On the interfacial oscillation of an evaporating bubble of 2-propanol/water in a single-side heated square capillary

• Main Authors: Chia-I Rau, 饒家宜
• Other Authors: Chen-li Sun
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/pk3d9w

碩士 === 國立臺灣大學 === 機械工程學研究所 === 106 === The present study reports an investigation on the interfacial oscillation of an evaporating bubble of 2-propanol/water mixture in a single-side heated square capillary. The influences of the concentration and the wall superheat are studied. For a mixture with concentration higher than the azeotrope oscillates vigorously at high wall superheat (35°C and 55°C). The oscillation is attributed to the Marangoni convection arising from both thermocapillarity and solutocapillarity. On the other hand, for a mixture with lower mole fraction, the thin liquid layer on the heated side billows slightly and deforms near the top wall of the capillary while the wavy movement may be caused by Helmholtz instability, the deformation is due to the weak surface-tension skin unable to support the condensate. In addition, we employ image processing to quantify the velocity and oscillating frequency of the liquid-vapor interface. At high wall superheats, the liquid-vapor interface of low-concentration mixture travels at faster velocity. This is because the higher wall superheats and the larger ratio of liquid to vapor density both help to produce more vapor. In this study, the oscillating frequency varies from 160 Hz to 220 Hz. Although interface of mixture with higher concentration tends to oscillate faster, the growing trend is placid. With the infrared camera, we also record the temperature distribution of the capillary wall during the bubble growth. The data indicate that the surface temperature drops twice when both sides of the liquid-vapor interfaces of the bubble pass the measure points sequentially. The temperature drops at different wall superheats are approximately 15°C and 25°C.