泄露性事故闪蒸喷雾流动规律与雾化机理研究

The explosive flashing spray commonly occurs during the accidental release of flammable and toxic pressure liquefied gases in chemical or nuclear industry, when the failure of a vessel or pipe in the form of a small hole will result in the formation of flashing jet containing a mixture of droplets and vapor. This violent release might produce catastrophic consequences to the equipment, human bodies and environment. Flashing spray is dominated by the non-equilibrium thermodynamics, and the internal flow inside the nozzle has significant effect on the spray characteristics. The knowledge and understanding of the mechanisms involved in those releases become an important issue in the prevention of these consequences and the minimization of their impact. This project will use different types of working fluids and different microscale nozzles to form the flashing spray as the simulation of the accidental release. Based on the comprehensive experimental study and theoretical analysis, the formation, development and transition of the two phase flow in the internal nozzle, the mechanism of broken-up of the superheated liquid in the near-nozzle field and the spray and thermal characteristics of the liquid droplets in the spray will be studied, aimed to investigate the influence of the internal flow on the behavior of flashing spray. A deeper knowledge and understanding of the dynamic interaction between the internal flow and outside spray is obtained. Further, a theoretical mode coupling the initial parameters, nozzle sizes, internal flow and spray characteristics is expected to established. The project achievements will benefit in the relevant applications of establishing the risk assessments and minimizing the impact for the release hazard. Additionally, this project will provide experimental data for the validation of the computational fluid dynamics of the flashing spray.

石油化工过程工业中，易燃易爆高压液体或者液化气体由于容器或者管道破损发生泄漏形成闪蒸喷雾事故，对工业生产、人们生命与自然环境产生严重危害。闪蒸喷雾是由非平衡热力学破碎占主导因素引起的过热液体剧烈破碎雾化，同时喷嘴内流体复杂流动特性对闪蒸喷雾具有重要影响。针对这一背景，本项目针对不同种类工质应用不同形式喷嘴形成闪蒸喷雾，通过机理实验和理论分析相结合，研究微尺度喷嘴内（内径为毫米级）气液两相流形成、发展与转变规律，喷嘴外过热液体沸腾破碎机理、液滴动力学与热特征规律，揭示喷嘴内流动规律对闪蒸喷雾特性作用机制与影响规律，建立耦合喷雾初始与喷嘴条件、喷嘴内流动与闪蒸喷雾特性的多过程多参数理论模型。为相关行业实现对泄露性闪蒸喷雾事故有效评估以及降低灾害损失提供理论支撑，具有重要的学术意义与实用价值。

石油化工过程工业中，易燃易爆高压液体或者液化气体由于容器或者管道破损发生泄漏形成闪蒸喷雾事故，对工业生产、人们生命与自然环境产生严重危害。闪蒸喷雾是由非平衡热力学破碎占主导因素引起的过热液体剧烈破碎雾化，喷嘴内流体复杂流动特性对闪蒸喷雾具有重要影响。此外，闪蒸喷雾撞壁会在其他容器、设备壁面产生强烈的冷却效应，掌握壁面动态传热特性是对撞壁形成安全风险评估的判断依据。本项目针对不同种类工质通过不同形式喷嘴形成闪蒸喷雾，通过机理实验和理论分析相结合，研究得到微尺度喷嘴内气液两相流形成、发展与转变规律，近场雾化破碎、液滴动力学与热特征，揭示了喷嘴内多种两相流型对闪蒸喷雾特性影响规律。对多工况条件下闪蒸喷雾撞壁的动态传热规律开展了实验研究，提出了适用于复杂结构的瞬态热流密度计算方法，获得了喷射压力、温度、距离对不同温度壁面撞击所产生的瞬态表面温度、热流、液膜等参数动态变化特性，提出了传热理论关联式。针对喷雾群中单个液滴蒸发，建立了一种基于Hill涡的新液滴蒸发液相模型，模型具有计算高效，并能准确预测瞬态蒸发阶段液滴内部温度空间分布的优点。应用OpenFOAM开展了低沸点、高挥发性介质闪蒸喷雾数值模拟研究，重点考虑了非平衡沸腾相变对闪蒸喷雾破碎的影响作用，数值计算与实验结果吻合良好，并对实验无法准确测量的近喷嘴浓密雾场的液滴与蒸气分布特点，以及不同喷雾条件下的闪蒸喷雾行为开展了系统研究。研究结果不仅从实验与理论方面推进了对复杂闪蒸喷雾物理机理的认识程度，所获得研究方法与结果可为诸多工业应用提供帮助。