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Research Papers: Evaporation, Boiling, and Condensation

An Experimental Study on Flow Boiling Heat Transfer From a Downward-Facing Finned Surface and Its Effect on Critical Heat Flux

[+] Author and Article Information
A. R. Khan

Department of Nuclear Engineering
and Management,
School of Engineering,
The University of Tokyo,
7-3-1 Hongo,
Bunkyo-ku 113-8654, Tokyo, Japan
e-mail: ark8@njit.edu

N. Erkan

Nuclear Professional School,
School of Engineering,
The University of Tokyo,
2-22 Shirakata,
Tokai-mura 319-1188, Ibaraki, Japan
e-mail: erkan@vis.t.u-tokyo.ac.jp

K. Okamoto

Nuclear Professional School,
School of Engineering,
The University of Tokyo,
2-22 Shirakata, Tokai-mura 319-1188, Ibaraki, Japan
e-mail: okamoto@n.t.u-tokyo.ac.jp

1Corresponding author.

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF HEAT TRANSFER. Manuscript received September 26, 2016; final manuscript received June 15, 2017; published online August 29, 2017. Assoc. Editor: Amitabh Narain.

J. Heat Transfer 140(2), 021501 (Aug 29, 2017) (10 pages) Paper No: HT-16-1608; doi: 10.1115/1.4037154 History: Received September 26, 2016; Revised June 15, 2017

During a severe accident, ex-vessel cooling may pose a risk for larger-powered reactors. The current in-vessel retention (IVR) (through ex-vessel cooling) capability may not be sufficient for the larger-powered reactors, and critical heat flux (CHF) conditions may eventually lead to vessel failure. A manner in which the CHF can be increased is by applying a structured surface design on the outer surface of the reactor pressure vessel (RPV). A simple design proposed in this work is the pin–fin. An experimental investigation was performed to observe the effect of the pin–fin on CHF with a downward-facing heated surface in flow boiling conditions. A reduced pressure of approximately 0.05 MPa allowed for saturation at approximately 81 °C. A range of flow rates corresponding to mass flux of 202–1456 kg/m2 s were applied in the experiments. The results showed an increase in the CHF when compared to a bare surface. An average CHF enhancement of 61% was observed from the finned surface. An enhancement of approximately 19% was observed in the heat transfer coefficient. As seen in nanoparticle/nanofluid enhancement, an increase in the CHF also leads to an increase in the superheat. Even though an increase in the CHF had been observed, the CHF for the finned and bare surfaces occurred at approximately similar superheat.

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References

Figures

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Fig. 1

Experimental facility used to study reduced pressure flow boiling

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Fig. 2

Midsection schematic of the finned surface test section

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Fig. 3

Examples of increasing temperatures during CHF: (a) 647 kg/m s2 bare surface, (b) 647 kg/m s2 fin surface, (c) 971 kg/m s2 bare surface, (d) 971 kg/m s2 fin surface, (e) 1456 kg/m s2 bare surface, and (f) 1456 kg/m s2 fin surface

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Fig. 4

Heat flux versus wall superheat for B-1 and F-1 (1456 kg/m2 s)

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Fig. 5

Heat flux versus wall superheat for B-2 and F-2 (1295 kg/m2 s)

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Fig. 6

Heat flux versus wall superheat for B-3 and F-3 (1133 kg/m2 s)

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Fig. 7

Heat flux versus wall superheat for B-4 and F-4 (971 kg/m2 s)

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Fig. 8

Heat flux versus wall superheat B-5 and F-5 (647 kg/m2 s)

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Fig. 9

Heat flux versus wall superheat B-6 and F-6 (324 kg/m2 s)

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Fig. 10

Heat flux versus wall superheat for B-7 and F-7 (202 kg/m2 s)

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Fig. 11

Bare and finned surface CHF data for all flow rates

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Fig. 12

(a) Steady-state pre-CHF bare surface boiling images: (a) 202 kg/m s2, (b) 324 kg/m s2, (c) 647 kg/m s2, (d) 971 kg/m s2, (e) 1133 kg/m s2, (f) 1295 kg/m s2, and (g) 1456 kg/m s2. (b) Steady-state pre-CHF finned surface boiling images: (a) 202 kg/m s2, (b) 324 kg/m s2, (c) 647 kg/m s2, (d) 971 kg/m s2, (e) 1133 kg/m s2, (f) 1295 kg/m s2, and (g) 1456 kg/m s2.

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Fig. 13

Comparison of Katto and Kurata correlation with bare surface data

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Fig. 14

Comparison of original and modified correlations with bare surface data

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Fig. 15

Comparison of modified Katto and Kurata correlation with finned surface data

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Fig. 16

Comparison of the modified correlations and experimental data

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Fig. 17

Heat transfer coefficients for both surfaces compared with the modified correlations

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Fig. 18

Illustration of boiling curve shift causing heat transfer and CHF enhancement

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Fig. 19

Superheat at CHF (ΔTSAT,CHF) for bare and finned surfaces

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