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Research Papers: Evaporation, Boiling, and Condensation

Pool Boiling Heat Transfer Characteristics of Inclined pHEMA-Coated Surfaces

[+] Author and Article Information
Abdolali Khalili Sadaghiani

Mechatronics Engineering Program,
Sabanci University,
Orta Mahalle,
Tuzla, Istanbul 34956, Turkey
e-mail: akhalilisadaghiani@sabanciuniv.edu

Ahmad Reza Motezakker

Mechatronics Engineering Program,
Sabanci University,
Orta Mahalle,
Tuzla, Istanbul 34956, Turkey
e-mail: ahmadrezam@sabanciuniv.edu

Alsan Volkan Özpınar

Materials Science & Nanoengineering Program,
Sabanci University,
Orta Mahalle,
Tuzla, Istanbul 34956, Turkey
e-mail: avozpinar@sabanciuniv.edu

Gözde Özaydın İnce

Faculty of Engineering and Natural Sciences,
Sabanci University Nanotechnology and
Applications Center (SUNUM),
Sabanci University,
Orta Mahalle,
Tuzla, Istanbul 34956, Turkey
e-mail: gozdeince@sabanciuniv.edu

Ali Koşar

Mem. ASME
Mechatronics Engineering Program,
Center of Excellence for Functional
Surfaces and Interfaces,
Sabanci University,
Orta Mahalle,
Tuzla, Istanbul 34956, Turkey
e-mail: kosara@sabanciuniv.edu

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received September 3, 2016; final manuscript received March 5, 2017; published online June 21, 2017. Assoc. Editor: C.A. Dorao.

J. Heat Transfer 139(11), 111501 (Jun 21, 2017) (11 pages) Paper No: HT-16-1552; doi: 10.1115/1.4036651 History: Received September 03, 2016; Revised March 05, 2017

New requirements for heat exchangers offered pool boiling heat transfer on structured and coated surfaces as one of the promising methods for effective heat removal. In this study, pool boiling experiments were conducted on polyhydroxyethylmethacrylate (pHEMA)-coated surfaces to investigate the effect of surface orientation on bubble dynamics and nucleate boiling heat transfer. pHEMA coatings with thicknesses of 50, 100, and 200 nm were deposited using the initiated chemical deposition (iCVD) method. De-ionized water was used as the working fluid. Experiments were performed on horizontal and inclined surfaces (inclination angles of 10 deg, 30 deg, 50 deg, and 70 deg) under the constant heat flux (ranging from 10 to 80 kW/m2) boundary condition. Obtained results were compared to their plain surface counterparts, and heat transfer enhancements were observed. Accordingly, it was observed that the bubble departure phenomenon was affected by heat flux and wall superheat on bare silicon surfaces, while the supply path of vapor altered the bubble departure process on pHEMA-coated surfaces. Furthermore, the surface orientation played a major role on bubble dynamics and could be considered as a mechanism for fast vapor removal from surfaces. Bubble coalescence and liquid replenishment on coated surfaces had a promising effect on heat transfer coefficient enhancement on coated surfaces. For horizontal surfaces, a maximum enhancement of 25% relative to the bare surface was achieved, while the maximum enhancement was 105% for the inclined coated surface under the optimum condition. iCVD was proven to be a practical method for coating surfaces for boiling heat transfer applications due to the obtained promising results.

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References

Figures

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Fig. 1

Raman spectrum taken from the pHEMA films having the thickness of 200 nm (a) before the boiling experiments and (b) after the boiling experiments

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Fig. 2

(a) Three-dimensional image and (b) depth histogram of an area of 10 μm square of the pHEMA film with the thickness of 200 nm

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Fig. 3

Schematic of the experimental setup

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Fig. 4

Validation with available nucleate pool boiling correlations in the literature [48,49]

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Fig. 5

Bubbles and active nucleation sites on pHEMA-coated surfaces with thickness of (a) 100 nm for heat flux of 20 kW/m2, (b) silicon surface for heat flux 20 kW/m2, (c) pHEMA-coated surface with thickness of 100 nm for heat flux of 30 kW/m2, and (d) silicon surface for heat flux 30 kW/m2

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Fig. 6

Effect of heat flux on active nucleation sites on (a) pHEMA-coated surface at 20 kW/m2 heat flux, (b) silicon surface at 20 kW/m2 heat flux, (c) pHEMA-coated surface at 40 kW/m2 heat flux, and (d) silicon surface at 40 kW/m2 heat flux

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Fig. 7

Illustration of bubble measurement technique showing diametrical points logged (+) and the calculated centroid location (×) of a bubble

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Fig. 8

Heat transfer coefficients for pHEMA-coated surfaces with thicknesses of (a) 50, (b) 100, and (c) 200 nm and bare silicon surfaces (d) heat transfer enhancement

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Fig. 9

(a) Bubble movement on pHEMA-coated surfaces and (b) schematic of moving bubble in the growth stage

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Fig. 10

Bubble growth on (a) bare silicon plate and (b) pHEMA-coated surface; (c) and (d) bubble coalescence and interaction upon the departure on coated surfaces; (e) schematic of bubble departure on coated surface; and (f) schematic of bubble coalescence on the coated surface

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Fig. 11

Effect of surface orientation on active nucleation sites on the surface with coating thickness of 100 nm

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Fig. 12

Bubble movement and collision on inclined surface

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Fig. 13

Schematic of heat transfer enhancement mechanism on the inclined pHEMA-coated surface

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Fig. 14

Effect of inclination angle on pool boiling curve for (a) 100 nm coated surface, (b) 200 nm coated surface, and (c) percent of heat transfer coefficient enhancement

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