海洋条件下沸腾传热跨尺度机理研究

A lot of heat exchangers with boiling heat transfer have been applied to ships nowadays. However, classic formulas of boiling heat transfer result in great discrepancy during the design of heat exchangers under ocean conditions. And investigation of heat transfer characteristics of boiling under ocean conditions should be strengthened. In this project, a profound study about multiscale mechanism of pool boiling under ocean conditions will be done by combining three kinds of research approach: theoretical analysis, numerical simulation based on Lattice Boltzmann method (LBM) and experimental exploring. The mechanical model of bubbles at pool boiling will be built to study the effects of additional inertial forces on the dynamic evolution of bubbles. A liquid-vapor phase change Lattice Boltzmann model combining additional inertial forces and moving boundary under ocean conditions will be developed to investigate the whole dynamical evolution process of bubbles, including nucleation, growth, coalescence, detachment and sloshing rising. And pool boiling curves under ocean conditions from natural convection regime to nucleate boiling regime, to transition boiling regime, to film boiling regime will be obtained numerically for the first time. The influence of rolling amplitude and rolling frequency on pool boiling heat transfer will be analyzed. Finally, the visualization experiment platform will be set up to observe the dynamic evolution of boiling bubbles under ocean conditions, and pool boiling curves will be measured. The experimental results are compared with theoretical analysis and results from lattice Boltzmann method, and the multiscale mechanism of boiling heat transfer under ocean conditions will be revealed in this project.

舰船动力系统使用大量涉及沸腾传热的换热器，经典沸腾传热公式在海洋条件下换热器的设计中误差较大，亟需加强海洋条件下沸腾传热的分析研究。本项目采用理论分析、格子Boltzmann方法数值模拟和实验测量这三种手段研究海洋条件下的池沸腾传热问题的跨尺度机理。理论分析构建池沸腾汽泡的受力模型，研究附加惯性力对沸腾汽泡动态演化过程的影响。数值模拟采用格子Boltzmann方法的汽液相变模型，添加附加惯性力的作用，结合动边界模型，分析海洋摇摆条件下池沸腾汽泡的成核、生长、合并、脱离及震荡上升等整个动态演化过程；并计算得到包含自然对流、核态沸腾、过渡沸腾和膜态沸腾的整个池池沸腾曲线；分析摇摆幅度、摇摆频率对池沸腾传热的影响。最后，搭建池沸腾过程的可视化实验台架，研究海洋条件下沸腾汽泡的动态演化过程和池沸腾曲线。实验结果与理论分析、格子Boltzmann方法数值模拟相互对比验证，揭示海洋条件下沸腾传热的跨尺度机理。

舰船动力系统大量使用沸腾相变换热器，在实际的设计过程中通常采用较大的设计裕量，造成巨大的材料和空间浪费，亟需探明海洋条件池沸腾热质传递机理。本项目针对海洋条件附加惯性力场作用下池沸腾传热特有的跨尺度机理开展了系统性的基础研究。分析了沸腾汽泡在摇摆条件、起伏条件受力的理论模型。同时，发展了包含附加惯性力的格子Boltzmann介观数值模拟方法，计算了海洋条件下池沸腾的换热曲线，分析了海洋条件下汽泡成核、生长、滑动、合并、脱离和震荡上升等跨尺度动态行为。并且，设计和搭建了模拟海洋条件的六自由度平台，用于池沸腾传热的可视化实验研究，并对理论分析和数值模拟结果进行验证。结果表明，海洋条件下的附加惯性力小于重力的十分之一，海洋条件对汽泡动态行为的影响较大，但由于附加惯性力场良好的周期性，海洋条件对平均换热系数和临界热流密度的影响一般不超过11%。摇摆条件能够促进汽泡成核，加剧汽泡合并，加速汽泡脱离，并且汽泡震荡生长的相位变化滞后于系统的摇摆运动。而起伏条件对池沸腾传热的影响较小，与理论分析和数值模拟结果一致。本项目的研究成果可以为舰船动力系统池沸腾换热器的设计和运行提供较精确的理论指导，有利于海洋强国战略的实施。