Abstract:

The measurement of frozen droplet is crucial for understanding droplet icing mechanisms and predicting icing processes. Here, a Fourier transform infrared spectrometer was used to measure the absorption spectra of pure water at room temperature (295.7K) and ice at various temperatures (253.2—270.7K). Based on the Beer-Lambert law, a droplet height inversion model was developed, and the combinations of optimal wavelengths were identified by analyzing the spectral data. A measurement system based on absorption spectroscopy was also developed. The influence of spot position on measurement accuracy was analyzed. On this basis, the freezing processes of droplets with different volumes (5μL, 10μL and 20μL) were measured by the developed system and imaging method simultaneously. Meanwhile, temperature changes were monitored by thermocouples to assess whether the droplets had completely frozen. It was showed that the maximum deviations between the two methods were 3.4% and 19.2% for droplets at room temperature and frozen droplets, respectively, since the measurement accuracy was affected by the droplet tip that formed after freezing.

Key words: measurement system, frozen, droplet, absorption spectroscopy, droplet height

摘要：

冻结液滴测量对深入探讨液滴结冰机制以及预测结冰过程具有重要意义。本文利用傅里叶变换红外光谱仪测量室温下（295.7K）纯水以及不同温度下（253.2~270.7K）冰的吸收光谱。基于比尔-朗伯定律构建了液滴高度反演模型，通过分析纯水与冰的光谱数据选取最优波长组合，研制了一套基于吸收光谱技术的冻结液滴高度测量系统，并探究了该系统中光斑位置对测量结果的影响。在此基础上，利用该系统并结合图像法对不同体积（5μL、10μL和20μL）的液滴冻结过程进行测量，同时通过分析热电偶所测液滴温度的变化来判断其是否已经完全冻结。结果表明，两种方法测得的常温与冻结液滴高度最大偏差分别为3.4%与19.2%，这是由液滴冻结后形成的尖端使测量系统中光线发生强烈偏转所导致的。

关键词: 测量系统, 冻结, 液滴, 吸收光谱, 液滴高度