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Water droplet freezing on an ice surface is a common phenomenon and poses hazards to a lot of applications, including wind turbines, aircraft, and power transmission lines. Since the water droplet temperature is critical, many studies have been carried out to understand the influence of the water droplet temperature on both the impact and freezing processes of droplets on different surfaces. However, the past research studies mainly focused on supercooled water droplets, not on hot water droplets. For applications such as hot-water ice-drilling, the understanding of freezing of hot water droplets on an ice surface is necessary. In the present study, we report the detailed dynamic motions of a hot water droplet impacting on an ice surface. The impact and freezing processes of the hot water droplet on the ice surface are recorded by two cameras. The effects of the water droplet temperature and the ice surface temperature on the impact and freezing processes of the water droplet were experimentally investigated. The results showed that, at the same ice surface temperature, the increase of the water droplet temperature resulted in the increase of the maximum spreading factor, the reduction of the height of the ice bead, and the slight increase of the freezing time. In addition, during the droplet spreading process, the experimental results of the normalized contact diameter fitted well with the exponential model and the water droplet temperature was found to have an apparent influence on the lamella thickness. [ABSTRACT FROM AUTHOR]

In the present study, we carried out an experimental investigation of the impinging and freezing processes of a supercooled large water droplet on an ice surface. One high speed camera was used to measure the dynamic motions of the water droplet while two charge coupled device (CCD) cameras were adopted to obtain the images of the freezing process and the freezing morphologies, respectively. The effects of the water droplet temperature and the ice surface temperature on the impact and freezing processes of the water droplet were carefully evaluated. The results showed that the subcooling degree of the water droplet had an apparent influence not only on the spreading process but on the freezing morphology as well. When the subcooling temperature of the water droplet was high (e.g., Tw = –3.0 °C), a triangle cross-section profile formed. However, once the subcooling temperature of the water droplet was relatively low (e.g., Tw = –9.0 °C), the final ice morphology consisted of two parts: one part was a cone-like bead in the center while the other part was an ice ring at the periphery. Moreover, at the same water droplet temperature, raising the ice surface temperature led to an increase in the maximum spreading factor. [ABSTRACT FROM AUTHOR]