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Thermal engineering Lab. , department of Science and Mechanical engineering , Kansai university

2011 / 01 / 06 - 07 (Thu.-Fri.). Seminar on neutron imaging @KURRI. 中性子ラジオグラフィを用いた 円管内沸騰二相流のボイド率定量評価. Quantitative evaluation of void fraction of boiling two-phase flow in a tube using neutron radiography.

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Thermal engineering Lab. , department of Science and Mechanical engineering , Kansai university

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  1. 2011 / 01 / 06 - 07 (Thu.-Fri.) Seminar on neutron imaging @KURRI 中性子ラジオグラフィを用いた円管内沸騰二相流のボイド率定量評価 Quantitative evaluation of void fraction of boiling two-phase flow in a tube using neutron radiography Thermal engineering Lab.,department of Science and Mechanical engineering,Kansai university 谷口 斉 (関大院)

  2. Contents 1. Background and objective2. Experimental apparatus3. Image processing method (Consideration of measurement error)4. Experimental result5. Summary

  3. Background Drop flow Annular flow Bubbly flow Slug flow Annular flow Isothermal two-phase flow Churn flow Slug flow 流動様式の予測相関式 限界熱流束の予測(液膜流モデル) ・・・断熱二相流のデータを基本とする. Bubbly flow Boiling two-phase flowJ.G.Collier,J.R.Thome (1972) 壁面沸騰,環状流液膜の蒸発は再現不能.

  4. Neutron radiography Objective 中性子ラジオグラフィを用いて沸騰二相流のボイド率定量評価,液膜測定に関する検討を行う. ・Scatter・Absorption・Transmission Radiation Source I0 I Detector ・測定対象に非接触 ・金属は透過し,水に対して強く減衰 ⇒金属管内を流れる水の沸騰二相流の測定に適している.

  5. Experimental apparatus(flow loop and test section) Electrode Electrode

  6. Experimental apparatus(imaging system) Neutron source Beam port o Flamefor test loop Pit(Depth=1.0 m) Camera box

  7. Experimental apparatus(imaging system) Camera Test section 7.0 mm Thermocouple 31.7 mm(1024 pixel) 31.7 mm(1024 pixel)

  8. Image processing method w L G S:輝度値,G:ゲイン,O:オフセット ボイド率 a 液相透過厚さ と 気相透過厚さの比

  9. Measurement error Grid Test section Grid Converter Reactor 1MWExposure 30 s (1)Scattered neutron Direct shadow method Nondestructive Testing and Evaluation Vol.16, pp.345-354 N. Takenaka ; H. Asano ; T. Fujii ; M. Matsubayashi

  10. Measurement error Grid Reactor 1MWExposure 30 s (1)Scattered neutron Non compensated Direct shadow method Without teleconverter Compensated Without teleconverter Nondestructive Testing and Evaluation Vol.16, pp.345-354 N. Takenaka ; H. Asano ; T. Fujii ; M. Matsubayashi

  11. Measurement error Reactor 1MW (2)Gray scale ・Dynamic range ⇒ 透過方向の分解能 ・輝度は整数しか取れない ⇒測定誤差となる. - = SG SL Dynamic range Without teleconverter

  12. Measurement error (3)Geometric unsharpness(Vertical) Vertical D L=4675mm L’=25mm Ig’ D’ D’ Beam port Test section Converter Beam port 縦方向 Ig’= 0.401 mm (D’=75 mm,L/D’=62.3)

  13. Measurement error LiF Reactor 1MWExposure 30 s (3)Geometric unsharpness(Horizontal) Without slit(D=10 mm) With Slit(D=2.5 mm) L=4675mm L’=25mm L=4675mm L’=25mm Ig Ig’ D D Test section Test section Beam port Beam port Converter Converter Ig = 0.054 mm Ig = 0.013 mm ・L/Dを上げることでボケを低減し平行度を上げることで(照射時間は長くなるが)Dynamic rangeを上げる. Without slit With slit

  14. Measurement error Reactor 1MWExposure 30 s (3)Geometric unsharpness(Horizontal) Without slit(D=10 mm) With Slit(D=2.5 mm) L=4675mm L’=25mm L=4675mm L’=25mm Ig Ig’ D D Test section Test section Beam port Beam port Converter Converter Ig = 0.054 mm Ig’ = 0.013 mm With teleconverter Without slit : 500 With slit : 120 Without slit With slit

  15. Experimental result Discussion point □ NRG using high-speed camera in KUR □ Development of void fraction □ Point of net vapor generation(PNVG) □ Application to measurement of liquid film thickness

  16. Experimental result Isothermal two-phase flow(Slug flow)(Reactor 5 MW) Shading correction jG = 0.40 m/s jL = 0.23 m/s (Playback speed:1/5)

  17. Experimental result Void fraction 0.00 1.00 Reactor 1MWExposure 30 s Boiling two-phase flow(Static image) ps = 0.3 MPa G = 300 kg/m2s -0.110 -0.023 -0.009 -0.002 0.004 0.050 0.165 xeq (middle)

  18. Experimental result = Constant Time averaged void fraction(cross sectional average)(Effect of vertical position) PNVG PNVG PNVG 下流側に比べて沸騰開始点のxeqが高い.⇒気泡の発達や合体に伴う ボイド率の上昇が少ない.

  19. Experimental result = Constant Time averaged void fraction(cross sectional average)(Estimation of PNVG) ○低熱流束条件・PNVGはSekoguchiによる推算式が近い値.・PNVG以降のボイド率の発達⇒加熱部出口付近についてはDrift flux modelがよく一致. ○高熱流束条件・PNVG以降のボイド率の発達⇒どの相関式も定量的には不一致.

  20. Experimental result Time averaged liquid phase thickness(Center of the tube) 管中心のボイド率⇒液相透過厚さ 環状流中の液相⇒液膜と液滴液膜厚さ測定への応用

  21. Summary 中性子ラジオグラフィを用いて沸騰二相流のボイド率測定を行い以下の結論を得た. ・熱出力5MW運転時において高速度カメラを用いて流れを撮影したところ,500fps程度の撮影速度以上で定性的な評価を見込める動画が得られることを確認した. ・同じ熱流束条件において軸方向にボイド率分布を測定することで,PNVGの推定を行ったところ,PNVG自体は既存の相関式と近い値を示すが,PNVG以降のボイド率の発達の仕方について,従来の相関式と異なる特性を示した. ・沸騰流中の液相透過厚さを計測することで,液膜あるいは液滴の計測に応用が可能であると考えられる.

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