True Wall Shear Stress

Boundary Calculation

Forces at the interface between the fluid and the wall dictate the flow rate and the pressure drop. Calculating the true wall shear stress involves the use of the Bagley plot to find the pressure loss at an effective length of zero.

Correction Application

Raw data from a single die length often overestimates the viscosity of a material. By using the true wall shear stress, engineers can create a master viscosity curve that is independent of the machine geometry. A pilot result that lacks this correction will fail to predict the behavior in a different production machine with a different die setup.

Data Consistency

Reliable models require inputs that reflect the material itself rather than the test equipment. Measuring the true wall shear stress allows for a direct comparison between different batches and suppliers. Production yields rely on this consistency to maintain a stable process window across different manufacturing sites.