Mixing and stirring operations are important unit operations in the field of chemical engineering. Therefore, design and optimization of these aspects have an important impact on the development of new processes and pants. Siemens Axiva has implemented the tool of "Integrated Process Development" (lPD) part of which is the investigation of mixing and stirring processes with classical methods and with Computational Fluid Dynamics (CFD). This contribution presents examples showing strengths and shortcomings of both methods. Depending on the specific problem experimental tests, CFD, or a combination of both approaches can be sensible.