Effects of Mixing Chamber Geometry and Flow on Spray Characteristics from an Internal Mixing Twin-Fluid Atomizer

Abstract

The influences of the mixing chamber geometry of an internal-mixing, twin-fluid atomizer on atomization was examined by visualization of the flow pattern within the mixing chamber and measurement of the Sauter mean diameter of the spray. When the water jet entered as a column state into the outlet hole of the mixing chamber, the breakup of the water was complicatedly changed, with an increase in the atomizing air/water mass ratio. The breakup of the water within the mixing chamber for this flow pattern is divided into four steps: 1. Breakup of the water jet through the outlet hole, 2. Breakup of the water film on the outlet hole surface, 3. Breakup of the water jet in the mixing chamber, 4. Breakup of the water film on the side and top surfaces of the mixing chamber. When the outlet hole of the mixing chamber was located at a coaxial position to the water and atomizing air flow, atomization is mainly occurred at the breakup of the water jet through the outlet hole. The Sauter mean diameter could be reduced by changing the mixing chamber length, the outlet hole diameter, and the ratio of the outlet hole length/diameter. When the outlet hole of the mixing chamber was located at an eccentric position to the water and atomizing air flow, the flow pattern of the water within the mixing chamber was changed to a film state. In this case, atomization mainly occurred at the breakup of the water films on the side and top surfaces of the mixing chamber and the outlet hole surface at all the atomizing air/water mass ratios, and the Sauter mean diameter becomes smaller than that in the case of the outlet hole at a coaxial position to the water and atomizing air flow.