# The Impact of Single- and Multicomponent Liquid Drops on a Heated Wall: Child Droplets
## 3 Results and Discussion
### Effect of a Group of the Governing Parameters  
#### 3.2.1 Velocity, Size, and Impinging Angle  
Table 4 presents how two key factors defining the inertia force, namely, size and velocity of drops, affected the impact characteristics. We demonstrated the variation ranges of the drop size and velocity, as well as of the Weber number. These ranges corresponded to the two observed regimes--intense breakup or deposition of the drops on a wall and formation of a thin liquid film. In this regard, the results were generalized by the data obtained in all the tests performed with an initial drop size ranging from 0.5 mm to 3 mm. To find the boundary of transition between two impact regimes, the range was divided into four subranges, in particular, 0.5-1 mm, 1-2 mm, 2-2.5 mm, and 2.5-3 mm (Table 4). The experiments showed that the drop velocity critically affects the transition boundary between deposition and breakup. Table 4 demonstrates that the drop breakup stably occurred when their size ranged from 0.5 to 3 mm and velocity exceeded 2 m/s. The general range of the critical impact velocities is 2-2.5 m/s. It correlates well with findings [19] describing the stable breakup at a velocity of higher than 2.12 m/s. The snapshots of the tests depicted the common pattern in the range of initial drop sizes of up to 1.5-2 mm: the larger the droplet, the lower impact velocity required for its breakup. As expected, the critical Weber numbers could be attained by increasing the size or velocity of a drop. The contribution of these two parameters was noticeably different. In particular, to produce a greater number of small child droplets, it was necessary to increase the size of the parent drop, but to get the minimum size \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Rd [mm]** & \multicolumn{2}{c}{**Weber Numbers**} & \multicolumn{2}{c}{**Threshold Velocities [m/s]**} & \multicolumn{2}{c}{**Impingement Angles**} \\ \hline  & **Deposition** & **Breakup** & Deposition & Breakup & Deposition & Breakup \\
0.5–1 & 0–195 & 195–630 & 0–2.28 & 2.28–3 & 0–7/3 & \(\pi\)/3–\(\pi\)/2 \\
1–2 & 0–163 & 163–630 & 0–2.14 & 2.14–3 & 0–\(\pi\)/4 & \(\pi\)/4–\(\pi\)/2 \\
2–2.5 & 0–442 & 442–630 & 0–2.51 & 2.51–3 & 0–\(\pi\)/5 & \(\pi\)/5–\(\pi\)/2 \\
2.5–3 & 0–300 & 300–630 & 0–1.89 & 1.89–3 & 0–\(\pi\)/8 & \(\pi\)/8–\(\pi\)/2 \\ \hline \end{tabular}
\end{table} 
Table 4: Threshold velocities, impingement angles, and Weber numbers sufficient for drop breakup when impinging on the wall. of the child droplets, it was reasonable to increase the velocity. Therefore, the expected shift of the transition boundary from deposition to breakup occurred with the growth of \(R_{\rm d}\) at lower impact velocities and, consequently, Weber numbers (see Table 4 for the first two ranges of the drop sizes). In the case of large initial drops, we recorded a strong surface deformation that promoted both the reduction and growth of the transient (critical) velocities (Table 4). Large drops most often had a shape of disk or ellipsoid. The disk shape was typical of lower critical velocities but the ellipsoid one required higher impact velocities. The same reasons allowed us to make similar conclusions in terms of the transient critical Weber numbers. Table 4 depicts a wide range of We for the four subranges of the initial sizes, namely, We = 180-420. Table 4 starkly illustrates the role of the impinging angle in determining the impact regime. The larger the parent drop was, the smaller the impinging angle would be enough for intense secondary atomization. This is largely caused by a high inertia force. A small parent drop could be deposited on a surface if the impinging angle was less than \(\pi\)/3. Therefore, to enhance the drop breakup during the impingement, our recommendation is to utilize an impinging angle ranging from \(\pi\)/3 to \(\pi\)/2. These results extend the numerical and experimental findings by [PERSON] and [PERSON] [20] in terms of the drop impact on an inclined wetted surface.