Determination of coalescence frequencies in liquid—liquid dispersions: effect of drop size dependence

Abstract

The size dependence of the drop coalescence frequency is investigated by measurement of transient drop size distributions in purely coalescing systems (with negligible drop break-up). A two-pronged approach is employed to estimate the bivariate coalescence frequency function, using such experimental data. First, coalescence frequency expressions derived from mechanistic models of the relative motion of the drops are evaluated based on their ability to predict the experimental transient size spectra. Second, experimental drop size distributions which exhibit a property known as self-similarity are analyzed through an inverse problem in order to extract the coalescence frequency function directly from the data. Results indicate that the coalescence frequency of small droplets (10–50 μm in diameter) is lower than that predicted from a constant coalescence efficiency model. In addition, experiments show that, given favorable initial conditions, self-similar drop size distributions can be manifest. In the cases where similarity behavior is observed, the frequencies obtained from the inverse problem are in qualitative agreement with the mechanistic models that describe the data best.