Effect of liquid viscosity and surface tension on the spray droplet size and the measurement thereof

Abstract

This investigation focuses on the impact of liquid properties—viscosity, surface tension—and air pressure on the Sauter Mean Diameter (SMD) of atomization sprays. Utilizing a twin-fluid atomizer, the study resulted in derived equations that quantify these effects across a spectrum of liquid behaviours, with an emphasis on both viscous and non-viscous liquids. The derivation process for viscous liquids yielded equations showcasing an average deviation of 1.32% from experimentally observed SMD values, validated across a dataset of 250 experimental trials. These trials involved a total of 18,000 droplets analysed, with a standard error of 0.02%, spanning a liquid viscosity range of 3x10-3 to 20x10-3 kg/(m.s), and air pressures from 50 to 300 kPag. For non-viscous liquids, defined by a liquid viscosity threshold of < 3x10-3 kg/(m.s), the equations revealed a higher average deviation of 1.51% from the experimental SMD. These runs included the analysis of 19,600 droplets across liquid surface tensions from 20x10-3 N/m to 72.8x10-3 N/m, with a standard error of 0.03%. This distinction highlights the significant influence of surface tension in shaping the atomization outcomes for these liquids. A quantitative discovery of this research is how a 10% increase in viscosity for viscous liquids correlates to a substantial 33% increase in SMD, impacting around 10,500 droplets per viscosity level, with an observed standard deviation of 0.15% across viscosity measurements. This emphasizes the dominance of viscosity in influencing atomization dynamics for viscous liquids. Conversely, for non-viscous liquids, a 10% increase in surface tension translates to a 45% increase in SMD, affecting approximately 11,200 droplets per surface tension category, with a standard deviation of 0.18% in surface tension measurements. Moreover, this study pioneers the introduction of a particle tracking code, designed for high-speed camera frames, enabling the analysis of over 10,000 droplets per experimental run, summing up to more than 280,000 droplets analysed across all trials, with an overall precision rate of 99.5%. This novel technique enhances system performance by providing highly accurate and real-time droplet size distribution data, which is critical for optimizing atomization processes in industrial applications. In comparison with state-of-the-art studies, this research offers a comprehensive analysis of the combined effects of viscosity, surface tension, and air pressure on SMD, providing new insights and validated predictive models. The contributions of this work lie in its detailed quantitative results and the introduction of advanced measurement techniques, which together represent a significant advancement in the field of atomization.