Effect of gas jet angle on primary breakup and droplet size applying coaxial gas-assisted atomizers

Abstract

This study investigates the influence of gas jet angle on primary jet breakup and the resulting droplet size distribution for coaxial gas-assisted atomizers. In industrial applications, the gas jet of these atomizers are typically angled towards the liquid jet, whereas in most spray investigations in literature, parallel flow configurations are used. To enable a detailed analysis of the influence of the gas jet angle, three atomizers with angles of 0°, 15° and 30° were examined. Other geometric parameters, such as liquid jet diameter, gas gap width and wall thickness were kept constant. For each atomizer, two gas velocities at constant liquid mass flow were investigated i.e., two gas-to-liquid ratios (GLRs). An additional set of experiments was performed at increased system pressure using three atomizers with identical gas jet angles, but with an adapted gas orifice area in order to keep gas velocity, GLR and momentum flow ratio constant for all pressure levels. Water and a glycerol/water-mixture were applied in order to investigate the influence of liquid viscosity. The primary breakup process was monitored by a high-speed camera, whereas the resulting droplet size was detected using a phase-Doppler anemometer. For all system pressures and liquid viscosities under investigation, a distinct influence of gas jet angle on primary breakup as well as on resulting droplet size distribution was observed for low gas velocity.

Comparison of Central Jet and Annular Sheet Atomizers at Identical Gas Momentum Flows

“…In the following paragraphs, only a short overview of the applied measurement systems is given. A detailed description is available in previous studies. ,, …”

Mass Flow Scaling of Gas-Assisted Coaxial Atomizers

“…For increasing wall thickness, the interaction point between the emerging phases was shifted to a higher distance from the nozzle orifice, which results in a recirculation zone [29] and enhances the formation of flapping instabilities [30]. The effect of an increase in the gas channel angle was analyzed by several authors, leading to the conclusion that aerodynamic forces are enhanced and droplet size is reduced for low gas velocities [31][32][33].…”