Using the Lagrangian Multiphase Model with Time Models

Unsteady Simulation

In unsteady simulations, the approach can be categorized as a discrete element method [655]. In this method, the solution at a given instant in time is the state (position, velocity, temperature, and so on.) of each parcel. The number of nominally identical particles that a parcel represents, or particle count, is part of the state of the parcel. Optionally, the tracks of parcels can also be recorded in unsteady simulations: these tracks are the history of the parcel state, which can be visualized as a trajectory.

Steady Simulation

In steady simulations, the approach can be categorized as a trajectory method [655]. The solution is typically the tracks of the parcels, and the variation of state (velocity, temperature, and so on) along them. Each track records the complete lifetime of one parcel, from when it is injected to when it leaves the domain. The particle flow rate along each track is part of its state.

Parcels are indeed supposed to leave the domain in steady simulations. This approach is unsuitable for configurations that permanently carry particles in the continuous phase, whether through flow features (for example, recirculation zones) or geometry (for example, mixing vessels). For these configurations, an unsteady simulation can be more appropriate.