CHARACTERIZATION OF A VELOCITY-MODULATION ATOMIZER

A novel liquid droplet generator, or atomizer, capable of generating e ither monodisperse droplet streams or a polydisperse spray, has been c haracterized using phase-Doppler anemometry and two visualization tech niques. The atomizer consists of a piezoelectric driver in a circular housing with an orifice plate across the end of the housing. Unlike co nventional droplet generators or atomizers, this device directly induc es a high-amplitude velocity perturbation of the liquid jet. Orifice p lates with a circular hole (diameter: 34 or 98 mum) or a rectangular h ole (527 x 31 mum2) were used. In the low-power mode, the atomizer wit h a circular orifice generated a stream of monodisperse water droplets with a diameter 1.5 to 3.4 times the jet diameter and a separation 2. 3 to 26 times the jet diameter at 10 to 68 kHz. Droplets smaller than the minimum size predicted by Rayleigh's criterion can be generated wi th an increased modulation power. The droplet velocity can be adjusted in a wide range (4 to 26 m/s), and a high Reynolds number (approximat ely 250) can be attained. In the high-power mode, the atomizer produce d a polydisperse water spray with a Sauter mean diameter less than hal f the jet (equivalent) diameter. The rectangular orifice required sign ificantly less driving power to generate a spray. This atomizer is sui table for both fundamental studies and practical applications.