bubble behavior and flow structure on bubble collapse
TRANSCRIPT
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* 2012.11. 24 ** 305-8573 1–-1–-1 TEL: (029)853-5487 FAX: (029)853-5487 E-mail: [email protected]
Bubble Behavior and Flow Structure on Bubble Collapse Phenomena in a Venturi Tube
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 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.
Keywords: Micro-bubble, Bubbly flow, Venturi tube, Void fraction measurement, Shock
1.
[1]
Ivany, Hammitt and Mitchell[2]
Thang and Davis[3]
Wang
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id v
eloc
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L [m
/s]
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20 m/s
PIV Bernoulli’s principle
Fig. 7 Flow fields and liquid velocity in the venturi tube measured by PIV with jLin = 1.66 m/s.
20
15
10
5
0
Liqu
id v
eloc
ity u
L [m
/s]
353025201510z [mm]
Bubble collapse
Bubbles
20 m/s
Fig. 8 Flow fields and liquid velocity in the venturi tube measured by PIV with jLin = 2.49 m/s.
PIV
PIV
Fig. 8
10 m/s
10 m/s
const.1 2L L Cpu (4)
00
z = 17 mm = 0.289 0.082 [-] uL = 15.7 m/s p = 10.1 1.1 kPa (4)
1 175 20 kJ/m3 2 10.1 1.1 kJ/m3 C = 185 21 kJ/m3
z = 17 mmz =
27 mm = 0.165 0.068 [-] uL = 10.2 m/sp = 77.6 1.4 kPa (4)1 87.4 7 kJ/m3 2 77.6 1.4 kJ/m3
C = 165 9 kJ/m3
CC
3.3PIV
Fig. 9
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Fig. 9 (a) jLin = 1.66 m/s
jLin = 1.66 m/s60 kPa
Fig. 9 (b) jLin = 2.49 m/s
10 kPa
20 mm 10 kPa
0.4 [-]
Fig. 9(c) jLin = 3.32 m/sjLin = 2.49 m/s
jLin = 2.49 m/s 3.32 m/s300 kPa jLin = 3.32 m/s
jLin = 2.49 m/s
jLin = 3.32 m/s0.8 [-] z =
10 mm 0.4 [-]200 kPa jLin = 2.49 m/s
z = 10 mm
jLin = 3.32 m/s0.8 [-]
400
300
200
100
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Void fractionPressure
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400
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400
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(c) jLin = 3.32 m/s Fig. 9 Pressure profiles and void fraction profiles
to the flow direction in the venturi tube for each liquid superficial velocity.
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Bubble collapse
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Fig. 10 Gas-liquid mixture velocity and sonic speed profiles around the throat and the bubble collapse points for each liquid superficial velocity.
3.4
Mach
UmD [m/s] cm [m/s] Mach[3]
LG
2LL
2GG
mD 11 uuU (5)
LGm 1
pc (6)
m
mD
cUM (7)
G, L[kg/m3] u [m/s]
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G pp (8)
0
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GG
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u 0G
(9)
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u L
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Q A
G (8)
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Fig. 10PIV
jLin = 1.66 m/s
jLin = 2.49 m/s 3.32 m/s
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Bubble collapse (jLin= 3.32 m/s)
2.49 m/s
1.66 m/s
Bubble collapse(jLin= 2.49 m/s)
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
[1] Fujiwara, A., Takagi, S., Watanabe, K. and Matsumoto, Y., Experimental Study on the New
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/0123452 !�üù�û#�þþ�ø�$�#û÷�þ��ÿ÷�ø��ù�"þüü�ù��þü®���þø�þøü���"��þ"÷�"ö�ü��#�ÿþü�ù��þü÷�þ�þö�6þ"#��ö �ÿþ#���þ��ÿ÷üþ÷�"����þ���÷�þ"ø�÷���#���þ�ùø7�ø"�ÿ÷üþ×,�#÷ü�#�þþ�ø�$�÷�þ®ÿ�ûþ6þ�®ù÷�$þ�÷���#�ÿþü�ù��þü#��ö ü�ù��ø��øü�÷����þ"ø����ÿþ#�þþ�ø�$ø��þ�#÷�þ÷�"�ÿþ��ÿþü�ù��ø��øü�������þ���÷�þ"×ï���þ6þ���ÿøü�÷����þ�#�ÿþü�ù��þü®�ÿþü����$÷$ø�÷�ø���#�ÿþ#�þþ�ø�$ø��þ�#÷�þøü6þ�8þ##þ��ø6þ×-þÿ÷6þ9þþ�ü��"8ø�$�ÿþ÷��ùø�÷9øùø�8�#�ù��÷ü��ø�ø��÷"ø÷�ø�����ÿþ÷$ø�÷�ø�$öþ�ÿ�"®÷�"#���"�ÿ÷��ÿþ#�þþ�þ����þ���÷�ø��þ##ø�øþ��8�#ü�ù��þüøüøö���6þ"$�þ÷�ù898�ÿøüø��÷"ø÷�ø��×!��ÿøü�÷�þ�®�ÿþþ##þ��ü�#�ÿþ#�þþ�ø�$�÷�þ÷�"�ÿþ�ù��÷ü��ø�ø��÷"ø÷�ø�����ÿþ#�þþ�þ����þ���÷�ø���ÿ÷�÷��þ�øü�ø�ü÷�þ�þ����þ"×
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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).
[2] Ivany, R. D., Hammit, F. G. and Mitchell, T. M., Cavitation Bubble Collapse Observations in a Venturi, J. Basic Eng., Vol. 88(3), 649-657 (1966).
[3] Thang, N.T. and Davis, M.R., Pressure Distribution in Bubbly Flow Through Venturis, Int. J. Multiphase Flow, Vol. 7(2), 191-210 (1981).
[4] Wang, Y. and Chen, E., Effects of Phase Relative Motion on Critical Bubbly Flows through a Converging-diverging Nozzle, Phys. Fluids, Vol. 14(9), 3215-3223 (2002).
[5] Kaneko, A., Nomura, Y., Takagi, S., Matsumoto, Y. and Abe, Y., Bubble break-up phenomena in a venturi tube, Trans. JSME Ser. B, Vol. 78(786), 207-217 (2012).
[6] Fukano, T., Measurement of Time Varying Thickness of Liquid Film flowing with High Speed Gas Flow by a Constant Electric Current Method (CECM), Nucl. Eng. Des., Vol. 184(2-3), 363-377 (1998).
[7] Uesawa, S., Kaneko, A., and Abe, Y., Measurement of Void Fraction in Dispersed Bubbly Flow Containing Micro-bubbles with Constant Electrilc Current Method, Flow Meas. Instrum., Vol. 24, 50-62 (2012).
[8] Maxwell, J. C., A Treatise on Electricity & Magnetism. Vol. 1, 435-441, Dover Publications, New York (1954).
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