# 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
#### 3.2.3 Wall Material  
Figure 6 shows how the impact regimes vary if we use a fine-meshed screen and a substrate made of various materials. Based on experimental results [6; 7; 8; 9], we formulated an assumption that the fine-meshed screen allowed an increase in the number of small child droplets. When a drop impinged on the screen, dumbbell-shaped child droplets emerged. The liquid surface area grew by 2.2 times (Figure 6b). However, the impact on a solid surface could provide better drop atomization at the same We. In particular, if the screen is used, the size of child droplets could reach 350-500 \(\upmu\)m (Figure 6c). If the cellular construction size is assumed even smaller, the falling drop will disintegrate more slowly and into larger fragments because the pressure will be insufficient to squeeze the liquid out of the mesh.  
During the impact on a surface, the kinetic energy of a drop mainly defined the breakup characteristics, namely the number and size of child droplets. If the surface was smooth, then the contact area would be minimum during the impact. However, if the surface was rough, then the surface area of a drop would considerably increase during impact. In particular, we managed to provide for the growth of this parameter by two to three times. In this case, the friction force acting upon the drop impinging on a rough surface also grew. As a result, the kinetic energy of the drop impinging on a smooth surface was used to break it up. In the case of a rough surface, a part of the kinetic energy dissipated due to friction. Moreover, when the surface was extremely rough, i.e., in the case of the screen, the vertical elements of such a surface prevented the breakup. A part of the drop passing through a cell could not transform in the cross direction. Besides, the top of the drop could disintegrate as much as it protruded from the mesh cell.  
When comparing the breakup characteristics of the drops contacting with copper, steel, and glass surfaces, we established the distributions depicted in Figure 6c. For the metal surfaces, the distributions  
Figure 5: (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—T_\(\approx\) 20 °C; _3,4—T_\(\approx\) 50 °C; _5,6—T_\(\approx\) 100 °C; _7,8—T_\(\approx\) 180 °C; (b) \(S_{1}\)/\(S_{0}\)(We); (c) size distribution of child droplets at We = 200 and at different wall temperatures: _1—T_\(\approx\) 20 °C; _2—T_\(\approx\) 50 °C; _3—T_\(\approx\) 100 °C; _4—T_\(\approx\) 180 °C.  
Figure 6: (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) at a wall temperature of about 100 °C: _1, 2—_copper surface; _3, 4—_steel surface; _5, 6—_glass surface; _7, 8—_metal mesh; (b) \(S_{1}\)/\(S_{0}\)(We); (c) size distribution of child droplets at We = 200 and at different wall configurations: _1—_copper surface; _2—_steel surface; _3—_glass surface; _4—_metal mesh.  
were quite close in terms of character and size, but the contact with a glass surface mostly produced small child droplets. However, the liquid surface area grew more noticeably when we used metal substrates (Figure 6b). The higher the Weber number, the more noticeable these patterns. This could be explained by a considerable difference in heat fluxes from the wall to the approaching droplet. For the metal substrates, these heat fluxes were notably higher due to higher thermal conductivity and diffusivity compared to glass. The higher the heat flux, the more intensely a drop broke up.