EXPERIMENTS ON AIR-BLAST ATOMIZATION OF VISCOELASTIC LIQUIDS, PART 1: QUIESCENT CONDITIONS

Motivated by the need to improve spray coating, an experimental investigation into viscoelastic atomization using preformulated model test liquids is presented. These test liquids had similar values of surface tension, density, and rate-independent shear viscosity, but varying extensional viscosity. Through the use of these test liquids, the effects of elasticity were systematically isolated and found to act against the breakup of a spray issuing from a plain-jet air-blast atomizer. Flash photography revealed large-scale filamentary structures at breakup, which delayed discrete droplet formation until farther downstream, where relative air-liquid velocities were reduced. The lower relative velocities near breakup produced an increase in the volumetric median diameter, as was confirmed by analysis of high-magnification shadowgraphs. The hindering influence of elasticity on atomization was further substantiated through particle image velocimetry measurements, which indicated that the elastic droplets, owing to their greater inertia, were better able to maintain their initial momentum.