(518f) Viscoelastic Lift Forces on Non-Spherical Particles in Pressure-Driven Flows: Theory, Experiments, and Visualization

When particles are in a pressure-driven flow of a non-Newtonian fluid, the particles can acquire lift forces due to the imbalance of normal stresses on the particle surface. This phenomenon has been well-studied for spherical particles, but the role of particle shape is still in its early stages. In this work, we develop a theory to describe the rigid body motion of a non-spherical particle in a polymeric fluid. The theory is based on a retarded expansion in the Deborah number (i.e., second order fluid model), for the case when the particle is in a quadratic (i.e., pressure-driven) flow. We find that for particles in a circular tube flow, spherical particles move to the center of the tube faster than prolate and oblate particles of the same volume, due to the unique orientation dynamics of the spheroids in the polymeric fluid. We also find that prolate particles move slower than oblate particles of the same aspect ratio. These trends are verified by performing microfluidic experiments where we visualize polystyrene particles of various shapes moving through circular capillaries in a Boger fluid with weak viscoelasticity (De = O(0.01)) and vanishing inertia (Re = O(0.0001)).

In the last part of the talk, we will discuss our latest work in developing holographic imaging techniques to visualize the 3D position and orientation of a spheroid in a complex medium. Specifically, we developed a new forward reconstruction method that allows one to resolve the orientation of semi-transparent spheroids with an O(1) aspect ratio, where the lens effect from the particle often makes it difficult to perform such methods. This method avoids the large computational complexities of backward reconstruction techniques. We will discuss how this method could be used to infer the particle’s orientation in viscoelastic fluids for the applications listed above.

This work was funded by the American Chemical Society Petroleum Research Fund (grant ACS PRF 61266-DNI9) and partially by NSF CBET 170091