Experimental Analysis and Predictive Modeling of Droplet Impingement and Spreading onto a Solid, Smooth Surface

An experimental study of the impact and spreading process of water droplets on a smooth glass surface is presented. Impact droplet velocity, diameter, Reynolds number, and Weber number varied from 1.3 to 3.1 m/s, 2.5 to 4.2 mm, Re 3610 to 12100, and We 60 to 515, respectively. The impact surface was smoothed to $\raise.5ex\hbox{$\scriptstyle 1$}\kern-.1em/ \kern-.15em\lower.25ex\hbox{$\scriptstyle 4$} \quad \lambda $ to minimize solid-surface induced flow instabilities during expansion. A high speed digital camera was used to capture the droplet motion at 2200 Hz with an image plane spatial resolution of $\sim $16 $\mu $m. The size of the data set allowed for calculation of uncertainty related to characteristic spread time, \textit{$\tau $}$_{max}$, and maximum spread ratio, \textit{$\beta $}$_{max}$. Applying previous literature values for \textit{$\beta $}$_{max}$ and a newly formulated model for \textit{$\tau $}$_{max}$ as boundary functions, a new function predicting radial expansion from impact to \textit{$\beta $}$_{max}$ was defined. A statistical comparison with existing literature models for the entire expansion process was made based upon the experimental results obtained.