含不凝气体的蒸汽与过冷水混合流动冷凝换热机理及强化传热技术研究

Direct contact condensation of steam with non-condensable gas in subcooled water is the main heat transfer process both in the recycling frontier of low-quality exhausted steam from iron production or coal carbonization and in the passive safety systems of nuclear plant. Our precedent researches, which include the study on steam bubble and steam jet condensed in water, have shown the existence of non-condensable gas can change the flow patterns of steam bubble and steam jet-plume, simultaneously deteriorating their condensation heat transfer coefficients. Employing experimental and numerical methods, the steam bubbles’ dynamic behaviors (including transformation, collapse, cohesion, et al), micro structures near the interface, distribution and content ratio of phases, instant and average condensation heat transfer coefficients under different content of non-condensable gas and its properties will be studied by this project. The influence of non-condensable gas on the steam-jet structure, velocity filed, temperature filed, pressure field and condensation heat transfer coefficients will be studied. Meanwhile, based on the experimental results, a numerical model to simulating the DDC of steam with non-condensable gas will be established, verified and corrected. To enhance the heat transfer of steam with non-condensable gas condensed in water, a corrugation shaped primary nozzle will be designed and optimized. The condensation heat transfer phenomenon of steam and water with non-condensable gas in newly designed ejector will be studied numerically and experimentally. All these research works would help provide fundamental theories and methods for the development and design of related industrial equipment where condensation of steam with non-condensable gas in water occurs.

含不凝气体蒸汽与过冷水直接接触冷凝换热是钢铁、焦化等工业领域低品位蒸汽余热回收和核电厂非能动安全系统的主要换热过程。前期初步研究已证实不管对蒸汽气泡还是蒸汽射流与水直接接触冷凝，不凝气体的存在改变了蒸汽气泡和射流汽羽形态，降低了凝结传热系数。本项目采用实验和数值模拟相结合研究方法获得不凝气体含量和分布对蒸汽气泡凝结变形动力学行为（变形、破碎、聚合）、相界面结构、相分布、组分含率和凝结传热系数影响的物理机制。研究不凝气体对蒸汽射流凝结产生的汽羽结构变化、两相流场中温度、压力、速度分布以及凝结传热系数的影响规律。依据实验结果的验证与修正，建立适合于含不凝气体蒸汽直接接触冷凝的数值模型。提出采用波纹状喷嘴强化含不凝气体蒸汽射流凝结换热的新方法，对其结构参数进行优化，并研制新型汽水喷射器系统。该项目研究可为含不凝气体的蒸汽直接接触冷凝换热相关工业设备的设计和开发提供理论依据。

研究含不凝气体蒸汽直接接触冷凝对余热回收及相关换热器设计均具有重要意义。本项目采用可视化实验，自主开发气泡图像处理程序，实现了气泡体积、表面积、中心位置等特征参数的提取,实验发现冷凝过程中气泡表面出现“褶皱”、“断开”现象，气泡形状在冷凝过程中逐渐从“拉长”或“压扁”向着“球状”接近。采用改进后的Lee模型对纯蒸汽气泡和含不凝气体的蒸汽气泡的冷凝相变过程进行模拟，得到了不凝气体含量和分布对蒸汽气泡运动、变形、相界面结构、气泡内组分含率等影响规律。在含不凝气体的蒸汽射流冷凝实验中，使用高速摄像机连续拍摄冷凝气羽，使用MATLAB处理图像获得含气率分布状况，研究发现不凝气体会恶化冷凝传热从而使气羽变大变长，流场中的含气率分布具有自相似特性，得到了自相似形状因子和发散率，分析获得了含空气蒸汽射流冷凝的预测气羽长度和平均冷凝传热系数的关联式。基于欧拉-欧拉两流体模型，建立了含不凝气体蒸汽直接接触冷凝的数值模型，获得了不凝气体对蒸汽射流凝结产生的汽羽结构变化、两相流场中温度、压力、速度分布以及凝结传热系数的关联式。对气-水在U形管内流动的流型进行了识别，发现了5种不同的流型，提出了基于气相表观流速和液相表观流速的流型图。提出了一种结合功率谱分布的偏度与时域波动的多尺度熵率定量识别U形管两相流流型的新方法，此方法可为工业现场非透明管道内两相流流型的在线识别提供指导。对含不凝气体的汽水喷射器内两相流动和凝结换热规律进行数值模拟和实验研究，针对含不凝气体蒸汽射流凝结换热特点，研制了汽水喷射器系统。该项目揭示不凝气体对汽泡和射流凝结相变换热影响的物理本质和基本规律，为相关工业设备的设计和开发提供了理论依据。