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United States Department of Agriculture

Agricultural Research Service

Title: Droplet Shape Oscillations: Effects on Spray Impaction and Retention and Fourier Analysis of Their Natural Frequencies

Authors
item Brazee, Ross
item Cooper, Jane - OARDC-OSU
item Bukovac, M - MICH STATE UNIV
item Reichard, Donald - USDA-ARS-ATRU (DECEASED)

Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 14, 1999
Publication Date: N/A

Interpretive Summary: During spray applications to agricultural crops, there has been concern that spray droplets distortions in flight or at impact may limit the performance of additives intended to improve retention and reduce drift losses to the environment. In-flight dynamic distortions of spray droplets typically used in crop protection were observed under laboratory conditions with high-speed video methods. In addition, a mathematical model was used to estimate accompanying changes in droplet surfaces areas. Data showed that rapid distortions occur over a wide range of droplet sizes. Results also indicate rapid droplet distortions can limit surfactant performance such that droplets may arrive at a plant surface without the necessary reductions in surface tension to promote retention on the crop. These findings are essential to efforts to development of formulations and application methods to improve coverage and retention and reduce losses in the environment.

Technical Abstract: In-flight shape oscillations for 111 to 383 um diameter spray droplets were observed under moderate dynamic conditions using high-speed videography. Fourier analysis of oscillations determined droplet natural frequencies of 9 to 1.5 kHz, results which agreed satisfactorily with a capillary- oscillation model. In addition, a general ellipsoidal model was employed to estimate accompanying changes in droplet surface areas. Results sugges droplet oscillations can limit surfactant adsorption at liquid-air and liquid solid interfaces such that droplets may arrive at a plant surface without the desired lowering of surface tension being achieved. Consequently, full benefits of a surfactant in reducing droplet reflection and promoting retention may not be realized. However, droplet shape oscillations can enhance fluid motions within droplets, with some increase in rates of surfactant transfer to the interface. Results also showed the high natural frequencies characteristic of droplet sizes below 200 um may impose limits on cinematography or videography when attempting to observe droplet distortions or identify energy dissipation pathways at droplet impact.

Last Modified: 12/21/2014
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