Michael Ehrentraut demonstrates the validity of stationary numerical flow simulations (CFD) of viscoplastic fluids in a laboratory mixing system using experimental data. The simulation methodology employed allows for significantly faster calculations compared to transient propagation calculations for mixing. A characteristic feature of mixing such fluids is the formation of so-called cavities, which locally restrict the mixing within the mixing system. For the numerical consideration of cavities, their boundary is defined by a velocity criterion. It is shown that the volumes of the defined cavities can be regarded as a measure of mixing within the mixing system.