567 * 2012.11. 24 ** ⟃ἼᏛᏛ㝔ࢸࢫࢩሗᕤᏛ◊✲⛉ᵓ㐀ࢠᕤᏛᑓᨷ 305-8573 Ⲉᇛ┴ࡤࡃࡘᕷኳ⋤ 1–-1–-1 TEL: (029)853-5487 FAX: (029)853-5487 E-mail: [email protected]ࢳ⟶ෆẼἻᚤ⣽⌧㇟ࡅ࠾ẼἻᣲὶ≉ᛶ Bubble Behavior and Flow Structure on Bubble Collapse Phenomena in a Venturi Tube ⃝ ఙ 㑻 㔠 Ꮚ ᬡ Ꮚ 㔝 ᮧ ᗣ ㏻ 㜿 㒊 ㇏ UESAWA Shin-ichiro KANEKO Akiko NOMURA Yasumichi ABE Yutaka Abstract A micro-bubble generator with a venturi tube generates a large number of micro-bubbles with a diameter of 10 Pm – 1 mm by bubble collapse. The bubble collapse is caused by pressure recovery in the diverging region of the venturi tube. The pressure recovery is expected to be a shock for supersonic flow in gas-liquid two-phase flow. However, a profile of Mach numbers to flow direction of the venturi tube has not been estimated experimentally. The present study reveals mechanisms of a bubble collapse. In order to achieve the objectives, we observe bubble behavior with the bubble collapse. In addition, we measure pressure and volumetric void fraction profiles in the flow direction. Pressure is measured by a differential pressure gauge. Void fraction is measured by a constant electric current method and Maxwell’s theory. From these measurements, gas-liquid mixture velocity, sonic speed and Mach number are estimated. In experimental results, bubble collapse is observed with high liquid inlet velocity. When bubble collapse is caused, bubbles expand once into a divergence region of the venturi tube. After that, they contracted rapidly and broken up into a great number of tiny bubbles. Pressure decreases sharply around the throat and increase at the bubble collapse point. On the other hand, the void fraction increase downstream from the throat and decrease around the bubble collapse point. From these results, it is confirmed that the flow is supersonic flow between the throat and the bubble collapse point, while it becomes subsonic flow downstream of the point. Therefore, it is proposed that a shock is present at the bubble collapse point. Keywords: Micro-bubble, Bubbly flow, Venturi tube, Void fraction measurement, Shock 1. ⥴ ゝ ༑ࢡ࣓ࢺ௨ୗࡢẼἻᚄᣢࡘᚤ⣽ ẼἻࡣࢡࡤࠊẼἻ⏺㠃྾╔ᛶ ࡢࠊẼἻෆ⁐ࡢࢫゎ㏿ᗘࡢ㧗ᅽ ࡞ࡢ≉ᚩ᭷ࡍࡇࠋࡢ≉ᚩ⏕ࠊࡋࢡࡣỈ㉁ί➼ࡢᕤᴗⓗ࡞ᛂ⏝ࢻࢹࢢࢸࢫࢩ㐀ᙳ௦⾲ࡉ་ ⒪ᢏ⾡➼⮳ᵝ࡞ࠎศ㔝ᛂ⏝࡞ࡧ◊ ⾜ࡀ✲࠸ ࠋከࡢࡃࢡⓎ⏕⨨ࡢ୰ࠊ ࢳ⟶ᘧࢡ⏕ᡂ⨨ࡣࢳ⟶ ෆ㉳ࡁẼἻࡢᚤ⣽⌧㇟⏝ࡋࢡ⏕ᡂࡍ᪉ἲ࠶ࠊ㧗࠸Ẽ┦ᐜ✚ὶ㔞 ẚసࡀ⬟࠶[1]ࠋࠊࡓᚤ⣽⌧㇟ ࢡ⏕ࡢᡂࠊẼἻᔂቯ ᅽຊἼࡢⓎ⏕ẼἻᚤ⣽ࡢᛴ⦰ ẼἻෆࡢࢫ㧗ᅽ㧗 ࢣ ࢱࢡࡋࡢຠᯝᮇᚅࡉ࠸ ࠋࡢࡇ࡞࠺ẼἻᚤ⣽⌧㇟࠸ࡘࠊᐇ㦂 ゎᯒࡢ୧᪉◊✲ࡀ㐍࠸ࠋIvany, Hammitt and Mitchell[2]ࡣࢳ⟶ෆࡢࢸࢩẼἻࡢᔂቯࡢど࡞ࡧᅽຊィ ⾜ࢫࠊ࠸ࢺୗὶ⏕ࡌ㧗ᅽ㒊࠸࠾Ẽ Ἳࡀᡥᖹ≧࡞ࡇ♧ࡋ࠸ࠋThang and Davis[3]ࡣᆶ┤᪉ࡢࢳ⟶ෆࡢẼᾮ┦ ὶࡢ㟼ᅽィ ⾜ࠊ࠸ࢳ⟶ᣑ㒊 ࡢᅽຊᅇ☜ㄆࠋࡓࡋࡢࡑࡓᅽຊศᕸࡀẼᾮ ┦ὶࡅ࠾⾪ᧁἼ࠶ࡇ♧၀ ࠋࡓࡋWang
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Bubble Behavior and Flow Structure on Bubble Collapse ...
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Abstract A micro-bubble generator with a venturi tube generates a large number of micro-bubbles with a diameter of 10 m – 1 mm by bubble collapse. The bubble collapse is caused by pressure recovery in the diverging region of the venturi tube. The pressure recovery is expected to be a shock for supersonic flow in gas-liquid two-phase flow. However, a profile of Mach numbers to flow direction of the venturi tube has not been estimated experimentally. The present study reveals mechanisms of a bubble collapse. In order to achieve the objectives, we observe bubble behavior with the bubble collapse. In addition, we measure pressure and volumetric void fraction profiles in the flow direction. Pressure is measured by a differential pressure gauge. Void fraction is measured by a constant electric current method and Maxwell’s theory. From these measurements, gas-liquid mixture velocity, sonic speed and Mach number are estimated. In experimental results, bubble collapse is observed with high liquid inlet velocity. When bubble collapse is caused, bubbles expand once into a divergence region of the venturi tube. After that, they contracted rapidly and broken up into a great number of tiny bubbles. Pressure decreases sharply around the throat and increase at the bubble collapse point. On the other hand, the void fraction increase downstream from the throat and decrease around the bubble collapse point. From these results, it is confirmed that the flow is supersonic flow between the throat and the bubble collapse point, while it becomes subsonic flow downstream of the point. Therefore, it is proposed that a shock is present at the bubble collapse point.
Fig. 11 Mach number profiles to the flow direction in the venturi tube for each liquid superficial velocity.
(7)Mach Fig. 11
jLin = 1.66 m/s Mach1
jLin = 2.49 m/s 3.32 m/s1
Mach1
Mach 1
4.
Mach
Mach
NomenclatureA : cross-sectional area ]m[ 2
cm : sonic speed ]sm[j : superficial velocity ]sm[M : Mach number ][p : pressure ]Pa[Q : volume flow rate min]L/[u : cross-sectional average velocity ]sm[UmD : gas-liquid mixture velocity ]sm[v : electric voltage ratio ][z : vertical coordinate in the venturi tube ]m[Greek letters
: bulk void fraction ][ : gas volume flow ratio ][ : mass density ]mkg[ 3
SubscriptsG : gas phase L : liquid phase in : inlet of a venturi tube 0 : atmosphere
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Micro-bubble Generator and Its Application to Water Purification System, Proceedings of ASME FEDSM’03 4th ASME/JSME Joint Fluid Engineering Conference, CD-ROM, FEDSM2003-45162 (2003).
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