Analysis and Comparison of Primary Droplet Characteristics in the Near Field of a Prefilming Airblast Atomizer

Abstract

As the dominating parameters influencing the Sauter mean diameter of the spray produced by a prefilming airblast atomizer, the air velocity, liquid surface tension and atomizing edge thickness could be identified. Correlations for the prediction of the droplet sizes produced by prefilming airblast atomizers are compared to droplet sizes measured close to the atomizing edge. The measurements were performed using three geometrical variants of a planar atomizer over a wide range of operating conditions. The diagnostics are based on a particle and ligament tracking technique, that enables simultaneous measurement of the liquid blobs and ligaments formed at the atomizing edge and the droplets in the primary breakup region of the atomizer. The comparison between measured and calculated droplet diameter indicates, that most of the correlations are capable of reproducing the correct tendency. However, since the measurement data of most correlations were collected in a region where secondary atomization effects can obscure the initial droplet sizes in the primary breakup region, the droplet sizes are generally predicted too small.