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.