Abstract:

An investigation was conducted to quantify the unsteady heat transfer and phase changing process of a large droplet impinging onto cold surface under different surface temperature, through high speed imaging and infrared thermal imaging technology. In addition, a new method of deicing was presented. The deicing experiment using high-frequency nanosecond pulse dielectric barrier discharge plasma actuator was conducted, and thermodynamic analysis was also carried out. The results reveal that cold surface temperature has little effect on the spreading process, but has obvious effect on receding process,oscillation process and final ice shape. The icing starts at the bottom of the droplet, with the decrease of the wall surface temperature, the temperature difference between droplet and cold wall surface get bigger, hence the underlying liquid droplet freeze faster, the liquid film on the top of droplet get thinner, and the time needed for freezing phase change get shorter. By using high-frequency nanosecond pulse dielectric barrier discharge, the deicing effect is obvious, and the discharge area acts seem as a “heat source”. According to the way it functions, the process of deicing can be divided into two stages.

Key words: phase change, cold surface, heat transfer, nanosecond pulse, dielectric barrier discharge

摘要：

对大液滴撞击过冷壁面结冰的传热和相变过程进行了实验研究，采用高速成像技术与红外测温成像技术对液滴撞击不同温度过冷壁面时的动态过程进行拍摄记录。另外提出一种新的除冰方式，利用高频纳秒脉冲介质阻挡放电等离子体激励器进行了除冰的实验验证，并进行了热力学分析。实验结果表明：壁面温度的变化对液滴铺展过程影响较小，最大铺展系数几乎不变，但对液滴收缩与振荡过程以及最终结冰冰形有较大的影响；结冰从液滴底层开始，壁面温度越低，液滴与过冷壁面温差越大，底层液滴结冰更快，而上层液膜经过回缩、振荡之后，液膜厚度更薄，结冰相变所需时间也更短；利用高频纳秒脉冲介质阻挡放电除冰效果显著，其放电区域作用相当于是一个“热源”且根据其作用方式的不同，除冰过程可分为两个阶段。

关键词: 相变, 冷壁面, 传热, 纳秒脉冲, 介质阻挡放电