Experimental Study of Sprays from Annular Liquid Jet Breakup

Abstract

An experimental investigation has been conducted to study the characteristics of sprays produced from the breakup of annular water jets exposed to inner airstreams, simulating twin-fluid atomization, by using phase Doppler anemometry. The spray characteristic parameters, such as droplet Sauter mean diameter (SMD), mean velocity, velocity fluctuation, and droplet number density, have been measured for various radial and axial locations and under various liquid and airflow velocities at the nozzle exit. The results indicate that the spray characteristic parameters are almost symmetric about the spray axis. At each axial spray cross section, the droplet mean axial velocity reaches the maximum value in the spray center and decreases from the spray center to the edge. Further, the droplet axial velocity has a jet-like selfsimilar spatial distribution along the radial and axial directions when normalized by appropriate reference parameters. Similar universal correlation is observed for the droplet fluctuation velocity and turbulent intensity as well. The SMD has a minimum value at the spray center and increases toward the spray periphery. The SMD at the spray centerline has a more complex variation in the downstream direction because of secondary atomization at high air velocity near the nozzle exit and droplet entrainment and migration farther downstream. The droplet number density has a radial distribution similar to that of the SMD, whereas its value at the spray center increases with the distance from the nozzle exit, and is reduced by the high air and liquid flow velocity.