Computational Fluid Dynamics (CFD) simulations have been performed in two and three-dimensional microchannels to characterize the viscoelastic flow field using OpenFOAM solver. The conservation of mass and momentum equations coupled with the Giesekus constitutive model are solved. The computational domain consists of a straight main channel that is &nbsp;in width and a square-shaped cavity with an expansion ratio of 1:4 placed in the middle of the main channel. The numerical study is carried in microchannels with various aspect ratios on the depth of the microchannel. The viscoelastic fluid's physical properties are extracted from the xanthan gum (XG) solution given in Reference [1].Due to the difficulty in solving hyperbolic equations on the high Weissenberg number viscoelastic flows, the mesh convergence study is performed with three different types of meshes, including tetrahedral, hexahedral, and polyhedral. This study will compare the flow and stress fields among three types of meshes with different cell densities. Furthermore, 2D results will be compared against 3D cross-sectional planes to determine the influence of the wall. The first normal stress difference is analyzed to involve the elastic lift force for particle tracking in future studies for nanoparticle separations. The viscoelastic fluid shows excellent potential for nanoparticle separation in microfluidic devices. Compared to the traditional Newtonian fluid that requires external fields, such as a heating source or magnets, to provide extra particle forces, viscoelastic fluid shows assertive elastic behavior near expansion and contraction areas. A high level of normal stresses drives different sized nanoparticles to specific locations. This inherent feature makes nanoparticle separation more energy efficient and reduces the difficulty of microfluidic device operation as the only variable is the inlet flow rate. This computational study demonstrates that the successful design and optimization of viscoelastic flow nanoparticle separators requires accurate characterization of viscoelastic flow and stress fields. As the simulation process being validated, this study can help with future improvements to achieve higher flow rates.&nbsp;Reference[1] Raihan, Mahmud Kamal, et al. "Vortex trapping and separation of particles in shear thinning fluids." Applied Physics Letters 116.18 (2020): 183701.

Computational Study of Viscoelastic Flows in Microchannels

Paper Proceedings: https://asmedigitalcollection.asme.org/FEDSM/FEDSM2021/volume/85284

ASME 2021 Fluids Engineering Division Summer Meeting (FEDSM2021)

Supporting the need among researchers worldwide for additional online and multimedia content, ASME now offers the ASME Conference Video Collection. This platform will collect and provide long-term access to conference presentation videos, encompassing all technology areas within ASME's technical conference and events program. About 30,000-40,000 engineers across all mechanical engineering and related disciplines participate in ASME conferences each year. This includes authors of approximately 6,000 to 8,000 technical papers published by ASME, the majority of whom also submit video presentations for our virtual conferences. The video collection will be available as an add-on to existing product packages or as a separate subscription.