Disintegration of liquid sheets

Abstract

The development, stability, and disintegration of liquid sheets issuing from a two-dimensional air-assisted nozzle have been studied. Detailed measurements of mean drop size (SMD) and velocity have been made using a phase Doppler particle analyzer. Without air flow the liquid sheet converges toward the axis as a result of surface tension forces. There is a linear increase in convergence length with increases in liquid flow rate. With air flow a quasi-two-dimensional expanding spray is formed. It is shown that the air flow is responsible for the formation of large, ordered, and small, chaotic ‘‘cell’’ structures. These structures are bounded by large diameter ligaments containing thin membranes inside. The ligaments are the origin of the large droplets in the spray and the membranes contribute to the formation of the smaller droplets. The air flow causes small variations in sheet thickness to develop into major disturbances with the result that disruption starts before the formation of the main breakup region. The phase Doppler measurements show that the spray two-dimensionality breaks down at a short distance from the nozzle in the downstream region. Boundary layer growth and turbulent mixing result in the redistribution of droplets according to their size class. The droplets detached from the central part of the sheet are subject to further breakup because of high local relative velocities. Droplets detached from the rims are outside the main air flow field and have diameters close to that of the rims. The spray acquires a Gaussian velocity profile in both the Y and Z directions.