Three-Dimensional Imaging System for Analyses of Dynamic Droplet Impaction and Deposit Formation on Leaves

Abstract

<abstract><title><italic>Abstract. </italic></title> A system was developed to assess the dynamic processes of droplet impact, rebound, and retention on leaf surfaces with three-dimensional (3-D) images. The system components consisted of a uniform-size droplet generator, two high-speed digital video cameras, a constant-speed track, a leaf holder, and light sources. The droplet generator produced uniform droplets of 100 to 800 μm diameter. The video cameras captured droplet impact images from two different angle views for 3-D droplet impaction analyses. The camera speed used to capture images was up to 50,000 frames per second, with image resolution up to 1280 × 800 pixels. The constant-speed track was used to mount and drive the droplet generator at constant speeds ranging from 1.6 to 10 km h^-1. The leaf holder supported leaves at various orientations and distances from the droplet generator. Waxy and hairy leaves and water solutions amended with a non-ionic surfactant were used to verify the system functions. Five motion processes of droplets after they impacted on waxy and hairy leaf surfaces were observed: complete retention, split retention, slide retention, splash, and rebound. The droplet motion and deposition process before and after impact were quantitatively analyzed with a 3-D image program. In conclusion, the imaging system was able to precisely observe and quantitatively analyze droplet impaction and deposit formation on waxy or hairy leaves when droplet diameter, droplet discharge speed, droplet discharge height, nozzle travel speed, leaf surface orientation, and spray formulation were variables.