Airblast atomization at conditions of low air velocity

Abstract

Spray quality is determined by a series of measurements of drop size distribution and mean drop size. The atomizer employed is a two-dimensional design, producing a flat liquid sheet of variable thickness sandwiched between two coflowing nitrogen gas streams. The range of test conditions is chosen to simulate those typically found in a gas turbine combustor during startup, when air velocities are low. Four different liquids—tap water, heating oil, aviation kerosine (Jet-A), and a high-viscosity mixture of glycerine and distilled water—are used to investigate the effects of liquid physical properties on atomization quality. The results generally confirm those obtained in previous studies in regard to the effects of relative velocity, air/liquid mass flow ratio, and liquid physical properties on Sauter mean diameter. However, the significant dependence of mean drop size on initial liquid film thickness reported by other investigators is not observed in this study. Also, the results suggest the existence of a threshold of relative velocity below which atomization of the liquid sheet is not possible. As the relative velocity is reduced, the Sauter mean diameter eventually reaches a maximum value, and any further reduction in relative velocity results in the loss of the spray.