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INVITED PAPERS

Heat Transfer and Critical Heat Flux of Subcooled Water Flow Boiling in a SUS304-Tube With Twisted-Tape Insert

[+] Author and Article Information
Koichi Hata1

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

Suguru Masuzaki

National Institute for Fusion Science, 322-6 Oroshi-cho, Toki, Gifu 509-5292, Japanmasuzaki@lhd.nifs.ac.jp

1

Corresponding author.

J. Thermal Sci. Eng. Appl 3(1), 012001 (Mar 17, 2011) (12 pages) doi:10.1115/1.4003609 History: Received September 18, 2010; Revised February 03, 2011; Published March 17, 2011

Abstract

The subcooled boiling heat transfer and the steady state critical heat fluxes (CHFs) in a short SUS304-tube with twisted-tape insert are systematically measured for mass velocities $(G=4016–13,950 kg/m2 s)$, inlet liquid temperatures $(Tin=285.8–364.0 K)$, outlet pressures $(Pout=764.8–889.0 kPa)$, and exponentially increasing heat input ($Q=Q0 exp(t/τ)$ and $τ=8.5 s$) by the experimental water loop comprised of a multistage canned-type circulation pump controlled by an inverter. The SUS304 test tube of inner diameter $(d=6 mm)$, heated length $(L=59.5 mm)$, effective length $(Leff=49.1 mm)$, $L/d$$(=9.92)$, $Leff/d$$(=8.18)$, and wall thickness $(δ=0.5 mm)$ with average surface roughness $(Ra=3.89 μm)$ is used in this work. The SUS304 twisted-tape with twist ratios $y$$[=H/d=(pitch of 180 deg rotation)/d]$ of 2.39, 3.39, and 4.45 are used. The relations between inner surface temperatures and heat fluxes for the SUS304-tubes with various twisted-tape inserts are explored for different flow regimes ranging from single-phase flows to CHF. The subcooled boiling heat transfers for SUS304-tubes with various twisted-tape inserts are compared with authors’ empty SUS304-tube data and the values calculated by authors’ and other workers’ correlations for the subcooled boiling heat transfer. The influences of the twisted-tape insert, the twist ratio, and the swirl velocity on the subcooled boiling heat transfer and the CHFs are investigated into details, and the correlations of the subcooled boiling heat transfer and the CHFs for turbulent flow of water in the SUS304-tubes with twisted-tape inserts are given based on the experimental data. The precision or accuracy of a more widely set of correlations in predicting the present set of data is evaluated. The correlations can describe the subcooled boiling heat transfer coefficients and the CHFs obtained in this work from $−25%$ to $+15%$ difference.

Figures

Figure 1

Schematic diagram of experimental water loop

Figure 2

Vertical cross-sectional view of 6 mm inner diameter test section with the twisted-tape insert

Figure 3

Photograph of the SUS304 twisted-tape coated with epoxy resin and alumina thermal spraying

Figure 4

SEM photograph for the SUS304 test tube of d=6 mm with the rough finished inner surface

Figure 5

Measurement and data processing system

Figure 6

Typical heat transfer processes for the SUS304 test tube of d=6 mm and Leff=49.1 mm with the twisted-tape of y=3.39 at usw=5.5–18.3 m/s on τ=around 8.5 s

Figure 7

Typical photograph for SUS304 test tube of d=6 mm burned out in CHF experiment with the twisted-tape of y=3.39

Figure 8

Time variations in Pin, Pout, q, and Ts for the SUS304 test tube of d=6 mm and Leff=49.1 mm with the twisted-tape of the twist ratio y of 3.39 at Pout=863.3 kPa, ΔTsub,in=157.9 K, u=18.3 m/s, and τ=8.4 s

Figure 9

Time variations in Tin, Tout, ΔTsub,in, ΔTsub,out, q, and Ts for the SUS304 test tube of d=6 mm and Leff=49.1 mm with the twisted-tape of the twist ratio y of 3.39 at Pout=863.3 kPa, ΔTsub,in=157.9 K, u=18.3 m/s, and τ=8.4 s

Figure 10

Heat transfer processes for the SUS304 test tubes of d=6 mm and Leff=49.1 mm with the twisted-tape of y=3.39 and the empty SUS304 test tube of d=6 mm and Leff=49.1 mm

Figure 11

Values of n versus swirl velocity for SUS304 test tubes with the twisted-tapes of y=2.39, 3.39, and 4.45, and those versus flow velocity for empty SUS304 and Pt test tubes

Figure 12

Values of ΔTsat at CHF point versus swirl velocity for SUS304 test tubes with the twisted-tapes of y=2.39, 3.39, and 4.45, and those versus flow velocity for empty SUS304 test tubes of d=3 mm and 6 mm

Figure 13

qcr,sub,st versus ΔTsub,out for SUS304 test tube of d=6 mm and L=59.5 mm with the twisted-tape of y=3.39 at Pout≅800 kPa

Figure 14

qcr,sub,st versus ΔTsub,out for SUS304 test tube of d=6 mm and L=59.5 mm with the twisted-tape of y=2.39 at Pout≅800 kPa

Figure 15

qcr,sub,st versus ΔTsub,out for SUS304 test tube of d=6 mm and L=59.5 mm with the twisted-tape of y=4.45 at Pout≅800 kPa

Figure 16

Ratio of CHF data for SUS304 test tubes of d=6 mm and L=59.5 mm with the twisted-tapes of y=2.39, 3.39, and 4.45 to the values derived from the outlet CHF correlation for the circular tube with various twisted-tape inserts versus ΔTsub,out at Pout≅800 kPa

Figure 17

qcr,sub,st versus ΔTsub,in for SUS304 test tube of d=6 mm and L=59.5 mm with the twisted-tape of y=3.39 at Pin=775–974 kPa

Figure 18

qcr,sub,st versus ΔTsub,in for SUS304 test tube of d=6 mm and L=59.5 mm with the twisted-tape of y=2.39 at Pin=824–952 kPa

Figure 19

qcr,sub,st versus ΔTsub,in for SUS304 test tube of d=6 mm and L=59.5 mm with the twisted-tape of y=4.45 at Pin=810–920 kPa

Figure 20

Ratio of CHF data for SUS304 test tubes of d=6 mm and L=59.5 mm with the twisted-tapes of y=2.39, 3.39, and 4.45 to the values derived from the inlet CHF correlation for the circular tube with various twisted-tape inserts versus ΔTsub,in at Pin=775–974 kPa

Figure 21

Values of (Bosw)cr/(Bosw)con versus swirl velocity for SUS304 test tubes with the twisted-tapes of y=2.39, 3.39, and 4.45, and those of Bocr/Bocon versus flow velocity for empty SUS304 test tubes of d=3 mm and 6 mm

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