Analysis of behavior of single water droplet after impingement on a flat surface of different properties

Behavior of single rain droplet after impingement on a flat surface placed horizontally was studied. Most studies concerning rain droplet impingement done so far have been aimed at the impact force measurement carried out experimentally from the mechanical, civil, and agricultural engineering point of view.. However, the precise analysis of the behavior of the thin water film spreading on the surface after collision was not performed. Hence, we conducted the test to find out how a droplet behaved in association with data collection of the water spreading speed and the radius of a water circle. In order to find out the effect of the surface property on the droplet’s behavior, the surface of a specimen on which the droplet impacted was to be of different wettability: hydrophilicity, hydrophobicity and superhydrophobicity. The amount of water dripped from the micro pipette was carefully controlled to produce the droplet with a diameter corresponding to the average size of natural rain drops. The very minute plastic particles with some micron diameter were added to water to drop for the image analysis after the test. For the image analysis, the particle tracking velocimetry was employed.