Polydisperse multiphase flows occur in many areas of engineering, particularly the process and energy industries. These flows can be simulated with computational fluid dynamics using suitable models. OpenFOAM includes the multiphaseEulerFoam solver for dispersed multiphase flows which includes a population balance model for the particle size distribution, based on the method of classes.

The population balance method solves an “integro-partial differential equation” for the number density function for the distribution of particle volume. The number density function is split into size groups (the method of classes) which are each assigned a single particle size to represent the range. The number density function is integrated to produce number concentrations for each size range which can be converted to size group fractions. Transport equations are solved for each size group fraction with careful numerics to ensure boundedness.

Polydisperse multiphase flows are disperse flows with significant variation in particle size. Particle size may change due to agglomeration during collisions and breakup due to shear forces. In OpenFOAM, multiphaseEulerFoam includes models based on particle size, with the option of computing size distribution using the population balance method. The method is developed by Helmholtz-Zentrum Dresden – Rossendorf in collaboration with VTT Finland, integrated into OpenFOAM with help in software design from CFD Direct.

Multiphase flows describe a variety of problems that involve the combined flow of several phases — gas, liquid or solid. These flows can be simulated using computational fluid dynamics with the volume of fluid approach which uses phase fractions to define the quantity of each phase in a given reqion of the flow. Disperse multiphase flows involves small bubbles of gas, solid, or liquid particles (i.e. droplets, bubbles, etc) in a continuous phase. OpenFOAM includes the multiphaseEulerFoam solver which can use the phase fraction both to capture phase interfaces by an abrupt 0 – 1 transition and to define fractional volume of particles in regions in disperse phases.