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ARS Home » Plains Area » College Station, Texas » Southern Plains Agricultural Research Center » Aerial Application Technology Research » Research » Publications at this Location » Publication #351904
Title: Nonlinear derivation of spread factor due to viscous energy losses

Author
item WILDE, SCOTT - Former ARS Employee
item Hoffmann, Wesley
item Fritz, Bradley - Brad

Submitted to: Journal of ASTM International
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2018
Publication Date: 10/11/2018
Citation: Wilde, S.C., Hoffmann, W.C., Fritz, B.K. 2018. Nonlinear derivation of spread factor due to viscous energy losses. Journal of ASTM International. 1610:53-60. https://doi.org/10.1520/STP161020170241.
DOI: https://doi.org/10.1520/STP161020170241

Interpretive Summary: Water sensitive papers provide for a quick and easy visual and quantitative assessment of spray deposition from agrochemical spray applications. Deposition characteristics such as the amount of the surface covered as well as spray droplet sizes that deposited can be determined from sprayed cards. However, the process of the spray droplets going from a three-dimensional solid volume to a two dimensional stain on the card results in a spreading of the spray material on the card. The degree of the this spread, which depends on the physical properties of the spray, must be accounted for to provide an accurate assessment of coverage and size. A physics based computational model, that accounts for a solution's physical properties, was developed to calculate the degree of spread a droplet experiences when depositing on water sensitive cards. This physical model will provide applicators and researchers a means to quickly determine and account for different behaviors of spray solutions on water sensitive cards in order to obtain accurate deposition characteristics which can then be used to managing systems to enhance application efficacy.

Technical Abstract: Water sensitive cards provide a quick and easy method to evaluate the coverage and deposition from spray applications. The most common metric recorded is the percent coverage as measured by droplet size, which is highly influenced by the stain diameter resulting from the droplet deposition and spread on the card. Complicating this process is the fact that the stain diameter, and thus the spread factor, is impacted by the physical properties of the spray solution, meaning different spray solutions require unique spread factor relationships to accurately estimate the droplet size and deposition on water sensitive cards. Since past techniques for determining spread factor have been cumbersome and time consuming, more empirical process was developed using the physical properties of the spray and an energy balance equation. The specific objective of this work was to develop a formula for calculating spread factor on water sensitive papers based on the physical properties of the spray.