Three-dimensional imaging system for analyses of dynamic droplet impaction and deposition formation on leaves

Authors: DONG, X - Chinese Academy Of Agriculture & Mechanical Sciences; Zhu, Heping; YANG, X - Chinese Academy Of Agriculture & Mechanical Sciences

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/21/2013
Publication Date: 12/2/2013
Publication URL: http://handle.nal.usda.gov/10113/58492
Citation: Dong, X., Zhu, H., Yang, X. 2013. Three-dimensional imaging system for analyses of dynamic droplet impaction and deposition formation on leaves. Transactions of the ASABE. 56(5):1641-1651.

Interpretive Summary: Current spray technology research mainly focuses on equipment and application improvements to improve spray delivery accuracy. However, after droplets reach targets, they are subject to the effects of impact, spread, rebound, retention, absorption and evaporation. These microscopic processes directly affect the biological effectiveness and efficiency of spray applications on pests. This research developed a three-dimensional sophisticated system for analyses of dynamic droplet impaction, rebound and deposition formation on leaves. The system was able to manipulate variable sizes, impact speeds and impact angles of droplets to independently test the dynamic impaction of droplets on different types of leaves with different spray solutions under controlled experimental conditions. This accomplishment would provide insights into pesticide droplet impaction and deposition formation on plant leaf surfaces to bridge the gaps of knowledge between the spray application technologies and biological control effectiveness. These underlying mechanisms would eventually advance pesticide spray application technologies and strategies to stabilize droplet retention on targets to increase biological control effectiveness and reduce pesticide waste from droplet rebound and runoff.

Technical Abstract: 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. The video cameras captured droplet impact images from two different angle views for 3-D droplet impaction analyses. The speed of cameras to capture images was up to 50,000 frames per second with image resolution up to 1,280×800 pixels. The speed track was used to mount and drove the droplet generator at constant speeds ranging from 1.6 to 10 km/h. 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 impaction 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 deposition formation on hairy or waxy leaves when droplet diameter, droplet discharge speed, droplet discharge height, nozzle travel speed, leaf surface orientation, and spray formulation were variables.