The Particle Tracking option allows inclusion of dispersed, condensed-phase material in the form of particles. The Particle Tracking feature accounts for particle formation and destruction, and can be used to determine properties about the amount of particulates in the system.

To describe some of the theory behind the Particle Tracking feature, we first need to define particles in this context. Like gaseous species, each type of particle corresponds to a symbolic representation in the chemistry set and has properties associated with it. To form particles from the gas phase, one or more nucleation events need to be defined to identify the particle properties at inception. Chemical composition and thermodynamic properties of the particle are defined in this way. The definition of the particle and its properties are described in Description and Properties of Particles in the Chemkin Input Manual.

The nucleation "reaction" is used to define how the particle (or nucleus) is created from gas-phase species. The nucleation reaction is an irreversible reaction that provides the particle inception rate and defines the size and the surface coverage of the nucleus. After the nuclei are formed, they start to interact with each other as well as with the gas mixture around them. While particle-particle interactions such as coagulation are non-chemical processes, interactions between particles and the surrounding gas mixture can result in chemical processes taking place on the particle surface. These surface processes might result in mass growth or reduction of the particle or might just simply recondition the particle surface. To include the effects from all these surface processes, a surface mechanism is needed to describe all surface reactions and associated surface species on the particle. The Particle Tracking feature then determines the impact of individual surface reactions on the particle sizes from the expression of the surface reactions

The sections below describe the concept and theory behind the Particle Tracking computations along with implementation and numerical solution considerations.