Experimental investigation of droplet moving on a horizontal metal plate driven by cold airflow

The deformation and movement of droplets are a fundamental phenomenon in nature and industry. The droplet under shear airflow is involved in many aspects, and research on the droplet under different experimental conditions, such as airflow temperature, is still lacking. A series of experiments on droplet motion under different conditions were carried out. The speed and temperature of airflow ranged from 17.0 m/s to 35.0 m/s and −17.0 °C to 20.0 °C, respectively. The droplet volume varied from 5.0 to 40.0 μL. The droplet properties did not change under the cold airflow in the test time, which indicated that it did not freeze and remained liquid for a period of time. During the whole droplet motion in the view, no solidification is observed. The characteristic parameters including the position of the droplet centre, the wetting length, the droplet height and the difference between the cosines of the front contact angle and the rear contact angle (cah) of droplet were obtained by image post-processing. The maximum length ratio and the maximum height ratio of droplet deformation were discussed. The morphology of a droplet during its motion was classified into three regimes according to the droplet Reynolds number, S (sliding slightly), SS (sliding and moving), and SRS (sliding and rivulet formation, and separation). A map of the regimes of droplet motion under different conditions was obtained. It is found that when the Re_d is in a range from 0 to 25, the droplet motion is Regime I (S). With the Re_d increasing, the different regimes appeared. The order in which they appear is S, SS, and SRS. This study provides experimental reference data for the study of the droplet motion in different temperatures and shear of airflow.