过冷度对蒸汽气泡破碎及微气泡喷射过程的影响
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摘要
为研究过冷度对蒸汽气泡破碎及微气泡喷射过程的影响,利用高速摄像机记录不同过冷度下过冷池中蒸汽气泡凝结过程。实验结果表明:在低过冷度(ΔTsub=17K)下,蒸汽气泡界面波动发展缓慢,气泡不会破碎,而是逐渐分裂凝结;在高过冷度(40K<ΔTsub<75K)下,蒸汽气泡表面上的波动剧烈发展,随后气泡会突然破碎,并形成大量微气泡;在ΔTsub=30K时,气泡突然破碎前会有小气泡分裂现象发生。40K<ΔTsub<75K时气泡破碎形成的微气泡的直径和速度在量级上与气泡微细化沸腾区域的微气泡接近。随过冷度的升高,微气泡的直径减小,速度增加,且蒸汽气泡破碎前其表面上波动的波数迅速增加,波动的最大幅值先增加后减少。
In order to investigate the effect of subcooling on vapor bubble collapse and microbubble emission,the condensation process of vapor bubbles in a subcooled pool at different subcoolings was recorded with a high-speed video camera.The results show that the development of surface wave emerged on the bubble surface is slow and the vapor bubbles are condensed and split up gradually without sudden collapse at low subcooling(ΔTsub=17K).At high subcooling(40K<ΔTsub<75K),the surface wave on the surface is violent and the vapor bubbles will collapse suddenly with the emission of a large number of microbubbles.Nevertheless,the process of tiny bubbles splitting offfrom large bubble is observed before sudden collapse of bubble at liquid subcooling of30 K.The diameter and velocity of microbubbles after collapse of vapor bubble are within the same order of magnitude of those in microbubble emission boiling at 40K<ΔTsub<75K.Furthermore,the diameter of microbubble decreases,while the velocity increases with the increase of subcooling.In addition,the wave number of the surface wave on bubble surfaces increases and the maximum amplitude of the surface wave increases firstly and then decreases with the increase of subcooling.
In order to investigate the effect of subcooling on vapor bubble collapse and microbubble emission,the condensation process of vapor bubbles in a subcooled pool at different subcoolings was recorded with a high-speed video camera.The results show that the development of surface wave emerged on the bubble surface is slow and the vapor bubbles are condensed and split up gradually without sudden collapse at low subcooling(ΔTsub=17K).At high subcooling(40K<ΔTsub<75K),the surface wave on the surface is violent and the vapor bubbles will collapse suddenly with the emission of a large number of microbubbles.Nevertheless,the process of tiny bubbles splitting offfrom large bubble is observed before sudden collapse of bubble at liquid subcooling of30 K.The diameter and velocity of microbubbles after collapse of vapor bubble are within the same order of magnitude of those in microbubble emission boiling at 40K<ΔTsub<75K.Furthermore,the diameter of microbubble decreases,while the velocity increases with the increase of subcooling.In addition,the wave number of the surface wave on bubble surfaces increases and the maximum amplitude of the surface wave increases firstly and then decreases with the increase of subcooling.
引文
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[2]SHOJI M,YOSHIHARA M.Burnout heat flux of water on a thin wire[C]∥Proceedings of 28th National Heat Transfer Symposium of Japan.Japan:[s.n.],1991:121-123.
[3]TANGE M,TAKAGI S,WATANABE M,et al.Microbubble emission boiling in a microchannel and minichannel[J].Thermal Sciences Engineering,2004,12:23-29.
[4]SUZUKI K,KOKUBU T,NAKANO M,et al.Enhancement of heat transfer in subcooled flow boiling with microbubble emission[J].Exp Therm Fluid Sci,2005,29:827-832.
[5]SUZUKI K,NOMURA T,HONG C,et al.Subcooled flow boiling with microbubble emission in a microchannel[C]∥Proceedings of the MNHMT 2009.Shanghai:[s.n.],2009:18327.
[6]SUZUKI K,SUZUKI K,HONG C,et al.Bubble motion in subcooled boiling with microbubble emission[C]∥Proceedings of Interdisciplinary Transport PhenomenaⅦ.Dresden,Germany:[s.n.],2009.
[7]SUZUKI K,YUKI K,KAWAMURA H,et al.Microbubble emission boiling:An effect of pressure on subcooled flow boiling with microbubble emission[C]∥Proceedings of Interdisciplinary Transport PhenomenaⅥ.Volterra,Italy:[s.n.],2011.
[8]SUZUKI K,INAGAKI F,HONG C.Subcooled boiling in the ultrasonic field:On the cause of microbubble emission boiling[J].Heat Transfer Engineering,2011,32(7-8):673-682.
[9]SUZUKI K,YUKI K,HONG C.Subcooled boiling with microbubble emission:On mechanism of MEB generation[C]∥22nd International Symposium on Transport Phenomena.Delft,Netherlands:[s.n.],2011.
[10]WANG G D,CHENG P.Subcooled flow boiling and microbubble emission boiling phenomena in a partially heated microchannel[J].International Journal of Heat and Mass Transfer,2009,52:79-91.
[11]WANG H,PENG X F,SURESH V G,et al.Microbubble return phenomena during subcooled boiling on small wires[J].International Journal of Heat and Mass Transfer,2007,50:163-172.
[12]UENO I,HATTORI Y.Microbubble formation in abrupt condensation of vapor bubble exposed to subcooled pool[C]∥Proceedings of the InterPACK’09.Shanghai:[s.n.],2009.
[13]UENO I,HATTORI Y,HOSOYA R.Condensation and collapse of vapor bubbles injected in subcooled pool[J].Microgravity Science and Technology,2011,23:73-77.
[14]PAN L M,TAN Z W,CHEN D Q,et al.Numerical investigation of vapor bubble condensation characteristics of subcooled flow boiling in vertical rectangular channel[J].Nuclear Engineering and Design,2012,248:126-136.