Experimental Investigation of Spray Characteristics of Pre-filming Air-blast Atomizers

A bulk of a liquid dispersed into single droplets using the kinetic energy of a high-velocity gas in an air-blast atomizer is frequently employed in technical atomization processes. The atomized liquid is primary situated on a surface (prefilming surface) to form a thin liquid film before being exposed to high-velocity air flow. Moreover, the performance of spray processes is affected by the variation in the atomizer geometry, liquid physical properties and operational conditions. The purpose of this study is to examine and describe the influence of the nozzle geometry and a wide range of test conditions on the spray performance of prefilming air-blast atomizers. In order to evade the commonly complicated internal flow, an important but simple geometry was selected. Liquid break up mechanisms close to the atomizer exit were investigated using shadowgraphy associated with particle tracking. Furthermore, high-resolution local velocity and droplet size measurements were performed using phase Doppler anemometry (PDA). On the whole, the break up mechanism is considerably influenced by either air pressure and liquid flowrates or atomization edge size. Droplet size distribution profile of the different spray parameters in axial and radial directions are studied. The location of the maximum droplet mean velocity and the minimum Sauter mean diameter (SMD) within the spray are determined. The prefilming surface area and atomization edge size were observed to influence the liquid sheet breakup, droplet velocity and droplet size. With an atomization edge length increase of 5.7 mm, the global SMD increased to a maximum of 70% within different operation conditions.