Spot size comparisons on oil- and water-sensitive paper
2001
Fox, R.D. | Salyani, M. | Cooper, J.A. | Brazee, R.D.
Water- and oil-sensitive paper (WSP and OSP) was attached to tree leaves and to a tower bracket between trees. Petroleum spray oil was applied at a constant rate in four concentrations of spray oil in water (1:5.9, 1:10, 1:50, and 1:100) with 17 treatments. WSP and OSP were sprayed in a laboratory with 8001 and 8004 flat fan nozzles. Spot size on oil- and water-sensitive paper, placed at the same location for the same spray condition, were compared by assuming the spots came from the same droplet size population. The spot sizes were sorted by size and divided into 25 classes with the same number of spots in each class. The mean size of each population was calculated for each size class and the ratio of water to oil spots was calculated. To reduce the effect of spot overlap, only sprayed samples with low populations (less than 20% coverage) of water and oil spots were used. Measured spot size ratios were compared to ratios calculated from droplet diameter ratios computed from volume mixtures and from known spread factors on water and oil sensitive paper. Water:oil spot size ratios predicted using known mixture ratios and spread factors agreed quite well with laboratory measured spot size ratios. However, spot size ratios measured for field experiments did not agree with predicted values. This may have been due to larger water spots touching, or oil spots separating into several globules as the water portion of the spray droplet evaporates.
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