基于小波变换的直接接触凝结过程研究

Investigation on characteristics of direct contact condensation basing on wavelet transform

为研究蒸汽直接接触凝结时的凝结状态及特征,本文利用高速摄像仪和水声换能器采集凝结时的可视化结果及声学信号。实验结果表明,随过冷度和蒸汽流量升高发现4个不同的凝结区域:光滑气泡区、体积波动区、过渡区和毛细波区。对声压波动信号进行db2小波7层分解发现,由气泡破碎和气泡分裂引入的低频声压波动的接近,而不同凝结区域的高频波动不同。小波变换得到的各子信号的能量和相对能量分布在同一凝结区域接近,不同凝结区域存在显著差异,可用于不同凝结状态的识别。

To investigate the condensation state and steam characteristics in direct-contact condensation,we recorded images and acoustic signals using a high-speed video camera and an underwater acoustic transducer,respectively,during the condensation period. The experimental results show that four different condensation regions are encountered as the vapor flow and degree of supercooling are increased： smooth bubbles,volume fluctuation,transition,and capillary waves. By carrying out seven layers of decomposition for the Daubechies db2 wavelet of the sound pressure signal,we find that the low-frequency sound pressure oscillations induced by bubble collapse and bubble split-up are similar. However,the high-frequency oscillations are different for different condensation regions. Furthermore,the absolute and relative energies attained by wavelet transform are distributed in the same condensation region,whereas marked differences exist between different condensation regions. This feature could be used to distinguish between different condensation states.