The mean diameter with the same ratio of volume to surface area as the entire ensemble is known as the Sauter mean diameter. The Sauter mean diameter is used in Fluent to describe the interfacial area concentration. This is an important parameter for predicting mass, momentum and energy transfers through the interface between the phases. Population Balance Methods in Fluent allows the predication of the Sauter mean diameter of the disperse phases and hence a more accurate modeling compared to the monodisperse framework.