过冷沸腾时气泡表面波触发机制及对气泡动力学行为影响

有研究发现，在一定过冷度的沸腾条件下气泡表面上会形成表面波并影响沸腾传热过程，但其形成机制及对气泡动力学和传热机理的影响需进一步探究。本项目拟采用高速摄像和PIV/PLIF技术，结合基于MATLAB环境的数字图像分析技术，获取不同过冷沸腾条件下气泡表面波的波动特征和参数，以探明表面波的发生条件及其对气泡动力学行为和换热过程的影响。试验中通过外加声场和添加表面活性剂调控气泡表面波的特征参数，并结合示踪技术测量气泡周围微观流场和温度场，以获取反映表面波影响的详实试验数据；在试验基础上，结合气泡表面不稳定性分析理论和CFD方法，揭示过冷沸腾时气泡表面波的触发机制和形成过程，并探究表面波引起的微对流对界面传热和传质的影响及机理。在经典气泡动力学理论基础上，建立能反映表面波影响的气泡动力学方程以及核态沸腾传热计算方法。项目的研究成果可丰富和发展现有的气泡动力学理论，对进一步探明沸腾机理具有积极意义。

It was illustrated that surface wave could form on the surface of a vapor bubble in subcooled boiling at certain liquid subcooling, and affected the heat transfer process, while its formation mechanism and its effects on dynamic behaviors of the bubble and boiling heat transfer mechanism need to be further investigated. In this project, transient features and parameters of the surface wave on a vapor bubble during subcooled boiling under different conditions will be obtained firstly with the aid of a high-speed video camera and PIV/PLIF technique, combining with digital image analysis technique developed based on MATLAB environment. It helps to explore the conditions for the occurrence of surface wave as well as its influence on bubble behavior and heat transfer characteristics during subcooled boiling. The parameters of surface wave on a bubble will be realized by applying an acoustic field and adding surfactant to the working fluid. Meanwhile, variations in temperature and flow fields around the bubble surface could be measured with the tracer technique. Thus, detailed experimental data could be presented for illustrating the influence of surface wave. On the basis of experimental studies, CFD method and theory of interface instability analysis will be applied to help reveal the mechanism triggering the wave on a bubble surface and its evolution under subcooled boiling condition. Effects and mechanism of micro convection introduced by surface wave on heat and mass transfer process at the interface will be investigated as well. A new equation based on classical bubble dynamics for predicting bubble motion will be established considering the influence of surface wave, with which an improved method might be presented for calculating nucleate boiling heat transfer. The outcome of this project could give an enrichment and improvement to the current theory of bubble dynamics, and will also play a positive role in future unveiling the mechanism of boiling.