Experimental investigation of surface tension and viscosity on hollow cone spray atomization due to ethanol blending

This paper explores the atomization of ethanol-containing solutions with varying properties. Mixtures of ethanol and deionized (DI) water with different ethanol concentrations (10 %, 20 %, and 50 %) were atomized, along with DI water mixed with 2.5 % surfactant. The droplet size and velocity distribution within the swirling hollow cone spray were analyzed using a Phase Doppler Particle Analyzer (PDPA). The study emphasizes the significant role of viscous, inertial, and surface tension forces in the atomization of the tested mixtures. The trends of the droplets' Sauter Mean Diameter (SMD) along the spray axis were measured and validated with previous experimental results. The results show that mixtures with lower surface tension produce finer and faster droplets, while those with higher viscosity result in larger and slower droplets. When inertial forces are dominant and the surface tension is relatively low, finer spray breakup occurs; conversely, larger droplets form during the spray breakup when viscous forces are more prominent. For the 10 %-ethanol mixture, viscous, inertial, and surface tension forces appear to be in an optimal balance, leading to the formation of fine droplets with only a slight tendency for coalescence downstream. When viscous forces prevail, coalescence occurs in the downstream areas of the spray.