In this section, effect surface heat transfer coefficient of substrate on different parameters for hollow droplet is plotted and related physics are described. Surface roughness is accounted at thermal convective resistance at droplet substrate interface. In these cases, impact speed was 100 m/s.
Figure 4.6 shows the variations of temperature with time at a bottom point in the droplet which is just above the substrate surface with different heat transfer coefficient. This graph shows comparison of cooling curve for the different heat transfer coefficient (5×107 W/(m2K) and 5×106 W/(m2K)). It can be seen that at higher heat transfer coefficient cooling rate is more as a results interface velocity is high.
Figure 4-7 shows the interface position at different heat transfer coefficient. It can be observed that interface position is higher up to time 12 µs for the case of higher heat transfer coefficient as compared to lower heat transfer coefficient. The reason behind this is that at higher heat transfer coefficient heat transfer from the droplet to substrate is high as a results interface velocity is high and interface growth will be high. But after time 12 µs interface position is ahead for the case of lower heat transfer coefficient. Solidification happens only at neck and latent heat released at this point of time defuse very