A Method for Determining Droplet Size Distributions and Evaporational Losses Using Paper Impaction Cards and Dye Tracers

In liquid spraying operations, droplet size distributions are often measured using paper witness cards. Stain size measurements of collected aerosol stains are converted to the original droplet sizes using a predetermined spreadfactor regression. The regression is developed from control stains. However, drying conditions effecting the spreading process cannot always be matched in the laboratory. Thus, a method of deducing the spreadfactor directly from actual trial stains was developed and tested using thickened diethyl malonate and Whatman 1 Filter Paper. The method uses the spectra properties of the tracer dyes in the test fluid. The dyes are removed by solvent extraction from individual stains on the witness cards and quantitatively analyzed to determine the original droplet size. After the initial study, further work was conducted in measuring droplet free fall evaporation. It was found that the methodology can accurately measure evaporation under field trial conditions.