Drop impact on small targets with different target-to-drop diameters ratio

Drop impact on small cylindrical targets has been experimentally studied. Special attention has been drawn to the effect of the different target-to-drop diameters ratio on the evolution of the drop spreading after colliding with the surface. Three distinct regions have been identified as related to the ratio of the target-to-drop diameters (beta(t) D-t/D-0), and the maximum spreading to drop diameters beta(max) D-ma/D-0. The particular response of each type group was analyzed to define the specific spreading characteristics. The small target is an obstacle on the drop way, yet it does not stop its vertical velocity completely, as for the larger surfaces. A drop that impacts a small target continues to flow, not only radially but with some vertical velocity, in accordance with an appropriate energy balance. The analysis yielded expressions for the maximal spread of each impact type. Type-A was observed for (1 < beta(t) <= beta(max)) and demonstrated mainly a radial spread, type-B (1/2 < beta(t) <= 1) with two directional spread; radial and vertical, and type-C for (beta(t) <= 1/2) a very small obstacle which barely affects the drop flow. The present analysis yielded expressions for the maximal spread of each impact type. (C) 2018 Elsevier Ltd. All rights reserved.