An Approach to Design an Air-Liquid Supersonic Ejector for Producing Aerosol Spray

This study aims to design a supersonic ejector, referred to as a liquid spray gun, with a simple operating procedure for producing an aerosol spray with adjustable droplet size distributions. A CFD model was developed to determine the influence of nozzle exit position and the primary air pressure on the supersonic patterns formed within the ejectors, providing a valuable insight into their internal physics. Based on the single-phase numerical results, at an air primary pressure of 2 bar, the flow may not reach a choking condition, possibly resulting in unstable ejector operation. However, at pressures exceeding 5 bar, the jet patterns emerging from the primary nozzle cause flow separation or the formation of vortex rings. This phenomenon leads to a flow configuration comparable to the diameter of the mixing tube, thereby reducing the available area for entrainment of suction flow. The suitable ejector was identified with a nozzle exit position of 13 mm and a primary pressure ranging from 3 to 4 bar. Consequently, a high-speed imaging shadowgraph system was successfully developed to experimentally analyze the water spray pattern within the designed ejector. The experimental results indicate that the ejector performs effectively under different operating conditions, producing a fine water spray with predominantly small droplet sizes below 30 μm when the air pressure is within the range of 3 to 4 bar. These results highlight the capability of the supersonic ejector as a spray gun for generating aerosols suitable for contaminated surface cleaning and other relevant applications. © 2024 SAE International. All rights reserved.