Internal two-phase flow and spray characteristics of outside-in-liquid twin-fluid atomizers

Abstract

Despite its wide industrial applications, the internal-mixing twin-fluid atomization suffers a major problem of spray unsteadiness. This work links the flow characteristics inside a newly designed outside-in-liquid (OIL) atomizer with the spray stability and quality by flow visualization and digital image processing. The results show that the inhomogeneous bubbly and slug flow regimes cause an unwanted intermittent flow inside the exit orifice and an unstable coarse spray, while the stable-annular or the wavy-annular chamber flows provide a favorable continuous annular flow inside the exit orifice and a stable fine spray. By proposing a new parameter considering liquid/gas momentum ratio per liquid injection hole, a flow regime map is constructed, and the transition criterion between the favorable annular flow and the unfavorable intermittent flow regimes inside the exit orifice is obtained. A direct relation between the Sauter mean diameter of the spray droplets and the internal flow transition parameter is found. This study indicates that, under specific internal geometries, the optimized OIL atomizer can overcome the spray unsteadiness problem and hence is suitable for applications requiring high spray stability and quality.