Several industrial fluid flow applications involve a secondary phase with a size distribution. The size distribution of particles, including solid particles, bubbles, or droplets, can evolve in conjunction with transport and chemical reaction in a multiphase system. The evolutionary processes can be a combination of different phenomena like nucleation, growth, dispersion, dissolution, aggregation, and breakage producing the dispersion. Thus in multiphase flows involving a size distribution, a balance equation is required to describe the changes in the particle population, in addition to momentum, mass, and energy balances. This balance is generally referred to as the population balance. Cases in which a population balance could apply include crystallization, precipitative reactions from a gas or liquid phase, bubble columns, gas sparging, sprays, fluidized bed polymerization, granulation, liquid-liquid emulsion and separation, and aerosol flows.

This chapter describes the theory behind the population balance model available in Ansys Fluent. Information in this chapter is organized into the following sections: