蒸汽夹带作用下高温颗粒表面拖曳力模型研究

Study on Drag Force Model of High-Temperature Particle Under Steam Entrainment

高温熔融物在冷却剂中的沉降过程关系到蒸汽爆炸的触发及后续过程的发展,影响严重事故缓解措施的设计与实施。基于高温颗粒表面蒸汽膜的夹带作用,通过理论建模与实验拟合的方法,构建了预测粗混合阶段颗粒在冷却剂中沉降过程的拖曳力系数的半经验关系式,表示为颗粒弗洛德数(Fr_(p))与夹带雷诺数(Re_(α))的函数。通过与高温钢球下落冷液中沸腾运动过程实验结果的比较,验证了粗混合初期蒸汽的夹带作用是颗粒沉降的主导因素。另外,沉降速度的变化受高温颗粒的直径影响。颗粒的直径越小,其沉降特征越接近于“冷颗粒”,这主要与蒸汽夹带作用的降低有关。

The settling process of high-temperature melt in coolant is related to the triggering of steam explosion and the development of follow-up process,and affects the design and implementation of serious accident mitigation measures.Based on the entrainment of the steam film on the surface of high-temperature particles,a semi-empirical relation for predicting the drag force coefficient of particles in the coolant during the coarse mixing stage is constructed by means of theoretical modeling and experimental fitting,which can be expressed as a function of particle Froude number(Fr_(p))and entrainment Reynolds number(Re_(α)).By comparing with the experimental data of boiling motion in the falling coolant of high-temperature steel ball,it is verified that the entrainment effect of steam in the initial stage of coarse mixing is the main factor of particle settling.In addition,the change of settling velocity is affected by the diameter of high-temperature particles.The smaller the diameter of the particles is,the closer the settling characteristics are to the"cold particles",which is mainly related to the decrease of steam entrainment.