THEORETICAL STUDIES ON THE INFLUENCE OF REFRACTIVE INDEX GRADIENTS WITHIN MULTICOMPONENT DROPLETS ON SIZE MEASUREMENTS BY PHASE DOPPLER ANEMOMETRY

The response of a phase Doppler instrument has been predicted for the sizing of evaporating multicomponent droplets. This study uses the theoretical model of Schneider and Hirleman [1] and extends its application to droplets consisting of liquid mixtures. The results obtained for binary heptane/dodecane droplets are discussed for different scattering angles. The internal refractive index gradients considerably affect the relation between phase difference and droplet diameter at mean scattering angles of Θ = 30° and Θ = 160°. However, the absolute variations of the calibration curves are smaller compared to those observed for a single component droplet. Additionally a mean scattering angle of Θ = 70° has been investigated. These results clearly demonstrate the insensitivity of the Θ = 70° scattering configuration on internal refractive index variations and thus confirm the recommendation of Pitcher et al. [2] ,who considered minimizing errors due to unknown but homogeneous refractive indices.