Simulation of the Efficiency of Static Mixers

Within the Sulzer Corporation the behavior and efficiency of static mixers is predicted by means of CFD. Typical mixers are the SMX mixer and the CompaX mixer. As the SMX mixer is used for laminar mixing and homogenization of high viscous fluids, the CompaX mixer is applied for turbulent flow regimes. Simulations carried out for these mixers have been validated with measurements. Key values to evaluate the efficiency are the pressure loss and mixing quality. The pressure loss for both mixer types can be directly gained from the CFD simulation. But it is not possible to predict the mixing quality of laminar mixers directly from CFD simulations as for laminar flows the numerical diffusion is significantly higher than the real molecular diffusion. Thus, to predict the mixing quality of laminar mixers a trajectory method is applied. The molecular diffusion along the trajectories is taken into consideration by a Monte Carlo method. For turbulent flows diffusive mass transfer plays only a minor role. Therefore, the mixing quality can be gained directly from the CFD simulation. Furthermore, for structural analysis the forces acting on the mixer elements induced by the flow, the residence time distribution of fluid elements in the mixer and heat exchange with the duct wall is of particular interest.