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# Transient Critical Heat Fluxes of Subcooled Water Flow Boiling in a Short Vertical Tube Caused by Exponentially Increasing Heat Inputs

[+] Author and Article Information
Koichi Hata1

Institute of Advanced Energy, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japanhata@iae.kyoto-u.ac.jp

Nobuaki Noda

National Institute for Fusion Science, 322-6 Oroshi-cho, Toki, Gifu 509-5292, Japan

1

Corresponding author.

J. Heat Transfer 130(5), 054503 (Apr 08, 2008) (9 pages) doi:10.1115/1.2887850 History: Received December 16, 2006; Revised November 29, 2007; Published April 08, 2008

## Abstract

The transient critical heat fluxes (CHFs) of the subcooled water flow boiling for the flow velocities $(u=4.0–13.3m∕s)$, the inlet subcoolings $(ΔTsub,in=68.08–161.12K)$, the inlet pressures $(Pin=718.31–1314.62kPa)$, the dissolved oxygen concentrations ($O2=2.94ppm$ to the saturated one), and the exponentially increasing heat inputs ($Q0exp(t∕τ)$, $τ=16.82msto15.52s$) are systematically measured with an experimental water loop comprised of a pressurizer. The SUS304 tubes of the inner diameters ($d=3mm$, $6mm$, $9mm$, and $12mm$), heated lengths $(L=33.15–132.9mm)$, $L∕d=5.48–11.08$, and wall thickness ($δ=0.3mm$ and $0.5mm$) with the rough finished inner surface (surface roughness, $Ra=3.18μm$) are used in this work. The transient CHF data $(qcr,sub=6.91–60MW∕m2)$ are compared with the values calculated by the steady state CHF correlations against inlet and outlet subcoolings. The transient CHF correlations against inlet and outlet subcoolings are derived based on the experimental data. The dominant mechanisms of the subcooled flow boiling CHF for a high heating rate are discussed.

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Copyright © 2008 by American Society of Mechanical Engineers
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## Figures

Figure 1

Schematic diagram of experimental apparatus

Figure 2

Vertical cross-sectional view of 3 mm, 6 mm, 9 mm, and 12 mm inner diameter test sections

Figure 3

SEM photograph of the rough finished inner surface

Figure 4

Measurement and data processing systems

Figure 5

The relations between saturated dissolved oxygen concentration (O2), nitrogen one (N2), air one (air) and air/O2, and water temperature

Figure 6

The qcr,sub for d=3 mm and L=33.15 mm with the rough finished inner surface at ΔTsub,in=145 K for τ=16.82 ms to 15.52 s

Figure 7

The qcr,sub for d=6 mm and L=60 mm with the rough finished inner surface at ΔTsub,in=145 K for τ=38.07 ms to 8.22 s

Figure 8

The qcr,sub for d=9 mm and L=49.3 mm with the rough finished inner surface at ΔTsub,in=90 K for τ=25.61 ms to 8.91 s

Figure 9

The qcr,sub for d=12 mm and L=132.9 mm with the rough finished inner surface at ΔTsub,in=70 K and 90 K for τ=85.51 ms to 7.92 s

Figure 10

Ratios of qcr,sub,st for d=3 mm, 6 mm, 9 mm, and 12 mm with the rough finished inner surface to the values derived from Eq. 1 versus ΔTsub,in at Pin=718.31–1314.62 kPa

Figure 11

Ratios of qcr,sub,st for d=3 mm, 6 mm, 9 mm, and 12 mm with the rough finished inner surface to the values derived from Eq. 2 versus ΔTsub,out at Pout=800 kPa and 1100 kPa

Figure 12

(qcr,sub−qcr,sub,st)/qcr,sub,st for d=3 mm, 6 mm, 9 mm, and 12 mm versus τu/{σ/g/ρl−ρg)}0.5 with u=4.0−13.3 m/s at Pin=718−1314 kPa

Figure 13

Ratios of qcr,sub for d=3 mm, 6 mm, 9 mm, and 12 mm (286 points) to corresponding values calculated by Eq. 8 versus τu/{σ/g/ρl−ρg)}0.5

Figure 14

Ratios of qcr,sub for the wide range of exponential periods (286 points) to corresponding values calculated by Eq. 2 versus τu/{σ/g/ρl−ρg)}0.5

Figure 15

Ratios of qcr,sub for d=3 mm, 6 mm, 9 mm, and 12 mm (286 points) to corresponding values calculated by Eq. 9 versus τu/{σ/g/ρl−ρg)}0.5

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