### 6.2.1. Drag Force on Particles

The aerodynamic drag force on a particle is proportional to the slip velocity, , between the particle and the fluid velocity:

| (6–12)

where is the drag coefficient and is the effective particle cross-section. The drag coefficient, , is introduced to account for experimental results on the viscous drag of a solid sphere. The coefficient is calculated in the same way as for Eulerian-Eulerian multiphase flow.

Using the new variable , this leads to the following contribution to the right hand side and linearization coefficient of Equation 6–7:

| (6–13)

| (6–14)

The particle momentum source due to drag is calculated from the following equation:

| (6–15)

The source, , added to the continuous phase is then multiplied with the number rate for that particle.

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