An image processing method to measure droplet impact and evaporation on a solid surface

We employ high-speed visualization to quantify the impact and evaporation of a droplet on a solid surface. The time-varying droplet shapes are recorded using a high-speed camera and an image processing method is developed for measurement for droplet dimensions, dynamic contact angle, and volume. The method is based on the liquid-gas and liquid-solid interface detection using Canny's method and Otsu's method for threshold digitalization. To obtain the dynamic contact angle, a higher-order polynomial is fitted along the pixels near the contact line. The droplet volume is measured assuming an axisymmetric geometry of the droplet and numerically integrating the identified pixels in the droplet. We demonstrate the detection of the complex topology of the deforming liquid-gas interface of an impacting and evaporating droplet on a solid surface. We plot the time-variation of droplet dimensions, namely, wetted diameter, maximum diameter, height; dynamic contact angle, and droplet volume. The contact angle and volume measurements are verified with known analytical values. Three case studies are considered to demonstrate the capability of the proposed method, namely, sessile evaporating droplet, bouncing droplet, and spreading viscous droplet on a solid surface.