Figure 4-4 shows solid-liquid interface position

Figure 4-4 shows solid-liquid interface position (solidified thickness) near the axis with time for the hollow droplet and dense droplet case. As the droplet is above the substrate, it first come to substrate then start solidify, it can be observed from figure 4-4 that solidification starts at time 0.2 µs for both the case. It can be seen that the solid-liquid interface is at same position for both case. But after time 0.4 µs the solid-liquid interface for the case of hollow droplet is ahead. It can be concluded that occurrence of counter jet in the case of hollow droplet caused the higher solid-liquid interface growth by taking some part of latent heat released during solidification. Solidified thickness is always higher in case of hollow droplet due to occurrence of counter jet.Figure 4-5 shows the spreading ratio variation with time of both the case hollow droplet and dense droplet. The graph shows that the spreading ratio in the case of dense droplet is higher in comparison of the case of hollow droplet. Due to occurrence of counter jet during hollow droplet impact some part of liquid in the cell impacting on substrate goes towards axis and other part goes toward periphery. While in case dense droplet whole liquid before solidification goes towards periphery. In this way more liquid goes towards periphery in case of dense droplet in compared to case of hollow droplet. That causes higher spreading ratio for case of dense droplet. For the present case the maximum spreading factor is nearly 3.3 in case of dense droplet and 3.1 for the hollow droplet impact.