DROPLET TRANSPORT IN SIMPLEX AND AIR-ASSISTED SPRAYS

This article reports an experimental study of drop transport phenomena in sprays. Three-dimensional characteristics of a research simplex at omizer (RSA) with and without atomizing air are measured to provide th e benchmark database. Methanol flow rate and pressure are controlled a t 1.26 g/s and 357 kPa, respectively. The atomizing air is supplied at a pressure of 3.57 kPa with an air-to-liquid mass ratio of 0.64. The performance of the spray with and without atomizing air is measured by a two-component phase Doppler particle analyzer (PDPA). Results show that the spray cone angle and Sauter mean diameter (SMD) decrease in t he air-assist case. On the other hand, both axial and azimuthal veloci ty increase, while the radial velocity remains the same even under ato mizing air condition. It is also found that SMD increases along the ax ial and radial directions for both cases. Analysis of the histogram da ta shows that the transport of part of the smaller drops from the oute r region to the central region is the key process responsible for the SMD increase downstream. The drop transport phenomenon is further supp orted by the drop number density increase and higher velocity fluctuat ion at the spray central region in the downstream region. Comparison o f the velocity profiles for both cases also shows that the transition length from a wake to a jet profile is shorter in the air-assist case. Furthermore, the axial, radial, and azimuthal velocity fluctuations o f the dispersed phase (u', v', w') increase in both the central region and the spray sheet in the air-assist case. However, it is found that this increase is due to the interaction between the droplet and the g as phases in the spray sheet but not due the velocity gradient mechani sm as has been widely adapted in the shear layer flow problem.