蒸汽浸没射流凝结的汽穴/汽泡演化及压力振荡机理研究

The submerged steam jet condensed in subcooled and quiescent water could be characterized by high Reynolds, large density difference and phase-change heat transfer, then the vapor liquid interface is in the dynamic and thermodynamic imbalance state, and results in the pressure oscillation. It's very important to reveal the pressure oscillation mechanism and characteristic for the design and safe operation of related devices. Thus, the phenomenon of steam jet condensation process in subcooled water will be investigated, based on methods that combine the dynamic visualization experiment, image processing technology and steam bubble dynamics method. Firstly, the influence law of the turbulent flow and condensation on the size of steam cavity and detachment bubble will be studied through the single nozzle/ hole steam jet studies, then the quantitative variation laws of the pressure oscillation characteristic (intensity and frequency) and their propagation feature with the influence factors would be obtained; Meanwhile, the coupling interaction between the jet flow of dynamic and thermodynamic imbalance state on vapor liquid interface would be analyzed, then the dynamic evolution model of steam cavity and detachment bubble is proposed to reveal the mechanism of pressure oscillation. Secondly, the pressure oscillation characteristic and its propagation feature of multi-holes is gained through the study of multi-holes steam jets, and the superimposed effect of multi-holes characteristic parameters on the pressure oscillation characteristic and their propagation feature will be revealed. Finally, the quantitative characterization method of pressure oscillation characteristics is set up, which could be used to predict and control the intensity and frequency of pressure oscillation. The present project may deepen the understanding the phenomenon of steam jet condensation, and also provide a beneficial reference for the design of related devices.

蒸汽浸没射流凝结具有高雷诺数、大密度差和强相变换热的特点，由于汽液相界面处于动力学和热力学不平衡状态而产生压力振荡，因此揭示压力振荡特性和产生机理对相关设备的安全运行有重要意义。为此，本项目拟采用动态可视化实验、图像处理技术和汽泡动力学分析等方法对蒸汽浸没射流凝结过程进行研究。首先对单喷嘴/单孔蒸汽射流展开研究，查清射流和凝结对汽穴和脱离汽泡尺寸的影响规律，获得压力振荡频率和强度随各影响因素的定量变化规律；通过研究动力学和热力学不平衡特性对汽液相界面的耦合作用机制，建立汽穴和脱离汽泡的动态演化模型，进而揭示射流凝结的汽穴/汽泡演化以及压力振荡产生机理。其次对多孔射流开展研究并获得其压力振荡特性及传播特性，揭示多孔射流特征参数对压力振荡及其传播特性叠加效应的影响机制。最后，建立压力振荡特性的定量表征方法，获得预测和控制压力振荡强度和频率的方法。本研究将为相关工业设备的设计和开发提供理论依据。

蒸汽浸没射流凝结由于其高效的传热传质特性被广泛应用于能源、化工、航海等领域。但蒸汽浸没射入过冷水中凝结伴随有明显的压力振荡现象，产生的压力波会对相关设备造成破坏。揭示射流凝结振荡压力波的产生和传播机理，对消除或削弱凝结振荡压力波的冲击尤为重要。本项目开展了单孔/多孔蒸汽浸没射流凝结形态的可视化研究和凝结压力振荡特性研究，首先建立了汽羽和汽泡的图像处理方法，实现了汽液相界面的精细表征。结果表明：凝结振荡区的射流凝结形态主要以汽泡形式存在，分析了汽泡动态变化过程，获得了汽泡直径随影响参数的变化规律；稳定凝结区射流凝结形态以汽羽形态形式存在，汽羽凝结动态过程主要包含汽羽生长、汽羽颈缩、汽羽尾部汽泡脱离和汽羽鼓胀等周期性变化阶段。其次，建立蒸汽浸没射流数值计算模型，获得了音速蒸汽射流及超音速蒸汽射流典型凝结形态及其内部的流动及传热机理；然后，对单孔和多孔蒸汽射流凝结振荡区和稳定凝结区的凝结压力振荡特性，对于不同孔数和孔间距的多孔喷嘴，压力振荡主频随冷却水温度的升高而降低，随着蒸汽质量流率的增加呈现先增加后减小的变化趋势，最高点出现在凝结振荡区向稳定凝结区转变的过渡区域；振荡主频随着孔间距的增大逐渐增大，随着孔数的增多而减小。在此基础上，率先发现第二主频现象。最后，揭示了凝结振荡区凝结压力振荡由汽泡振荡产生的机理；建立了汽泡凝结压力振荡及其传播特性的理论模型，实现了对凝结压力振荡主频和压力振荡能量传播规律的预测。稳定凝结区射流振荡与汽羽穿透长度周期性的变化有关，结合汽液相界面不稳定理论，揭示了稳定凝结区汽羽动态变化机理，并提出第一主频是汽羽周期性波动引起，而第二主频则由脱离后汽泡振荡引起。并建立了第二主频能量传播特性的理论模型，实现了其能量传播规律的预测。经过本项目研究，揭示了蒸汽浸没射流凝结振荡第一主频和第二主频的产生机制，为射流凝结在实际工业应用提供理论指导。