Case Study 4 Local Orientational Dynamics - Two Dimensional Raman Scattering

6 Case Study 4 Local Orientational Dynamics -Two Dimensional Raman Scattering 

7 Case Study 5 Spatially Resolved Stress Measurements in Non-Newtonian Flows 

Because the birefringence measurement is an integrated effect along the path of the beam in the sample, it is important that the flow be two-dimensional with the neutral axis parallel to the axis of that beam. For that reason, the width of the flow channel (which defines the length of the beam in the sample) must be relatively large relative to its height. A rule of thumb that is often used is a factor of 10, and the value used in this work was 

The experiments were run by pumping the fluid through the channel at a specified flow rate. Once a steady state flow had been achieved, velocity and birefringence measurements were carried out at various locations in the flow field by translating the flow channel relative to the optical train. The translation of the channel was in the direction perpendicular to the mean flow direction and this was repeated for a number of locations along the axis of the channel. 

As the flow accelerates into the gaps around the cylinder, it possesses a greater relative amount of extension. Ultimately, at distances far downstream from the cylinder, the flow is expected to relax back toward a parabolic profile. In these plots, the symbols represent the measured velocities and the solid curves are the results of a finite element, numerical simulation. The constitutive equation used was a four constant, Phan-Thien-Tanner mod-el[193], which was adjusted to fit steady, simple shear flow shear and first normal stress difference measurements. The fit to the velocity data is very satisfactory. 

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