Wind tunnel study on the size distribution of droplets after collision induced breakup of levitating water drops

Wind tunnel experiments on collisions between drop pairs of 2.5 and 0.5 mm diameter have been performed and the coalescence and breakup events have been recorded by a high-speed digital camera. From the comprehensive analysis of the captured images, the most important parameters utilized in numerical models, such as coalescence efficiency, breakup type, number of fragments and fragment size distribution after breakup were determined. The experimentally obtained parameters have been compared to parameterizations based on earlier laboratory studies of Low and List, and on direct numerical simulations. A very good agreement between experimental results and parameterizations has been found. However, the parameterization based on direct numerical simulation fails to forecast the number of fragments of small sizes. Ultimately, a piece of puzzle is provided to the very important but still incomplete experimental data set of drop-drop collision outcome.