Morphology of multiple drop impacts onto heated surfaces

The paper reports experimental results on multiple drop impacts onto a heated solid surface. Line-arrays made of three water drops of millimetric size were produced by “on demand” drop generator. The impact drop size was kept constant while the impact velocity was varied to obtain Weber numbers ranging between 110 and 660. The influence of drop-drop interaction was evidenced by comparison with experiments performed under the same condition using single drops. The wall temperature was changed from 80°C to 260°C, to cover the various evaporation regimes. Also drop spacing was varied to study the effect of this parameter on the drop-drop interaction. Finally two plates with different values of surface roughness were used to evidence its effects on secondary atomisation and impact morphology. A high resolution CCD camera was used to collect images and many peculiar structures were observed during drop impact and boiling. The emphasis is put on the morphology of the impact process, which strongly depends on wall temperature and on the dynamical effects caused by to drop-drop interaction.