Traditional rotational rheometry has been dealing with ideal flow conditions (viscometric flows) using plate, cone-plate or concentric cylinder geometries to characterize complex materials, preferably in the linear viscoelastic region.

Complex fluids, however are often difficult to measure under these conditions. Sedimentation during testing or slippage at the sample-tool interface have a significant effect on the results and reduce the operation range of the instruments.

Furthermore do viscoelastic flows by no means represent the real flow situation in batch or continuous reactors and processing machines during mixing and/or incorporation of additives, etc. For example, in order to simulate and to understand the gelatinization of starch, a mixing element is used as the standard geometry to avoid settling of the non soluble starch particles since the early days of rheological testing.