Experimental study on the effects of successive supercooled large droplets impacting
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摘要: 目前过冷大水滴（SLD）撞击结冰机理未能清楚解释SLD间的相互干扰对撞击结冰过程的影响。实验用高速相机拍摄双SLD偏移一定位置相继撞击壁面结冰的物理过程，研究双SLD落点间的偏移、相继撞击的时间间隔对结冰形态及结冰速度的影响。实验表明：双SLD间的相互干扰会抑制撞击后的回缩行为进而影响结冰形态，降低结冰速度，延长双SLD完全冻结时间：双SLD落点位置偏移量的大小对结冰形态和结冰速度的影响均很大，相继撞击时间间隔的长短对结冰形态影响不大，主要影响结冰速度。Abstract: The understanding of the impacting-icing mechanism of supercooled large droplet (SLD) is still limited to a single SLD. The interactions between droplets have not been taken into consideration. A high-speed camera is used to record the impacting-freezing process of two SLDs that are offset a certain distance away from each other and successively impact on the substrate. The experiment studies the relationship between the offsets of two SLDs, the time intervals of successive impacts and the freezing morpholog as well as the freezing speed. The experiment shows that the interactions between SLDs can inhibit the SLD shrinkage behavior and prolong the freezing time. The size of the offset affects the shrinkage rate which decides the final freezing morphology. The freezing time of two SLDs decreases rapidly with the slight increase of the offset of two SLDs in a small range. The time interval of the successive impacts is inversely proportional to the freezing time and has a weak effect on the formation of the freezing morphology.
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Key words:
- supercooled large droplet /
- impact /
- offset /
- time interval /
- freezing morphology /
- freezing speed
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图 1 实验的总体布局图
1, 9循环冷却水浴箱; 2 SLD发生器; 3螺旋微调支架; 4低温环境; 5支架底座; 6高速相机; 7平行光源系统; 8撞击表面; 10~13水压调节系统; 14温度监控仪; 15 PC终端
Figure 1. The overall layout of the experiment
图 3 观测系统以及低温撞击实验平台
1平行光源; 2撞击实验表面及制冷芯片; 3高速相机
Figure 3. High-speed shooting system and test piece platform
图 4 双SLD相继撞击壁面实验示意图
Figure 4. Schematic diagram of two SLDs successively impacting on the surface
图 6 双SLD相继撞击壁面结冰过程图
Figure 6. The freezing process diagram of two SLDs impacting on the substrate
图 7 不同实验工况对比图：(a)单SLD撞击结冰(b)、(d) L/D为0, Δt分别为0.6s和0.9s. (c)和(e) L/D分别为0.5和1.2, Δt为0.6s
Figure 7. Contrast images of different experimental conditions: (a) a single SLD impacts and freezes; (b), (d) L/D=0, Δt=0.6s, 0.9s; (c), (e) L/D=0.5, 1.2, Δt= 0.6s
图 8 SLD间的干扰和回缩率之比的关系
Figure 8. Relationships between interactions and the ratio of the shrinking rate
图 10 不同实验工况下完全冻结时间对比图
Figure 10. Contrast images of complete freezing time under different experimental conditions
图 11 结冰时间变化率与双SLD间的干扰的关系
Figure 11. Relationship between the rate of freezing time and interactions
表 1 实验变量表
Table 1. Experimental variables
Experimental variable L/D Δt/s Value 0~1.5 0.3、0.6、0.9 
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