过冷度对蒸汽气泡破碎及微气泡喷射过程的影响

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(40KΔTsub75K)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。40KΔTsub75K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。

Effect of Subcooling on Vapor Bubble Collapse and Microbubble Emission

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 (ΔT_sub=17 K). At high subcooling (40 K<ΔT_sub<75 K), 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 off from large bubble is observed before sudden collapse of bubble at liquid subcooling of 30 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 40 K<ΔT_sub<75 K. 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.