Normal Stress Measurements on Viscoelastic Fluids Using Holographic Interferometry to Measure the Free Surface in the Weissenberg Effect
Results obtained to date for viscometric flows of simple fluids have not provided a very detailed picture of the normal stresses for these fluids. The normal stress ratio N2/N1 is generally agreed to lie in the range -0.1 to -0.4 for moderately concentrated polymer solutions, but some experiments show a larger range. Most difficulty is experienced measuring N2, due mainly to its nature (being the difference in stress between the two directions normal to the flow). The use of the shape of the free surface as a measure of the state of stress in a fluid has been explored on a limited scale over the past 30 years1. Theoretical work by Bohme2,3 has shown that, in restricted circumstances, it is possible to obtain expressions for the shape of the free surface of a second order fluid being sheared between two rotating solid surfaces of revolution. The experiments described here are an attempt to obtain the separate values of ψ1,0 and ψ2,0 from measurements of the Weissenberg effect in spherical symmetry (see eqn. 4), and compare them with the value of (ψ1,0 + 4. ψ2,0) from a cylindrical geometry.
KeywordsViscoelastic Fluid Holographic Interferometry Fluid Surface Elastic Fluid Bearing Plate
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