Abstract
In this study, the complexity of a steady-state flow through porous media is revealed using confocal laser scanning microscopy (CLSM). Micro-particle image velocimetry (micro-PIV) is applied to construct movies of colloidal particles. The calculated velocity vector fields from images are further utilized to obtain laminar flow streamlines. Fluid flow through a single straight channel is used to confirm that quantitative CLSM measurements can be conducted. Next, the coupling between the flow in a channel and the movement within an intersecting dead-end region is studied. Quantitative CLSM measurements confirm the numerically determined coupling parameter from earlier work of the authors. The fluid flow complexity is demonstrated using a porous medium consisting of a regular grid of pores in contact with a flowing fluid channel. The porous media structure was further used as the simulation domain for numerical modeling. Both the simulation, based on solving Stokes equations, and the experimental data show presence of non-trivial streamline trajectories across the pore structures. In view of the results, we argue that the hydrodynamic mixing is a combination of non-trivial streamline routing and Brownian motion by pore-scale diffusion. The results provide insight into challenges in upscaling hydrodynamic dispersion from pore scale to representative elementary volume (REV) scale. Furthermore, the successful quantitative validation of CLSM-based data from a microfluidic model fed by an electrical syringe pump provided a valuable benchmark for qualitative validation of computer simulation results.Graphic
Highlights
Fluid flow through porous media is a multi-scale process that brings together fundamental laws of physics at the molecular level and empirical relations at macro scale level
The presented work is based on measurements and simulations of a sub-representative elementary volume (REV) (Representative Elementary Volume) porous medium consisting of hundreds of pores
Confocal laser scanning microscopy allows for imaging fluid movement in microfluidic models
Summary
Fluid flow through porous media is a multi-scale process that brings together fundamental laws of physics at the molecular level and empirical relations at macro scale level. We used microfluidic models to study laminar flow in porous media at the micrometer–millimeter length scale. A microfluidic model is a sheet of material containing a simple or complex network of small channels (see the review paper by Karadimitriou and Hassanizadeh 2012, for definitions of micromodels). Microfluidic techniques are emerging in heterogeneous catalysis (Xu et al 2013; Zhang et al 2019; Yue 2018) and advanced sensing technology (e.g., Hogan et al 2017), among others. Crucial for the success of microfluidic technology is understanding the behavior of fluids in their channels (Squires and Quake 2005), for instance
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