On the validity of different methods to estimate breakup frequency from single drop experiments

Abstract Single drop breakup visualizations are the golden standard for experimentally measuring breakup frequency, g, in turbulent flows. There is a growing demand for empirically obtained breakup frequencies, for population balance equation (PBE) based predictive modelling and for comparing to theoretical suggestions. However, five different methods to estimate g from a breakup visualization can be found in previous investigations, many of them contradictory. This study uses analytical and numerical methods to show that only two of the five suggestions result in estimates that are valid (where ‘valid’ means that the breakup frequencies are meaningful in a PBE setting). This case is also used to discuss the difference between the stochastic one drop deformation/breakup view of turbulent fragmentation and the deterministic number density based PBE description, arguing that some aspects of the breakup process will be challenging to describe within the PBE framework, regardless of the choice of breakup frequency model.