A. Sakurai

K. Fukuda

K. Hata

M. Shiotsu

N. Noda

National Institute for Fusion Science (NIFS-Repository)

§18. The Effect of Diameter on CHFs in Vertical Heated Tubes with Upward Flow of Subcooled Water Hata, K. (Inst. of Advanced Energy, Kyoto Univ.) Fukuda, K. (Dept. of Nuclear Eng., Kobe Univ. of Mer-cantile Marine) Shiotsu, M. (Dept. of Eng. Sci. and Tech., Kyoto Univ.) Sakurai, A. (Future Energy Research Association) Noda, N. Flow boiling critical heat fluxes (CHFs) on solid surfaces in highly sub cooled flowing water at various pressures were studied recently by many researchers, because boiling with phase change in subcooled water is an attractive cooling method for high heat flux components such as plasma facing ones in fusion experimental facilities. However, there were few data of CHFs in highly subcooled and pressurized water systematically measured for wide ranges of independent variables such as flow rate, subcooling and pressure until quite recently. The CHFs for inlet subcoolings (dTsub,m) on inner surface of a short tube in water flowing upward at various pressures had been measured for various flow velocities using a 9 mm inner-diam. (ID) test tubel). It was clarified that the CHFs were clearly divided into three groups for low, intermediate and high d Tsub,in' Namely, first, the CHFs for low d T sub,in decrease down to the minimum one, secondly those for intermediate d T sub,in increase up to a certain CHFs, and thirdly those for high dT sub,in also increase with the different increasing rate of CHFs lower than that for the intermediate dTsub,in with an increase in dTsub,in' Though the CHFs for lower and intermediate dTsub;in were clearly dependent on the pressures, those for high d Tsub,in were almost independent of the pressure. The different CHFs mechanisms for the d Tsub,in were suggested. The experimentally measured CHFs for 9 mm ID test tube for low, intermediate and high dTsub,in are well expressed by the following correlations!). (CHFs correlation for low dT b,in) = 1.32 x 106 p0.261U O.287 + ~.61 X 103 -1.73x 102 P Lr . q cr,sub V jLJ sub,1n (CHFs correlation for high dTsub,m) q cr,sub = K 3 (u) L1Tsub ,in 0.73 86 (1) (2) (3) (4) The CHFs for 6 and 12 mm ID test tubes were measured at the same experimental conditions of 9 mm ID test tube. The measured CHFs for low, intermediate and high d T sub,in were compared with those for the 9 mm ID test tube in Fig. 1. The trends of CHFs against low, intermediate and high d Tsub,in measured for both test tubes were almost identical with that already obtained from 9 mm ID test tube. The ratios of experimentally measured CHFs for the pressure of 800 kPa at the velocity of 9.9 m/s to corresponding ones calculated from the correlations for low, intermediate and high dTsub,in, qcr,ex!qcr,cah are shown in Fig. 2 with the tube diameter as a parameter. The ratios for the intermediate and high dTsub,in up to about 140 K were almost within around ±10% differences of unity as shown in Fig. 2. o Water Vertical Tube Pressure 800kPa --- -- D (mm) 6 9 12 u " 0 0 4.0 mls ... • • 6.9 mls v 0 <> 9.9 mls .13.3 mls f).. T sub,in (K) Fig. 1 CHFs versus d T sub,in for several flow velocities at a pressure of 800 kPa with curves derived from correlations. 1.4 ~12 .&> : ~1 ~ .Q = ~0.8 c::I" 0.6 pressure 800kPa u=9.9m/s qc~.sub:exI: experimental data qc~.sub:cal :calculation data - - - -1-;: - '1- i f - ~- - -~ - - - - -e, ~: : B ~ \iQ) § - ~ -i - - - <>~ i - - -~- - - - - - - -i i D(mm) i i v 6 1 : 0 9 . ! <> 12 o 20 140 160 180 Fig. 2 Ratio between measured CHFs and calculated CHFs derived from correlations versus inlet subcooling. Reference 1) Hata K., Fukuda K., Shiotsu M., Sakurai A., Noda N., Motojima O. and Iiyoshi A., 1998, Critical Heat Fluxes in Subcooled Boiling of Water Flowing Upward in a Vertical Tube for Wide Ranges of Liquid Velocity, Subcooling and Pressure, Proc. of 6th International Conference on Nuclear Engineering, Paper No. ICONE-6362, pp.I-16. 

The Effect of Diameter on CHFs in Vertical Heated Tubes with Upward Flow of Subcooled Water

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