Abstract:

Signals of sound pressure oscillations during vapor condensation and transition of condensation regimes were investigated using a high-speed video camera and a hydrophone. Results indicate three different condensation regimes with the increase of subcooling and vapor injection rates, which are referred to as bubble oscillation regime, transition regime and capillary wave regime. In addition, two waveforms occur in the detected signals, of which sources are vapor bubble split-up and collapse. The kurtosis of the signals presents step changes, which is close to the transformation threshold of condensation regimes. The peak at frequency of 150—300 Hz appears in spectra in all condensation regimes, which may be resulted from the periodic variation in vapor volume. The peaks with frequency higher than 7000 Hz appear only in transition and capillary wave regimes and may be the resultant of the high-frequency oscillation in pressure caused by sudden collapse of vapor bubbles. The bubble collapse frequency increases with the increase of subcooling and vapor injection rates and is close to the frequency of the first peak in spectra with an error within ±20%.

Key words: condensation, bubble collapse, sound pressure oscillation signal, gas-liquid flow, heat transfer

摘要：

利用高速摄像仪和水声换能器研究蒸汽凝结时的声压波动信号和凝结区域的转变。结果表明,随过冷度和蒸汽流量升高分别出现3个不同的凝结区域——体积波动区、过渡区和毛细波区。此外,观察到两种分别对应气泡分裂和破碎的声压波动波形。声压波动信号的峰度存在阶跃变化,且阶跃处与凝结区域转变的阈值接近。幅度谱的低频区域存在频率在150~300 Hz的峰值,其可能是由蒸汽体积周期性变化引入。在过渡区和毛细波区发现频率高于7000 Hz的峰值,其可能是由气泡突然破碎引入的局部压力高频振荡造成的。蒸汽气泡破碎频率随过冷度和蒸汽流量增加而增加,且与幅度谱中首峰频率接近,误差在±20%以内。

关键词: 凝结, 气泡破裂, 声压波动信号, 气液两相流, 传热