Formation and breakup of ligaments from a high speed rotary bell cup atomizer (Part 1: Observation and quantitative evaluation of formation and breakup of ligaments)

Abstract

We experimentally investigated the effects of operational conditions and liquid properties on the formation and breakup of ligaments from a high-speed rotary bell cup atomizer. Glycerin ethanol solutions and glycerin water solutions of different viscosity and surface tension were supplied. The rotational speed of bell cup ranged from 8000 rpm to 30000 rpm. The liquid volume flow rate was varied from 150 mL/min to 600 mL/min. We observed by photography with 180 nsec flash exposure, the shape of the liquid film divided by grooves and breakup behavior of ligaments ejected from a bell cup. From pictures obtained, we quantitatively evaluated by image processing based on edge detection, the width of liquid film divided by groove, the diameter and length of ligaments and the diameter of droplets generated. The results are summarized as follows: (1) The ligament diameter at bell cup edge increased with the increase in liquid volume flow rate and liquid viscosity. (2) The ligament diameter decreased rapidly for ligament axial length l < 300 μm, but more slowly for l > 300 μm. (3) The breakup distance of ligament increased with the increase in liquid volume flow rate and liquid viscosity. (4) The droplet diameter was determined by both the diameter of ligament at the front tip and the wavelength of capillary wave. (5) The gamma distribution well described the experimentally obtained droplet size distribution with the shape factor n of approximately 20. ©2013 The Japan Society of Mechanical Engineers.