## 8.18. Transient Simulations: What is Different for Particles?

Although this topic has been discussed in many areas of the particle tracking modeling documentation, this section attempts to summarize the most important differences between steady-state and transient runs with respect to the particle solver.

In a transient run:

- You have to specify the number of particles injected per time step and not the total number of injected particles.

- Iteration control of the particle solver refers to the coefficient loop within a time step and not to the outer loop iteration.

- Different under-relaxation coefficients are used for the generated particle sources.

- The solver OUT file of a transient particle run contains additional information about time integrated particle boundary fields, mass, momentum, and energy flows.

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