Within the particle transport model, the total flow of the particle phase is modeled by tracking a small number of particles through the continuum fluid. The particles could be solid particles, drops or bubbles.

The application of Lagrangian tracking in CFX involves the integration of particle paths through the discretized domain. Individual particles are tracked from their injection point until they escape the domain or some integration limit criterion is met. Each particle is injected, in turn, to obtain an average of all particle tracks and to generate source terms to the fluid mass, momentum and energy equations. Because each particle is tracked from its injection point to final destination, the tracking procedure is applicable to steady-state flow analysis.