液滴撞击高温表面的关键换热现象及模型研究

In the reflooding process of nuclear reactor, droplets impact rod bundle and remove heat from cladding. Moreover, the Leidenfrost phenomenon also has an influence on the determination of the position of the quenching front. The existing studies usually neglect the heat removed by these Leidenfrost drops. However, the experimental results show that it has an important influence on the surface temperature distribution of fuel assembly. In this project, heat transfer phenomena during single drop impingement on a hot surface is investigated by experimental, numerical and theoretical studies. In the experiment, high-speed photography method are employed to measure the vapor layer dynamics between the heated surface and the droplet. The numerical simulation method is used to analysis the radiative heat transfer. Based on the experimental and numerical results, the influence from the properties of droplet on the heat transfer process is investigated based on the instability theory and the force balance. And the heat transfer model will be proposed based on the heat conduction and radiation. The proposed model will provide a better prediction accuracy for the safety analysis of the reflooding process.

核反应堆堆芯再淹没过程中，从骤冷前沿夹带来的液滴撞击高温组件表面的冷却过程决定最高包壳温度，是再淹没中至关重要的问题。液滴撞击高温表面时的浸润性（即Leidenfrost现象）还影响骤冷前沿位置的判定，继而影响再淹没速率的判断。针对浸润性与撞击冷却特点，本项目采用实验观测和数值模拟进行研究。实验方面利用高速摄像和干涉技术观测撞击过程中蒸汽层形态演变、液滴形态拓扑变化，基于蒸汽层形态锁定影响Leidenfrost现象中沸腾模式转变的关键液滴运动特征并确定Leidenfrost温度。采用直接数值模拟研究膜态沸腾下能量分配、传热特性、液滴滞留时间和铺展面积并揭示温度变化对辐射换热在总换热量中所占比例的影响规律。阐明液滴运动特征对沸腾模式转变、液滴形态拓扑变化的影响规律，揭示导热和辐射换热的作用机理，建立膜态沸腾下液滴撞击传热模型。项目研究成果将为反应堆再淹没过程中组件包壳温度的预测奠定科学基础。

核反应堆堆芯再淹没过程中，从骤冷前沿夹带来的液滴撞击高温组件表面的冷却过程决定最高包壳温度，是再淹没中至关重要的问题。液滴撞击高温表面时的浸润性（即Leidenfrost现象）还影响骤冷前沿位置的判定，继而影响再淹没速率的判断。针对浸润性与撞击冷却特点，本项目采用实验观测和数值模拟进行研究。实验方面利用高速摄像和干涉技术观测撞击过程中蒸汽层形态演变、液滴形态拓扑变化，基于蒸汽层形态锁定影响Leidenfrost现象中沸腾模式转变的关键液滴运动特征并确定Leidenfrost温度。采用直接数值模拟研究膜态沸腾下能量分配、传热特性、液滴滞留时间和铺展面积并揭示温度变化对辐射换热在总换热量中所占比例的影响规律。阐明液滴运动特征对沸腾模式转变、液滴形态拓扑变化的影响规律，揭示导热和辐射换热的作用机理，建立膜态沸腾下液滴撞击传热模型。项目研究成果将为反应堆再淹没过程中组件包壳温度的预测奠定科学基础。基于上述工作，发表期刊论文5篇，其中包括核工程顶级期刊3篇和核工权威期刊2篇，会议论文5篇，基金进展汇报口头报告1次，协助培养博士生2名，硕士生2名。