Droplet size distribution in swirl nozzles

•Volume distribution of a pressure swirl nozzle can be bimodal.•Liquid sheet can break up into ligaments with two different characteristic length scales.•Fitting a mixture of two lognormal distribution directly to volume distribution gives good result.•LISA model can provide length scales for major mode with large droplets.•Minor model with small droplets is responsible for 5% of total volume. The present work was aimed at developing a correlation for the droplet size distribution for pressure swirl nozzles. The droplet size distributions for different injection pressures, orifice diameters, and fluid viscosities are measured using Malvern Spraytec Dropsizer. We have developed a mixture distribution with two lognormal distributions that fits well to the measured volume distributions. A correlation is developed for the droplet size distribution that fits the major peak of the distribution. The correlation parameters are related to the Kelvin-Helmholtz wavelength on the liquid sheet and the sheet thickness at the nozzle exit. This distribution function can be used to determine the Sauter Mean diameter and other spray statistics.