蒸汽爆炸粗混合过程中的蒸发阻力模型

EVAPORATION DRAG MODEL OF HIGH TEMPERATURE SPHERES MOVEMENT DURING COARSE MIXING STAGE

在蒸汽爆炸的粗混合过程中,由于液体的快速蒸发,高温金属液滴的周围会产生一层很薄的蒸汽膜,此时液滴周围的边界层流动与没有液体蒸发时有很大的不同,因此,常温情况下的小球在连续液体中运动时的通用阻力模型在这种情况下是不适用的．本文通过受力分析,考虑了高温小球受力的分布和表面蒸发对小球周围力的影响,从阻力的基本机理上分析了蒸发状态下小球的运动阻力,分别提出了高温颗粒穿过自由表面时与其在液体中运动时的蒸发阻力模型．分析表明,当小球温度高于2500 K,特别是在靠近自由表面的区域,由于小球表面液体蒸发而产生的蒸发阻力作用非常明显．分析指出,小球的入水初速、小球表面的液体蒸发速率以及汽膜厚度都是影响小球运动阻力大小的重要因素．

A thin layer vapor film surrounds high temperature metal drops due to rapid evaporation of liquid in the coarse mixing stage of vapor explosion. The flow in the boundary layer around the metal drops is greatly different from the flow without evaporation, and then the general drag model of spheres in room temperature cannot be adopted in this situation. In this paper, concerning the forces distribution and surface evaporation effect, a evaporation drag model for one high temperature sphere penetrating the liquid surface and moving inside coolant is proposed respectively based on the analysis of acting forces on the sphere. It is indicated that the drag force due to evaporation is very obvious when the temperature of sphere is higher than 2500 K, especially in the region nearby free surface. It is pointed out that the inlet velocity, vapor generation speed and film thickness are main factors in the size of drag force.