# The Impact of Single- and Multicomponent Liquid Drops on a Heated Wall: Child Droplets
## 3 Results and Discussion
### Prospects of the Drop Breakup When Impacting onto a Surface  
Figure 11 illustrates the comparison between the experimental data and the results of studies [8; 9; 10] as the relative liquid surface area versus the Weber number. With an increase in the Weber number, the maximum size of a child droplet grew. This was because the increase in the number of secondary droplets resulted in higher inertia, which resisted the surface tension force. Finally, this led to a longer spreading time of a drop over the surface. The characteristics obtained by other researchers [8; 9; 10] differ from those presented in this study by 8% to 32%. This result illustrates the importance of further research of the drop impact on a wall in terms of developing a more informative dimensionless criterion,  
Figure 10: **(a) Regime map of the drop impact on the wall (circle—deposition of the first drop and coalescence with all others, square—breakup) as a function of We(Oh): 1,2—water; 3,4—slurry (30 wt% of coal, 70 wt% of water); 5,6—emulsion (30 vol.% of transformer oil, 70 vol.% of water); 7,8—emulsion (30 vol.% of castor oil, 70 vol.% of water); (b) \(S_{1}/S_{0}\)(We); (c) size distribution of child droplets at We = 200: 1—water; 2—slurry (30 wt% of coal, 70 wt% of water); 3—emulsion (30 vol.% of transformer oil, 70 vol.% of water); 4—emulsion (30 vol.% of castor oil, 70 vol.% of water). **  
which would account for not only inertia and surface tension but also other factors markedly affecting the impingement characteristics. This will make it possible to develop comprehensive regime maps with an account of all the governing characteristics, namely, dimensions, temperature, thermophysical properties of a material, hydrophilicity, hydrophobicity, roughness, etc. To date, this task has not been solved and it remains urgent for the global scientific community. We can conclude that the dispersion of the ratios \(R_{\mathrm{d}}\)/\(r^{\mathrm{m}}_{\mathrm{d}}\) noticeably increases with the growing Weber number (Figure 11). For the total surface area of the liquid, we got moderate confidence intervals even at high Weber numbers (Figure 12). This was because an increase in the inertial force led to a noticeable deformation of the drop surface. The contact area strongly depended on the drop shape. In particular, the contact area was the highest with disk-shape drops, the lowest for vertical ellipsoids, and moderate for spheres. The larger the contact area, the thinner the film at the surface. At high impact velocities, this film broke up into a large number of smaller secondary droplets. This was especially noticeable when disk-shaped drops impinged on a wall. In the case of spheres and ellipsoids, the number of larger secondary droplets considerably increased because of the smaller contact area and higher thickness of the liquid film on the surface. A moving drop rotated about its center of mass, so it could take various shapes directly before impact. That is why the dispersion of the experimental values in Figure 11 was quite noticeable. However, the differences in the mean size of child droplets were not that large. Therefore, the ratio \(S_{1}\)/\(S_{0}\) grew with an increase of the Weber number more monotonously (Figure 12). Figure 11: Ratio between the initial drop radius and maximum radius of secondary droplets vs. We: 1—[8]; 2—[9]; 3—[10]; 4—experimental data for water. Figure 12: Comparison of breakup characteristics of a single drop and a group of smaller droplets impinging on a surface as a function of \(S_{1}\)/\(S_{0}\)(We): 1—single drop (\(V_{0}\approx 600\)\(\mu\)L), 2—three drops (\(V_{0}\approx 200\)\(\mu\)L for each one), 3—two drops (\(V_{0}\approx 200\)\(\mu\)L for each one). Figure 11 illustrates significant differences in the ratios \(S_{1}\)/\(S_{0}\) in the case of impinging drops with different initial volumes. In particular, we performed experiments with a single large drop and three smaller ones. The total volume of the three drops equaled that of the single one.