2 s

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Fig. 6

f(experimental)/f(theoretical)—Reynolds number profile

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Fig. 17

Bubbles emerging from the crosslinked pHEMA coated plate

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Fig. 16

Bubbles emerging from the noncoated plate

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