## 8.12. Restrictions for Particle Transport

The following limitations apply to the Lagrangian particle tracking model in ANSYS CFX:

- When combined with the `Eulerian-Eulerian` multiphase model, only a single continuous phase may contain particles. There is no exchange of momentum between particles and a dispersed Eulerian phase.

- There are no particle source terms to the turbulence equations; therefore, turbulence is not modulated by the discrete phase.

- Particle interactions might be important in flows where the discrete phase volumetric concentration is greater than 1% (ref. [67]). In such cases, the solid particle-particle interaction should be used.

- You cannot create Additional Variables in particles.

- In steady-state simulations that involve mesh movement, particles are still solved at the user-specified intervals. For accuracy reasons we recommend to solve particles after each time step by setting the solution interval to '1'. Note that this will also ensure that particle mass flows through GGI interfaces will always be written to the results file.

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