过冷水滴碰撞过程的实验研究

Experimental Investigation of Binary Supercooled Water Droplet Collision

针对目前结冰环境的粒径演化研究仍基于常温水滴碰撞结果与实际过冷情况差别大的问题,设计实验研究了常温与过冷水滴碰撞行为的差别:通过水滴发生器产生两水滴链并以一定角度碰撞,其过程通过高速相机记录.实验中水滴的碰撞韦伯数范围为0~100,温度范围为25^-5℃.结果发现,随着温度的降低,水滴碰撞结果发生明显的改变:(1)合并区域向分离区域扩展;(2)反射分离区域向高韦伯数方向移动;(3)拉伸分离区域向高碰撞参数方向移动.分析显示水滴的表面张力和黏性变化是导致该结果的主要原因.这说明过冷水雾碰撞演化将导致粒径明显大于以常温水滴碰撞模型预测的结果.

The prediction of droplet size distribution is always based on water droplet collision outcome at room temperature, which has a great difference with that in freezing environment. Because of this, the outcome of binary water droplet collisions was investigated experimentally within a certain temperature range. Two mono-disperse droplet chains were produced by means of piezoelectric droplet generators and two high speedcameras were used to observe the collision process. Values of the Weber number based on the small droplet sizes are from 0 to 100. Droplet temperature varies from 25 ℃ to --5 ℃. Compared with the outcome at room temperature, the result of the supercooled water droplet collision has obviously changed. （1） The coalescence region extends to the separation region. （2） The reflexive separation region move towards the region with high Weber number value. （3） The stretching separation region is slightly shifted downward. From the perspective of the supercooled water properties, the influence of temperature on collision results was discussed. The droplet size distribution of supercooled spray has a great difference with the result based on water droplet collision at room temperature.