Extensional flow of polymeric dispersions

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Abstract
A general‐purpose extensional flow mixer, EFM, was recently introduced. To improve the understanding of its performance and potentials, several fundamental studies were initiated. These can be divided into two groups: (i) studies of the model drop deformation and breakup, and (ii) studies of the flow through EFM. Experimental, theoretical, and numerical methods (finite or boundary element methods, FEM or BEM, respectively) have been employed. The paper summarizes these efforts. The experimental study of flow of Newtonian and viscoelastic drops through a slit showed a difference in deformability. Initially, the former are reluctant to deform, but then deformaiton is rapid, whereas the viscoelastic drops initially deform readily, but then the deformation slows down. The slit flow does not flatten drops with diameters at least ten‐fold smaller than the slit gap. A comparison of the experimental data with the BEM 2‐D simulation showed that BEM provides good description of deformability. The effects of shear and elongation stress, the viscosity ratio, the drop diameter to channel gap ratio, the initial drop position, the interfacial tension coefficient, and elasticity of the dispersed phase were examined using the BEM. Simulation of flow through EFM was carried out using either FEM or Binding's theory. Both methods are suitable for computing the pressure losses and the stress fields. Analysis of flow lines can be used for optimization of the mixer's geometry.