Kyung Hyun Ahn

Bead-spring chain model for the dynamics of dilute polymer solutions: Part 2. Comparisons with experimental data

Abstract Comparisons are made between experimental rheological data and theoretical predictions obtained from a recently developed algorithm which incorporates three major molecular concepts in a theory for dilute polymer solutions (hydrodynamic interaction, excluded volume and nonlinear springs). These predictions include the radius expansion factor, the apparent chain expansion factor, the molecular weight dependence of the intrinsic viscosity, the frequency dependence of oscillatory flow birefringence, and the shear rate dependence of the intrinsic viscosity. This paper shows that a bead-spring chain model quantitatively predicts these quantities when the relevant molecular concepts are incorporated, suggesting that the rheological properties of dilute polymer solutions can be explained and predicted in terms of these molecular parameters.

Effect of Viscoelasticity on Drop Deformation in 5:1:5 Contraction/Expansion Micro‐Channel Flow

We implemented a finite element‐front tracking method (FE‐FTM) to understand the drop dynamics in microfluidic applications. We investigated the effect of viscoelasticity of both drop and medium. The Oldroyd‐B model was used for viscoelastic fluid, and DEVSS‐G/SUPG/Matrix logarithm were applied to improve numerical stability. We applied the algorithm to a drop deformation problem in 5:1:5 planar contraction—narrow channel—expansion flow. One of our goals is to propose the strategy to control the drop shape by exploring the effect of viscoelasticity of drop and medium. Here, we studied three different viscosity ratios between drop and medium by setting the ratio as 100 (more viscous drop), 1 and 0.01 (more viscous medium). In Newtonian fluids, the effects of drop size and capillary number (Ca) were investigated to get physical insights on drop deformation. As for fluid elasticity, the effect of Deborah number (De) was especially enhanced in more viscous drop case, while the effect was insignificant in othe...