Dispersive element droplet distribution

As explained throughout the book, disperse multiphase systems are characterized by multiple phases, with one phase continuous and the others dispersed (i.e. in the form of distinct particles, droplets, or bubbles). The term polydisperse is used in this context to specify that the relevant properties characterizing the elements of the disperse phases, such as mass, momentum, or energy, change from element to element, generating what are commonly called distributions. Typical distributions, which are often used as characteristic signatures of multiphase systems, are, for example, a crystal-size distribution (CSD), a particle-size distribution (PSD), and a particle-velocity distribution. 

In the population balances, the local bubble size distribution is modeled. In practice, it means that the numbers of bubbles of various sizes are counted. The bubble size distribution is discretized into a number of size categories, and the number of bubbles belonging to each of the size categories is counted in each of the CFD volume elements. The dispersed phase is here referred as bubbles, but it may be liquid droplets or solid precipitates as well. 

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