A study of parameters that influence the accuracy of the Planar Droplet Sizing (PDS) technique

A combined theoretical and experimental study of the parameters affecting t he accuracy of Planar Droplet Sizing (PDS) measurements is presented. The p rinciple of the PDS technique relies on the assumption that the intensity e mitted by a fluorescent dye added to a liquid is proportional to the volume of a resulting droplet during atomisation and that the scattered light int ensity is proportional to its surface area, allowing measurement of Sauter Mean Diameter (SMD) by taking the ratio of these intensities. A geometrical optics light scattering approach was extended to calculate the fluorescenc e intensity emitted by a droplet, in addition to providing the scattered li ght intensity integrated over the collection aperture. The theoretical appr oach quantified the influences of scattering angle, refractive index, dropl et size and dye concentration on the PDS technique. Experiments with monodi sperse droplet streams confirmed the calculations in terms of dependence of the scattered and fluorescence intensities. The limitations of the techniq ue have been established together with an appropriate calibration procedure for application in dense sprays.